Academic Commons Search Results
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Academic Commons Search Resultsen-usAdvances in Multiscale Methods with Applications in Optimization, Uncertainty Quantification and Biomechanics
http://academiccommons.columbia.edu/catalog/ac:202066
Hu, Nanhttp://dx.doi.org/10.7916/D8FX79N8Fri, 19 Aug 2016 19:22:30 +0000Advances in multiscale methods are presented from two perspectives which address the issue of computational complexity of optimizing and inverse analyzing nonlinear composite materials and structures at multiple scales. The optimization algorithm provides several solutions to meet the enormous computational challenge of optimizing nonlinear structures at multiple scales including: (i) enhanced sampling procedure that provides superior performance of the well-known ant colony optimization algorithm, (ii) a mapping-based meshing of a representative volume element that unlike unstructured meshing permits sensitivity analysis on coarse meshes, and (iii) a multilevel optimization procedure that takes advantage of possible weak coupling of certain scales. We demonstrate the proposed optimization procedure on elastic and inelastic laminated plates involving three scales. We also present an adaptive variant of the measure-theoretic approach (MTA) for stochastic characterization of micromechanical properties based on the observations of quantities of interest at the coarse (macro) scale. The salient features of the proposed nonintrusive stochastic inverse solver are: identification of a nearly optimal sampling domain using enhanced ant colony optimization algorithm for multiscale problems, incremental Latin-hypercube sampling method, adaptive discretization of the parameter and observation spaces, and adaptive selection of number of samples. A complete test data of the TORAY T700GC-12K-31E and epoxy #2510 material system from the NIAR report is employed to characterize and validate the proposed adaptive nonintrusive stochastic inverse algorithm for various unnotched and open-hole laminates. Advances in Multiscale methods also provides us a unique tool to study and analyze human bones, which can be seen as a composite material, too. We used two multiscale approaches for fracture analysis of full scale femur. The two approaches are the reduced order homogenization (ROH) and the novel accelerated reduced order homogenization (AROH). The AROH is based on utilizing ROH calibrated to limited data as a training tool to calibrate a simpler, single-scale anisotropic damage model. For bone tissue orientation, we take advantage of so-called Wolff’s law. The meso-phase properties are identified from the least square minimization of error between the overall cortical and trabecular bone properties and those predicted from the homogenization. The overall elastic and inelastic properties of the cortical and trabecular bone microstructure are derived from bone density that can be estimated from the Hounsfield units (HU). For model validation, we conduct ROH and AROH simulations of full scale finite element model of femur created from the QCT and compare the simulation results with available experimental data.Civil engineering, Mechanicsnh2350Civil Engineering and Engineering MechanicsDissertationsMethods for Analysis of Urban Energy Systems: A New York City Case Study
http://academiccommons.columbia.edu/catalog/ac:197659
Howard, Bianca Nicholehttp://dx.doi.org/10.7916/D8W66KQWFri, 15 Apr 2016 18:25:44 +0000This dissertation describes methods developed for analysis of the New York City energy system. The analysis specifically aims to consider the built environment and its' impacts on greenhouse gas (GHG) emissions. Several contributions to the urban energy systems literature were made. First, estimates of annual energy intensities of the New York building stock were derived using a statistical analysis that leveraged energy consumption and tax assessor data collected by the Office of the Mayor. These estimates provided the basis for an assessment of the spatial distribution of building energy consumption. The energy consumption estimates were then leveraged to estimate the potential for combined heat and power (CHP) systems in New York City at both the building and microgrid scales. In aggregate, given the 2009 non-baseload GHG emissions factors for electricity production, these systems could reduce citywide GHG emissions by 10%. The operational characteristics of CHP systems were explored further considering different prime movers, climates, and GHG emissions factors. A combination of mixed integer linear programing and controlled random search algorithms were the methods used to determine the optimal capacity and operating strategies for the CHP systems under the various scenarios. Lastly a multi-regional unit commitment model of electricity and GHG emissions production for New York State was developed using data collected from several publicly available sources. The model was used to estimate average and marginal GHG emissions factors for New York State and New York City. The analysis found that marginal GHG emissions factors could reduce by 30% to 370 g CO₂e/kWh in the next 10 years.Energy, Mechanical engineering, Civil engineeringbnh2111Mechanical EngineeringDissertationsWave propagation and strain localization in a fully saturated softening porous medium under the non-isothermal conditions
http://academiccommons.columbia.edu/catalog/ac:194445
Na, SeonHong; Sun, WaiChinghttp://dx.doi.org/10.7916/D8DR2VBXMon, 22 Feb 2016 00:00:00 +0000The (THM) coupling effects on the dynamic wave propagation and strain localization in a fully saturated softening porous medium are analyzed. The characteristic polynomial corresponding to the governing equations of the THM system is derived, and the stability analysis is conducted to determine the necessary conditions for stability in both non-isothermal and adiabatic cases. The result from the dispersion analysis based on the Abel–Ruffini theorem reveals that the roots of the characteristic polynomial for the THM problem cannot be expressed algebraically. Meanwhile, the dispersion analysis on the adiabatic case leads to a new analytical expression of the internal length scale. Our limit analysis on the phase velocity for the non-isothermal case indicates that the internal length scale for the non-isothermal THM system may vanish at the short wavelength limit. This result leads to the conclusion that the rate-dependence introduced by multiphysical coupling may not regularize the THM governing equations when softening occurs. Numerical experiments are used to verify the results from the stability and dispersion analyses.Engineering, Civil engineering, Geophysical engineering, Elastic waves, Fluid mechanics, Stability, Elastic solids, Deformations (Mechanics)ws2414Civil Engineering and Engineering MechanicsArticlesCitizen Sensors for SHM: Towards a Crowdsourcing Platform
http://academiccommons.columbia.edu/catalog/ac:194289
Ozer, Ekin; Feng, Maria Q.; Feng, Dongminghttp://dx.doi.org/10.7916/D8WH2PT2Mon, 15 Feb 2016 00:00:00 +0000This paper presents an innovative structural health monitoring (SHM) platform in terms of how it integrates smartphone sensors, the web, and crowdsourcing. The ubiquity of smartphones has provided an opportunity to create low-cost sensor networks for SHM. Crowdsourcing has given rise to citizen initiatives becoming a vast source of inexpensive, valuable but heterogeneous data. Previously, the authors have investigated the reliability of smartphone accelerometers for vibration-based SHM. This paper takes a step further to integrate mobile sensing and web-based computing for a prospective crowdsourcing-based SHM platform. An iOS application was developed to enable citizens to measure structural vibration and upload the data to a server with smartphones. A web-based platform was developed to collect and process the data automatically and store the processed data, such as modal properties of the structure, for long-term SHM purposes. Finally, the integrated mobile and web-based platforms were tested to collect the low-amplitude ambient vibration data of a bridge structure. Possible sources of uncertainties related to citizens were investigated, including the phone location, coupling conditions, and sampling duration. The field test results showed that the vibration data acquired by smartphones operated by citizens without expertise are useful for identifying structural modal properties with high accuracy. This platform can be further developed into an automated, smart, sustainable, cost-free system for long-term monitoring of structural integrity of spatially distributed urban infrastructure. Citizen Sensors for SHM will be a novel participatory sensing platform in the way that it offers hybrid solutions to transitional crowdsourcing parameters.Mechanical engineering, Information technology, Civil engineering, Structural health monitoring, Human computation, Smartphoneseo2327, mqf2101, df2465Civil Engineering and Engineering MechanicsArticlesA Vision-Based Sensor for Noncontact Structural Displacement Measurement
http://academiccommons.columbia.edu/catalog/ac:194292
Feng, Dongming; Feng, Maria Q.; Ozer, Ekin; Fukuda, Yoshiohttp://dx.doi.org/10.7916/D8CJ8DBFMon, 15 Feb 2016 00:00:00 +0000Conventional displacement sensors have limitations in practical applications. This paper develops a vision sensor system for remote measurement of structural displacements. An advanced template matching algorithm, referred to as the upsampled cross correlation, is adopted and further developed into a software package for real-time displacement extraction from video images. By simply adjusting the upsampling factor, better subpixel resolution can be easily achieved to improve the measurement accuracy. The performance of the vision sensor is first evaluated through a laboratory shaking table test of a frame structure, in which the displacements at all the floors are measured by using one camera to track either high-contrast artificial targets or low-contrast natural targets on the structural surface such as bolts and nuts. Satisfactory agreements are observed between the displacements measured by the single camera and those measured by high-performance laser displacement sensors. Then field tests are carried out on a railway bridge and a pedestrian bridge, through which the accuracy of the vision sensor in both time and frequency domains is further confirmed in realistic field environments. Significant advantages of the noncontact vision sensor include its low cost, ease of operation, and flexibility to extract structural displacement at any point from a single measurement.Mechanical engineering, Information technology, Civil engineering, Template matching (Digital image processing), Earth movements and building, Structural health monitoring, Detectorsdf2465, mqf2101, eo2327, yf2290Civil Engineering and Engineering MechanicsArticlesToward Environmentally Sustainable Construction Processes: The U.S. and Canada’s Perspective on Energy Consumption and GHG/CAP Emissions
http://academiccommons.columbia.edu/catalog/ac:194136
Ahn, Changbum; Lee, SangHyun; Pena-Mora, Feniosky A.; Abourizk, Simaanhttp://dx.doi.org/10.7916/D8T153G7Wed, 10 Feb 2016 00:00:00 +0000In the building and construction sector, most efforts related to sustainable development have concentrated on the environmental performance of the operation of buildings and infrastructure. However, several studies have called for the need to mitigate the considerable environmental impacts, especially air pollutant emissions and energy consumption, generated by construction processes. To provide a point of reference for initiating the development of environmentally sustainable construction processes, this article identifies energy consumption and air emissions resulting from construction activities and examines previous approaches utilized to assess such environmental impact. This research also identifies the opportunities and challenges to mitigate such environmental impact from construction processes, based on the investigation of current technology policies, regulations, incentives, and guidelines.Civil engineering, Environmental studies, Sustainable construction, Environmental management, Construction industry--Environmental aspectsfp2214Civil Engineering and Engineering MechanicsArticlesDesign, Data Collection, and Driver Behavior Simulation for the Open- Mode Integrated Transportation System (OMITS)
http://academiccommons.columbia.edu/catalog/ac:194097
Wang, Lianghttp://dx.doi.org/10.7916/D82F7N7SFri, 29 Jan 2016 00:00:00 +0000With the remarkable increase in the population and number of vehicles, traffic has become a severe problem in most metropolitan areas. Traffic congestion has imposed tight constraints on economic growth, national security, and mobility of riders and goods. The open-mode integrated transportation system (OMITS) has been designed to improve the traffic condition of roadways by increasing the ridership of vehicles and optimizing transportation modes through smart services integrating emerging information communication technologies, big data management, social networking, and transportation management. Even a modest reduction in the number of vehicles on roadways will lead to a considerable cost savings in terms of time and money. Additionally the reduction in traffic jams will lead to a significant decrease in both gasoline consumption and greenhouse gas emissions. As a result, novel transportation management is critical to reduce vehicle mileage in the peak time of the road network. The OMITS was proposed to enhance transportation services in respect to the following three aspects: optimization of the transportation modes by multimodal traveling assignment, dynamic routing and ridesharing service with advanced traveler information systems, and interactive user interface for social networking and traveling information. Therefore, the OMITS encompasses a broad range of advanced transportation research topics, say dynamic trip- match, transportation-mode optimization, traffic prediction, dynamic routing, and social network- based carpooling. This dissertation will focus on a kernel part of the OMITS, namely traffic simulation and prediction based on data containing the distribution of vehicles and the road network configuration. A microscopic traffic simulation framework has been developed to take into account various traffic phenomena, such as traffic jams resulting from bottlenecking, incidents, and traffic flow shock waves. Four fundamental contributions of the present study are summarized as follows: Firstly, an accurate and robust vehicle trajectory data collection method based on image data of unmanned aerial vehicle (UAV) has been presented, which can be used to rapidly and accurately acquire the real-time traffic conditions of the region of interest. Historically, a lack in the availability of trajectory data has posed a significant obstacle to the enhancement of microscopic simulation models. To overcome this obstacle, a UAV based vehicle trajectory data collection algorithm has been developed. This method extracts vehicle trajectory data from the UAV’s video at different altitudes with different view scopes. Compared with traditional methods, the present data collection algorithm incorporates many unique features to customize the vehicle and traffic flow, through which vehicle detection and tracking system accuracy can be considerably increased. Secondly, an open mechanics-based acceleration model has been presented to simulate the longitudinal motion of vehicles, in which five general factors—namely the subject vehicle’s speed and acceleration sensitivity, safety consideration, relative speed sensitivity and gap reducing desire—have been identified to describe drivers’ preferences and the interactions between vehicles. Inspired by the similarity between vehicle interactions and particle interactions, a mechanical system with force elements has been introduced to quantify the vehicle’s acceleration. Accordingly, each of the aforementioned five factors are assumed to function as an individual trigger to alter each vehicle’s speed. Based on Newton’s second law of motion, the subject vehicle’s longitudinal behavior can be simulated by the present open mechanics-based acceleration model. By introducing feeling gap, multilane acceleration behavior is included in the presented model. The simulation results fit realistic conditions for the traffic flow and the road capacity very well, where traffic shockwaves can be observed for a certain range of the traffic density. This model can be extended to more general scenarios if other factors can be recognized and introduced into the modeling framework. Thirdly, a driver decision-based lane change execution model has been developed to describe a vehicle’s lane change execution process, which includes two steps, i.e. driver’s lane selection and lane change execution. Currently, most lane change models focus on the driver’s lane selection, and overlook the driver’s behavior during a process of lane change execution which plays a significant role in the simulation of traffic flow characteristics. In this model, a lane change execution is analyzed as a driver’s decision-making process, which consists of desire point setting, priority decision-making, corresponding actions and achievement of consensus analysis. Compared with the traditional lane change execution models, the present model describes a realistic lane change process, and it provides more accurate and detailed simulation results in the microscopic traffic simulation. Based on the presented open mechanics-based acceleration model and the driver decision- based lane change execution model, a reverse lane change model has further been developed to simulate some complex traffic situations such as reverse lane change process at a two-way-two- lane road section where one lane is blocked by a traffic incident. Based on this reverse lane change model, information on the average waiting time and road capability can be obtained. The simulation results show that the present model is able to reflect real driver behavior and the corresponding traffic phenomenon during a reverse lane change process Through a homogenization process of the microscopic vehicle motion, we can obtain the macroscopic traffic flow of the roadway network within certain time and spatial ranges, which will be integrated into the OMITS system for traffic prediction. The validation of the models through future OMITS operations will also enable them to be high fidelity models in future driverless technologies and autonomous vehicles.Civil engineering, Travel time (Traffic engineering), Traffic engineering--Mathematical models, Travel time (Traffic engineering)--Mathematical models, Traffic flow--Computer simulation, Traffic congestion--Computer simulationlw2451Civil Engineering and Engineering MechanicsDissertationsAdvanced Vision-Based Displacement Sensors for Structural Health Monitoring
http://academiccommons.columbia.edu/catalog/ac:193930
Feng, Dongminghttp://dx.doi.org/10.7916/D8C8294GWed, 27 Jan 2016 00:00:00 +0000Most existing structural health monitoring (SHM) techniques are based on measured acceleration data. Such practice, however, is highly expensive to operate, mainly due to cumbersome, time-consuming and expensive installation of sensors and their data acquisition systems. As an emerging noncontact method, the vision-based displacement sensor systems have attracted significant research interests and offered a promising alternative to the conventional sensors for SHM. However, most existing vision-based sensors require physical access to the structure to install a predesigned target panel, which has a higher contrast and thus is easier to track. Besides, most studies are carried out in controlled laboratory environments. The accuracy and robustness of vision sensors in the outdoor field conditions have not been fully investigated. It is also noted that current researches are mainly focusing on the measurement performance evaluation of vision sensors, without discussing the use of the measured displacement data for SHM. This dissertation develops a high-precision vision sensor system for remote and real-time measurement of multipoint structural displacements by tracking natural targets on structural surfaces. Two sets of software packages are developed respectively based on two advanced template matching algorithms (i.e., the upsampled cross correlation and the orientation code matching) incorporated with different subpixel techniques. Comprehensive experiments, including laboratory shaking table tests and field bridge tests, are carried out to evaluate its performance. Satisfactory agreements are observed between the displacements measured by the proposed vision sensor and those measured by high-performance reference displacement sensors. Moreover, this study examines the robustness of the vision sensor against ill environmental conditions such as dim light, background image disturbance and partial template occlusion. This dissertation further explores the potentials of the vision sensor for fast and inexpensive SHM applications, by demonstrating the usefulness of the displacement data for experimental modal analysis, finite element (FE) model updating, damage detection, etc. For a three-story frame structure, the modal analysis shows that the obtained natural frequencies and mode shapes from displacement measurements by using one camera match well with those by using four accelerometers. In fact, the vision sensor can achieve smoother mode shapes which would make damage localization more accurate, while the resolution of mode shapes from accelerometers is limited by the sensor number. This has been demonstrated from the damage detection result of beam structures based on the mode shape curvature (MSC) index. To address the needs for monitoring aging railway and highway bridges, coupled train-track-bridge and vehicle-bridge FE models are firstly developed to study the dynamic interactions between bridges and moving trains/vehicles. Subsequently, a time-domain model updating approach for railway bridges is proposed based on the in-situ measurement of the bridges’ dynamic displacement histories by the proposed vision sensor. This dissertation further proposes a bridge damage detection procedure that utilizes vehicle-induced displacement response and the MSC index without requiring prior knowledge about the traffic excitation.Civil engineering, Structural health monitoring, Buildings--Protection, Bridges--Inspection, Bridges--Maintenance and repair, Buildings--Maintenance and repair, Building inspectiondf2465Civil Engineering and Engineering MechanicsDissertationsThe Multiscale Damage Mechanics in Objected-oriented Fortran Framework
http://academiccommons.columbia.edu/catalog/ac:193936
Yuan, Zifenghttp://dx.doi.org/10.7916/D8KS6RCJWed, 27 Jan 2016 00:00:00 +0000We develop a dual-purpose damage model (DPDM) that can simultaneously model intralayer damage (ply failure) and interlayer damage (delamination) as an alternative to conventional practices that models ply failure by continuum damage mechanics (CDM) and delamination by cohesive elements. From purely computational point of view, if successful, the proposed approach will significantly reduce computational cost by eliminating the need for having double nodes at ply interfaces. At the core, DPDM is based on the regularized continuum damage mechanics approach with vectorial representation of damage and ellipsoidal damage surface. Shear correction factors are introduced to match the mixed mode fracture toughness of an analytical cohesive zone model. A predictor-corrector local-nonlocal regularization scheme, which treats intralayer portion of damage as nonlocal and interlayer damage as local, is developed and verified. Two variants of the DPDM are studied: a single- and two- scale DPDM. For the two-scale DPDM, reduced-order-homogenization (ROH) framework is employed with matrix phase modeled by the DPDM while the inclusion phase modeled by the CDM. The proposed DPDM is verified on several multi-layer laminates with various ply orientations including double-cantilever beam (DCB), end-notch-flexure (ENF), mixed-mode-bending (MMB), and three-point-bending (TPB). The simulation is executed in the platform of FOOF (Finite element solver based on Object-Oriented Fortran). The objective of FOOF is to develop a new architecture of the nonlinear multiphysics finite element code in object oriented Fortran environment. The salient features of FOOF are reusability, extensibility, and performance. Computational efficiency stems from the intrinsic optimization of numerical computing intrinsic to Fortran, while reusability and extensibility is inherited from the support of object-oriented programming style in Fortran 2003 and its later versions. The shortcomings of the object oriented style in Fortran 2003 (in comparison to C++) are alleviated by introducing the class hierarchy and by utilizing a multilevel programming style.Engineering, Civil engineering, Mechanics, Continuum damage mechanics--Mathematical models, Composite materials--Delamination, Finite element method, Civil engineering--Mathematical models, Damages--Mathematical modelszy2134Civil Engineering and Engineering MechanicsDissertationsMultiscale analysis of shear failure of thick-walled hollow cylinder in dry sand
http://academiccommons.columbia.edu/catalog/ac:193147
Guo, N.; Zhao, J.; Sun, WaiChinghttp://dx.doi.org/10.7916/D87P8Z4HWed, 20 Jan 2016 12:54:29 +0000A novel hierarchical multiscale model has been applied to simulate the thick-walled hollow cylinder tests in dry sand and to investigate the corresponding shear failures. The combined finite-element method and discrete-element method (FEM/DEM) model employs the FEM as a vehicle to advance the solution for a macroscopic non-linear boundary value problem incrementally. It is, meanwhile, free of conventional macroscopic phenomenological constitutive law, which is replaced by discrete-element simulations conducted with representative volume elements (RVEs) associated with the Gauss quadrature points of the FEM mesh. Numerical simulations proposed by the authors indicate that this multiscale approach is capable of replicating the evolution of cavity pressure during cavity expansion – before and after the onset of strain localisation – in qualitative agreement with laboratory tests. In particular, the curvilinear shear bands observed from experiments have been reproduced numerically. The information provided by the mesoscale DEM and the macroscale FEM reveals a close linkage between significant particle rotations taking place inside the dilative shear bands and the highly anisotropic microstructural attributes of the associated RVEs.Materials science, Mechanics, Civil engineeringws2414Civil Engineering and Engineering MechanicsArticlesA nonlocal multiscale discrete-continuum model for predicting mechanical behavior of granular materials
http://academiccommons.columbia.edu/catalog/ac:193162
