- Structural Engineering, Modeling and Simulation, Computational Modelling, Earthquake Engineering, Finite Element Methods, Computational Mechanics, and 16 moreStructural Dynamics, Finite Element Analysis (Engineering), Bridge Engineering, Structural Health Monitoring, Computational Science, Fluid structure interaction, Structural Optimization, Performance Based Earthquake Engineering, Smart Structure, Finite Volume Methods, Plasticity, Soil-Structure Interaction, Meshfree Methods, Nonlinear Elasticity, Verification and Validation, and Active Structures(Structural Dynamics, Finite Element Analysis (Engineering), Bridge Engineering, Structural Health Monitoring, Computational Science, Fluid structure interaction, Structural Optimization, Performance Based Earthquake Engineering, Smart Structure, Finite Volume Methods, Plasticity, Soil-Structure Interaction, Meshfree Methods, Nonlinear Elasticity, Verification and Validation, and Active Structures)edit
Some of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes, while a few more advanced models employ two damage variables. Models with a single... more
Some of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes, while a few more advanced models employ two damage variables. Models with a single variable have an inherent difficulty in accounting for the damage accrued due to tensile and compressive actions in appropriately different manners, and their mutual dependencies. In the current models that adopt two damage variables, the independence of these damage variables during cyclic loading results in the failure to capture the effects of tensile damage on the compressive behavior of concrete and vice-versa. This study presents a cyclic model established by extending an existing monotonic constitutive model. The model describes the cyclic behavior of concrete under multiaxial loading conditions and considers the influence of tensile/compressive damage on the compressive/tensile response. The proposed model, dubbed the enhanced concrete damage pla...
Research Interests:
Procedures and computer programs are developed for determining the response of soil-foundation-structure interaction systems during earthquakes and to investigate the nature of soil and interaction effects. Assuming the linear elastic... more
Procedures and computer programs are developed for determining the response of soil-foundation-structure interaction systems during earthquakes and to investigate the nature of soil and interaction effects. Assuming the linear elastic stress-strain behavior of the soil, the author develops a two-dimensional analytical model of soil-foundation-structure interaction. The model consists of one-dimensional structural members, a two-dimensional rigid foundation block, and quadrilateral finite elements which idealize soil deposits. The ...
The near fault (NF) line waves send out signal envelopes that oscillate over lengthy periods of time with periodic impulses. Like train bridges, train tracks demonstrate comparable track-bridge (TB...
Research Interests:
<p><strong>Title</strong>: Field Testing of a Non-ductile Reinforced Concrete Building in Turkey (NEES-2010-0929)</p> <p><strong>Year Of Curation: </strong>2013</p>... more
<p><strong>Title</strong>: Field Testing of a Non-ductile Reinforced Concrete Building in Turkey (NEES-2010-0929)</p> <p><strong>Year Of Curation: </strong>2013</p> <p><strong>Description: </strong>This project brings together the technical expertise and advanced testing capabilities of a group of researchers from the US and Turkey to provide unique data on behavior and performance of older reinforced concrete buildings. This type of construction comprises the majority of residential, public service (i.e., schools, hospitals), and commercial buildings in the industrial heartland of Turkey; and there are a significant number of similarly vulnerable buildings within more active seismic regions in the USA (e.g., California, Washington, Utah, South Carolina, etc). In California, the vulnerable buildings are typically pre-1973 vintage.</p> <p><strong>Award: </strong>http://www.nsf.gov/awardsearch/showAward?AWD_ID=0755333</p> <p><strong>PIs & CoPIs: </strong>Ertugrul Taciroglu, John Wallace</p> <p><strong>Dates: </strong>July 01, 2010 - December 15, 2010</p> <p><strong>Organizations: </strong>University of California, Los Angeles, CA, United States</p> <p><strong>Facilities: </strong>University of California, Los Angeles, CA, United States</p> <p><strong>Sponsor: </strong>NSF - 0755333</p> <p><strong>Keywords: </strong>health monitoring, system identification, vibration testing</p> <p><strong>Publications: </strong><br /> Kutay Orakcal, Hilmi Lus, Erdal Safak, "Ambient and Forced Vibration Testing of a Reinforced Concrete Building Before and After its Seismic Retrofitting"</p> <nb:citations></nb:citations>
