Showing papers on "OpenSees published in 2013"

Steel sheathed/CFS framed shear walls under dynamic loading: Numerical modelling and calibration

Abstract: This paper describes the numerical modelling using OpenSees of shear walls constructed of cold-formed steel (CFS) framing and flat steel sheathing. The first phase comprised non-linear models calibrated using existing reversed cyclic shear wall test data. The second phase involved more advanced models calibrated using data from dynamic shake table tests of single- and double-storey shear walls and additional ancillary component testing. These advanced models were able to accurately reproduce the shear strength and displacement time history and hysteretic response of the dynamically tested shear walls. The use of a building model that incorporates the second phase wall models is demonstrated for the evaluation of representative CFS framed structures using non-linear time history dynamic analyses.

Evaluating Code Criteria for Regular Seismic Behavior of Continuous Concrete Box Girder Bridges with Unequal Height Piers

Abstract: The seismic design and response prediction of irregular bridges supported on piers of unequal heights—a commonly adopted solution when crossing steep-sided valleys—represent a particularly challenging problem that is yet to be effectively addressed by seismic design code provisions worldwide. From a force-based design perspective, shorter piers are subjected to increased ductility demand, and consequently damage tends to localize in these relatively stiff piers at increasing seismic hazard levels. This paper presents an investigation of the seismic response of a few schemes of a three-span case-study continuous bridge (commonly encountered in practice), featuring two unequal piers with relative heights of 0.5, 0.64, 0.75, and 0.86, respectively. Static pushover and time history (under incrementally scaled-up actual records) nonlinear inelastic analyses are performed using OpenSees to check the validity of Eurocode 8 (EC8) and recently proposed AASHTO-LRFD provisions for regular seismic behavior of...

Numerical Modeling of Slender Reinforced Concrete Shear Wall Shaking Table Tests Under High-Frequency Ground Motions

Abstract: This article presents the numerical modeling of large-scale shake table tests of slender 8-story reinforced concrete (RC) shear wall specimens. Nonlinear time history analyses are carried out using reinforced concrete fiber elements (OpenSees, OS) and the finite element (FE) methods (VecTor2, VT2). The effects of the modeling assumptions are investigated, including: (a) the tension stiffening effect, (b) damping, (c) smeared vs. lumped reinforcement, and (d) the use of effective shear stiffness in OS. Good agreements are obtained between the numerical and experimental results. Using the proposed numerical modeling strategy, it is possible to investigate the nonlinear dynamic responses of slender RC wall structures with confidence.

p-y Plasticity Model for Nonlinear Dynamic Analysis of Piles in Liquefiable Soil

Abstract: Liquefiable soil-structure interaction material models are developed and implemented in the open-source finite-element modeling platform OpenSees. Inputs to the free end of the p-y materials include the ground motion and mean effective stress time series from a free-field soil column. Example simulations using a single p-y element attached to a soil element demonstrate key features. The models are then used to analyze centrifuge experiments of a single pile in a level liquefiable profile and a six-pile group in a sloping liquefiable profile that resulted in lateral spreading. Measured displacements and mean effective stress time series are used as inputs to isolate the response of the material models from predictive uncertainties in free-field ground motion and excess pore pressure. The predicted pile response agrees reasonably well with measurements. The cyclic mobility behavior of sand in undrained loading is shown to be an important mechanism affecting bending moments in the piles; neglecting t...

Nonlinear Seismic Response and Parametric Examination of Horizontally Curved Steel Bridges Using 3D Computational Models

Abstract: The seismic behavior of horizontally curved steel bridges is more complex than straight bridges because of their curvature and other parameters. Studies that attempt to develop methods to efficiently predict their seismic response have been somewhat limited to date. A computational modeling approach was examined to assist with understanding the seismic behavior of these bridges. The computational, three-dimensional (3D) bridge models consisting of the concrete deck, steel girders, cross-frames, pier columns and caps, and abutments and footings were created in OpenSees and examined for accuracy via application to a representative, three-span continuous curved steel plate girder bridge in Pennsylvania. Sensitivity studies in the form of tornado analyses were also carried out to investigate the influence of critical curved bridge parameters on the seismic response using a group of representative bridges. Each representative bridge was subjected to an ensemble of synthetic ground motions, and seismic ...