Liu, Yang; Sun, WaiChing; Yuan, Zifeng; Fish, Jacobhttp://dx.doi.org/10.7916/D8Z89C5PWed, 20 Jan 2016 00:00:00 +0000A three-dimensional nonlocal multiscale discrete-continuum model has been developed for modeling mechanical behavior of granular materials. In the proposed multiscale scheme, we establish an information-passing coupling between the discrete element method, which explicitly replicates granular motion of individual particles, and a finite element continuum model, which captures nonlocal overall responses of the granular assemblies. The resulting multiscale discrete-continuum coupling method retains the simplicity and efficiency of a continuum-based finite element model, while circumventing mesh pathology in the post-bifurcation regime by means of staggered nonlocal operator. We demonstrate that the multiscale coupling scheme is able to capture the plastic dilatancy and pressure-sensitive frictional responses commonly observed inside dilatant shear bands, without employing a phenomenological plasticity model at a macroscopic level. In addition, internal variables, such as plastic dilatancy and plastic flow direction, are now inferred directly from granular physics, without introducing unnecessary empirical relations and phenomenology. The simple shear and the biaxial compression tests are used to analyze the onset and evolution of shear bands in granular materials and sensitivity to mesh density. The robustness and the accuracy of the proposed multiscale model are verified in comparisons with single-scale benchmark discrete element method simulations.Materials science, Civil engineering, Mechanics, Multiscale modeling, Granular materials, Granular materials--Mathematical models, Strains and stresses, Anisotropy, Soil mechanics, Soil mechanics--Mathematical modelsyl2683, ws2414, zy2134, jf2695Civil Engineering and Engineering MechanicsArticlesExtension of OKID to Output-Only System Identification
http://academiccommons.columbia.edu/catalog/ac:192587
Vicario, Francesco; Phan, Minh Q.; Betti, Raimondo; Longman, Richard W.http://dx.doi.org/10.7916/D8GQ6XGBTue, 05 Jan 2016 00:00:00 +0000Observer/Kalman filter IDentification (OKID) is a successful approach for the estimation, from measured input-output data, of the linear state-space model describing the dynamic behavior of a structure. From such a mathematical model, it is possible to recover the modal parameters, which can be exploited to update a detailed numerical model of the structure, e.g. a Finite Element Model (FEM), to be used to predict the structural response to future excitation and to evaluate damage scenarios. This paper extends OKID to output-only system identification, i.e. to the case where only the response of the structure is measured and the input is unknown. The approach is suitable for structural health monitoring based on modal parameters, in particular for those civil infrastructures whose excitation is random in nature and in the way it is applied to the structure (e.g. wind, traffic) and therefore is difficult to measure. The paper rigorously proves the applicability of the OKID approach to the output-only case, presents the resulting new algorithms and demonstrates them via a numerical example.Mechanical engineering, Engineering, Civil engineering, Structural analysis (Engineering)--Mathematical models, Finite element method--Mathematical models, Structural engineeringfv2157, rb68, rwl4Civil Engineering and Engineering Mechanics, Mechanical EngineeringConferencesPerformance of Low-Quality Concrete as Recycled Aggregate
http://academiccommons.columbia.edu/catalog/ac:191943
Chang, Hubert; Morgan, Ryan; Aziz, Umed; Herfellner, Simon; Ho, Kennethhttp://dx.doi.org/10.7916/D81N80TPMon, 07 Dec 2015 00:00:00 +0000Since cement production is one of the most expensive and CO₂-productive processes in making concrete, our project seeks to minimize the consumption of new cement. Furthermore, we sought to recycle concrete on-site in accordance with the principle of embodied energy (the concept that a completed structure holds in it a certain amount of energy that was required to construct it, energy which is dispersed and lost if the building is demolished or severely modified). By using recycled materials for the largest bulk component of cement, we thus greatly reduce the input of energy in producing cast concrete. The usage of recycled concrete aggregate (RCA) is not a new phenomenon, but it has not been studied in the context of low-cost disaster reconstruction efforts. In our experiments, we sought to replicate the variability in concrete quality that is bound to happen on poorly supervised construction sites. It is well-documented that construction companies in developing nations frequently add water to increase the workability of fresh concrete, since they do not have access to chemical admixtures that make the mixing process easier. However, adding extra water beyond what is called for in a concrete mix decreases its final structural strength. It is also well-documented that construction companies in developing nations occasionally sell portions of their assigned cement on the black market for extra profit, and claiming that the proper amount was used in the mix. Our experimental design was therefore based on these two variables: incremental decreases in cement content and incremental increases in water content. These increments diverged from a control sample set that was designed to replicate structural-strength concrete. Testing was done at the standard 7-day cure interval. From our data, we were able to conclude that RCA is a reasonable low-cost aggregate even in the absence of admixtures, fly ash, or silica fume in the production of concrete structures. By comparing our data to structural codes, we are also able to estimate costs for the production of a single-story concrete dwelling, constructed from rubble that is processed on-site, and present two plausible modes of construction with on-site production and minimal usage of non-recycled material.Sustainability, Civil engineering, Haiti, Aggregates (Building materials)--Recycling, Concrete--Recycling, Sustainable development, Sustainable construction, Concrete--Curing, Buildings--Repair and reconstructionrcm2140, kh2446Civil Engineering and Engineering Mechanics, Earth InstituteArticlesMultiscale Modeling of Granular Materials
http://academiccommons.columbia.edu/catalog/ac:189226
Liu, Yanghttp://dx.doi.org/10.7916/D88W3CR1Tue, 06 Oct 2015 00:00:00 +0000Granular materials have a “discrete” nature whose global mechanical behaviors are originated from the grain scale micromechanical mechanisms. The intriguing properties and non-trivial behaviors of a granular material pose formidable challenges to the multiscale modeling of these materials. Some of the key challenges include upscaling of coarse-scale continuum equation form fine-scale governing equations, calibrating material parameters at different scales, alleviating pathological mesh dependency in continuum models, and generating unit cells with versatile morphological details. This dissertation aims to addressing the aforementioned challenges and to investigate the mechanical behavior of granular materials through multiscale modeling. Firstly, a three-dimensional nonlocal multiscale discrete-continuum model is presented for modeling the mechanical behavior of granular materials. We establish an information-passing coupling scheme between DEM that explicitly replicates granular motion of individual particles and a finite element continuum model, which captures nonlocal overall response of the granular assemblies. Secondly, a new staggered multilevel material identification procedure is developed for phenomenological critical state plasticity models. The emphasis is placed on cases in which available experimental data and constraints are insufficient for calibration. The key idea is to create a secondary virtual experimental database from high-fidelity models, such as discrete element simulations, then merge both the actual experimental data and secondary database as an extended digital database to determine material parameters for the phenomenological macroscopic critical state plasticity model. This expansion of database provides additional constraints necessary for calibration of the phenomenological critical state plasticity models. Thirdly, a regularized phenomenological multiscale model is investigated, in which elastic properties are computed using direct homogenization and subsequently evolved using a simple three-parameter orthotropic continuum damage model. The salient feature of the model is a unified regularization framework based on the concept of effective softening strain. The unified regularization scheme is employed in the context of constitutive law rescaling and the staggered nonlocal approach to alleviate pathological mesh dependency. Lastly, a robust parametric model is presented for generating unit cells with randomly distributed inclusions. The proposed model is computationally efficient using a hierarchy of algorithms with increasing computational complexity, and is able to generate unit cells with different inclusion shapes.Mechanics, Civil engineering, Geotechnologyyl2683Civil Engineering and Engineering MechanicsDissertationsCitizen Sensors for SHM: Use of Accelerometer Data from Smartphones
http://academiccommons.columbia.edu/catalog/ac:189133
Feng, Maria Q.; Fukuda, Yoshio; Mizuta, Masato; Ozer, Ekinhttp://dx.doi.org/10.7916/D80C4V6CTue, 06 Oct 2015 00:00:00 +0000Ubiquitous smartphones have created a significant opportunity to form a low-cost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and post-event damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Large-scale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, white-noise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from low-amplitude ambient vibration to high-amplitude seismic response. Encouraged by the results of this study, the authors are developing a citizen-engaging and data-analytics crowdsourcing platform towards a smartphone-based Citizen Sensor network for structural health monitoring and post-event damage assessment applications.Physics, Mechanical engineering, Civil engineeringmqf2101, yf2290, mm4230, eo2327Civil Engineering and Engineering MechanicsArticlesLow-Cost Aquifer Storage and Recovery: Implications for Improving Drinking Water Access for Rural Communities in Coastal Bangladesh
http://academiccommons.columbia.edu/catalog/ac:192485
Sultana, S.; Ahmed, K. M.; Mahtab-Ul-Alam, S. M.; Hasan, M.; Tuinhof, A.; Ghosh, S. K.; Rahman, M. S.; Zheng, Yan; Ravenscroft, P.http://dx.doi.org/10.7916/D8280709Thu, 01 Oct 2015 16:24:07 +0000Fresh water resources are scarce in rural communities in the southern deltaic plains of Bangladesh where both shallow and deep groundwater is frequently brackish, and fresh water ponds have been increasingly salinized by inundation during storm surges and brackish-water aquaculture. Low-cost aquifer storage and recovery (ASR) schemes were constructed at 13 villages in three coastal districts by developing storage in shallow confined fine to medium sand aquifers overlain by variable thicknesses of silt and clay. A typical ASR scheme consisted of a double-chambered graded sand filtration tank with a volume of 19.5 m3 that feeds filtered pond water to four to six large diameter (d=30.5 or 56 cm) infiltration wells through PVC pipes fitted with stop valves and flow meters. The infiltration wells were completed at 18–31 m below ground and filled with well-sorted gravel capped with a thin layer of fine sand that acts as a second stage filter. Infiltration rates at 13 sites averaged 3 m3/day (range: 3–6 m3/day) over one year of operation. At 11 sites where water was abstracted, the recovery rate ranged from 5 to 40%. The source pond source water frequently had turbidity values of ≥100 NTU. After sand filtration, the turbidity is typically 5 NTU. Despite this, clogging management involving frequent (monthly to weekly) manual washing to remove fine materials deposited in the sand filtration tank and the infiltration wells is found to be necessary and effective, with post-manual-washing operational infiltration rates restored to annual average values. E. coli counts in recovered water are greatly reduced compared to raw pond water, although E. coli is still detected in about half of the samples. Arsenic in recovered water was detected to be at level of > 100 μg/L repeatedly at three sites, suggesting that As risks must be carefully managed and require further investigation.Civil engineering, Water resources management, Area planning and developmentyz13Lamont-Doherty Earth ObservatoryArticlesVegetated Infrastructure for Urban Stormwater Management: Advances in Understanding, Modeling and Design
http://academiccommons.columbia.edu/catalog/ac:189499
Elliott, Robert M.http://dx.doi.org/10.7916/D8NV9HKSFri, 04 Sep 2015 00:00:00 +0000There are many documented environmental benefits to concentrating populations in cities. However, the impermeable nature of modern urban landscapes, which has been created by roads, buildings, and paved public spaces, has altered the natural cycle of water through today’s cities. As a result, a greater fraction of rainfall becomes runoff, creating stormwater pollution that degrades the very host environments needed to support city living. One attractive approach to urban stormwater management is the use of engineered and non-engineered vegetative systems to reduce the amount of rainfall that becomes runoff. When one considers the vast number of vegetative systems needed to bring about significant change, along with the variety of environmental niches in the urban landscape, it is clear that an array of “greening” strategies are needed. In turn, accurate performance data and models of these strategies are necessary to appropriately inform design and policy decisions. The research presented in this dissertation focuses on advancing the understanding, modeling, and design of three types of vegetated infrastructure with potential to address urban stormwater challenges: extensive green roofs, street trees, and vine canopies. The first research focus examines a nuance to a well-developed and well-studied technology: the extensive green roof. Nearly four years of environmental and runoff monitoring data from two full-scale extensive green roofs are used to determine how the time of year impacts hydrologic performance while considering the covariates of antecedent dry weather period, potential evapotranspiration and storm event size. Comparisons are made between thick and thin extensive green roof systems, and novel models are presented which account for seasonal variability. The second research focus evaluates the absorptive capacity of an existing type of urban vegetation: the street tree. In particular, this work looks at the permeability and infiltration capacity of the tree pit’s soil surface, which is often a controlling factor in the hydrologic performance of street trees. The resulting model links physical features of the tree pit to its ability to absorb water. Furthermore, the results indicate two simple, low-cost management strategies to improve urban stormwater capture via street trees. The third research focus explores the stormwater management potential for a new type of vegetated infrastructure: the horizontal vine canopy. Hydrologic performance data from sixteen vine canopies grown on a New York City rooftop are used to determine the capacity of the vines to retain stormwater, return water to the atmosphere via transpiration, and grow in the harsh rooftop conditions. Models and coefficients describing stormwater capture and plant transpiration are then presented and used to estimate the potential capacity of vine canopies to contribute to urban stormwater management. Exploration into new forms of vegetated infrastructure and facets of existing urban vegetation through the perspective of stormwater management has resulted in valuable findings and experimental methodologies. In several instances, these studies required new measuring equipment or sampling procedures, which were developed, validated, and made available for future research.Civil engineering, Sustainability, Urban forestryrme2123Civil Engineering and Engineering Mechanics, Earth InstituteDissertationsDispersion of CaCO₃ Nanoparticles by Sonication and Surfactant Treatment for Application in Fly Ash-Cement Systems
http://academiccommons.columbia.edu/catalog/ac:186782
Kawashima, Shiho; Seo, Jung-Woo Ted; Corr, David J.; Hersam, Mark C.; Shah, Surendra P.http://dx.doi.org/10.7916/D82V2F80Fri, 26 Jun 2015 11:42:16 +0000This research aims to offset the negative effects of fly ash on the early-age properties of cementitious materials with the use of calcium carbonate (CaCO₃) nanoparticles. The main focus is to enhance the effect of the nanoparticles by improving dispersion through ultrasonication and use of surfactants. CaCO3 aqueous suspensions with various surfactant types and concentrations are prepared and subjected to different sonication protocols (varying duration and amplitude). Dispersion and stability are quantitatively measured by comparing their absorbance spectra through spectrophotometry and qualitatively evaluated through SEM imaging. The effectiveness of sonicated CaCO₃ nanoparticle additions in accelerating setting and improving early-age compressive strength gain of fly ash-cement pastes is investigated. The sonication protocol is optimized and the most effective dispersion is achieved with polycarboxylate-based superplasticizer. Good agreement is found between the dispersion measurements and mechanical performance.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesNovel Evidence for the Formation of Semi-Permeable Membrane Surrounding the Portland Cement Particles During the Induction Period
http://academiccommons.columbia.edu/catalog/ac:186779
Hou, Pengkun; Kong, Deyu; Kawashima, Shiho; Qian, Jueshi; Corr, David J.; Shah, Surendra P.http://dx.doi.org/10.7916/D8BC3XQNFri, 26 Jun 2015 11:28:31 +0000This letter presents strong novel evidence for the semi-permeable membrane surrounding Portland cement during the induction period. In the cement hydration, heat curve obtained through high-resolution differential scanning calorimetry under isothermal conditions, one main and some other smaller endothermic peaks were detected. These endothermic peaks are believed to be caused by the osmotic expansion that occurs after the semi-permeable membrane forms, not the precipitation of calcium hydroxide or the imbibition of water during the induction period.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesModification Effects of Colloidal NanoSiO₂ on Cement Hydration and its Gel Property
http://academiccommons.columbia.edu/catalog/ac:186776
Hou, Pengkun; Kawashima, Shiho; Kong, Deyu; Corr, David J.; Qian, Jueshi; Shah, Surendra P.http://dx.doi.org/10.7916/D8KW5F7PFri, 26 Jun 2015 11:14:35 +0000To understand the effects of colloidal nanoSiO₂ (CNS) on cement hydration and gel properties in the early and later age, hydration heat, calcium morphology, hydroxide content, non-evaporable water (NEW) content and nanoscale mechanical properties were measured. Some comparison studies were conducted on silica fume (SF) paste, as well. Results revealed that the accelerating effect of CNS on hydration in the early age is achieved by the acceleration of cement dissolution and hydrate nucleation on reacted nanoSiO₂ particles. Although cement hydration can be greatly accelerated by CNS in the early age, its later age hydration is hindered. The NEW content of CNS-added paste experiences a higher rate of increase initially, but gradually becomes smaller than that of the control paste due to changes in the gel structure, making NEW content an unsuitable method for monitoring the hydration of CNS-added paste. However, nanoindentation results revealed that CNS modifies the gel structure to increase the high-stiffness C–S–H gel content.Engineering, Civil engineering, Nanotechnologysk2294Civil Engineering and Engineering MechanicsArticlesRate of Thixotropic Rebuilding of Cement Pastes Modified with Highly Purified Attapulgite Clays
http://academiccommons.columbia.edu/catalog/ac:186770
Kawashima, Shiho; Chaouche, Mohend; Corr, David J.; Shah, Surendra P.http://dx.doi.org/10.7916/D8V9877ZFri, 26 Jun 2015 11:03:46 +0000This study investigates the influence of highly purified, nano-sized attapulgite clays on the rate of structural rebuilding of cement pastes. A shear rheological protocol is implemented that measures the rate of rebuilding of pastes after being broken down under shear and maintained under stress corresponding to the weight of the material. This simulates a real casting situation during which the concrete is initially in motion, then cast in place and measures how quickly it gains green strength immediately after placement. The rate of recovery for different resting times and preshear conditions are considered. The strain rate decay curves are fitted with a compressed exponential model to obtain relaxation time. The results show that the purified attapulgite clays significantly accelerate rate of recovery of pastes, especially at early ages. However, this accelerating effect diminishes at longer resting times as hydration mechanisms begin to dominate.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesInfluence of Purified Attapulgite Clays on the Adhesive Properties of Cement Pastes as Measured by the Tack Test
http://academiccommons.columbia.edu/catalog/ac:186764
Kawashima, Shiho; Chaouche, Mohend; Corr, David J.; Shah, Surendra P.http://dx.doi.org/10.7916/D8CC0ZV1Fri, 26 Jun 2015 10:49:17 +0000This study evaluates the influence of small additions of highly-purified attapulgite clays (0.2% and 0.5% addition by mass of cement) on the adhesive properties of cement pastes. Adhesive properties are measured by the tack test, a novel method of evaluating the rheological properties of granular materials. To better understand the results of the tack test as they pertain to cementitious materials, a highly concentrated material that is evolving due to thixotropic rebuilding and hydration, they are supplemented with a measure of the viscoelastic properties over time obtained through low-amplitude oscillatory shear rheometry. The influence of different preshear conditions and resting times (age of paste) on the adhesive properties are determined. Results show the tack test to be a suitable method for obtaining useful information about the adhesive properties and structural evolution of the material in the fresh state.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesInfluence of Kaolinite Clay on the Chloride Diffusion Property of Cement-Based Materials
http://academiccommons.columbia.edu/catalog/ac:186761
Fan, Yingfang; Zhang, Shiyi; Kawashima, Shiho; Shah, Surendra P.http://dx.doi.org/10.7916/D8MW2G8QFri, 26 Jun 2015 10:42:08 +0000To constitute blended cement concrete with high chloride diffusion resistivity, the effects of kaolinite clay on the mechanical properties and chloride diffusivity of cement paste, mortar and concrete were investigated. Ordinary Portland cement was partially replaced by kaolinite clay at 0%, 1%, 3%, 5%, 7% and 9% by weight of cement. All blended cement-based samples were prepared using a w/c ratio of 0.5. The microstructure, workability, early-age and long-term flexural strength of pastes were tested. The chloride diffusivity of mortars was measured. And the compressive strength and chloride diffusivity of concrete were measured. Mercury Intrusion Porosimetry (MIP) was employed to evaluate porosity characteristics. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectra (EDS) were applied to investigate the micro morphology and chemical element distribution inside the cement matrix, and the rapid chloride migration (RCM) method was applied to test chloride diffusivity. The MIP test results show that the addition of clay improves the micro-pore structure in the cement paste and limits the introduction of chloride ions. SEM imaging suggests that the kaolinite clay is acting as both filler and accelerator of cement hydration. It is found that the addition of clay alters the water requirement of normal consistency and the setting time of cement, whereas it has little influence on the soundness. Compared to the control, the flexural strength of cement paste with 1% kaolinite clay increased by 30.41%, 39.04%, 36.27% and 38.32% at 1, 3, 7 and 90 days, respectively. The 28-day flexural strength only increased slightly. It is observed that the cement mortar with clay has lower chloride diffusion coefficient values compared to the plain mortar, the 28-day diffusion coefficient of chloride ion View the MathML source(DCl-) of cement mortar is decreased by 53.03% with 5% clay. The increase in compressive strength of the cement concrete with clay is 12%, 13.5%, and 28.4% compared to the control at 1%, 3% and 5% addition, respectively. The chloride diffusion coefficient of cement concrete decreases exponentially with the clay addition. The reduction of chloride diffusion coefficient of cement concrete is 8.68% and 18.87% at 1% and 5% clay, respectively. The 28-day compressive strength increases linearly with the chloride diffusion coefficient of the concrete.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesEffects of Colloidal Nanosilica on Rheological and Mechanical Properties of Fly Ash-Cement Mortar
http://academiccommons.columbia.edu/catalog/ac:186758
Hou, Pengkun; Kawashima, Shiho; Wang, Kejin; Corr, David J.; Qian, Jueshi; Shah, Surendra P.http://dx.doi.org/10.7916/D84T6HJ6Fri, 26 Jun 2015 10:23:43 +0000The present study is aimed at investigating the combined effects of colloidal nanosilica (CNS) and fly ash on the properties of cement-based materials. The fresh and hardened properties of mixtures with CNS of 10 nm size and two Class F fly ashes were evaluated. Results revealed that CNS accelerates the setting of fly ash–cement systems by accelerating cement hydration, while fly ash can offset the reduction in fluidity caused by CNS. The early-age strength gain (before 7 d) of fly ash–cement systems was improved by CNS. However, the strength gain of mixtures with CNS diminished at later ages (after 28 d), where strength was eventually comparable to or exceeded by mixtures without CNS. Results showed that lack of Ca(OH)₂, which results from the high pozzolanic reactivity of CNS at early ages, and the hydration hindrance effect of CNS on cement at later ages can be the critical reasons.Engineering, Civil engineering, Nanotechnologysk2294Civil Engineering and Engineering MechanicsArticlesModification of Cement-Based Materials with Nanoparticles
http://academiccommons.columbia.edu/catalog/ac:186755
Kawashima, Shiho; Hou, Pengkun; Corr, David J.; Shah, Surendra P.http://dx.doi.org/10.7916/D8DB810NFri, 26 Jun 2015 10:13:02 +0000This is a summary paper on the work being done at the Center for Advanced Cement-Based Materials at Northwestern University on the modification of cement-based materials with nanoparticles, specifically nanoclays, calcium carbonate nanoparticles, and nanosilica. The rheological properties of clay-modified cement-based materials are investigated to understand the influence of nanoclays on thixotropy. The influence of the method of dispersion of calcium carbonate nanoparticles on rate of hydration, setting, and compressive strength are evaluated. And an in-depth study on the mechanisms underlying the influence of nanosilica on the compressive strength gain of fly ash–cement systems is discussed. The motivation behind these studies is that with proper processing techniques and fundamental understanding of the mechanisms underlying the effect of the nanoparticles, they can be used to enhance the fresh-state and hardened properties of cement-based materials for various applications. Nanoclays can increase the green strength of self-consolidating concrete for reduced formwork pressure and slipform paving. Calcium carbonate nanoparticles and nanosilica can offset the negative effects of fly ash on early-age properties to facilitate the development of a more environmentally friendly, high-volume fly ash concrete.Engineering, Civil engineering, Nanotechnologysk2294Civil Engineering and Engineering MechanicsArticlesEffects of Colloidal NanoSiO2 on Fly Ash Hydration