Research Interests: Geology()
()
Website: https://github.com/NHERI-SimCenter/BRAILS What is BRAILS BRAILS is the acronym for Building Recognition using AI at Large-Scale, which is an AI-Based pipeline for city-scale building information modeling (BIM). What can BRAILS do... more
Website: https://github.com/NHERI-SimCenter/BRAILS What is BRAILS BRAILS is the acronym for Building Recognition using AI at Large-Scale, which is an AI-Based pipeline for city-scale building information modeling (BIM). What can BRAILS do BRAILS helps users create regional-scale database of building inventory, where buildings properties are extracted from satellite or street view images using deep learning. Why it's important BIM, as an efficient way for describing buildings, gives architecture, engineering, and construction (AEC) professionals the insight and tools to more efficiently plan, design, construct, and manage buildings and infrastructure. Natural disasters cause losses to human society by damaging or destroying buildings, which consequently endangers lives and goods. Buildings are the major components of a human built environment, hence are of the major considerations in planning for, responding to and recovering from disasters. BIM contains information showing build...
This work delineates the stable implementation of an innovative method of accounting for the effects of inertial soil-structure interaction in time domain time-history analyses through the use of recursive discrete-time digital filters as... more
This work delineates the stable implementation of an innovative method of accounting for the effects of inertial soil-structure interaction in time domain time-history analyses through the use of recursive discrete-time digital filters as approximations of frequency dependent foundation impedance functions. To this end, an algorithm inserting the recursive filter into a numerical integration scheme of the dynamic equations of motion is derived. Its implementation is then demonstrated by subjecting various elastic structure-foundation-soil systems to ground motion records. The resultant time histories are subsequently verified through comparison with those obtained both in the frequency domain and using various state-of-practice time domain solution methods. Finally, the stability of the combined integration-recursion algorithm is investigated both analytically and numerically.
Research Interests:
Research Interests:
Research Interests:
Transformer substations are among the most significant components of an electric power distribution system. These critical elements must remain operational during and after any extreme event, especially a severe earthquake. In past... more
Transformer substations are among the most significant components of an electric power distribution system. These critical elements must remain operational during and after any extreme event, especially a severe earthquake. In past studies, the interaction between the main plant and the electrical equipment (EE) in a transformer substation was usually ignored. While a few considered this interaction through numerical simulations, there were no experimental studies to validate the findings. The aim of the present paper is to analyze the seismic reaction of a substation with explicit consideration of the dynamic interaction between the main plant and the EE mounted inside—achieved through a shaking table test and numerical simulations. A 1:8 scale model of a transformer substation plant with EE on its second floor is built and tested on a shaking table. Dynamic response data are gathered during seismic excitations of the substation, with and without the EE. These measurements and the ...
Research Interests:
... Boğaziçi Üniversitesi Kuzey Kampüsü'nde bulunan Eğitim Teknolojileri B Blok (ET-B) binası depreme karşı güçlendirilmesi ... Depreme karşı güçlendirme çalışmaları, binanın taşıyıcı sistemineperde duvalar eklenmesi ve mevcut... more
... Boğaziçi Üniversitesi Kuzey Kampüsü'nde bulunan Eğitim Teknolojileri B Blok (ET-B) binası depreme karşı güçlendirilmesi ... Depreme karşı güçlendirme çalışmaları, binanın taşıyıcı sistemineperde duvalar eklenmesi ve mevcut kolonların mantolanması olarak gerçekleştirilmiştir. ...