Computing seismic fragility curves using polynomial chaos expansions

Abstract: Fragility curves are commonly used in civil engineering to estimate the vulnerability of structures to earthquakes. The probability of failure associated with a failure criterion (e.g. the maximal inter-storey drift being greater than a prescribed threshold) is represented as a function of the intensity of the earthquake (e.g. peak ground acceleration or spectral acceleration). Computing fragility curves relies upon running a large number of transient dynamic (possibly non linear) analyses using a set of synthetic or measured ground motions. In this paper we introduce sparse polynomial chaos expansions as a way to reduce the associated computational burden. Non stationary synthetic ground motions are generated using a method recently proposed by Rezaeian & Der Kiureghian, which is based on modulating a filtered Gaussian white noise process. Sparse PC expansions of the structural response are computed from a relatively small (e.g. 1,000) set of accelerograms and post-processed in order to evaluate the fragility curves. The approach is compared to the classical curves derived under the assumption of log-normality. For linear structures the lognormal assumption is validated by our calculations and the classical approach is improved using some analytical derivations. The various approaches are illustrated on a typical 3-storey building using the finite element software OpenSees.

Modeling the seismic response of cold-formed steel framed buildings: model development for the CFS-NEES building

Abstract: The objective of this paper is to investigate the response of a cold-formed steel framed building subjected to earthquake excitation primarily through nonlinear time history analysis employing the incremental dynamic analysis (IDA) framework. The two-story archetype building from the Cold-Formed Steel ‐ Network for Earthquake Engineering Simulation (CFS-NEES) project is analyzed using OpenSees. In the current ‘state-of-the-art’ model, fully nonlinear hysteretic pinching models for the shear walls are parameterized directly based on shear wall test data conducted as an earlier phase of the CFS-NEES project. Nonlinear behavior of the shear wall hold downs in tension and compression, shear anchors, and rigid diaphragm are also captured in the model. The normalized far field ground motion suite from FEMA P695 is employed as the input excitation. A series of analyses using scaled ground motions are completed up through large enough drift levels to insure collapse in the building models. The IDA procedure provides information about the performance of the building under general earthquake loading so that drift and other limits for collapse prevention (i.e. loss of stability for the building) can be explored. Comparison of the predicted inelastic base shear vs. elastic base shear provides a direct understanding of the relationship between IDA analysis and seismic response modification factors (e.g., R or more specifically R d ) as utilized in design practice and within the FEMA P695 procedure. Further refinement of the building model is underway; particularly, with respect to modeling the gravity framing, diaphragm, and non-structural elements. The fully developed model will be calibrated with test data from full scale shaking table tests of this building to be conducted in the summer of 2013. Modeling and analysis guidelines based on the sensitivity of the results to model fidelity will be developed as a resource to promote simulation in seismic design of cold-formed steel buildings.

Seismic performance of composite RCS special moment frames

Abstract: Composite Reinforced Concrete-Steel (RCS) frames which consist of Reinforced Concrete (RC) columns and Steel (S) beams were represented to combine the advantages of pure RC and steel frames. This system permits the primary steel beam to run continuous through the reinforced concrete column. This paper evaluates seismic performance of RCS frames based on FEMA-356, considering plastic rotations as acceptance criteria. The effect of joint deformations on overall behavior of RCS frames is studied through nonlinear static analysis (Pushover) that is performed in OpenSees software. It is concluded that the RCS joint behavior increases lateral load capacity of frame. Additionally, 3 RC frames are compared to RCS frames with columns similar to those of RC frames. The results show a great improvement on overall behavior since steel beams is used instead of RC beams.