http://academiccommons.columbia.edu/catalog/ac:186752
Hou, Pengkun; Wang, Kejin; Qian, Jueshi; Kawashima, Shiho; Kong, Deyu; Shah, Surendra P.http://dx.doi.org/10.7916/D8NS0T2PFri, 26 Jun 2015 09:49:38 +0000The influences of colloidal nanoSiO₂ (CNS) addition on fly ash hydration and microstructure development of cement–fly ash pastes were investigated. The results revealed that fly ash hydration is accelerated by CNS at early age thus enhancing the early age strength of the materials. However, the pozzolanic reaction of fly ash at later age is significantly hindered due to the reduced CH content resulting from CNS hydration and the hindered cement hydration, as well as due to a layer of dense, low Ca/Si hydrate coating around fly ash particles. The results and discussions explain why the cementitious materials containing nanoSiO₂ had a lower strength gain at later ages. Methods of mitigating the adverse effect of nanoSiO₂ on cement/FA hydration at later ages were proposed.Engineering, Civil engineering, Nanotechnologysk2294Civil Engineering and Engineering MechanicsArticlesInfluence of Clays on the Shrinkage and Cracking Tendency of SCC
http://academiccommons.columbia.edu/catalog/ac:186749
Gao, Xiaojian; Kawashima, Shiho; Liu, Xiaoyan; Shah, Surendra P.http://dx.doi.org/10.7916/D8X929FTFri, 26 Jun 2015 09:08:49 +0000The influence of different types of clay on the shrinkage and cracking tendency of fly ash modified self-consolidating concrete (SCCF) for the application of slipform paving were investigated in this study. The mortar phase of each mix was tested for autogenous shrinkage, total free shrinkage under drying and restrained shrinkage cracking. The mechanical properties (flexural strength, compressive strength, and modulus) were studied to supplement the results of the shrinkage and cracking tests. The plain SCCF mix was compared against the clay-modified SCCF mixes, as well as conventional SCC and slipform concrete (SFC) mixes. The results showed that the very early-age autogenous shrinkage of SCCF mortar was increased by the addition of clays due to adsorption effects. The effects of the clays on total shrinkage under long-term drying were found to depend mainly on the pozzolanic reactivity, but these effects were very slight at low dosages of about 1% by mass of binder. The early-age cracking tendency was aggravated by the clays composed of purified magnesium alumino silicate and metakaolin, but little influenced by the clay composed of kaolinite, illite and silica. Overall, the SCC mixture modified with both fly ash and a small amount of clay showed comparable shrinkage and early-age cracking performances as conventional SFC.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesEarly-Age Autogenous and Drying Shrinkage Behavior of Cellulose Fiber-Reinforced Cementitious Materials
http://academiccommons.columbia.edu/catalog/ac:186746
Kawashima, Shiho; Shah, Surendra P.http://dx.doi.org/10.7916/D85T3JN4Thu, 25 Jun 2015 16:37:39 +0000The objective of this study was to determine how the early-age shrinkage behavior of cementitious materials is affected by the addition of saturated cellulose fibers under sealed and unsealed conditions. The sealed condition simulates autogenous shrinkage exclusively while the unsealed condition introduces drying shrinkage, as well. Although the primary focus was to determine whether saturated cellulose fibers are suitable to mitigate autogenous shrinkage as an internal curing agent, evaluating their effect under drying conditions provided further insight into the overall shrinkage behavior of the composite material. At additions of 1% by mass of cement, the cellulose fibers were found to show significant drying shrinkage cracking control while providing some internal curing. In addition, early-age shrinkage test results were supplemented with a quantitative measure of fiber dispersion based on comparing theoretical and experimental values of the fiber volume fraction in hardened cementitious samples. Results indicated that improved dispersion leads to improved properties.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesInterfacial Transition Zones in Recycled Aggregate Concrete with Different Mixing Approaches
http://academiccommons.columbia.edu/catalog/ac:186743
Li, Wengui; Xiao, Jianzhuang; Sun, Zhihui; Kawashima, Shiho; Shah, Surendra P.http://dx.doi.org/10.7916/D8F76BQ9Thu, 25 Jun 2015 16:22:48 +0000Interfacial Transition Zone (ITZ) is an important phase that influences the mechanical properties of Recycled Aggregate Concrete (RAC). This paper is devoted to an investigation of the effect of different mixing approaches on the properties of ITZs in RAC. Nanoindentation and Scanning Electron Microscopy (SEM) were implemented to characterize nanomechanical properties and microstructures of the old and new ITZs. The results indicate that the indentation modulus of ITZs have different distribution trends when using different mixing approaches. It reveals that the Two-Stage Mixing Approach (TSMA) can improve the nanomechanical properties of the new ITZ by reducing the volume fraction of voids and Calcium Hydroxide (CH). The SEM observation also indicates that an obviously denser and more homogeneous microstructure was achieved in the new ITZ prepared by TSMA compared to a Normal Mixing Approach (NMA). Correlating the nanoindentation and SEM results with the compressive strength, it can be concluded that TSMA has a beneficial influence on the mechanical properties of RAC by improving the properties of the new ITZ.Engineering, Civil engineeringsk2294Civil Engineering and Engineering MechanicsArticlesExtreme Storm Surge Hazard Estimation and Windstorm Vulnerability Assessment for Quantitative Risk Analysis
http://academiccommons.columbia.edu/catalog/ac:186995
Lopeman, Madeleine Elisehttp://dx.doi.org/10.7916/D8BC3XNRThu, 07 May 2015 00:24:18 +0000Quantification of risk to natural disasters is a valuable endeavor from engineering, policy and (re)insurance perspectives. This work presents two research efforts relating to meteorological risk, specifically with regard to storm surge hazard estimation and wind vulnerability assessment.
While many high water level hazard estimation methods have been presented in the literature and used in industry applications, none bases its results on disaggregated tidal gauge data while also capturing the effects of the evolution of storm surge over the duration of a storm. Additionally, the coastal destruction wreaked by Hurricane Sandy in 2012 prompted motivation to estimate the event’s return period. To that end, this dissertation first presents the motivation for and development of the clustered separated peaks-over-threshold simulation (CSPS) method, a novel approach to the estimation of high water level return periods at coastal locations. The CSPS uses a Monte Carlo simulation of storm surge activity based on statistics derived from tidal gauge data. The data are separated into three independent components (storm surge, tidal cycle and sea level rise) because different physical processes govern different components of water level. Peak storm surge heights are fit to the generalized Pareto distribution, chosen for its ability to fit a wide tail to limited data, and a clustering algorithm incorporates the evolution of storm surge over surge duration. Confidence intervals on the return period estimates are computed by applying the bootstrapping method to the storm surge data.
Two case studies demonstrate the application of the CSPS to coastal tidal gauge data. First, the CSPS is applied to tidal gauge data from lower Manhattan. The results suggest that the return period of Hurricane Sandy’s peak water level is 103 years (95% confidence interval 38–452 years). That the CSPS estimate is significantly lower than previously published return periods indicates that storm surge hazard in the New York Harbor has, until now, been underestimated. The CSPS is also applied to all tidal gauge stations managed by the National Oceanographic and Atmospheric Administration (NOAA) for which the hourly water level time histories are at least 30 years long. Comparison to NOAA’s exceedance probability levels for these stations suggests that the CSPS estimates higher return levels than NOAA, but also that the NOAA values fall within the 95% CI from the CSPS for more than half of the stations tested.
This dissertation continues with a critical comparison of windstorm vulnerability models. The intent of this research is to provide a compendium of reference curves against which to compare damage curves used in the reinsurance industry. The models tend to represent specific types of construction and use varying characteristic wind speed measurements to represent storm intensity. Wind speed conversion methods are used to harmonize wind speed scales. The different vulnerability models analyzed stem from different datasets and hypotheses, thus rendering them relevant to certain geographies or structural typologies. The resulting collection of comparable windstorm vulnerability models can serve as a reference framework against which damage curves from catastrophe risk models can be evaluated.Civil engineering, Hydrologic sciences, StatisticsCivil Engineering and Engineering MechanicsDissertationsUrban Transport Project Prioritization Strategy in Developing Countries: A Scenario-Based Multi-Criteria Decision Analysis Perspective
http://academiccommons.columbia.edu/catalog/ac:186530
Liu, Muqinghttp://dx.doi.org/10.7916/D89022QTTue, 21 Apr 2015 15:20:08 +0000Given unprecedented levels of urbanization and motorization in developing countries and deteriorating infrastructure in developed countries, cities around the world have been facing the enormous challenge of delivering sustainable forms of infrastructure with fewer resources. In the developing world, the challenges in urban infrastructure investment become even more daunting as manifested by the staggering size of infrastructure funding gap. $1 trillion per annum over the period by 2020 is required by developing countries to meet the demand of rapid urbanization and to address the backlogs and deficiencies for infrastructure facilities (World Bank 2013). Therefore, prioritizing projects at the system level based on transparent and evidenced-based decision-making processes has emerged as one of the most promising ways to bridge such enormous funding gaps, especially for developing countries.
Nevertheless, effective prioritization of infrastructure projects is hindered by a series of constraints including institutionalized inefficiency, inadequate data obstructing decision making, insufficient coordination among various stakeholders, lack of public consultation, lack of technical capacity for project evaluation and prioritization, and lack of consideration of possible alternatives in the infrastructure planning. Although there has been considerable discussion regarding the shortcomings of contemporary metropolitan transportation planning, there has been little effort to develop a strategy for prioritizing urban transport projects in developing countries. This calls for a new approach to addressing the above-mentioned issues.
This thesis first presents the current status and general characteristics of urban transport decision-making in developed and developing countries alike. It then provides a comprehensive literature review on the evolution and application of scenario planning and multi-criteria, specifically in the field of transportation projects prioritization and transportation planning. As the main contribution of this research effort to current research, a novel project prioritization framework - which incorporates scenario planning into multi-criteria decision analysis (MCDA) for prioritizing urban transport projects - is proposed to support sustainable urban transport development, through the efficient use of existing project evaluation information and emergent scenario of various stakeholder's input. Such integration of scenario planning and MCDA provides a balanced view of both the analytical and intuitive components of the decision-making process and allow comparisons between different roles of various stakeholders.
The framework is then applied to set priorities for nine recent urban transport projects constructed within a two-year framework in the Tianjin Binhai New Area, China. In addition, a case study on World Bank's infrastructure investment portfolio in China is also conducted in which a selection of urban transport projects in eight different cities is ranked. The results show that the proposed framework could serve as a consistent, robust and comprehensive infrastructure project prioritization strategy that reconciles diverse perspectives among stakeholders while introducing sustainability in urban transport decision making and linking the prioritization process to the transportation planning that precedes it.Civil engineeringml2949Civil Engineering and Engineering MechanicsDissertationsCharacterization and Modeling of Ferromagnetic Particulate Nanocomposites for Strain and Fracture Sensing
http://academiccommons.columbia.edu/catalog/ac:185280
Jang, Sung-Hwanhttp://dx.doi.org/10.7916/D8Q23Z4RFri, 27 Mar 2015 00:00:00 +0000This dissertation investigates the multiphysical behavior of multi-walled carbon nanotubes (MWCNTs)/polydimenthylsiloxane (PDMS) composites containing chain-structured nickel particles for strain sensing. Compared with traditional strain gauges, this novel strain sensor exhibits high flexibility, large elongation, and high strain sensitivity and therefore has a wide application in structural health monitoring and fracture detection with minimal surface preparation. The scope of this study covers the material fabrication, numerical simulation of microstructure evolution, micromechanics-based characterization and modeling for the multi-physical properties, and experimental investigation of the strain sensitivity in sensing applications. MWCNT/PDMS composites with chain-structured ferromagnetic particles were fabricated using a solution casting method under an external magnetic field. Different concentrations of MWCNTs, as well as ferromagnetic particles, were well mixed in the pre-polymer matrix. An external magnetic field was applied during the curing process to align the particles into a chain structure. The morphology of MWCNTs and chain-structured nickel particles in the PDMS were investigated using an optical microscope and a scanning electron microscope. The electrical properties such as a percolation threshold and electrical conductivity of MWCNT/PDMS composites with different concentrations of chain-structured ferromagnetic particles were investigated for strain sensing application. For MWCNT/PDMS composites, a simplified model has been developed to predict their effective electrical conductivity. MWCNTs are well dispersed in a PDMS matrix, and the mixture is then cured and cast into thin films for electrical characterization. The MWCNTs are assumed to be statistically uniformly distributed in the PDMS matrix with the three-dimensional (3D) waviness. As the proportion of MWCNTs increases to a certain level, namely the percolation threshold, the discrete MWCNTs start to connect with each other, forming a 3D network which exhibits a significant increase in the effective electrical conductivity. The eight-chain model has been used to predict the effective electrical conductivity of the composite, in which the contact resistance between MWCNTs has been considered through the Simmons' equation. The eight-chain network features can be significantly changed to adjust to modifications to the mixing process, MWCNT length and diameter, and clustering and curling of MWCNTs. A Gaussian statistics-based formulation is used to calculated the effective length of a single MWCNT which is well dispersed in the matrix. The modeling results for the effective electrical conductivity agree with the experiments very well, they are highly dependent on the contact resistance between MWCNTs and the waviness of the MWCNTs. The effect of inter-nanotube distance and diameter of MWCNTs on the effective electrical conductivity of the MWCNT/PDMS composite is also discussed.Micromechanics-based modeling method of the microstructure evolution of ferromagnetic particles moving in the PDMS pre-polymer has been developed to understand the alignment mechanism and to optimize the fabrication procedure. Under a uniformly applied magnetic field, in the neighborhood of ferromagnetic particles, the magnetic field will be significantly distorted and the magnetic force induced will align particles into short chains, which will further merge into long chains. The experiments have been simulated with the equivalent inclusion method. This study has led to the development of a novel strain sensor. Both MWCNTs and ferromagnetic particles enhanced the electrical conductivity of the nanocomposites, but they exhibited different effects on the strain sensitivity of the sensor. When the proportion of MWCNTs that are well dispersed in PDMS is higher than the percolation threshold, the strain sensitivity reduces with the increase of MWCNTs in general; whereas a higher volume fraction of FPs produces a higher strain sensitivity when the chain-structure of FPs is sustained. The mechanisms causing this interesting phenomenon have been demonstrated through the microstructural evolution and micromechanics-based modeling method. These findings indicate that an optimal design of the volume fraction of FPs and MWCNTs exists to achieve the best strain sensitivity of this type of sensors. It is demonstrated that the nanocomposites containing 20 vol.% of nickel particles and 0.35 wt.% MWCNTs exhibits a high strain sensitivity of ~80.Civil engineering, Mechanical engineering, Engineeringsj2527Civil Engineering and Engineering MechanicsDissertationsStatistical pattern recognition based structural health monitoring strategies
http://academiccommons.columbia.edu/catalog/ac:194316
Balsamo, Lucianahttp://dx.doi.org/10.7916/D8ST7NNGThu, 29 Jan 2015 00:00:00 +0000Structural Health Monitoring (SHM) is concerned with the analysis of aerospace, mechanical and civil systems with the objective of identifying damage at its onset. In civil engineering applications, damage may be defined as any change in the structural properties that hinders the current or future performance of that system. This is the premise on which vibration-based techniques are based. Vibration-based methods exploit the response measured directly on the system to solve the SHM assignment. However, also fluctuations in the external conditions may induce changes in the structural properties. For these reasons, the SHM problem is ideally suited to be solved within the context of statistical pattern recognition, which is the discipline concerned with the automatic classification of objects into categories. Within the statistical pattern recognition based SHM framework, the structural response is portrayed by means of a compact representation of its main traits, called damage sensitive features (dsf). In this dissertation, two typologies of dsf are studied: the first type is extracted from the response of the system by means of digital signal processes alone, while the other is obtained by making use of a physical model of the system. In both approaches, the effects of external conditions are accounted for by modeling the damage sensitive features as random variables. While the first method uses outlier analysis tools and delivers a method optimally apt to perform the task of damage detection within the short-term horizon, the second approach, being model-based, allows for a deeper characterization of damage, and it is then more suited for long-term monitoring purposes. In the dissertation, an approach is also proposed that allows the use of the statistical pattern recognition framework when there is limited availability of data to model the damage sensitive features. All proposed methodologies are validated both numerically and experimentally.Civil engineering, Structural health monitoring, Pattern perception--Statistical methodslb2591Civil Engineering and Engineering MechanicsDissertationsStructural Identification, Health Monitoring and Uncertainty Quantification under Incomplete Information with Minimal Requirements for Identifiability
http://academiccommons.columbia.edu/catalog/ac:194310
Mukhopadhyay, Suparnohttp://dx.doi.org/10.7916/D8ZG6R1CWed, 21 Jan 2015 00:00:00 +0000Structural identification is the inverse problem of estimating the physical parameters, e.g. element masses and stiffnesses, of a model representing a structural system, using response measurements obtained from the actual structure subjected to operational or well-defined experimental excitations. It is one of the principal focal areas of modal testing and structural health monitoring, with the identified model finding a wide variety of applications, from obtaining reliable response predictions to timely detection of structural damage (location and severity) and consequent planning and validating of maintenance/retrofitting operations. However, incomplete instrumentation of the monitored system and ambient vibration testing generally result in spatially incomplete and arbitrarily normalized measured modal information, often making the inverse problem ill-conditioned and resulting in non-unique identification results. The problem of parameter identifiability addresses the question of whether or not a parameter set of interest can be identified from the available information. The identifiability of any parameter set of interest depends on the number and location of sensors on the monitored system. In this dissertation we study the identifiability of the mass and stiffness parameters of shear-type systems, including 3-dimensional laterally-torsionally coupled rigid floor systems, with incomplete instrumentation, simultaneous to the development of algorithms to identify the complete mass and stiffness matrices of such systems. Both input-output and output-only situations are considered, and mode shape expansion and mass normalization approaches are developed to obtain the complete mass normalized mode shape matrix, starting from the incomplete modal parameters identified using any suitable experimental or operational modal analysis technique. Methods are discussed to decide actuator/sensor locations on the structure which will ensure identifiability of the mass and stiffness parameters. Several possible minimal and near-minimal instrumentation set-ups are also identified. The minimal a priori information necessary in output-only situations is determined, and different scenario of available a priori information are considered. Additionally, tests for identifiability are discussed for both pre- and post-experiment applications. The different theoretical discussions are illustrated using numerical simulations and experimental data. It is shown that the proposed identification algorithms are able to obtain reliably accurate physical parameter estimates even under the constraints of minimal instrumentation, minimal a priori information, and unmeasured input. The different actuator/sensor placement rules and identifiability tests are useful for both experiment design purposes, to determine the necessary number and location of sensors, as well as in identifying possibilities of multiple solutions post-experiment. The parameter identification methods are applied for structural health monitoring using experimental data, and an approach is discussed for probabilistic characterization of structural damage location and severity. A perturbation based uncertainty propagation approach is also discussed for the identification of the distributions of mass and stiffness parameters, reflecting the variability in the test structure, using very limited measured and a priori information.Civil engineering, Mechanics, Mechanical engineering, Structural analysis (Engineering), Structural health monitoring, Mechanical engineering--Mathematical modelssm3315Civil Engineering and Engineering MechanicsDissertationsFeasibility of Frequency-Modulated Wireless Transmission for a Multi-Purpose MEMS-Based Accelerometer
http://academiccommons.columbia.edu/catalog/ac:178899
Sabato, Alessandro; Feng, Maria Q.http://dx.doi.org/10.7916/D8MG7N4RWed, 22 Oct 2014 00:00:00 +0000Recent advances in the Micro Electro-Mechanical System (MEMS) technology have made wireless MEMS accelerometers an attractive tool for Structural Health Monitoring (SHM) of civil engineering structures. To date, sensors’ low sensitivity and accuracy—especially at very low frequencies—have imposed serious limitations for their application in monitoring large-sized structures. Conventionally, the MEMS sensor’s analog signals are converted to digital signals before radio-frequency (RF) wireless transmission. The conversion can cause a low sensitivity to the important low-frequency and low-amplitude signals. To overcome this difficulty, the authors have developed a MEMS accelerometer system, which converts the sensor output voltage to a frequency-modulated signal before RF transmission. This is achieved by using a Voltage to Frequency Conversion (V/F) instead of the conventional Analog to Digital Conversion (ADC). In this paper, a prototype MEMS accelerometer system is presented, which consists of a transmitter and receiver circuit boards. The former is equipped with a MEMS accelerometer, a V/F converter and a wireless RF transmitter, while the latter contains an RF receiver and a F/V converter for demodulating the signal. The efficacy of the MEMS accelerometer system in measuring low-frequency and low-amplitude dynamic responses is demonstrated through extensive laboratory tests and experiments on a flow-loop pipeline.Civil engineering, Electrical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesExperimental Study of Rocking Motion of Rigid Bodies on Deformable Medium via Monocular Videogrammetry
http://academiccommons.columbia.edu/catalog/ac:179037