Research Interests:
Numerous experiments and prior analyses have confirmed that soil inelasticity, which is known to come into effect even at very low strain levels, can significantly affect site response and dynamic soil‐structure interaction (SSI)... more
Numerous experiments and prior analyses have confirmed that soil inelasticity, which is known to come into effect even at very low strain levels, can significantly affect site response and dynamic soil‐structure interaction (SSI) behavior. To date, only a few studies were able to consider multi‐axial wave propagation problems with appropriate models of soil nonlinearity. Most existing works are limited to either homogeneous soil configurations or equivalent linear soil models. The instances wherein soil nonlinearity is accurately considered have been confined to single element tests and one‐dimensional problems. In this study, an improved pressure‐dependent bounding surface plasticity soil model—with appropriate plastic strain rate direction definition and overshooting correction scheme—is implemented in Abaqus, and validated using recordings from both the Lotung borehole array and centrifuge test data on embedded flexible structures. The implemented model is capable of comprehensively reproducing complex soil behaviors, such as stiffness degradation, damping, dilatancy, and compaction while under a wide strain range, and under general loading conditions using only a few material parameters to be calibrated. Consequently, numerically predicted results are observed to be in better agreement with experimentally measured data, in comparison with linear and another plasticity model, which include accelerations, and bending and hoop strains along the walls of the specimen structures, for low‐ as well as high‐amplitude input motions.
Research Interests:
33rd Conference on Neural Information Processing Systems (NeurIPS 2019), Vancouver, Canada. Corresponding author: Chaofeng Wang, c_w@berkeley.edu In this paper, we provide two case studies to demonstrate how artificial intelligence can... more
33rd Conference on Neural Information Processing Systems (NeurIPS 2019), Vancouver, Canada. Corresponding author: Chaofeng Wang, c_w@berkeley.edu In this paper, we provide two case studies to demonstrate how artificial intelligence can empower civil engineering. In the first case, a machine learning-assisted framework, BRAILS, is proposed for city-scale building information modeling. Building information modeling (BIM) is an efficient way of describing buildings, which is essential to architecture, engineering, and construction. Our proposed framework employs deep learning technique to extract visual information of buildings from satellite/street view images. Further, a novel machine learning (ML)-based statistical tool, SURF, is proposed to discover the spatial patterns in building metadata. <br> The second case focuses on the task of soft-story building classification. Soft-story buildings are a type of buildings prone to collapse during a moderate or severe earthquake. Henc...
Research Interests:
Long-span bridges provide vital transportation links to metropolitan regions, and their damage during earthquakes will cause significant hardship. Recognizing their importance, the California Department of Transportation (Caltrans) and... more
Long-span bridges provide vital transportation links to metropolitan regions, and their damage during earthquakes will cause significant hardship. Recognizing their importance, the California Department of Transportation (Caltrans) and California Geological Survey have been deploying strong motion instrumentation on these structures for 25 years. In the present study, existing gaps between responses predicted using numerical models and real-life data are investigated through system identification and finite element model updating techniques for the Samoa Channel Bridge, located in Humboldt County. Seismic response of this bridge is different from its operational response, and the discrepancy increases with the shaking intensity. Also, while existing reduced-order numerical models of soil-pile interaction are observed to work well, they should be calibrated for specific vibration amplitudes.
Research Interests:
The seismic response of underground structures is a complex soil-structure interaction (SSI) problem in which two fundamental mechanisms are at play. Kinematic SSI is concerned with the motion of the structure in the presence of spatially... more
The seismic response of underground structures is a complex soil-structure interaction (SSI) problem in which two fundamental mechanisms are at play. Kinematic SSI is concerned with the motion of the structure in the presence of spatially variable ground motions and the interface pressures that develop as a result of different structural and free-field motions. Inertial SSI captures the soil reactions that develop to resist inertial forces associated with the acceleration of the structure. The kinematic component is generally considered to be most significant for embedded structures, due to their modest mass. Existing methods of analysis for the seismic response of embedded structures are not based on a rational conceptual framework that recognizes the essential role of SSI in the response prediction. These methods of analysis therefore have an unknown degree of reliability for the problem. We propose a two-year project that will significantly advance our understanding of SSI for em...