Simulating the Seismic Response of Concentrically Braced Frames Using Physical Theory Brace Models

Abstract: The aim of this paper is to assess the accuracy of brace models formulated in Drain 2DX and OpenSees by comparing the simulated results with those obtained from experimental tests. Both, Drain 2DX and OpenSees rely on the physical theory brace model. In this study, experimental tests conducted on the behaviour of structural hollow section braces subjected to symmetric and asymmetric quasi-static cyclic loading were selected for calibrating the numerical model. In addition, the predicted failure strain parameter resulted from a proposed empirical equation as a function of slenderness ratio, width-to-thickness ratio and steel properties was used to define the low-cycle fatigue material that was assigned to model braces in OpenSees. It is concluded that both Drain 2DX and OpenSees brace models give a good prediction in terms of maximum tensile and buckling force, as well as interstorey drift. However, in Drain 2DX, the brace model is not able to replicate the out-of-plan buckling and the braced frame model cannot provide an accurate response when the system experiences highly nonlinear demand. To emphasise the differences in performance between Drain 2DX and OpenSees, the behaviour of a 4-storey concentrically braced frame with zipper bracing configuration, located in Victoria, BC, was investigated.

Experimental and numerical studies on the cyclic behavior ofR/C hollow bridge piers with corroded rebars

Abstract: A comprehensive experimental program of cyclic tests on 1:3-scale models of bridge piers is going to be carried out at the Laboratory of Structures and Materials of the University of Basilicata. The testing models include eight RC single shaft piers with hollow circular cross section. Four piers have been realised using corroded steel rebars. In this paper, the results of preliminary numerical simulation analyses of the cyclic behaviour of the piers, carried out with Opensees using fiber-based models, are presented. Pull-out and lap-splice effects of steel rebars have been taken into account in the numerical analyses. First, the experimental specimens and the test set up are presented. Next, the results of the numerical analyses are discussed. In the numerical analyses, different configurations and levels of corrosion have been considered. The effective stiffness and equivalent damping of the piers is reported as a function of pier ductility and pier drift.

Development and application of a thermal analysis framework in OpenSees for structures in fire

Abstract: The last two decades have witnessed the shift of structural fire design from prescriptive approaches to performance-based approaches in order to build more advanced structures while reducing costs. However, it is recognised that the implementation of performance-based approaches requires several key elements that are currently not fully developed or understood. This research set out to address some of these issues by focusing on the development, validation and application of methodologies for accurate predictions of thermal responses of structures in fire using numerical methods. This research firstly proposed a numerical approach with the finite element and the discrete ordinates method to quantify the fire imposed radiative heat fluxes to structural members with cavity geometry. With satisfactory results from the verification and validation tests, it is used to simulate heat transfer to unprotected steel I-sections with symmetrical cavities exposed to post-flashover fires. Results show that the cavity geometry could strongly attenuate the radiative energy, while the presence of hot smoke enhances radiative transfer by emission. Average radiative fluxes for the inner surfaces of the I-sections are seen to increase with smoke opacity. In addition, the net radiative fluxes are observed to decrease faster

Nonlinear Dynamic Analysis and Seismic Coefficient for Abutments and Retaining Walls

Abstract: Two-dimensional computational models of bridge abutment-soil systems are developed using the OpenSees framework. Nonlinear hysteretic behavior of backfill and foundation soil is simulated through a...

A Seismic Reliability Assessment of Reinforced Concrete Integral Bridges Subject to Corrosion

Abstract: This paper seeks to determine the effect deterioration has on the seismic vulnerability of a 3 span integral concrete bridge. Traditionally it has been common to neglect the effects of deterioration when assessing the seismic vulnerability of bridges. However, since a lot of the bridges currently being assessed for retrofit are approaching the end of their design life, deterioration is often significant. Furthermore, since deterioration affects the main force resisting components of a bridge, it is reasonable to assume that it might affect its performance during an earthquake. For this paper, chloride induced corrosion of the reinforcing steel in the columns and in the deck has been considered. Corrosion is represented by a loss of steel cross section and strength. A 3 dimensional non-linear finite element model is created using the finite element platform Opensees. A full probabilistic analysis is conducted to develop time-dependent fragility curves. These fragility curves give the probability of reaching or exceeding a defined damage limit state, for a given ground motion intensity measure taken as Peak Ground Acceleration (PGA). This analysis accounts for variation in ground motion, material and corrosion parameters when assessing its overall seismic performance as well as the performance of its most critical components. The results of the study show that all components experience an increase in fragility with age, but that the columns are the most sensitive component to aging and dominate the system fragility for this bridge type.