Greenbaum, Raphaelhttp://dx.doi.org/10.7916/D83N2220Fri, 17 Oct 2014 00:00:00 +0000The study of rigid body rocking is applicable to a wide variety of structural and non-structural elements. The current applications range from bridge pier and shallow footing design to hospital and industrial equipment, even art preservation. Despite the increasing number of theoretical and simulation studies of rocking motion, few experimental studies exist. Of those that have been published, most are focused on a constrained version of the complete problem introducing modifications to the physical problem with the purpose of eliminating either sliding, uplift or the three dimensional response of the body. However, all of these phenomena may affect the response of an unrestrained rocking body. Furthermore, the majority of the experimental studies that have been published have used methods that are ill-suited to comprehensive three dimensional experimental analysis of the problem. The intent of this work is two-fold. First, to present a computer vision method that allows for the experimental measurement of the rigid body translation and rotation time histories in three dimensions. Experimental results obtained with this method will be presented to demonstrate that it obtains greater than 97% accuracy when compared against National Institute of Standards and Technology traceable displacement sensors. The experimental results highlight important phenomena predicted in some state-of-the-art models for 3D rocking behavior. Second, to present experimental evidence of the importance of characterizing the support medium as deformable instead of the commonly assumed rigid model. It will be shown in this work that this assumption of a rigid support may in some cases lead to non-conservative analysis that is unable to predict rocking motion and, in some cases, even failure.Engineering, Civil engineering, Computer scienceryg2102Civil Engineering and Engineering MechanicsDissertationsOKID as a general approach to linear and bilinear system identification
http://academiccommons.columbia.edu/catalog/ac:178859
Vicario, Francescohttp://dx.doi.org/10.7916/D8WS8RVCMon, 13 Oct 2014 00:00:00 +0000This work advances the understanding of the complex world of system identification, i.e. the set of techniques to find mathematical models of dynamical systems from measured input-output data, and exploits well-established approaches for linear systems to address nonlinear system identification problems. We focus on observer/Kalman filter identification (OKID), a method for simultaneous identification of a linear state-space model and the associated Kalman filter from noisy input-output measurements. OKID, developed at NASA, resulted in a very successful algorithm known as OKID/ERA (OKID followed by eigensystem realization algorithm). We show how ERA is not the only method to complete the OKID process, developing novel algorithms based on the preliminary estimation of the Kalman filter output residuals. The new algorithms do not only show potential for better performance, they also cast light on OKID, explicitly establishing the Kalman filter as central to linear system identification in the presence of noise, paralleling its role in signal estimation and filtering. The Kalman filter embedded in the OKID core equation is capable of converting the original problem, affected by random noise, into a purely deterministic problem. The new interpretation leads to the extension of OKID to output-only system identification, providing a new tool for applications in structural health monitoring, and raises OKID to the level of a unified approach for input-output and output-only linear system identification. Any algorithm for linear system identification formulated in the absence of noise can now optimally handle noisy data via a preliminary step consisting in solving the OKID core equation. The OKID framework developed for linear system identification is then extended to bilinear systems, which are of interest because several natural phenomena are inherently bilinear and also because high-order bilinear models are universal approximators for a wide class of nonlinear systems. The formulation of an optimal bilinear observer for bilinear state-space models, similar to the Kalman filter in the linear case, leads to the development of an extension of OKID to bilinear system identification. This is the first application of OKID to nonlinear problems, not only because bilinear systems are themselves nonlinear, but also because one can think of bilinear OKID as a technique to find bilinear approximations of nonlinear systems. Furthermore, the same strategy adopted in this work could be used to extend OKID directly to other classes of nonlinear models.Engineering, Mechanical engineering, Civil engineeringfv2157Mechanical EngineeringDissertationsModeling the hydro-mechanical responses of strip and circular punch loadings on water-saturated collapsible geomaterials
http://academiccommons.columbia.edu/catalog/ac:177849
Sun, WaiChing; Chen, Qiushi; Ostien, Jakob T.http://dx.doi.org/10.7916/D8PZ57CMFri, 03 Oct 2014 00:00:00 +0000A stabilized enhanced strain finite element procedure for poromechanics is fully integrated with an elasto-plastic cap model to simulate the hydro-mechanical interactions of fluid-infiltrating porous rocks with associative and non-associative plastic flow. We present a quantitative analysis on how macroscopic plastic volumetric response caused by pore collapse and grain rearrangement affects the seepage of pore fluid, and vice versa. Results of finite element simulations imply that the dissipation of excess pore pressure may significantly affect the stress path and thus alter the volumetric plastic responses.Civil engineering, Geological engineeringCivil Engineering and Engineering MechanicsArticlesA multiscale overlapped coupling formulation for large-deformation strain localization
http://academiccommons.columbia.edu/catalog/ac:177549
Sun, WaiChing; Mota, Alejandrhttp://dx.doi.org/10.7916/D8GQ6W87Mon, 22 Sep 2014 00:00:00 +0000We generalize the multiscale overlapped domain framework to couple multiple rate-independent standard dissipative material models in the finite deformation regime across different length scales. We show that a fully coupled multiscale incremental boundary-value problem can be recast as the stationary point that optimizes the partitioned incremental work of a three-field energy functional. We also establish inf-sup tests to examine the numerical stability issues that arise from enforcing weak compatibility in the three-field formulation. We also devise a new block solver for the domain coupling problem and demonstrate the performance of the formulation with one-dimensional numerical examples. These simulations indicate that it is sufficient to introduce a localization limiter in a confined region of interest to regularize the partial differential equation if loss of ellipticity occurs.Civil engineering, Mechanical engineeringws2414Civil Engineering and Engineering MechanicsArticlesEmpirical assessment of a RGB-D sensor on motion capture and action recognition for construction worker monitoring
http://academiccommons.columbia.edu/catalog/ac:194557
Han, SangUk; Achar, Madhav; Lee, SangHyun; Pena-Mora, Feniosky A.http://dx.doi.org/10.7916/D8NS0SC9Tue, 09 Sep 2014 00:00:00 +0000Background: For construction management, data collection is a critical process for gathering and measuring information for the evaluation and control of ongoing project performances. Taking into account that construction involves a significant amount of manual work, worker monitoring can play a key role in analyzing operations and improving productivity and safety. However, time-consuming tasks involved in field observation have brought up the issue of implementing worker observation in daily management practice. Methods: In an effort to address the issue, this paper investigates the performances of a cost-effective and portable RGB-D sensor, based on recent research efforts extended from our previous study. The performance of an RGB-D sensor is evaluated in terms of (1) the 3D positions of the body parts tracked by the sensor, (2) the 3D rotation angles at joints, and (3) the impact of the RGB-D sensor’s accuracy on motion analysis. For the assessment, experimental studies were undertaken to collect motion capture datasets using an RGB-D sensor and a marker-based motion capture system, VICON, and to analyze errors as compared with the VICON used as the ground truth. As a test case, 25 trials of ascending and descending during ladder climbing were recorded simultaneously with both systems, and the resulting motion capture datasets (i.e., 3D skeleton models) were temporally and spatially synchronized for their comparison. Results: Through the comparative assessment, we found a discrepancy of 10.7 cm in the tracked locations of body parts, and a difference of 16.2 degrees in rotation angles. However, motion detection results show that the inaccuracy of an RGB-D sensor does not have a considerable effect on action recognition in the experiment. Conclusions: This paper thus provides insight into the accuracy of an RGB-D sensor on motion capture in various measures and directions of further research for the improvement of accuracy.Civil engineering, Engineering, Machine learning, Construction industry--Data processing, Electronic monitoring in the workplace, Image convertingfp2214Civil Engineering and Engineering MechanicsArticlesDevelopment of Hierarchical Optimization-based Models for Multiscale Damage Detection
http://academiccommons.columbia.edu/catalog/ac:177209
Sun, Haohttp://dx.doi.org/10.7916/D8GQ6W2JSat, 06 Sep 2014 00:00:00 +0000In recent years, health monitoring of structure and infrastructure systems has become a valuable source of information for evaluating structural integrity, durability and reliability throughout the lifecycle of structures as well as ensuring optimal maintenance planning and operation. Important advances in sensor and computer technologies made possible to process a large amount of data, to extract the characteristic features of the signals, and to link those to the current structural conditions. In general, the process of data feature extraction relates to solving an inverse problem, in either a data-driven or a model-based type setting. This dissertation explores state-of-the-art hierarchical optimization-based computational algorithms for solving multiscale model-based inverse problems such as system identification and damage detection. The basic idea is to apply optimization tools to quantify an established model or system, characterized by a set of unknown governing parameters, via minimizing the discrepancy between the predicted system response and the measured data. We herein propose hierarchical optimization algorithms such as the improved artificial bee colony algorithms integrated with local search operators to accomplish this task. In this dissertation, developments in multiscale damage detection are presented in two parts. In the first part, efficient hybrid bee algorithms in both serial and parallel schemes are proposed for time domain input-output and output-only identification of macro-scale linear/nonlinear systems such as buildings and bridges. Solution updating strategies of the artificial bee colony algorithm are improved for faster convergence, meanwhile, the simplex method and gradient-based optimization techniques are employed as local search operators for accurate solution tuning. In the case of output-only measurements, both system parameters and the time history of input excitations can be simultaneously identified using a modified Newmark integration scheme. The synergy between the proposed method and Bayesian inference are proposed to quantify uncertainties of a system. Numerical and experimental applications are investigated and presented for macro-scale system identification, finite element model updating and damage detection. In the second part, a framework combining the eXtended Finite Element Method (XFEM) and the proposed optimization algorithms is investigated, for nondestructive detection of multiple flaws/defects embedded in meso-scale systems such as critical structural components like plates. The measurements are either static strains or displacements. The number of flaws as well as their locations and sizes can be identified. XFEM with circular and/or elliptical void enrichments is employed to solve the forward problem and alleviates the costly re-meshing along with the update of flaw boundaries in the identification process. Numerical investigations are presented to validate the proposed method in application to detection of multiple flaws and damage regions. Overall, the proposed multiscale methodologies show a great potential in assessing the structural integrity of building and bridge systems, critical structural components, etc., leading to a smart structure and infrastructure management system.Civil engineering, Mechanicshs2595Civil Engineering and Engineering MechanicsDissertationsDurability of Cement Composites Reinforced with Sisal Fiber
http://academiccommons.columbia.edu/catalog/ac:177197
Wei, Jianqianghttp://dx.doi.org/10.7916/D8DZ06MZWed, 03 Sep 2014 00:00:00 +0000This dissertation focuses mainly on investigating the aging mechanisms and degradation kinetics of sisal fiber, as well as the approaches to mitigate its degradation in the matrix of cement composites. In contrast to previous works reported in the literature, a novel approach is proposed in this study to directly determine the fiber's degradation rate by separately studying the composition changes, mechanical and physical properties of the embedded sisal fibers. Cement hydration is presented to be a crucial factor in understanding fiber degradation behavior. The degradation mechanisms of natural fiber consist of mineralization of cell walls, alkali hydrolysis of lignin and hemicellulose, as well as the cellulose decomposition which includes stripping of cellulose microfibrils and alkaline hydrolysis of amorphous regions in cellulose chains. Two mineralization mechanisms, CH-mineralization and self-mineralization, are proposed. The degradation kinetics of sisal fiber in the cement matrix are also analyzed and a model to predict the degradation rate of cellulose for natural fiber embedded in cement is outlined. The results indicate that the time needed to completely degrade the cellulose in the matrix with cement replacement by 30wt.% metakaolin is 13 times longer than that in pure cement. A novel and scientific method is presented to determine accelerated aging conditions, and to evaluating sisal fiber's degradation rate and durability of natural fiber-reinforced cement composites. Among the static aggressive environments, the most effective approach for accelerating the degradation of natural fiber in cement composites is to soak the samples or change the humidity at 70 ºC and higher temperature. However, the dynamic wetting and drying cycling treatment has a more accelerating effect on the alkali hydrolysis of fiber's amorphous components evidenced by the highest crystallinity indices, minimum content of holocellulose, and lowest tensile strength. Based on the understanding of degradation mechanisms, two approaches are proposed to mitigate the degradation of sisal fiber in the cement matrix. In order to relieve the aggressive environment of hydrated cement, cement substitution by a combination of metakaolin and nanoclay, and a combination of rice husk ash and limestone are studied. Both metakaolin and nanoclay significantly optimize the cement hydration, while the combination of these two supplementary cementitious materials validates their complementary and synergistic effect at different stages of aging. The presented approaches effectively reduce the calcium hydroxide content and the alkalinity of the pore solution, thereby mitigating the fiber degradation and improving both the initial mechanical properties and durability of the fiber-cement composites. The role of rice husk ash in cement modification is mainly as the active cementitious supplementary material. In order to improve the degradation resistance of sisal fiber itself, two novel, simple, and economical pretreatments of the fibers (thermal and sodium carbonate treatment) are investigated. Both thermal treatment and Na2CO3 treatment effectively improve the durability of sisal fiber-reinforced concrete. The thermal treatment achieves improvement of cellulose's crystallization, which ensures the initial strength and improved durability of sisal fiber. A layer consisting of calcium carbonate sediments, which protects the internals of a fiber from the strong alkali pore solution, is formed and filled in pits and cavities on the Na2CO3 treated sisal fiber's surface.Civil engineering, Materials sciencejw2938Civil Engineering and Engineering MechanicsDissertationsImproving the Quantification and Estimation of Damping for Bridges under Traffic Loading
http://academiccommons.columbia.edu/catalog/ac:185818
Brewick, Patrickhttp://dx.doi.org/10.7916/D8K072D5Mon, 07 Jul 2014 00:00:00 +0000It is important for engineers and designers to be able to accurately estimate the damping within a structure; however, this is not a trivial task. Simplifications are often made in an effort to make damping estimation easier, but these simplifications rely on assumptions that may not be universally true. One important assumption is that the excitation input for a structure may be modeled as broad-band noise, but traffic loading on a bridge likely violates that assumption. Traffic loads are characterized by the velocities of the vehicles and trains crossing the bridge, which gives the input specific frequency content. This added complexity increases the difficulty in accurately estimating the damping. The problem of traffic crossing a bridge was studied by creating a finite element model of a bridge using a beam system that consisted of a series of stringers resting on top of a larger girder. Traffic loads were then simulated using moving point loads and moving masses to represent cars and trains crossing the bridge. In addition to the traffic loading case, an ambient loading case was conducted using uniform broad-band noise as a means of comparison. The accelerations at several locations along the bridge span were recorded and used as input for a variety of operational modal analysis (OMA) methods. The OMA methods included both frequency domain techniques, such as Frequency Domain Decomposition (FDD), and time domain based identification, such as blind source separation (BSS). The results from the various OMA methods demonstrated how traffic loading creates distortion in the frequency response spectra of the bridge. This distortion had adverse effects for damping ratio estimation and in certain cases led to extreme errors. The mode shape estimates were not found to be affected by the distortion, but that meant that mode shape estimates could not be used to identify potentially erroneous damping estimates. The cause for the distortion was later identified as the driving frequencies produced by the vehicle-bridge interactions. The term ``driving frequency'' refers to the frequency created by a car traveling over a bridge or, by analogy, by a moving load traveling over a beam. This frequency is directly correlated with the speed of the vehicle and the length of the bridge. By considering a single moving point load traveling across the bridge, the responses of the stringers and girder were studied and the effects of the driving frequencies were better quantified in both the time and frequency domains. It was found that peaks in frequency domain appear at the even multiples of each car's driving frequency, and as more cars travel across the bridge the peaks of closely spaced driving frequency multiples begin to merge. As the number of cars increases to a full hour-long simulation and the car velocities become uniformly distributed over a given interval, numerous peaks merge together to form sustained regions of elevated energy in the frequency domain. These regions distort the frequency response spectra of the bridge and obscure the modal information. In order to deal with these distorted regions, a new approach to modal identification was proposed that focused on using partial information from the modal peaks. The peaks in the frequency domain were divided into left- and right-side spectra in order to take advantage of any undistorted portions of the modal peaks. These side spectra were analyzed using a curve-fitting approach based on combining optimization methods with clustering analysis. The presence of distortion presented certain challenges to traditional curve-fitting approaches, such as polynomial least squares, but the optimization algorithm was able to overcome these issues while also adding efficiency to the curve-fitting process. The clustering analysis was used to quickly find the optimal subsets within the optimization-based curve-fitting results. By performing curve-fitting to side spectra, different sets of modal parameters were produced that fit each side. It was found that the modal parameters for the intact or undistorted side compared favorably with the true modal parameters. While this optimization and clustering methodology could not account for all types of distortion, it demonstrated large improvements as compared to traditional OMA approaches for the modes most severely impacted by the distortion. Another potential benefit of this method is that the distributions within the final clusters could be used to provide ranges of possible values for the damping ratios instead of only a single value.Civil engineeringptb2110Civil Engineering and Engineering MechanicsDissertationsAlternative Metrics of Green Roof Hydrologic Performance: Evapotranspiration and Peak Flow Reduction
http://academiccommons.columbia.edu/catalog/ac:185821
Marasco, Danielhttp://dx.doi.org/10.7916/D89G5JZQMon, 07 Jul 2014 00:00:00 +0000Stormwater runoff presents an issue for many urban areas, triggering sewer overflows and water body pollution. Green roofs, engineered vegetative systems that replicate the stormwater absorption properties of natural landscapes, have become an attractive strategy for attenuating stormwater runoff. Historically, green roof hydrologic research has been focused on stormwater volume retention with less emphasis on evapotranspiration (ET) and stormwater detention. ET is associated with green roof environmental benefits, including stormwater runoff attenuation and urban heat island mitigation, and is an important parameter in hydrologic and energy models. Stormwater detention limits flow rate of stormwater into sewer systems, reducing the chance of sewer overflow. The aim of this research is to investigate green roof ET and stormwater detention behavior and develop methods to predict performance based on readily available environmental data. In order to study these hydrologic performance metrics, a series of four New York City green roofs were instrumented with sensors to measure rainfall, runoff, ET, and other environmental data. The green roofs span several extensive green roof installation types, specifically the vegetated mat, built-in-place, and modular tray systems. Environmental monitoring for this analysis began in January 2009 and concluded in October 2013. In the first study, a dynamic chamber method was developed to conduct high-resolution measurements of ET. Results show that monthly ET depths range from 2.2 to 153.6 mm. Chamber results were compared to two ET estimation methods, specifically the Penman-Monteith equation and an energy balance model. Dynamic chamber results were similar to Penman-Monteith estimates; however, the Penman-Monteith equation over-predicted bottommost ET fluxes during the winter, and under-predicted peak summer fluxes. In the second study, dynamic chamber measurements were used to investigate green roof behavior and the effectiveness of various predictive models, particularly in water-limited conditions. Comparison of Hargreaves, Priestley-Taylor, Penman, and Penman-Monteith equation results to chamber measurements reveals that the Priestley-Taylor equation best estimates ET. However, the Priestley-Taylor equation can still overestimate lower fluxes and underestimate high fluxes. Application of a storage model, antecedent precipitation index, and advection-aridity model indicates that the antecedent precipitation index best estimates ET in water-stressed conditions. In the third study, 501 rainfall events were used to characterize green roof stormwater detention behavior, through analysis of event peak rainfall rate reductions. Empirical models relating event peak runoff rate to rainfall depth and peak rainfall rate were developed. Roof-specific models allow for the comparison of peak reduction behavior among roofs, while a combined model allows for designers to estimate green roof event peak rainfall reduction performance. Model application shows that the modular tray system is most effective at reducing peak rainfall rate. Overall, this research provides valuable insight into green roof hydrologic performance. Analysis of environmental data reveals not only the ET and peak rainfall rate reduction performance of green roofs, but also the environmental factors that affect performance. Additionally, predictive models for ET and peak runoff rate investigated in this dissertation can be valuable tools for researchers, practitioners, and policymakers to estimate green roof hydrologic performance.Civil engineering, Environmental engineering, Hydrologic sciencesdem2124Civil Engineering and Engineering MechanicsDissertationsEvaluating Green Roof Stormwater Management in New York City: Observations, Modeling, and Design of Full-Scale Systems
http://academiccommons.columbia.edu/catalog/ac:188478
Carson, Tylerhttp://dx.doi.org/10.7916/D8TM789PMon, 07 Jul 2014 00:00:00 +0000In the United States, an aging and overburdened urban infrastructure has become a substantial challenge for civil engineers. Among these challenges, systems for stormwater management are of significant concern, considering their direct impact on environmental quality, local ecosystems, and the hydrologic cycle. Given the high costs for rehabilitation of traditional stormwater infrastructure in urban settings, low impact, or "green" development strategies have become critical components in plans for meeting future stormwater management goals. In particular, New York City (NYC) has pledged $1.5 billion over the next 20 years to improve environmental quality through the mitigation of urban runoff, where utilization of green infrastructure is a primary goal. Cost effective implementation of this, and similar plans around the world, requires comprehensive understanding of green infrastructure functionality. In response, this dissertation investigates the stormwater management potential of full-scale green roofs in NYC through lenses of observation, modeling, and design. Exploration of this topic has resulted in new findings which quantify the: influence of dominant environmental and physical properties on green roof hydrologic performance, envelope of potential green roof rainfall capture in NYC, and predictive efficiency of contemporary hydrologic models for green roof assessment. This work has also lead to new methods for the: extension of green roof observations to account for the influence of rainfall distribution, parameterization of green roof hydrologic processes, and prediction of full-scale green roof rainfall capture in advance of construction. Going forward, these findings and methods are useful for informing green roof policy, planning, and design; where, in particular, this information supports the development of green roof policies that correlate to specific stormwater management goals. In summation, the characterization of green roof stormwater management in NYC, as presented in this dissertation, has contributed to the understanding of, among other topics, green roof design, urban stormwater management, hydrologic modeling, and the broad interdisciplinary field of urban ecological systems.Civil engineering, Water resources management, Hydrologic sciencesCivil Engineering and Engineering MechanicsDissertationsA validated methodology to estimate the reliability and safety of suspension bridge cables
http://academiccommons.columbia.edu/catalog/ac:174439