This paper is aimed at quantifying the variability in predicted seismic response of bridges due to uncertainty in exterior shear key behavior. Shear keys are usually modeled as sacrificial elements; however, experiments show that the... more
This paper is aimed at quantifying the variability in predicted seismic response of bridges due to uncertainty in exterior shear key behavior. Shear keys are usually modeled as sacrificial elements; however, experiments show that the behavior of shear keys depend on their reinforcement detailing, and the construction joint between the shear key and the bridge abutment's stem wall. This paper focuses on modeling approaches for shear keys in bridges with box-girder deck and seat-type abutments. Construction of this type of bridge is common in California since 2000. An enhanced ductile shear key model, generated based on experimental results is used in this study. As for sacrificial (brittle) shear keys, a simplified analytical model is developed based on experimental evidence. The model matrix is comprehensive and comprises bridges with various abutment skew angles and a suite of forty near-fault ground motions. Three parameter lognormal distribution is employed for probabilistic ...
In this study, we formulate an improved finite element model updating method to address the numerical difficulties associated with ill conditioning and rank-deficiency. These complications are frequently encountered model updating... more
In this study, we formulate an improved finite element model updating method to address the numerical difficulties associated with ill conditioning and rank-deficiency. These complications are frequently encountered model updating problems, and occur when the identification of a larger number of physical parameters is attempted than that warranted by the information content of the experimental data. Based on the standard Bounded Variables Least-squares (BVLS) method, which incorporates the usual upper/lower-bound constraints, the proposed method (henceforth referred to as BVLSrc) is equipped with novel sensitivity-based relative constraints. The relative constraints are automatically constructed using the correlation coefficients between the sensitivity vectors of updating parameters. The veracity and effectiveness of BVLSrc is investigated through the simulated, yet realistic, forced vibration testing of a simple framed structure using its frequency response function as input data....
By harvesting data from publicly available sources, locations of bridges in a region as well as their essential structural and geotechnical properties, and hazard exposure can be extracted. This data is crucial in image-based modeling... more
By harvesting data from publicly available sources, locations of bridges in a region as well as their essential structural and geotechnical properties, and hazard exposure can be extracted. This data is crucial in image-based modeling procedures, given images are best utilized for geometry and material-type extraction, hence they provide only a part of the data necessary for constructing detailed structure-specific models. ShakeReady database, currently under development, contains a collection of bridge data obtained from web-based resources (Figure 1).
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
AbstractSoft-story buildings are seismically vulnerable during earthquakes. The identification of such buildings is vital in seismic risk mitigation to assess the seismic resilience of a given urba...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
We present data and metadata from a centrifuge testing program that was designed to investigate the seismic responses of buried circular and rectangular culverts. The specimen configurations were based on Caltrans Standard Plans, and the... more
We present data and metadata from a centrifuge testing program that was designed to investigate the seismic responses of buried circular and rectangular culverts. The specimen configurations were based on Caltrans Standard Plans, and the scope of research was to compare the experimental findings with the design method described in the NCHRP Report 611 as well as to formulate preliminary recommendations for Caltrans practice. A relatively flexible pipe and a stiff box-shaped specimen embedded in dense sand were tested in the centrifuge at the Center for Geotechnical Modeling at University of California, Davis and were subjected to a set of broadband and harmonic input motions. Responses were recorded in the soil and in the embedded structures using a dense array of instruments. Measured quantities included specimen accelerations, bending strains, and hoop strains; soil accelerations, shear-wave velocities, settlements, and lateral displacements; and accelerations of the centrifuge...