Montoya, Arturo Humbertohttp://dx.doi.org/10.7916/D8FJ2DWZMon, 02 Jun 2014 00:00:00 +0000The safety of suspension bridges depends on its main cables which are constructed of thousands of high strength steel wires radially clamped together at certain locations along the cable. After many years of service, these cables are showing signs of serious distress with many wires corroded and even broken inside. A new methodology to determine the reliability and safety of this structure is suggested in this research work. A three dimensional random field simulation is used to determine the remaining tensile strength in the cable. The key idea is to determine how an individual wire break affects the load transfer to the surrounding wires. This local damage eventually causes a global reduction in the load carrying capacity of the cable, up to a complete failure. A Monte Carlo technique is used to generate realizations of the wires' strength within a finite element model. Among the major contributions of the thesis is a novel technique for modeling the contact-friction mechanism between thousands of wires that account for load recovery in broken wires due to friction induced by radial clamps. The idea is to place elasto-plastic springs at the contact points between wires. These springs have varying parameters depending on their proximity to the clamping loads and are assigned according to the Boussinesq's solution to a point load in half space. While traditional contact algorithms have difficulties converging on this problem, this technique converges in few iterations. Moreover, parallelization of the problem enables a full stochastic analysis to determine the effect of corrosion uncertainty on the cable's failure load. This method represents a dramatic improvement compared to the current inspection methods that are unreliable and expensive.Civil engineeringahm2113Civil Engineering and Engineering MechanicsDissertationsEstimating inelastic sediment deformation from local site response simulations
http://academiccommons.columbia.edu/catalog/ac:174397
Borja, Ronaldo I.; Sun, WaiChinghttp://dx.doi.org/10.7916/D87W69BNThu, 29 May 2014 00:00:00 +0000Significant insight into the dynamic local site response of a horizontally layered sediment deposit to seismic excitation can be gained from numerical simulations. In this paper we use a nonlinear local site response analysis code SPECTRA to estimate the coseismic sediment deformation at a seismically active site in Lotung, Taiwan. We address some basic issues relevant for interpreting the simulation results, including the impact of noise and baseline offsets present in the input ground motion. We also consider the sensitivity of the predicted deformation responses to statistical variations of sediment constitutive properties. Finally, we apply a suite of hypothetical strong ground motions to the base of the sediment deposit to better understand the pattern of inelastic deformation likely to result from strong seismic shaking.Engineering, Civil engineering, Geophysical engineeringws2414Civil Engineering and Engineering MechanicsArticlesA unified method to predict diffuse and localized instabilities in sands
http://academiccommons.columbia.edu/catalog/ac:171903
Sun, WaiChinghttp://dx.doi.org/10.7916/D8N014KKWed, 19 Mar 2014 00:00:00 +0000A simplified method to analyse diffuse and localized bifurcations of sand under drained and undrained conditions is presented in this paper. This method utilizes results from bifurcation analysis and critical state plasticity theory to detect the onset of pure and dilatant shear band formation, static liquefaction and drained shear failures systematically. To capture the soil collapse observed in experiments, the instability state line concept originated by Chu, Lo and Lee in 1993 is adopted. Emphasis is given to examine how the presence of pore-fluid may facilitate or delay instability after yielding occurs. The predictions of instabilities are compared with experimental data from triaxial compression tests on Toyoura and Changi sands.Engineering, Civil engineeringws2414Civil Engineering and Engineering MechanicsArticlesAnalysis of the Electromagnetic Signature of Reinforced Concrete Structures for Nondestructive Evaluation of Corrosion Damage
http://academiccommons.columbia.edu/catalog/ac:168045
Roqueta, Gemma; Jofre, Lluís; Feng, Maria Q.http://dx.doi.org/10.7916/D80Z716FFri, 06 Dec 2013 00:00:00 +0000This paper presents a nondestructive corrosion damage detection method for reinforced concrete structures based on the analysis of the electromagnetic signature of the steel rebar corrosion. The signature of the corrosion on the scattered field upon microwave illumination is first numerically analyzed. First-order quality factor parameters, the energy and the mean propagation delay, are proposed to quantify the corrosion amount in the structure. To validate the model, low-profile ultra-wide-band antennas (3-12 GHz) are fabricated and measured. Measurements on 12 reinforced concrete samples with induced corrosion are performed, using three different antenna setups. The experiments demonstrate a good correlation between an increase in the corrosion amount with a decrease in the energy and an increase in the time delay of the propagated signal.Civil engineering, Electromagneticsmqf2101Civil Engineering and Engineering MechanicsArticlesVision-Based Displacement Sensor for Monitoring Dynamic Response Using Robust Object Search Algorithm
http://academiccommons.columbia.edu/catalog/ac:168066
Fukuda, Yoshio; Feng, Maria Q.; Narita, Yuto; Kaneko, Shun'ichi; Tanaka, Takayukihttp://dx.doi.org/10.7916/D8MP517ZFri, 06 Dec 2013 00:00:00 +0000This paper develops a vision-based displacement measurement system for remote monitoring of vibration of large-size structures such as bridges and buildings. The system consists of one or multiple video cameras and a notebook computer. With a telescopic lens, the camera placed at a stationary point away from a structure captures images of an object on the structure. The structural displacement is computed in real time through processing the captured images. A robust object search algorithm developed in this paper enables accurate measurement of the displacement by tracking existing features on the structure without requiring a conventional target panel to be installed on the structure. A sub-pixel technique is also proposed to further reduce measurement errors cost-effectively. The efficacy of the vision system in remote measurement of dynamic displacements was demonstrated through a shaking table test and a field experiment on a long-span bridge.Civil engineeringyf2290, mqf2101Civil Engineering and Engineering MechanicsArticlesLeveraging Policy for Renewable Energy Development in Industrialized Countries and Emerging Markets
http://academiccommons.columbia.edu/catalog/ac:166725
Tang, AmyFri, 25 Oct 2013 00:00:00 +0000Renewable energy has the ability to play a dominate role in addressing both rising energy demand and the need for sustainable growth. Various policy measures and incentives have aided its growth in both developed and developing countries. This dissertation analyzes existing policies and financial mechanisms used to encourage renewable energy development through three academic papers. I first propose the carbon revenue bond as a new financing tool to complement the environmental credit markets that exist in developed countries. Stochastic modeling techniques are used to simulate future credit prices and determine bond value. Use of the carbon revenue bond is illustrated through three examples of wind energy projects in the European, Australian and New Jersey markets. In the absence of mature markets in developing countries, I develop the strategic structure matrix as a new framework to explain the various effects of policy measures in order to better shape future policy design. By synthesizing previous literature on how organizations are able to affect the diffusion of a new technology, the strategic structure matrix is able to deepen understanding of how policy can influence renewable energy growth. The explanatory power of the framework is demonstrated through a case study on the different paces of wind power diffusion in five Indian states. Lastly, I evaluate the Clean Development Mechanism as a tool to encourage investment from developed nations for renewable infrastructure in developing countries. I create an agent-based model to simulate investment decisions under different improvements to the program, providing quantitative support for the effectiveness of some improvements over others. In addition to each paper's individual contributions, the findings collectively provide important implications for the future of renewable energy policy and its ability to support continued sustainable growth.Alternative energy, Civil engineeringCivil Engineering and Engineering MechanicsDissertationsBuilding Eco-Informatics: Examining the Dynamics of Eco-Feedback Design and Peer Networks to Achieve Sustainable Reductions in Energy Consumption
http://academiccommons.columbia.edu/catalog/ac:165189
Jain, Rishee Kumarhttp://hdl.handle.net/10022/AC:P:21642Mon, 16 Sep 2013 00:00:00 +0000The built environment accounts for a substantial portion of energy consumption in the United States and in many parts of the world. Due to concerns over rising energy costs and climate change, researchers and practitioners have started exploring the area of eco-informatics to link information from the human, natural and built environments. Specifically, they have begun exploring the use of normative eco-feedback systems to encourage energy efficient behavior and reduce building energy consumption. A normative eco-feedback system provides building occupants with information regarding their own energy consumption and the energy consumption of others in their peer network. While such eco-feedback systems have been observed to drive significant reductions in energy consumption, little is known about the specific system and peer network dynamics that are driving observed reductions. Without this deeper understanding, researchers run the risk of designing eco-feedback systems with low efficacy and may therefore fail to capitalize on potential energy savings. The central aim of this dissertation is to investigate the impact eco-feedback system design and peer network dynamics have on occupant energy consumption behavior. To enable both energy consumption and network data collection, I developed a web-based of an eco-feedback system prototype for an 69 unit residential building in New York City and utilized the system in three empirical experiments. The first experiment was designed to ascertain the effect eco-feedback interface design components have on energy consumption behavior. Analysis of time stamped interface usage and energy consumption data revealed evidence that providing users with incentives and information on their historical consumption levels encourages conservation behavior. Results also suggested that penalizing users for using more energy is not effective in driving energy reductions and instead discourages user engagement. To further understand the effect eco-feedback system design has on energy consumption behavior, a second experiment was conducted using an email-based eco-feedback system. The aim of this study was to examine the role feedback representation plays in encouraging reductions in energy consumption. Participants were broken into two different study groups; one group was provided with feedback in kWh, while a second group was provided with feedback in the equivalent trees required to offset emissions associated with their kWh energy usage. Results revealed that users who received feedback in the form of equivalent trees were more likely to reduce their consumption and had a less dramatic response-relapse effect to feedback emails than their counterparts who received feedback in kWh. The third experiment aimed to characterize the impact peer networks have on modifying energy consumption behavior. Specifically, the experiment was designed to determine if social influence drives energy savings in eco-feedback systems. Analysis of user interaction and energy consumption data was conducted by developing an algorithmic approach based on stochastic and social network test procedures. Social influence was found to impact energy consumption behavior and results indicated the potential of utilizing social influence and peer networks as a means to encourage energy conservation.Civil engineering, Information sciencerkj2106Civil Engineering and Engineering MechanicsDissertationsDevelopments in Extended Finite Element Methods for Extraction of Strain Energy Release Rates and Computational Nanomechanics for SWCNT Aggregates
http://academiccommons.columbia.edu/catalog/ac:161859
Lan, Mengyuhttp://hdl.handle.net/10022/AC:P:20560Tue, 04 Jun 2013 00:00:00 +0000In the first part, a new analytical approach, within the extended finite element (XFEM) framework, is proposed to compute Strain Energy Release Rates (SERRs) directly from Irwin's integral. Crack tip enrichment functions in XFEM allow for evaluation of integral quantities in closed form (for some crack configurations studied) and therefore results in an accurate and efficient method. The effects of high order enrichments, mesh refinement and the integration limits of Irwin's integral are examined in benchmark numerical examples. The results indicate that high order enrichment functions have significant effect on the convergence, in particular when the integral limits are finite. When the integral limits tend to zero, simpler SERR expressions are obtained and high order terms vanish. Nonetheless, these terms contribute indirectly via coefficients of first order terms. The analytical formulation is then extended to cracks in arbitrary orientations. Several benchmark examples are investigated including off-center cracks, inclined cracks and crack growth problems. On all these problems, the method is shown to work well, giving accurate results. Moreover, due to its analytical nature, no special postprocessing is required which leads to a fast approach to obtain Strain Energy Release Rates. Thus it is concluded that this method may provide a good alternative to the popular J-integral method. In the second part of the thesis, the stress-strain behavior of short single walled carbon nanotube (SWCNT) aggregates is investigated by a novel incremental constrained minimization approach. An AIREBO potential is used to model the interactions within and between CNTs. The idea is to homogenously disperse SWCNTs in the computational cell at random positions and orientations following spherical uniform distributions, and incrementally deform the cell while restraining the movement of atoms at the ends of nanotubes. The stress-strain response of the system is obtained in each loading direction and it is shown to converge to an isotropic behavior (a similar response in all directions) as the number of CNTs in the system increases. In addition, it is shown that the Young's modulus of the system increases linearly with the CNT aggregates density and the method agrees well with results obtained from molecular dynamics simulations running at near zero degrees kelvin, which are obtained at only a fraction of the CPU time required for MD methods.Civil engineeringml3065Civil Engineering and Engineering MechanicsDissertationsStochastic Analysis Of Storm-Surge Induced Infrastructure Losses In New York City
http://academiccommons.columbia.edu/catalog/ac:161467
Hwang, Yunjihttp://hdl.handle.net/10022/AC:P:20422Thu, 23 May 2013 00:00:00 +0000Hurricanes are among the most catastrophic types of natural hazards, with the potential to cause serious losses in lives and property. While hurricanes rarely have a huge impact on the New York City area, they do have the potential to cause major damage to the city's transportation infrastructure. This research will deal with two main considerations--fragility curves and exceedance curves of vulnerable points in that infrastructure. The primary objective of this study is to provide a model for predicting future hurricane related storm surge patterns and for estimating possible levels of damage from future events in order to develop planning strategies to mitigate against possible damage. The first step is to describe the frequency of past storm surge events in New York City from 1920 to 2012 and determine a probability distribution for hurricane hazard about the maximum daily and yearly storm surges. The second step is to estimate potential probabilistic models by looking at the empirical data on storm surges in New York City. The last step is to concentrate on the reliability assessment for several infrastructures subjected to hurricane loading and storm surges. No significant studies have been conducted using the available empirical data on storm surge heights in New York City, despite the fact that since an observation station was installed in the Battery, New York in 1920, daily and yearly maximum water levels at that location have been documented by the National Oceanic and Atmospheric Administration (NOAA). Considering the available daily maximum sea water levels from 1920 to 2012 yields a total of 31,148 data points (2,394 days of maximum height data are unfortunately missing); 92 data points of maximum sea water levels are also available. This is the first study to utilize the nearly century's worth of empirical data obtained by the observation station at the Battery. Extensive goodness of fit testing (including the use of various probability papers) is performed on the empirical daily maximum sea water level data. It is concluded that the daily maximum sea water levels at the Battery from 1920 to 2012 follow closely a logistic distribution, with a mean value of 8.10 feet and a coefficient of variation (COV) of 9.63%. The methodology of analyzing the yearly maximum sea water levels is quite similar to that used for the daily sea water levels (and the analysis is performed independently). It is found that the yearly maximum sea water levels at the Battery from 1920 to 2012 follow closely a generalized extreme value (GEV) distribution with a mean value of 10.72 feet and a COV of 10.07%. Then, applying exact and asymptotic Extreme Value Theory, the parent GEV distribution is used to determine the probability distributions for maximum sea water levels over a range of different multi-year periods including 1, 10, 50, 100, 200, and 500 years. Finally, the total volume of flood-vulnerable infrastructure is generated and flood damage probabilities when related to the established probability distributions for sea water levels are considered. The flood vulnerabilities of different parts of the built infrastructure in New York City are studied; specifically, the subway system and the tunnel system. The concept of fragility curves is used to express these vulnerabilities. Conclusions and recommendations are provided for estimating losses probabilistically over different periods, retrofitting and strengthening the infrastructure to reduce future potential losses, and determining repair priorities. This is very useful for cost-benefit analysis.Civil engineeringyh2265Civil Engineering and Engineering MechanicsDissertationsSpace-Time Multiscale-Multiphysics Homogenization Methods for Heterogeneous Materials
http://academiccommons.columbia.edu/catalog/ac:161219
Bailakanavar, Mahesh Rajuhttp://hdl.handle.net/10022/AC:P:20351Fri, 17 May 2013 00:00:00 +0000We present a unified, homogenization framework for computational analysis of heterogeneous materials consisting of multiple length scales, multiple time scales and coupled-multiple physics. The research efforts also addresses the technological issues associated with modeling the morphological details of microstructures with randomly distributed inclusions. The Random Sequential Adsorption (RSA) algorithm is improved to accurately and effectively model the morphological details of materials with randomly distributed inclusions. The proposed algorithm is more robust; computational efficient and versatile in comparison to the existing methods. A temporal homogenization scheme is developed and integrated with the previously developed spatial homogenization theory for fatigue life analysis of heterogeneous materials. The unified space-time multiscale homogenization model is validated for fatigue life prediction of elevated temperature Ceramic Matrix Composites (CMCs). In the final phase of the research a mathematical model for coupled moisture diffusion-mechanical deformation is developed. This model is integrated with the spatial homogenization framework to analyze problems consisting of multiple length scales and coupled-multiple physics. The unified multiscale-multiphysics model is validated for evaluating the degradation of physical and mechanical properties of short glass fiber and carbon fiber filled thermoplastic material systems.Civil engineeringmrb2217Civil Engineering and Engineering MechanicsDissertationsModeling and Simulation of Random Processes and Fields in Civil Engineering and Engineering Mechanics
http://academiccommons.columbia.edu/catalog/ac:188460
Benowitz, Brett Alexanderhttp://dx.doi.org/10.7916/D8P26XGNWed, 15 May 2013 00:00:00 +0000This thesis covers several topics within computational modeling and simulation of problems arising in Civil Engineering and Applied Mechanics. There are two distinct parts. Part 1 covers work in modeling and analyzing heterogeneous materials using the eXtended Finite Element Method (XFEM) with arbitrarily shaped inclusions. A novel enrichment function, which can model arbitrarily shaped inclusions within the framework of XFEM, is proposed. The internal boundary of an arbitrarily shaped inclusion is first discretized, and a numerical enrichment function is constructed "on the fly" using spline interpolation. This thesis considers a piecewise cubic spline which is constructed from seven localized discrete boundary points. The enrichment function is then determined by solving numerically a nonlinear equation which determines the distance from any point to the spline curve. Parametric convergence studies are carried out to show the accuracy of this approach, compared to pointwise and linear segmentation of points, for the construction of the enrichment function in the case of simple inclusions and arbitrarily shaped inclusions in linear elasticity. Moreover, the viability of this approach is illustrated on a Neo-Hookean hyperelastic material with a hole undergoing large deformation. In this case, the enrichment is able to adapt to the deformation and effectively capture the correct response without remeshing. Part 2 then moves on to research work in simulation of random processes and fields. Novel algorithms for simulating random processes and fields such as earthquakes, wind fields, and properties of functionally graded materials are discussed. Specifically, a methodology is presented to determine the Evolutionary Spectrum (ES) for non-stationary processes from a prescribed or measured non-stationary Auto-Correlation Function (ACF). Previously, the existence of such an inversion was unknown, let alone possible to compute or estimate. The classic integral expression suggested by Priestley, providing the ACF from the ES, is not invertible in a unique way so that the ES could be determined from a given ACF. However, the benefits of an efficient inversion from ACF to ES are vast. Consider for example various problems involving simulation of non-stationary processes or non-homogeneous fields, including non-stationary seismic ground motions as well as non-homogeneous material properties such as those of functionally graded materials. In such cases, it is sometimes more convenient to estimate the ACF from measured data, rather than the ES. However, efficient simulation depends on knowing the ES. Even more important, simulation of non-Gaussian and non-stationary processes depends on this inversion, when following a spectral representation based approach. This work first examines the existence and uniqueness of such an inversion from the ACF to the ES under a set of special conditions and assumptions (since such an inversion is clearly not unique in the most general form). It then moves on to efficient methodologies of computing the inverse, including some established optimization techniques, as well as proposing a novel methodology. Its application within the framework of translation models for simulation of non-Gaussian, non-stationary processes is developed and discussed. Numerical examples are provided demonstrating the capabilities of the methodology. Additionally in Part 2, a methodology is presented for efficient and accurate simulation of wind velocities along long span structures at a virtually infinite number of points. Currently, the standard approach is to model wind velocities as a multivariate stochastic process, characterized by a Cross-Spectral Density Matrix (CSDM). In other words, the wind velocities are modeled as discrete components of a vector process. To simulate sample functions of the vector process, the Spectral Representation Method (SRM) is used. The SRM involves a Cholesky decomposition of the CSDM. However, it is a well known issue that as the length of the structure, and consequently the size of the vector process, increases, this Cholesky decomposition breaks down (from the numerical point of view). To avoid this issue, current research efforts in the literature center around approximate techniques to simplify the decomposition. Alternatively, this thesis proposes the use of the frequency-wavenumber (F-K) spectrum to model the wind velocities as a stochastic "wave," continuous in both space and time. This allows the wind velocities to be modeled at a virtually infinite number of points along the length of the structure. In this work, the relationship between the CSDM and the F-K spectrum is first examined, as well as simulation techniques for both. The F-K spectrum for wind velocities is then derived. Numerical examples are then carried out demonstrating that the simulated wave samples exhibit the desired spectral and coherence characteristics. The efficiency of this method, specifically through the use of the Fast Fourier Transform, is demonstrated.Mechanics, Civil engineeringbab2140Civil Engineering and Engineering MechanicsDissertationsThermal Conductivity of Fiber-Reinforced Lightweight Cement Composites
http://academiccommons.columbia.edu/catalog/ac:161111
Hochstein, Daniel Peterhttp://hdl.handle.net/10022/AC:P:20303Tue, 14 May 2013 00:00:00 +0000This dissertation describes the development of a multiscale mathematical model to predict the effective thermal conductivity (ETC) of fiber-reinforced lightweight cement composites. At various stages in the development of the model, the results are compared to experimental values and the model is calibrated when appropriate. Additionally at each stage the proposed model and its results are compared to physical upper and lower bounds placed on the ETC for the different types of structural models. Fiber-reinforced lightweight cement mortar is a composite material that contains various components at different scales. The model development begins with a study of neat cement paste and is then extended to include normal weight fine aggregate, lightweight aggregate, and reinforcing fibers. This is accomplished by first considering cement mortar, then models for lightweight cement mortar and fiber-reinforced cement mortar are considered separately, and finally these two are joined together to study fiber-reinforced lightweight cement mortar. Two different experimental techniques are used to determine the ETC of the different materials. The flash method is used to determine the ETC of the neat cement paste and cement mortar samples, and a recently developed transient technique is used for the remainder of the samples. The model for the ETC of cement paste is derived from a lumped parameter model considering the water-cement ratio and saturation of the paste. The results are calibrated using experimental data generated during this project and are in good agreement with values found in the literature. The models for the ETC of cement mortar, fiber-reinforced cement mortar, lightweight cement mortar, and fiber-reinforced lightweight cement mortar are all based on a differential multiphase model (DM model). This is capable of predicting the ETC of a composite material with various ellipsoidal inclusion phases. It is shown how the DM model can be modified to include information about the maximum volume fraction of the inclusions. A linear packing model is introduced which allows the gradation of the different inclusion phases to be considered. Additionally other factors that affect the ETC are discussed, including the presence of an interfacial transition zone around the inclusions and the relative size of the different constituent phases. The model developed in this report is not only able to predict the effective thermal conductivity for a material, but it can also be used to minimize the effective thermal conductivity by optimizing the structure of the composite. This is done through proper selection of the types and amounts of the various constituents, along with their size, shape, and gradation.Civil engineering, Mechanical engineeringdph2115Civil Engineering and Engineering MechanicsDissertationsNeuro-fuzzy application for concrete strength prediction using combined non-destructive tests
http://academiccommons.columbia.edu/catalog/ac:158498
Na, U. J.; Park, T. W.; Feng, Maria Q.; Chung, L.http://hdl.handle.net/10022/AC:P:19611Tue, 02 Apr 2013 00:00:00 +0000The application of the neuro-fuzzy inference system to predict the compressive strength of concrete is presented in this study. The adaptive neuro-fuzzy inference system (ANFIS) is introduced for training and testing the data sets consisting of various parameters. To investigate the influence of various parameters which affect the compressive strength, 1551 data pairs are collected from the technical literature. These data sets cover early and late compressive strengths from 3 to 365 days and low and high strength in the range 6·3–107·7 MPa. To reflect the effects of other uncertain parameters and in situ conditions, the results of non-destructive tests (NDTs) such as ultrasonic pulse velocity (UPV) and rebound hammer test are also included as input parameters, in addition to mix proportion and curing histories. For the testing of trained ANFIS models, 20 cube specimens and 210 cylinders are prepared, and compressive test and NDTs are conducted. For the comparative study of the applicability of ANFIS models combined with NDT results, four ANFIS models are developed. Depending on whether the input parameters of ANFIS models include NDT results or not, these are distinguished from each other. Among the four models, the ‘ANFIS-UR' model having the parameters for both UPV and rebound hammer test results shows the best accuracy in the prediction of compressive strength.Mechanical engineering, Civil engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesNonlinear Static Procedure for Fragility Curve Development
http://academiccommons.columbia.edu/catalog/ac:158492
Shinozuka, Masanobu; Feng, Maria Q.; Kim, Ho-Kyung; Kim, Sang-Hoonhttp://hdl.handle.net/10022/AC:P:19609Mon, 01 Apr 2013 00:00:00 +0000This study examines the fragility curves of a bridge by two different analytical approaches; one utilizes the time-history analysis and the other uses the capacity spectrum method. The latter approach is one of the simplified nonlinear static procedures recently developed for buildings. In this respect, a sample of 10 nominally identical but statistically different bridges and 80 ground-motion time histories are considered to account for the uncertainties related to the structural capacity and ground motion, respectively. The comparison of fragility curves by the nonlinear static procedure with those by time-history analysis indicates that the agreement is excellent for the state of at least minor damage, but not as good for the state of major damage where nonlinear effects clearly play a crucial role. Overall, however, the agreement is adequate even in the state of major damage considering the large number of typical assumptions under which the analyses of fragility characteristics are performed.Mechanical engineering, Civil engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesUse of Microwaves for Damage Detection of Fiber Reinforced Polymer-Wrapped Concrete Structures
http://academiccommons.columbia.edu/catalog/ac:158495
Feng, Maria Q.; De Flaviis, Franco; Kim, Yoo Jinhttp://hdl.handle.net/10022/AC:P:19610Mon, 01 Apr 2013 00:00:00 +0000Jacketing technology using fiber reinforced polymer (FRP) composites is being applied for seismic retrofit and rehabilitation of reinforced concrete (RC) columns designed and constructed under older specifications. In this study, the authors develop an electromagnetic (EM) imaging technology for detecting such damage as voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column otherwise attainable by jacketing. This technology is based on the reflection analysis of a continuous EM wave sent toward and reflected from layered FRP–adhesive-concrete medium: Voids and debonding areas will generate air gaps which produce additional reflections of the EM wave. In this study, dielectric properties of various materials involved in the FRP-jacketed RC column were first measured using a plane-wave reflectometer. The measured properties were then used for a computer simulation of the proposed EM imaging technology. The simulation demonstrated the difficulty in detecting damage by using plane waves, as the reflection contribution from the voids and debonding is very small compared to that from the jacketed column. In order to alleviate this difficulty, dielectric lenses were designed and fabricated, focusing the EM wave on the bonding interface. Finally, three concrete columns were constructed and wrapped with glass–FRP jackets with various voids and debonding conditions artificially introduced in the bonding interface. Using the proposed EM imaging technology involving the especially designed and properly installed lenses, these voids and debonding areas were successfully detected. This technology can be used to assess the jacket bonding quality during the initial jacket installation stage and to detect debonding between the column and the jacket caused by earthquake and other destructive loads.Mechanical engineering, Civil engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesA technique to Improve the Empirical Mode Decomposition in the Hilbert-Huang Transform
http://academiccommons.columbia.edu/catalog/ac:158503
Feng, Maria Q.; Chen, Yangbohttp://hdl.handle.net/10022/AC:P:19533Fri, 29 Mar 2013 00:00:00 +0000The Hilbert-based time-frequency analysis has promising capacity to reveal the time-variant behaviors of a system. To admit well-behaved Hilbert transforms, component decomposition of signals must be performed beforehand. This was first systematically implemented by the empirical mode decomposition (EMD) in the Hilbert-Huang transform, which can provide a time-frequency representation of the signals. The EMD, however, has limitations in distinguishing different components in narrowband signals commonly found in free-decay vibration signals. In this study, a technique for decomposing components in narrowband signals based on waves’ beating phenomena is proposed to improve the EMD, in which the time scale structure of the signal is unveiled by the Hilbert transform as a result of wave beating, the order of component extraction is reversed from that in the EMD and the end effect is confined. The proposed technique is verified by performing the component decomposition of a simulated signal and a free decay signal actually measured in an instrumented bridge structure. In addition, the adaptability of the technique to time-variant dynamic systems is demonstrated with a simulated time-variant MDOF system.Mechanical engineering, Civil engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesVariation of Modal Parameters of a Highway Bridge Extracted from Six Earthquake Records
http://academiccommons.columbia.edu/catalog/ac:158512
Feng, Maria Q.; Ulusoy, Hasan; Gomez, Hugo http://hdl.handle.net/10022/AC:P:19532Fri, 29 Mar 2013 00:00:00 +0000Between 2005 and 2010 six earthquakes triggered a monitoring system consisting of 11 acceleration channels installed on the West Street On-Ramp, a three-span curved highway bridge located in the city of Anaheim, California. In this paper, three different system identification techniques are applied to the acceleration records to investigate and corroborate the dynamic properties of the bridge, that is, vibration frequencies, associated damping ratios and mode shapes. The identification techniques are applied to each one of the six seismic events. The identified frequencies and damping ratios are shown to be dependent variables of the earthquake intensity. In general, larger earthquake intensities result in reduced vibration frequencies and higher damping ratios of the bridge. Sensitivity analysis using a simple finite element model reveals that soil softening at the abutments considerably contributes to the variation in frequencies because of changes in the support conditions and ultimately in the global stiffness of the structure. In addition, mathematical models in the state space description are identified from the recorded response and excitation measurements. The state space models successfully replicate the bridge measured response to the earthquake from which it is constituted. The models also provide a reasonable prediction of the bridge response to a different earthquake.Mechanical engineering, Civil engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesStatistical Analysis of Fragility Curves
http://academiccommons.columbia.edu/catalog/ac:158182
Feng, Maria Q.; Shinozuka, Masanobu ; Kim, Ho-Kyung ; Kim, Sang-Hoon http://hdl.handle.net/10022/AC:P:19479Wed, 27 Mar 2013 00:00:00 +0000This paper presents a statistical analysis of structural fragility curves. Both empirical and analytical fragility curves are considered. The empirical fragility curves are developed utilizing bridge damage data obtained from the 1995 Hyogo-ken Nanbu (Kobe) earthquake. The analytical fragility curves are constructed on the basis of the nonlinear dynamic analysis. Two-parameter lognormal distribution functions are used to represent the fragility curves with the parameters estimated by the maximum likelihood method. This paper also presents methods of testing the goodness of fit of the fragility curves and estimating the confidence intervals of the two parameters (median and log-standard deviation) of the distribution. An analytical interpretation of randomness and uncertainty associated with the median is provided.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesApplication of Neural Networks for Estimation of Concrete Strength
http://academiccommons.columbia.edu/catalog/ac:158191
Feng, Maria Q.; Kim, Jong-In ; Kim, Doo Kie ; Yazdani, Frank http://hdl.handle.net/10022/AC:P:19482Wed, 27 Mar 2013 00:00:00 +0000The uniaxial compressive strength of concrete is the most widely used criterion in producing concrete. Although testing of the uniaxial compressive strength of concrete specimens is done routinely, it is performed on the 28th day after concrete placement. At this point, it is too late to make improvements if the test result does not satisfy the required strength. Therefore, the strength estimation before the placement of concrete is highly desirable. This study presents the first effort in applying neural network-based system identification techniques to predict the compressive strength of concrete based on concrete mix proportions. Back-propagation neural networks were developed, trained, and tested using actual data sets of concrete mix proportions provided by two ready-mixed concrete companies. The compressive strengths estimated by the neural networks were verified by laboratory testing results. This study demonstrated that the neural network techniques are effective in estimating the compressive strength of concrete based on the mix proportions. Application of these techniques will contribute significantly to the concrete quality assurance.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesFragility analysis of bridges under ground motion with spatial variation
http://academiccommons.columbia.edu/catalog/ac:158185
Feng, Maria Q.; Kim, Sang-Hoon http://hdl.handle.net/10022/AC:P:19480Wed, 27 Mar 2013 00:00:00 +0000Seismic ground motion can vary significantly over distances comparable to the length of a majority of highway bridges on multiple supports. This paper presents results of fragility analysis of highway bridges under ground motion with spatial variation. Ground motion time histories are artificially generated with different amplitudes, phases, as well as frequency contents at different support locations. Monte Carlo simulation is performed to study dynamic responses of an example multi-span bridge under these ground motions. The effect of spatial variation on the seismic response is systematically examined and the resulting fragility curves are compared with those under identical support ground motion. This study shows that ductility demands for the bridge columns can be underestimated if the bridge is analyzed using identical support ground motions rather than differential support ground motions. Fragility curves are developed as functions of different measures of ground motion intensity including peak ground acceleration, peak ground velocity, spectral acceleration, spectral velocity and spectral intensity. This study represents a first attempt to develop fragility curves under spatially varying ground motion and provides information useful for improvement of the current seismic design codes so as to account for the effects of spatial variation in the seismic design of long-span bridges.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesMicrowave Reflection Tomographic Array fo rDamage Detection of Civil Structures
http://academiccommons.columbia.edu/catalog/ac:158188
Feng, Maria Q.; Kim, Yoo Jin ; Jofre, Luis ; De Flaviis, Franco http://hdl.handle.net/10022/AC:P:19481Wed, 27 Mar 2013 00:00:00 +0000Microwave tomographic imaging technology using a bifocusing operator has been developed in order to detect the internal voids/objects inside concrete structures. The imaging system consists of several cylindrical or planar array antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. An imaging algorithm using a numerical focusing operator was developed, which allows the recovery of a two-dimensional object from its scattered field. Numerical simulation demonstrated that a subsurface image can be successfully reconstructed by using the proposed tomographic imaging technology. For experimental verification, a prototype planar antenna array was fabricated and tested on a concrete specimen.Electrical engineering, Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesLong-Term Monitoring and Analysis of a Curved Concrete Box-Girder Bridge
http://academiccommons.columbia.edu/catalog/ac:158218
Feng, Maria Q.; Lee, Sungchil; Hong, Seok-Heehttp://hdl.handle.net/10022/AC:P:19491Wed, 27 Mar 2013 00:00:00 +0000Capital investment in national infrastructure is significant. The need to maintain and protect critical infrastructure links has led in recent years to significant developments in the area of structural health monitoring. The objective is to track a structure’s long-term performance, typically using sensors, and to successively compare the most recently measured responses with prior response history. During construction of the West Street On-Ramp, a curved concrete box girder bridge, located in the city of Anaheim (California), eleven accelerometers were permanently installed on its bridge deck. The associated data acquisition system was configured to record once a specified threshold acceleration response was exceeded; during the period 2002–2010 a total of 1350 datasets including six earthquakes, for each of the eleven sensors, were acquired. This automatically acquired data was supplemented, during the summer of 2009, with responses measured during controlled vehicle tests. Six accelerometers were additionally installed on the frame of the weighed test vehicle. This paper presents the findings of the analyses of these measured data sets and serves to inform owners and managers as to the potential feedback from their instrumentation investment. All response histories were analyzed using frequency domain techniques for system identification. Extraction of the modal characteristics revealed a continuous reduction, of approximately 5%, in the first three natural frequencies over the period of the study. The measured responses from the vehicle sensors are discussed in the context of identifying the potential for bridge frequency measurement using instrumented vehicles.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesLong-Term Monitoring and Identification of Bridge Structural Parameters
http://academiccommons.columbia.edu/catalog/ac:158221
Feng, Maria Q.; Soyoz, Serdarhttp://hdl.handle.net/10022/AC:P:19492Wed, 27 Mar 2013 00:00:00 +0000Vibration of a new concrete bridge was monitored and change in the bridge structural stiffness was identified accordingly over a 5-year period. This three-span 111-m long bridge is instrumented with 13 acceleration sensors at both the superstructure and the columns. The sensor data are transmitted to a server computer wirelessly. Modal parameters of the bridge, that is, the frequencies and the modal shapes were identified by processing 1,707 vibration data sets collected under traffic excitations, based on which the bridge structural parameters, stiffness and mass, and the soil spring values were identified by employing the neural network technique. The identified superstructure stiffness at the beginning of the monitoring was 97% of the stiffness value based on the design drawings. In the identified modal frequencies, a variation from −10% to +10% was observed over the monitoring period. In the identified stiffness values of the bridge superstructure, a variation from −3% to +3% was observed over the monitoring period. Based on the statistical analysis of the collected data for each year, 5% decrease in the first modal frequency and 2% decrease in the superstructure stiffness were observed over the 5-year monitoring period. Probability density functions were obtained for stiffness values each year. Stiffness threshold values for the collapse of the bridge under the operational loading can be determined. Then the number of years can be assessed for which the area under the proposed probability density functions is greater than the threshold value. So the information obtained in this study is valuable for studying aging and long-term performance assessment of similar bridges.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesUse of Supervisory Control and Data Acquisition for Damage Location of Water Delivery Systems
http://academiccommons.columbia.edu/catalog/ac:158203
Feng, Maria Q.; Shinozuka, Masanobu; Liang, Jianwenhttp://hdl.handle.net/10022/AC:P:19486Wed, 27 Mar 2013 00:00:00 +0000Urban water delivery systems can be damaged by earthquakes or severely cold weather. In either case, the damage cannot easily be detected and located, especially immediately after the event. In recent years, real-time damage estimation and diagnosis of buried pipelines attracted much attention of researchers focusing on establishing the relationship between damage ratio (breaks per unit length of pipe) and ground motion, taking the soil condition into consideration. Due to the uncertainty and complexity of the parameters that affect the pipe damage mechanism, it is not easy to estimate the degree of physical damage only with a few numbers of parameters. As an alternative, this paper develops a methodology to detect and locate the damage in a water delivery system by monitoring water pressure on-line at some selected positions in the water delivery systems. For the purpose of on-line monitoring, emerging supervisory control and data acquisition technology can be well used. A neural network-based inverse analysis method is constructed for detecting the extent and location of damage based on the variation of water pressure. The neural network is trained by using analytically simulated data from the water delivery system with one location of damage, and validated by using a set of data that have never been used in the training. It is found that the method provides a quick, effective, and practical way in which the damage sustained by a water delivery system can be detected and located.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesBaseline Models for Bridge Performance Monitoring
http://academiccommons.columbia.edu/catalog/ac:158197
Feng, Maria Q.; Kim, Doo Kie; Yi, Jin-Hak; Chen, Yangbohttp://hdl.handle.net/10022/AC:P:19484Wed, 27 Mar 2013 00:00:00 +0000A baseline model is essential for long-term structural performance monitoring and evaluation. This study represents the first effort in applying a neural network-based system identification technique to establish and update a baseline finite element model of an instrumented highway bridge based on the measurement of its traffic-induced vibrations. The neural network approach is particularly effective in dealing with measurement of a large-scale structure by a limited number of sensors. In this study, sensor systems were installed on two highway bridges and extensive vibration data were collected, based on which modal parameters including natural frequencies and mode shapes of the bridges were extracted using the frequency domain decomposition method as well as the conventional peak picking method. Then an innovative neural network is designed with the input being the modal parameters and the output being the structural parameters of a three-dimensional finite element model of the bridge such as the mass and stiffness elements. After extensively training and testing through finite element analysis, the neural network became capable to identify, with a high level of accuracy, the structural parameter values based on the measured modal parameters, and thus the finite element model of the bridge was successfully updated to a baseline. The neural network developed in this study can be used for future baseline updates as the bridge being monitored periodically over its lifetime.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesMicrowave Subsurface Imaging Technology for Damage Detection
http://academiccommons.columbia.edu/catalog/ac:158194
Kim, Yoo Jin; Feng, Maria Q.; De Flaviis, Franco; Jofre, Luishttp://hdl.handle.net/10022/AC:P:19483Wed, 27 Mar 2013 00:00:00 +0000This paper presents a technology for detecting invisible damage inside concrete, which is based on reconstruction of dielectric profile (image) of the concrete illuminated with microwaves sent from and received by antenna arrays controlled by specialized software. The imaging system developed in this study consists of an 8X8 transmitting and an 8X8 receiving arrays, an innovative numerical bifocusing operator for improving image resolution, and imaging software for reconstructing a two-dimensional image from the scattered field. The effectiveness of the of the developed technology in detecting steel and voids inside concrete has been demonstrated through numerical simulation and experiments.Civil engineering, Mechanical engineering, Electrical engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesModeling of Traffic Excitation for System Identification of Bridge Structures
http://academiccommons.columbia.edu/catalog/ac:158200
Feng, Maria Q.; Tan, Chin-Anhttp://hdl.handle.net/10022/AC:P:19485Wed, 27 Mar 2013 00:00:00 +0000In long-term health monitoring of bridge structures, system identification is often performed based only on the system output (bridge vibration responses) because the system input (traffic excitation) is difficult to measure. To facilitate the identification of the bridge properties, traffic excitation is commonly modeled as spatially uncorrelated white noise. A physical model of a stationary stream of vehicles (moving loads) arriving in accordance with a Poisson process, traversing an elastic beam, shows that the traffic excitation is spatially correlated. Employing the dynamic nodal loading approach, this spatial correlation results in a frequency-dependent excitation spectrum density matrix, and shifts the response spectra obtained from those excited by spatially uncorrelated white noise. It is shown that the application of system identification techniques based on the conventional excitation model may result in misleading structural properties. Hence, this study further proposes an output-only gray-box identification technique for bridge structures, in which knowledge about the nature of the traffic excitation, such as its spatial correlation, is implanted into an autoregressive-moving-average (ARMA) model. The identifiability of the ARMA model so constructed is assured and the feasibility of the proposed identification technique is demonstrated by a numerical example.Computer science, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesNonlinear Damping Identification in Precast Prestressed Reinforced Concrete Beams
http://academiccommons.columbia.edu/catalog/ac:158227
Feng, Maria Q.; Franchetti, Paolo; Modena, Claudiohttp://hdl.handle.net/10022/AC:P:19494Wed, 27 Mar 2013 00:00:00 +0000This article presents a damage detection method for prestressed reinforced concrete (PRC) elements based on free vibration tests and nonlinear damping identification. Integrated static and dynamic experiments were carried out on three precast PRC beam specimens. The static loading induced different levels of damage to the beams. At each damage level, impulsive loading was applied to the beams and the free vibration response was measured. The dynamic response data were processed using different methods including the multi-input multi-output (MIMO) curve fitting and the Hilbert transform techniques. A strong correlation is observed between the level of concrete damage (cracks) and the amount of nonlinear energy dissipation that can be modeled by means of quadratic damping. The nonlinear damping can be extracted from the free vibration response for each vibration mode. The proposed method is suited for quality control when manufacturing precast PRC members, and can be further extended for in situ detection of damage in concrete structures under ambient vibration.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesLarge-Scale Shake Table Test Verification of Bridge Condition Assessment Methods
http://academiccommons.columbia.edu/catalog/ac:158212