Research Interests:
The present article introduces an algorithm for path planning and assembly of infinitesimal and real-sized particles by using a distance and path based permutation algorithm. The main objective is to define non-overlapping particle paths... more
The present article introduces an algorithm for path planning and assembly of infinitesimal and real-sized particles by using a distance and path based permutation algorithm. The main objective is to define non-overlapping particle paths subject to minimal total path length during particles positioning and assembly. Thus, a local minimum is sought with a low computational cost. For this reason, an assignment problem, to be specific Euclidean bipartite matching problem, is presented, where the particles in the initial (random selection) and final (particle assembly) configurations are in one-to-one correspondence. The cost function for particle paths is defined through Euclidean distance of each particle between the initial and final configurations. Principally, a cost flow problem is formed and solved by determining an optimal permutation subject to the total Euclidean distance of the particles and their non-overlapping paths. Monte Carlo simulations are carried out for non-overlapping paths; thus, non-colliding particles, and then total path distances of the obtained sets are minimized, resulting in an optimal solution which may not be necessarily the global optimum. Case studies on basic and complex shaped infinitesimal and real-sized particle assemblies are shown with their total costs, i.e., path lengths. It is believed that the present study contributes to the current efforts in optical trapping automation for particle assemblies with possible applications, e.g., in the areas of micro-manufacturing, microfluidics, regenerative medicine and biotechnology.
Research Interests:
Research Interests:
Abstract In this study, a numerically robust finite element procedure is described, which is based on explicit time-stepping, for high-fidelity simulations of inelastic and post-buckling cyclic responses of braced frame systems. The use... more
Abstract In this study, a numerically robust finite element procedure is described, which is based on explicit time-stepping, for high-fidelity simulations of inelastic and post-buckling cyclic responses of braced frame systems. The use of an explicit time-stepping method with properly chosen increments permits accurate results while avoiding (implicit) equilibrium iterations throughout the entire loading history, during which multiple yielding and buckling events occur. A number of essential techniques for properly calibrating the discrete models and to constrain their responses in order to obtain quasi-static outcomes are provided. The procedure is globally and locally validated (verified) using experimental data (implicit numerical simulations) from three types of specimens—namely, individual braces, and single and multi-story braced frame systems with diagonal and X-brace arrangements—under both monotonic and cyclic loading protocols. Results from these validation and verification studies indicate that the proposed simulation methodology can accurately capture sub-member (i.e., plastic hinges), member, and system behavior very accurately; and thus, it can be confidently used—e.g., as a virtual laboratory—to predict the responses of braced frames with configurations and dimensions other than those tested, and to seek optimum designs beyond those offered by basic guidelines.
Research Interests:
In this preliminary study, we present the development of a high-fidelity finite element model for the Samoa Bridge located in Humboldt County, California. This carefully constructed global model is calibrated using data recorded during a... more
In this preliminary study, we present the development of a high-fidelity finite element model for the Samoa Bridge located in Humboldt County, California. This carefully constructed global model is calibrated using data recorded during a strong earthquake, and is shown to capture the salient features of observed response. The model can be utilized to assess the validity and effectiveness of existing seismic analysis and design procedures for long-span bridges.
Research Interests:
The focus of this study is the application of novel as well as existing methods of modal system identification and finite element model updating techniques to experimental data. The data are collected during a small earthquake and from... more
The focus of this study is the application of novel as well as existing methods of modal system identification and finite element model updating techniques to experimental data. The data are collected during a small earthquake and from ambient vibrations. The specimen structure ...
Research Interests:
ABSTRACT Long-span bridges usually experience different input excitations at their ground supports that emanate from differences in wave arrival times, and soil conditions, as well as loss of coherency in arriving waves. These spatial... more
ABSTRACT Long-span bridges usually experience different input excitations at their ground supports that emanate from differences in wave arrival times, and soil conditions, as well as loss of coherency in arriving waves. These spatial variations can drastically influence the dynamic response; hence, this phenomenon must be considered in any vibration-based identification method. There are numerous Multi-Input Multi-Output (MIMO) identification techniques that may be applied to data recorded at long-span bridges that experience spatial variations in their input motions. However, inertial soil-structure interaction effects severely reduce the accuracy of these techniques because the actual Foundation Input Motion (FIM) cannot be recorded during earthquakes. In this study, we present an extension to a novel blind identification method that we had developed earlier, which enables the method to handle multiple input motions. For the sake of simplicity, we only consider wave passage effects—that is, all unknown input motions are assumed to be identical except for a known/unknown phase-delay. This method comprises two steps. In the first step, the spatial time-frequency distributions of recorded responses are used for extracting the mode shapes and the modal coordinates. This is achieved through a Blind Source Separation (BSS) technique. In the second step, cross relations among the extracted modal coordinates are used for identifying the natural frequencies, damping ratios, modal contribution factors, along with the unknown input motions through a least-squares technique. Both simulated and experimental examples are provided, which suggest that the method is capable of accurately identifying the dynamic characteristics of long-span bridges from recorded response signals without the knowledge of input motions, even in the presence of wave passage effects due to phase-delays.