Feng, Maria Q.; Chen, Yangbo; Soyoz, Serdarhttp://hdl.handle.net/10022/AC:P:19489Wed, 27 Mar 2013 00:00:00 +0000Methods that identify structural component stiffness degradation by pre- and postevent low amplitude vibration measurements, based on a linear time-invariant (LTI) system model, are conceptually justified by examining the hysteresis loops the structural components experience in such vibrations. Two large-scale shake table experiments, one on a two-column reinforced concrete (RC) bridge bent specimen, and the other on a two-span three-bent RC bridge specimen were performed, in which specimens were subjected to earthquake ground motions with increasing amplitude and progressively damaged. In each of the damaged stages between two strong motions, low amplitude vibrations of the specimens were aroused, and the postevent component stiffness coefficients were identified by optimizing the parameters in a LTI model. The stiffness degradation identified is consistent with the experimental hysteresis, and could be quantitatively related to the capacity residual of the components.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesStress–strain model for concrete confined by FRP composites
http://academiccommons.columbia.edu/catalog/ac:158209
Feng, Maria Q.; Youssef, Marwan N.; Mosallam, Ayman S.http://hdl.handle.net/10022/AC:P:19488Wed, 27 Mar 2013 00:00:00 +0000In this paper, a stress–strain model for concrete confined by fiber reinforced polymer (FRP) composites is developed. The model is based on the results of a comprehensive experimental program including large-scale circular, square and rectangular short columns confined by carbon/epoxy and E-glass/epoxy jackets providing a wide range of confinement ratios. Ultimate stress, rupture strain, jacket parameters, and cross-sectional geometry were found to be significant factors affecting the stress–strain behavior of FRP-confined concrete. Such parameters were analyzed statistically based on the experimental data, and equations to theoretically predict these parameters are presented. Experimental results from this study were compared to the proposed semi-empirical model as well as others from the literature.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesDamage Detection Based On Damping Analysis Of Ambient Vibration Data
http://academiccommons.columbia.edu/catalog/ac:158224
Feng, Maria Q.; Soyoz, Serdar; Frizzarin, Michele; Franchetti, Paolo; Modena, Claudiohttp://hdl.handle.net/10022/AC:P:19493Wed, 27 Mar 2013 00:00:00 +0000Enabling an automated, remote and rapid detection of structural damage, sensor-based structural health monitoring is becoming a powerful tool for maintenance of civil engineering structures. In this study, a baseline-free, time-domain damage detection method was developed for concrete structures, which is based on analysis of nonlinear damping from measured structural vibration responses. The efficacy of the proposed method was demonstrated through a large-scale concrete bridge model subjected to different levels of seismic damage caused by shaking table tests. By applying the random decrement signature technique, the proposed method successfully identified, from its ambient vibration responses, nonlinear damping of the bridge associated with the seismic damage. The amount of the nonlinear damping increases as the seismic damage becomes more severe. This paper also compares the damage detection results with those obtained by stiffness-based methods, demonstrating a strong correlation between the increase in nonlinear damping and the decrease in structural stiffness associated with the increase in damage severity.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesInstantaneous damage detection of bridge structures and experimental verification
http://academiccommons.columbia.edu/catalog/ac:158215
Feng, Maria Q.; Soyoz, Serdarhttp://hdl.handle.net/10022/AC:P:19490Wed, 27 Mar 2013 00:00:00 +0000An extended Kalman filtering (EKF) method was developed and applied to instantaneously identify elemental stiffness values of a structure during damaging seismic events based on vibration measurement. This method is capable of dealing with nonlinear as well as linear structural responses. Identification of the structural elemental stiffness enables location as well as quantification of structural damage. The instantaneous stiffness values during an event can provide highly useful information for post-event capacity estimation. In this study, a large-scale shaking table test of a three-bent concrete bridge model was performed in order to verify the proposed damage detection method. The bridge model was shaken to different damage levels by a sequence of earthquake motions with increasing intensities. The elemental stiffness values of the structure were instantaneously identified in real time during the damaging earthquake excitations using the EKF method. The identified stiffness degradations and their locations agreed well with the structural damage observed by visual inspection and strain measurements. More importantly, the seismic response accelerations analytically simulated using the instantaneous stiffness values thus identified agreed well with the measured accelerations, demonstrating the accuracy of the identified stiffness. This study presents an experimental verification of a structural damage detection method using a realistic bridge model subjected to realistic seismic damage.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesNovel Fiber Optic Accelerometer System Using Geometric Moiré Fringe
http://academiccommons.columbia.edu/catalog/ac:158206
Feng, Maria Q.; Kim, Dae-Hyunhttp://hdl.handle.net/10022/AC:P:19487Wed, 27 Mar 2013 00:00:00 +0000This paper presents an innovative fiber optic accelerometer system for monitoring vibration of large-size structures. The system is composed of one (or multiple) sensor head and a control unit for driving the sensor and processing sensor data. The sensing mechanism is based on a novel integration of the moiré fringe phenomenon with fiber optics, resulting in accurate and reliable measurement. A prototype fiber optic accelerometer system has been successfully developed, including a sensor head, a low-cost control unit and a software package with a unique algorithm for processing the moiré fringe signals into accelerations with a high resolution. Finally, free vibration and shaking table tests were performed to identify the dynamic characteristics and demonstrate the high performance of the sensor system developed in this study.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesStructural Health Monitoring by Recursive Bayesian Filtering
http://academiccommons.columbia.edu/catalog/ac:158230
Feng, Maria Q.; Chen, Yangbohttp://hdl.handle.net/10022/AC:P:19495Wed, 27 Mar 2013 00:00:00 +0000A new vision of structural health monitoring (SHM) is presented, in which the ultimate goal of SHM is not limited to damage identification, but to describe the structure by a probabilistic model, whose parameters and uncertainty are periodically updated using measured data in a recursive Bayesian filtering (RBF) approach. Such a model of a structure is essential in evaluating its current condition and predicting its future performance in a probabilistic context. RBF is conventionally implemented by the extended Kalman filter, which suffers from its intrinsic drawbacks. Recent progress on high-fidelity propagation of a probability distribution through nonlinear functions has revived RBF as a promising tool for SHM. The central difference filter, as an example of the new versions of RBF, is implemented in this study, with the adaptation of a convergence and consistency improvement technique. Two numerical examples are presented to demonstrate the superior capacity of RBF for a SHM purpose. The proposed method is also validated by large-scale shake table tests on a reinforced concrete two-span three-bent bridge specimen.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesDetection of Ceramic Cracks Using a Distributed High-Resolution Brillouin Fiber Optic Sensor
http://academiccommons.columbia.edu/catalog/ac:158239
Feng, Maria Q.; Zou, Lufan; Imai, Michiohttp://hdl.handle.net/10022/AC:P:19498Wed, 27 Mar 2013 00:00:00 +0000A distributed sensor system is highly desirable for detecting, locating, and monitoring fine cracks at unknown locations in advanced ceramics. This paper presents a distributed high-resolution fiber optic sensor based on the Brillouin scattering principle, and its application in ceramic crack detection for the first time. The existence of cracks, together with their locations, is identified by measuring the strain distribution on a sensing fiber bonded to the ceramic surface. By employing the innovative coherent probe-pump interaction technique, the Brillouin sensor developed in this study achieves a high spatial resolution (100 mm) and measurement accuracy. Capable of detecting and locating fine cracks less than 40 μm, the efficacy of the distributed Brillouin fiber optic sensor is demonstrated through experiments.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesStructural Reliability Estimation with Vibration-Based Identified Parameters
http://academiccommons.columbia.edu/catalog/ac:158236
Feng, Maria Q.; Soyoz, Serdar; Shinozuka, Masanobuhttp://hdl.handle.net/10022/AC:P:19497Wed, 27 Mar 2013 00:00:00 +0000This paper presents a unique structural reliability estimation method incorporating structural parameter identification results based on the seismic response measurement. In the shaking table test, a three-bent concrete bridge model was shaken to different damage levels by a sequence of earthquake motions with increasing intensities. Structural parameters, stiffness and damping values of the bridge were identified under damaging seismic events based on the seismic response measurement. A methodology was developed to understand the importance of structural parameter identification in the reliability estimation. Along this line, a set of structural parameters were generated based on the Monte Carlo simulation. Each of them was assigned to the base bridge model. Then, every bridge model was analyzed using nonlinear time history analyses to obtain damage level at the specific locations. Last, reliability estimation was performed for bridges modeled with two sets of structural parameters. The first one was obtained by the nonlinear time history analysis with the Monte Carlo simulated parameters which is called nonupdated structural parameters. The second one was obtained by updating the first set in Bayesian sense based on the vibration-based identification results which is called updated structural parameters. In the scope of this paper, it was shown that residual reliability of the system estimated using the updated structural parameters is lower than the one estimated using the nonupdated structural parameters.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesCharacterization of Electromagnetic Properties for Durability Performance and Saturation in Hardened Cement Mortar
http://academiccommons.columbia.edu/catalog/ac:158233
Feng, Maria Q.; Kwon, Seung-Jun; Park, Sang Soonhttp://hdl.handle.net/10022/AC:P:19496Wed, 27 Mar 2013 00:00:00 +0000Electromagnetic (EM) properties—dielectric constant and conductivity are changed with porosity and saturation in cement-based materials. In this paper, dielectric constant and conductivity are measured in cement mortar with 5 different mixture conditions considering saturation. For the same mixture proportions, durability tests including porosity, chloride diffusion, air permeability, sorptivity, and water diffusion are performed. Among the continuously measured EM properties within 5–20 GHz of frequency range for different saturation, results under 60% of saturation which shows stable results are selected and averaged as one value. The averaged measurements utilizing results under 60% of saturation are compared with those from durability tests. Through the normalization using the results of W/C 40% which shows best durability performances, changing ratios of durability characteristics are evaluated with normalized dielectric constant and conductivity. The behaviors of EM properties with different saturation and their relationships with durability performances are studied.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesTesting and Long-Term Monitoring of a Curved Concrete Box Girder Bridge
http://academiccommons.columbia.edu/catalog/ac:158246
Feng, Maria Q.; Gomez, Hugo C.; Fanning, Paul J.; Lee, Sungchilhttp://hdl.handle.net/10022/AC:P:19501Wed, 27 Mar 2013 00:00:00 +0000Capital investment in national infrastructure is significant. The need to maintain and protect critical infrastructure links has led in recent years to significant developments in the area of structural health monitoring. The objective is to track a structure’s long-term performance, typically using sensors, and to successively compare the most recently measured responses with prior response history. During construction of the West Street On-Ramp, a curved concrete box girder bridge, located in the city of Anaheim (California), eleven accelerometers were permanently installed on its bridge deck. The associated data acquisition system was configured to record once a specified threshold acceleration response was exceeded; during the period 2002–2010 a total of 1350 datasets including six earthquakes, for each of the eleven sensors, were acquired. This automatically acquired data was supplemented, during the summer of 2009, with responses measured during controlled vehicle tests. Six accelerometers were additionally installed on the frame of the weighed test vehicle. This paper presents the findings of the analyses of these measured data sets and serves to inform owners and managers as to the potential feedback from their instrumentation investment. All response histories were analyzed using frequency domain techniques for system identification. Extraction of the modal characteristics revealed a continuous reduction, of approximately 5%, in the first three natural frequencies over the period of the study. The measured responses from the vehicle sensors are discussed in the context of identifying the potential for bridge frequency measurement using instrumented vehicles.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesSystem Identification of a Building from Multiple Seismic Records
http://academiccommons.columbia.edu/catalog/ac:158252
Feng, Maria Q.; Ulusoy, Hasan; Fanning, Paulhttp://hdl.handle.net/10022/AC:P:19502Wed, 27 Mar 2013 00:00:00 +0000This paper describes the identification of finite dimensional, linear, time-invariant models of a 4-story building in the state space representation using multiple data sets of earthquake response. The building, instrumented with 31 accelerometers, is located on the University of California, Irvine campus. Multiple data sets, recorded during the 2005 Yucaipa, 2005 San Clemente, 2008 Chino Hills and 2009 Inglewood earthquakes, are used for identification and validation. Considering the response of the building as the output and the ground motion as the input, the state space models that represent the underlying dynamics of the building in the discrete-time domain corresponding to each data set are identified. The time-domain Eigensystem Realization Algorithm with the Observer/Kalman filter identification procedure are adopted in this paper, and the modal parameters of the identified models are consistently determined by constructing stabilization diagrams. The four state space models identified demonstrate that the response of the building is amplitude dependent with the response frequency and damping, being dependent on the magnitude of ground excitation. The practical application of this finding is that the consistency of this building response to future earthquakes can be quickly assessed, within the range of ground excitations considered (0.005g–0.074g), for consistency with prior response—this assessment of consistent response is discussed and demonstrated with reference to the four earthquake events considered in this study. Inclusion of data sets relating to future earthquakes will enable the findings to be extended to a wider range of ground excitation magnitudes.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesEquivalent Modal Damping of Short-Span Bridges Subjected to Strong Motion
http://academiccommons.columbia.edu/catalog/ac:158243
Feng, Maria Q.; Lee, Sungchil; Kwon, Seung-Jun; Hong, Seok-Heehttp://hdl.handle.net/10022/AC:P:19500Wed, 27 Mar 2013 00:00:00 +0000In this paper four different methods are investigated for estimating the equivalent modal damping ratios of a short-span bridge under strong ground motion by considering the energy dissipation at the boundary. The Painter Street Overcrossing (PSO) is investigated because of seismic data availability. Computed responses using the response-spectrum method with the equivalent damping ratios estimates are compared with the recorded responses. The results show that the four methods provide reasonable estimation of equivalent modal damping ratios and that neglecting off-diagonal elements in the damping matrix is the most efficient and practical method. The equivalent damping ratio of the PSO was nearly 25% under an earthquake with peak ground acceleration of 0.55g, which is much higher than the conventional assumption of 5%.Mechanical engineering, Civil engineeringmqf2101 Civil Engineering and Engineering MechanicsArticlesIdentification of a Dynamic System Using Ambient Vibration Measurements
http://academiccommons.columbia.edu/catalog/ac:157987
Feng, Maria Q.; Kim, J.-M.; Xue, H.http://hdl.handle.net/10022/AC:P:19469Mon, 25 Mar 2013 00:00:00 +0000This paper demonstrates how ambient vibration measurements at a limited number of locations can be effectively utilized to estimate parameters of a finite element model of a large-scale structural system involving a large number of elements. System identification using ambient vibration measurements presents a challenge requiring the use of special identification techniques, which can deal with very small magnitudes of ambient vibration contaminated by noise without the knowledge of input forces. In the present study, the modal parameters such as natural frequencies, damping ratios, and mode shapes of the structural system were estimated by means of appropriate system identification techniques including the random decrement method. Moreover, estimation of parameters such as the stiffness matrix of the finite element model from the system response measured by a limited number of sensors is another challenge. In this study, the system stiffness matrix was estimated by using the quadratic optimization involving the computed and measured modal strain energy of the system, with the aid of a sensitivity relationship between each element stiffness and the modal parameters established by the second-order inverse modal perturbation theory. The finite element models thus identified represent the actual structural system very well, as their calculated dynamic characteristics satisfactorily matched the observed ones from the ambient vibration test performed on a large-scale structural system subjected primarily to ambient wind excitations. It is noted that newly developed optical fiber accelerometers were used for this ambient vibration test. The dynamic models identified by this study will be used for design of an active mass damper system to be installed on this structure for suppressing its wind vibration.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesDesign of a mega-sub-controlled building system under stochastic wind loads
http://academiccommons.columbia.edu/catalog/ac:157984
Feng, Maria Q.; Chai, Winstonhttp://hdl.handle.net/10022/AC:P:19468Mon, 25 Mar 2013 00:00:00 +0000Vibration control of high-rise buildings under wind loads with application of the mega-sub-control method is studied in this paper. A building with a megasub-configuration consists of two major structural components - a megastructure as the main structural frame and several sub-structures for residential and/or commercial usage. The authors have previously proposed a ‘megasub-control method’ in which the sub-structures are designed to serve as vibration control dampers. The control objective is to suppress certain critical building responses such as inter-story drifts of the mega-structure for the purpose of structural safety and acceleration response of the sub-structures for the purpose of protecting contents and improving human comfort. The feasibility of this method has been explored by the authors in previous publications. In this study, the procedure of optimally designing dynamic parameters of a megasub-controlled building under stochastic wind loads is developed, together with two possible structural configurations which provide a mega-sub-control mechanism. The mega-structure of a mega-sub-building is modeled as a cantilever beam to retain the dominant bending mode characteristics of highrise buildings, and the sub-structure as a shear building to retain the shear mode. The fluctuating wind speed is modeled as a non-white random process in both time and space domains. The power spectral density (PSD) of critical building responses is obtained using the random vibration theory. The mean square value (MSV) of those responses, as functions of the dynamic parameters including the stiffness and damping ratio of the sub-structures, are evaluated from their PSD by numerical integration in the frequency domain. The optimal values of the dynamic parameters are determined by minimizing the MSV of certain critical building responses. An example building is used to demonstrate the design procedure and the numerical simulation of the response quantities in the time domain is carried out to verify the MSV of the building responses obtained from the random vibration theory in the frequency domain. The results show that the proposed design procedure is suitable to apply to a mega-sub-building with different sub-structural configurations. The MSV obtained from the random vibration theory in the frequency domain and from the numerical simulation in the time domain exhibit an excellent agreement. It is also found that the megasub-control method is robust in the sense that slight change in the dynamic parameters affects the building's performance very little. With the design procedure developed, and the corresponding favorable building response demonstrated, this paper has enhanced the feasibility of application of the mega-sub-control method to actual high-rise buildings for wind vibration suppression.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesVibration control of super tall buildings subjected to wind loads
http://academiccommons.columbia.edu/catalog/ac:157981
Chai, Winston; Feng, Maria Q.http://hdl.handle.net/10022/AC:P:19467Mon, 25 Mar 2013 00:00:00 +0000Excessive vibration due to wind loads is a major obstacle in design and construction of a super tall building. The authors recently introduced an innovative method for controlling the wind response of super tall buildings, which takes advantage of the so-called mega-sub structural configuration. Preliminary investigation was performed under the assumption that the wind load is a white noise and the building can be modeled as a shear structure. In this paper, a more reasonable tall building model (a cantilever beam) and a more realistic wind load model (a non-white stochastic process in time and space) are employed to design passive and hybrid mega-sub control systems and to examine the performance of such controlled buildings. Building vibration in both along-wind and across-wind directions is examined. The control parameters of the proposed systems, including the frequency ratio of the sub to the mega structures, the damping ratio of the sub structure, and the feedback gains of the actuator force, are studied and their optimal values are obtained. For comparison, a tall building without control and one with the conventional tuned-mass-damper control are also studied under the same load conditions. The significant cost-effectiveness of the proposed mega-sub systems is demonstrated in reducing the acceleration and deformation responses of tall buildings to wind loads, not only enhancing the safety of structure and its contents but also improving the comfort of occupants.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesAn Optical Fiber Sensor for Measurement of Dynamic Structural Response
http://academiccommons.columbia.edu/catalog/ac:157972
Feng, Maria Q.http://hdl.handle.net/10022/AC:P:19464Mon, 25 Mar 2013 00:00:00 +0000This paper reports the development of and an experimental study on an optical fiber sensor for monitoring civil infrastructure systems. This optical sensor employs a vibrating wire whose tension can be modulated by external force, strain, or vibration and transformed into the change of frequency of wire vibration. The frequency of wire is detected by light sent to and reflected from the wire through an optical fiber cable. Compared to other optical fiber sensors developed so far, the proposed sensor has two significant advantages: one is that the sensing head is a vibrating wire (rather than an optical fiber), which can sense a specific physical quantity without being interfered by miscellaneous effects; the other is that the wire vibration is a well understood and reliable physical phenomenon and its frequency is optically measured and transmitted without attenuation or distortion through the optical fiber to recording and other devices. These advantages make the sensor extremely simple, reliable and robust, and hence more readily deployable in civil infrastructure applications. Three prototypes have been developed and their static and dynamic characteristics have been experimentally tested. One of the prototypes was embedded into a concrete specimen to measure its strain and the result agrees with that from a conventional strain gauge. The experimental study with prototypes demonstrates the high performance of the developed optical sensor in terms of accuracy, high frequency range, and other characteristics.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesVibration Control of Tall Buildings Using Mega Sub-Configuration
http://academiccommons.columbia.edu/catalog/ac:157975
Feng, Maria Q.; Mita, Akirahttp://hdl.handle.net/10022/AC:P:19465Mon, 25 Mar 2013 00:00:00 +0000An innovative vibration-control system is proposed to reduce the dynamic response of tall buildings to wind and seismic loads. This system takes advantage of the so-called megasubstructure configuration, which is especially popular in tall buildings. Substructures contained in the megastructure serve as energy absorbers so that no additional mass is required for the intended vibration control as seen in the conventional mass damper systems. The proposed system naturally resolves the difficulties in augmenting damping capacities of tall buildings associated with the high rigidity and deformation in the dominant bending mode. Dynamic characteristics of the proposed control system including the frequency response and the energy flow are investigated. Optimal values of structural parameters such as the damping ratio and stiffness of the substructure are determined. The feasibility and effectiveness of this unique control system in improving human comfort and protecting structures under both wind and earthquake loads are demonstrated through analytical and numerical analysis.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesAn Experimental Study of an Electro-Optical Displacement Sensor
http://academiccommons.columbia.edu/catalog/ac:157978
Feng, Maria Q.http://hdl.handle.net/10022/AC:P:19466Mon, 25 Mar 2013 00:00:00 +0000This paper presents the results of an experimental study on an innovative electro-optical fiber sensor developed for measuring the dynamic response of civil structures such as buildings and bridges, which can be used for non-destructive evaluation of structural systems. This electro-optical sensor employs an electric circuit, LC oscillator, in which inductance and capacitance are connected in parallel. The resonant frequency of the LC oscillator is modulated by the external displacement transmitted through the core of the induction solenoid. This frequency is detected from the optically-transmitted oscillatory signal and the LC oscillator is optically powered. Compared to the conventional optical fiber sensors developed so far, the proposed sensor has two significant advantages: 1) the sensing head is an electric circuit (rather than an optical fiber cable), which can sense a specific physical quantity without interference from miscellaneous effects and is expected to be much more durable than the sensing head made of optical fiber cable as seen in usual extrinsic optical fiber sensors; 2) the LC oscillator is a well understood and reliable circuit with its resonant frequency measurable and transmittable without attenuation or distortion through an optical fiber cable over a long distance to recording and other devices. These advantages make the sensor extremely simple to design and manufacture, durable, reliable, robust to use, and hence, more readily deployable in civil structural applications. A prototype electro-optical strain sensor has been developed and its static and dynamic characteristics were experimentally tested. This sensor was also installed on a steel frame to measure the dynamic strain response when subjected to seismic ground motions during a shaking table test. The experimental study using the prototype demonstrated excellent performance of the electro-optical sensor in terms of accuracy, wide frequency range, and other advantageous characteristics for civil structural applications.Civil engineering, Mechanical engineeringmqf2101Civil Engineering and Engineering MechanicsArticlesEnhancing Ballast Performance Using Geocell Confinement
http://academiccommons.columbia.edu/catalog/ac:156943
Leshchinsky, BenWed, 20 Feb 2013 00:00:00 +0000In past years, railroad transportation has been of growing interest due to its efficiency and advancement in railway technologies. However, many issues arise due to the variability in subsurface conditions along the sizeable lengths of track that exist. One very important issue is the need for significant upkeep and maintenance for railways passing over areas of poor soil conditions due to continuous deformation and a lack of stiffness from the ballasted foundation. One general solution for lack of substructure integrity has been confinement, applied through a variety of reinforcement types, including geocell. To investigate the effectiveness of geocell confinement on ballasted substructure integrity, a series of embankment model tests with different configurations of geocell placement (one layer and two layers of geocell) were constructed and loaded monotonically and cyclically for comparison to unreinforced, control tests. Upon the completion of these tests, the model embankments were simulated numerically using finite element procedures. The results were then used as validation for a parametric study, observing the effects of less competent geocell material, ballast and foundation conditions and their implications. Further numerical simulations were then performed on railroad embankments reinforced with and without geocell to model realistic railroad conditions and the effects of confinement on performance.The tests and numerical simulations demonstrate that geocell confinement effectively increased stiffness and strength of a ballast embankment, while reducing vertical settlement and lateral spreading. Additionally, the parametric study shows that the use of geocell provides a composite, "mattressing" effect that distributes subgrade stress more uniformly than without reinforcement, increasing bearing capacity and reducing settlement, especially on soft foundations or when using weaker ballast. The results suggested that in some site conditions, use of geocell might be an economical alternative to frequent maintenance and/or lower train speeds. Additionally, it implies that geocell might be cost-effective when used in combination withed degraded, weaker ballasts, i.e. inferior local or recycled materials. The use of geocell in ballast stabilization could prove to a sustainable solution for a common and expensive problem.Civil engineeringCivil Engineering and Engineering MechanicsDissertationsEnhanced Anisotropic Bounding Surface Model: Implementation and Simulation of Excavation in Soft Cohesive Soils
http://academiccommons.columbia.edu/catalog/ac:182197
Hung, Chinghttp://hdl.handle.net/10022/AC:P:18846Mon, 28 Jan 2013 00:00:00 +0000This dissertation describes the application of an enhanced anisotropic bounding surface model with non-associative flow rule, based on the anisotropic critical state theory and bounding surface plasticity. The model has exhibited a great potential to realistically simulate the mechanical behavior of cohesive soils, in non-linear finite element method associated with the coupling analysis for simulating deep excavation induced ground deformations. The first phase of this research illustrates efforts in integrating the enhanced anisotropic bounding surface model into finite element analysis (FEA) software. The implementations are validated against undrained isotropic and anisotropic triaxial test results for various types of cohesive soils, including those with strain softening behavior. The capability and limitation of the bounding surface models are assessed, and it is confirmed that complex soil behavior, such as the effects of stress anisotropy and over-consolidation nature, can practically be simulated using such bounding surface models integrated in FEA, especially for normally and overly consolidated Kaolin and Taipei silty clay specimens. Phase two presents the application of bounding surface models for the finite element deep excavation analyses. The simulations are evaluated through comparison with field measurements in Taipei City (TNEC and WTC sites) and Boston City (Post Office Square site). The case studies have demonstrated satisfactory agreement between the simulations and field measurements, especially for the TNEC and Post Office Square sites, while there is a less satisfactory agreement for the WTC site. Similar results are obtained for the different versions of bounding surface model, except that the isotropic version of the model tended to under-estimate the lateral deformation. The importance of adopting anisotropic hardening rules and a bounding surface in simulating for a more realistic ground response has been established due to the better simulation capability of the enhanced bounding surface model than that of some other bounding surface models. In addition, the difference in results between the non-associative and associative versions of bounding surface model was found to be rather negligible in the case of finite element analysis of deep excavation involved with collapse.Civil engineering, Mechanical engineering, Geologych2532Civil Engineering and Engineering MechanicsDissertationsThe Application Of Insurance As A Risk Management Tool For Alternative Dispute Resolution (ADR) Implementation In Construction Disputes
http://academiccommons.columbia.edu/catalog/ac:155046
Song, Xinyihttp://hdl.handle.net/10022/AC:P:15317Mon, 19 Nov 2012 00:00:00 +0000In modern days, construction projects have become more and more complex and intriguing. One source of the complexity arises from the large number of parties involved. This is especially the case for large-scale construction projects. Because of such complexity, disputes are almost inevitable and implementation costs associated with dispute resolution have become increasingly expensive. Because most projects operate on tight budgets, cost effective dispute resolution plays an important role in the success of a construction project. For this purpose, Alternative Dispute Resolution (ADR) techniques such as negotiation, mediation, and arbitration are being widely adopted in large-scale construction projects to resolve disputes in more effective and cost-saving ways. However, the risk of incurring dispute-related cost overruns always exists because of the uncertainty in the distribution of dispute occurrence and the effectiveness of contractually-predetermined ADR techniques. As a result, the traditional self-insured structure which simply retains all dispute resolution costs to the project through contingency fees is no longer considered economical. While many insurance policies cover the settlement of a dispute, such as professional liability insurance, no specific insurance policy is dedicated to cover the ADR implementation costs such as fees and expenses that are paid to the owner/contractor's employees, lawyers, claims consultants, third party neutrals, and other experts involved in the resolution process. To fill the gap, this dissertation proposes an insurance model to reduce the potential variations in the dispute resolution budget by pricing ADR techniques as an insurance product. It is designed to transfer the risk of dispute-related cost overruns from the project to a third-party insurance company. To achieve this goal, this dissertation focuses on three major tasks: 1) investigate the role of ADR implementation insurance in construction risk management, 2) construct a mathematical model to represent the risk attitudes of project participants using utility theory and derive the basic premium of ADR implementation insurance using insurance pricing theory, and 3) develops a comprehensive framework to determine the optimal insurance premium by considering two additional insurance limits a Deductible Limit (DL) and a Maximum Payment Limit (MPL). The objective of this dissertation is to provide project participants with an advantageous insurance policy that minimizes their total expected subjective loss. The model can serve as a decision-making support system to help project participants determine whether an ADR implementation insurance policy is attractive for a certain project. To illustrate the benefits of the proposed model, numerical examples are provided for simulation purpose. The results show that ADR implementation insurance, although not a tool to eliminate dispute resolution costs, is a powerful alternative in risk management to transfer the financial implications of ADR implementation risk to a third party.Civil engineeringxs2149Computer Science, Civil Engineering and Engineering Mechanics, Earth and Environmental EngineeringDissertationsSimulating Network Structure, Layering Multi-layer Network System and Developing Network Block Configuration Model to Understand and Improve Energy Conservation in Residential Buildings
http://academiccommons.columbia.edu/catalog/ac:153238
Chen, Jiayuhttp://hdl.handle.net/10022/AC:P:14887Thu, 11 Oct 2012 00:00:00 +0000The building sector is a major contributor to total energy consumption in most countries. Traditionally, researchers have focused on leveraging energy efficiency by improving building materials, in-house facilities and transmission equipment. More recently, however, there has been increased focus on research concerning demand-side energy consumption behavior. Current research suggests that energy efficient behavior of a building's occupants can be extensively enhanced through the sharing of energy consumption information among residents in a peer network. However, most of this research relies on experimental tests and does not theorize concepts related to peer network energy efficiency systematically. My dissertation addresses this research gap on two levels. First, I examined if and how the structure of peer networks can impact residents' conservation behaviors through network analysis by employing agent-based simulation techniques. Following confirmation of the impact that network structure has on user behavior, I created a layered network model to integrate information from various network layers and a block configuration model to reconstruct increasingly reliable random networks. In contrast to controlled energy efficiency experiments, real-world networks are large in size, heterogeneous in nature and regularly interact with other networks. By utilizing models developed in this dissertation, we are able to estimate the contribution of network structural coefficients to the energy consumption performance of peer networks. By comparing the layered network and block configuration model I developed with other conventional models, I prove the efficiency, accuracy and reliability of these improved models. These findings have implications for assessing network performance, creating accurate complex random networks for large-scale research, and developing strategies for network design to improve building energy efficiency. This research establishes a system to study residents' energy efficient behaviors from the perspective of peer networks and proposes some instructive models for further energy feedback system design.Civil engineering, Energy, Sociologyjc3252Civil Engineering and Engineering MechanicsDissertationsDamage Detection and System Identification using a Wavelet Energy Based Approach
http://academiccommons.columbia.edu/catalog/ac:152497
Joo, Duk Jinhttp://hdl.handle.net/10022/AC:P:14683Wed, 12 Sep 2012 00:00:00 +0000Structural Health Monitoring (SHM) is central to the goal of maintaining civil engineering structures safely and efficiently, and thereby securing people's lives and property. Furthermore, it plays an essential role in infrastructure design at a fraction of the capital cost of construction. In this thesis, we seek to address two of the central concerns of the SHM: parametric system identification and damage detection. The first proposed method seeks to identify the physical parameters of an analytical model. First, the connection coefficients for the scaling function were developed for deriving the responses of the velocity and displacement from the acceleration responses. Next, defining the dominant sets based on the relative energies of the Wavelet Components of the acceleration responses, the equations of motion of the system in the time domain were converted to a reduced representation of the equations of motion in terms of the DWT and of the DWPT. Finally, the least square error minimization was conducted over the dominant sets to estimate the best estimation of the physical parameters. The second proposed method seeks to detect damage in a structure. Motivated by the fact that the Empirical Mode Decomposition is seen to have different features from the Discrete Wavelet Transform when one investigates nonstationary signals, we have combined the Empirical Mode Decomposition with the Discrete Wavelet Transform to enhance the performance of the proposed method for identifying damage in the structure.Civil engineeringdj2111Civil Engineering and Engineering MechanicsDissertationsThe Dynamics of Rigid Bodies on Moving Deformable Support Media
http://academiccommons.columbia.edu/catalog/ac:152488
Chatzis, Emmanouilhttp://hdl.handle.net/10022/AC:P:14678Wed, 12 Sep 2012 00:00:00 +0000The rocking motion of a solid block on a moving deformable base is a dynamic problem, that despite its apparent simplicity, involves a number of complex dynamic phenomena such as impacts, sliding, geometric and material nonlinearities and, under some circumstances, chaotic behavior. For that reason, since the first model proposed by G. W. Housner in 1963, a number of alternative models have been proposed for its mathematical simulation. Although, with very few exceptions, the previous models in the literature make the simplified assumption that this motion is planar, this is usually not true since a body will probably not be aligned with the direction of the ground motion. Thus, even in the case where the body is fully symmetric, the rocking motion involves three dimensional rotations and displacements. Moreover, for reasons more related to functionality than safety, it is not uncommon for heavy mechanical and electrical equipment to be placed on wheels. Examples of such devices are medical carts, mechanical equipment in hospitals, electrical transformers and recently even supercomputers. Although wheels facilitate the operation of these devices, they also affect the response of these objects during earthquakes; not necessarily in a beneficial way. This dissertation develops suitable models for simulating the previous dynamic problems. The equations of motion and suitable contact models are developed for each case. The importance of phenomena often neglected in the literature is stressed. Suitable examples illustrate the complex dynamic character of the problems examined. Finally, a static contact problem is examined. A model is developed for systems of multiple jointed elastic beams, using exact shape functions. A special application of the method for the definition of pressure loads in the wires of the main cable of a suspension bridge is presented. Examples illustrate the robustness of the method and the special properties associated with pressure loads.Civil engineeringec2608Civil Engineering and Engineering MechanicsDissertationsHomogenization Methods for Problems with Multiphysics, Temporal and Spatial Coupling
http://academiccommons.columbia.edu/catalog/ac:148608
Kuznetsov, Sergeyhttp://hdl.handle.net/10022/AC:P:13697Thu, 28 Jun 2012 00:00:00 +0000There are many natural and man-made materials with heterogeneous micro- or nanostructure (fine-scale structure) which represent a great interest for industry. Therefore there is a great demand for computational methods capable to model mechanical behavior of such materials. Direct numerical simulation resolving all fine-scale details using very fine mesh often becomes very expensive. One of alternative effective group of methods is the homogenization methods allowing to model behavior of materials with heterogeneous fine-scale structure. The essence of homogenization is to replace heterogeneous material with some equivalent effectively homogeneous material. The homogenization methods are proven to be effective in certain classes of problems while there is need to improve their performance, which includes extension of the range of applicability, simplification, usage with conventional FE software and reducing computational cost. In this dissertation methods extending the range of applicability of homogenization are developed. Firstly, homogenization was extended of the case of full nonlinear electromechanical coupling with large deformations, which allows simulating effectively behavior of electroactive materials such as composites made of electroactive polymers. Secondly, homogenization was extended on wave problems where dispersion is significant and should be accounted for. Finally, the homogenization was extended on the case where the size of microstructure. The distinctive feature of the methods introduced in this dissertation is that they don't require higher order derivatives and can be implemented with conventional FE codes. The performance of methods is tested on various examples using Abaqus.Civil engineeringCivil Engineering and Engineering MechanicsDissertationsStress Transfer and Structural Failure of Bilayered Material Systems
http://academiccommons.columbia.edu/catalog/ac:146634
Prieto-Munoz, Pablo Arthurhttp://hdl.handle.net/10022/AC:P:13138Fri, 04 May 2012 00:00:00 +0000Bilayered material systems are common in naturally formed or artificially engineered structures. Understanding how loads transfer within these structural systems is necessary to predict failure and develop effective designs. Existing methods for evaluating the stress transfer in bilayered materials are limited to overly simplified models or require experimental calibration. As a result, these methods have failed to accurately account for such structural failures as the creep induced roofing panel collapse of Boston's I-90 connector tunnel, which was supported by adhesive anchors. The one-dimensional stress analyses currently used for adhesive anchor design cannot account for viscoelastic creep failure, and consequently results in dangerously under-designed structural systems. In this dissertation, a method for determining the two-dimensional stress and displacement fields for a generalized bilayered material system is developed, and proposes a closed-form analytical solution. A general linear-elastic solution is first proposed by decoupling the elastic governing equations from one another through the so-called plane assumption. Based on this general solution, an axisymmetric problem and a plane strain problem are formulated. These are applied to common bilayered material systems such as: (1) concrete adhesive anchors, (2) material coatings, (3) asphalt pavements, and (4) layered sedimentary rocks. The stress and displacement fields determined by this analytical analysis are validated through the use of finite element models. Through the correspondence principle, the linear-elastic solution is extended to consider time-dependent viscoelastic material properties, thus facilitating the analysis of adhesive anchors and asphalt pavements while incorporating their viscoelastic material behavior. Furthermore, the elastic stress analysis can explain the fracturing phenomenon of material coatings, pavements, and layered rocks, successfully predicting their fracture saturation ratio--which is the ratio of fracture spacing to the thickness of the weak layer where an increase in load will not cause any new fractures to form. Moreover, these specific material systems are looked at in the context of existing and novel experimental results, further demonstrating the advantage of the stress transfer analysis proposed. This research provides a closed-form stress solution for various structural systems that is applied to different failure analyses. The versatility of this method is in the flexibility and the ease upon which the stress and displacement field results can be applied to existing stress- or displacement-based structural failure criteria. As presented, this analysis can be directly used to: (1) design adhesive anchoring systems for long-term creep loading, (2) evaluate the fracture mechanics behind bilayered material coatings and pavement overlay systems, and (3) determine the fracture spacing to layer thickness ratio of layered sedimentary rocks. As is shown in the four material systems presented, this general solution has far reaching applications in facilitating design and analysis of typical bilayered structural systems.Civil engineeringpap2108Civil Engineering and Engineering MechanicsDissertationsEffects of Curing Temperature and Pressure on the Chemical, Physical, and Mechanical Properties of Portland Cement
http://academiccommons.columbia.edu/catalog/ac:140093
Pang, Xueyuhttp://hdl.handle.net/10022/AC:P:11410Mon, 10 Oct 2011 00:00:00 +0000This dissertation mainly focuses on studying the fundamental hydration kinetics and mechanisms of Portland cement as well as the effects of curing temperature and pressure on its various properties. An innovative test apparatus has been developed in this study to cure and test cement paste specimens under in-situ conditions, such as down-hole in oil wells with high temperature and high pressure. Two series of tests were performed using cement pastes prepared with four different classes of oilwell cement (namely Class A, C, G, and H cements). Specimens in groups of four were cured at temperatures ranging from ambient to 60 °C and pressures ranging from 0.69 to 51.7 MPa for a period of 48 or 72 hours. The density and w/c ratio of the specimens at the time of casting as well as at the end of the curing period were recorded. Total chemical shrinkage of the cement paste was measured continuously during the entire hydration period while tensile strength was obtained at the end of the curing period using both water pressure and splitting tension test methods. Due to capacity limitations of the test equipment, in-situ tensile strength was obtained for only one test series with a highest curing pressure of 13.1 MPa. Specimens from the other test series were depressurized before the tensile strength tests. Chemical shrinkage test is an important method of measuring cement hydration kinetics in that the normalized total chemical shrinkage is approximately equal to the degree of cement hydration. By studying the correlations between the chemical shrinkage and the non-evaporable water content of cement during hydration, a multi-linear model is first proposed to estimate the normalization factors for different types of cement under different curing conditions. Based on the hydration kinetics data obtained from chemical shrinkage test results, a new approach of modeling the effect of curing temperature and pressure on cement hydration kinetics is proposed. It is found that when a hydration kinetics curve is represented by an unknown function, the effect of curing condition on the curve can be modeled by incorporating a simple scale factor in this function. The relationship between this scale factor and curing condition is described by chemical kinetics laws. While the proposed new approach of modeling cement hydration kinetics has the advantage of being widely applicable to different types of cement, it only explains one influence factor of cement hydration (i.e. the curing condition). In order to take into account other influence factors and to further understand the fundamental mechanisms of cement hydration, a more complex particle-based numerical hydration model is developed by combining the two well-known cement hydration mechanisms, namely the nucleation and growth controlled mechanism and the diffusion controlled mechanism. The model is applied to experimental data of both C3S hydration in dilute suspensions and Class H cement paste hydration. Excellent agreement is observed between experimental and modeled results. Three rate-controlling parameters with clear physical meanings can be identified from the proposed model. Fitted model parameters are found to be in reasonable agreement with experimental observation. The dependencies of these parameters on particle size, cement composition, w/c ratio, and curing condition are also investigated. Finally, the importance of cement hydration kinetics is illustrated by showing their close correlations with the physical and mechanical properties. The various influence factors, including the curing temperature and pressure, of physical and mechanical property test results (particularly density and tensile strength) are evaluated. Potential damage mechanisms of cement paste specimens during depressurization are studied by analyzing the deformation behavior of the entire system consisting of the cement paste and pressurizing water.Civil engineering, Materials sciencexp2111Civil Engineering and Engineering MechanicsDissertations