Research Interests:
Research Interests: Engineering, Civil Engineering, Structural Engineering, Seismic Hazard, Nonlinear dynamics, and 13 morePerformance Assessment, Earthquake, Probability Distribution & Applications, Earthquake Engineering and Structural Dynamics, Structural modelling, Coefficient of Variation, Building Design, Building Codes, Reinforced concrete, Ground Motion, Economic Loss, Structural Response, and Probability Distribution(Performance Assessment, Earthquake, Probability Distribution & Applications, Earthquake Engineering and Structural Dynamics, Structural modelling, Coefficient of Variation, Building Design, Building Codes, Reinforced concrete, Ground Motion, Economic Loss, Structural Response, and Probability Distribution)
(Performance Assessment, Earthquake, Probability Distribution & Applications, Earthquake Engineering and Structural Dynamics, Structural modelling, Coefficient of Variation, Building Design, Building Codes, Reinforced concrete, Ground Motion, Economic Loss, Structural Response, and Probability Distribution)
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT Recently the authors have developed an output only (or blind) identification technique for modal identification of structures under ambient/free vibrations. In the present study, the said method is extended to incorporate non... more
ABSTRACT Recently the authors have developed an output only (or blind) identification technique for modal identification of structures under ambient/free vibrations. In the present study, the said method is extended to incorporate non stationary unknown input—a feature that existing output only methods are unable to replicate. The method employs a so-called PARAFAC technique to decompose the third order tensor that is built using the spatial time-frequency matrices of the response signals in order to find the mode shapes and modal coordinates&#39; auto Time-Frequency Distribution (TFD). The proposed method is first verified using a synthetic data set; and then used for extracting the modal parameters from vibration data recorded during shaketable tests on the &quot;IIEES Test Structure.&quot; The accuracy of the blind identification results is assessed through comparisons with a well established input output identification method—namely, a well known combination of the Eigensystem Realization Algorithm and the Observer/Kalman filter Identification, dubbed the ERA/OKID method. Next, rigidities of the connections of the IIEES Test Structure are identified through a finite element model updating procedure. Finally, the proposed method is validated through comparisons between responses predicted using the updated FE model, and those directly recorded in additional shaketable tests that were not used in model updating studies.
Research Interests:
Research Interests:
Research Interests:
Numerical methods used for seismic Soil-Foundation-Structure Interaction analyses of highway bridge structures can be classified into direct and substructuring approaches. In the time domain version of the direct approach, the nonlinear... more
Numerical methods used for seismic Soil-Foundation-Structure Interaction analyses of highway bridge structures can be classified into direct and substructuring approaches. In the time domain version of the direct approach, the nonlinear soil and foundation behaviors are explicitly included in the global model. The substructuring approach divides the system into two sub systems namely, a super structure that includes the bridge columns, bridge deck and bridge abutments, and a sub structure that includes the pile foundation and the surrounding soil media. The pile foundation and the soil media are analyzed in the frequency domain, and the foundations’ dynamic impedance functions and the kinematic motions are established at the pile-soil interfaces. These data are then used as boundary conditions in the nonlinear global seismic analysis of the bridge structure in the time domain. In this study, we introduce a frequency- and time domain iterative “handshake” approach that consistently i...