Seismic Performance of Quasi-Isolated Highway Bridges in Illinois

Abstract: The Illinois Department of Transportation (IDOT) commonly uses elastomeric bearings to accommodate thermal deformations in bridges, and these bearings have potential utility in seismic events. IDOT has developed an Earthquake Resisting System (ERS) using the displacement capacity of typical bearings to achieve a structural response similar to isolation. Project R27-70 was conducted to validate and calibrate the quasi-isolated ERS based on full-scale laboratory tests of bearings and computational models capturing full-bridge seismic response. The overall report is divided into two volumes. Volume 1 discussed the experimental program. This second volume focuses on the analytical program but also contains retainer design recommendations. Results from the experimental testing program were used to develop constitutive bearing models, which were incorporated into the finite element model of a three-span bridge with simply supported abutments and fixed bearings at one pier. A suite of 48 bridges was created to represent the most common highway bridge configurations in Illinois. Variables included superstructure type, pier type, pier height, elastomeric bearing type, and foundation flexibility. Two sets of ten synthetic ground motions from the New Madrid Seismic Zone were scaled to match the AASHTO seismic design spectra for Cairo, Illinois, and applied in the longitudinal and transverse directions. A total of 12,000 nonlinear dynamic analyses were conducted in OpenSees at six scale factors from 0.5 to 1.75 and used to create coarse incremental dynamic analyses. On the basis of the findings of the parametric study, most bridges in Illinois would not experience severe damage during a 75-year design life, and bearing unseating or span loss are not likely to occur in regions with moderate seismic hazard. Piers with fixed bearings commonly yielded for small earthquakes, but future calibration of fuse capacities may improve this behavior.

Nonlinear Dynamic Analysis of Modular Steel Buildings in Two and Three Dimensions

Abstract: Modular construction is a relatively new technique where prefabricated units are assembled on-site to produce a complete building. Due to detailing requirements for the assembly of the modules, these systems are prone to undesirable failure mechanisms during large earthquakes. Specifically, for multi-story Modular Steel Buildings (MSBs), inelasticity concentration in vertical connections can be an area of concern. Diaphragm interaction, relative displacements between modules and the forces in the horizontal connections need to be investigated. In this study, two 4-story MSBs with two different structural configurations were chosen to be analyzed. In the first model which was introduced in a study by Annan et al. (2009 a), some of the unrealistic detailing assumptions were challenged. To have a more accurate assessment of the structural capacity, in the second model, a more realistic MSB model was proposed. Using OpenSees, Incremental Dynamic Analyses (IDA) have been performed and conclusions were made.%%%%MAST

A modified constitutive model for FRP confined concrete in circular sections and its implementation with OpenSees programming

Abstract: OpenSees is a well-recognized open source platform with high compatibility, and it has a well-developed fiber element method to cope with nonlinear structural analysis. Fiber reinforced polymer (FRP) confined concrete can effectively improve the seismic performance of concrete structures. However, sophisticated constitutive models for FRP confined concrete are not available in the current version of OpenSees. In this paper, after reviewing several typical FRP confined concrete constitutive models, a modified constitutive model for FRP confined concrete in circular sections was proposed based on Lam and Teng (2003)’s model with four main modifications including the determination of FRP rupture strain, ultimate condition, envelope shape, and hysteretic rules. To embed the proposed constitutive model into OpenSees is a practical solution for engineering simulation. Hence, the secondary development of OpenSees New UserMat was briefly demonstrated and a set of critical steps were depicted in a flow chart. Finally, with the numerical implementations of a series of FRP confined concrete members covering a wide range of load cases, FRP confinement types and geometric properties, the utility and accuracy of the proposed model compared with Lam and Teng (2003)’s model and new material secondary development in OpenSees were well validated.

Seismic Soil-Foundation-Structure Interaction in Urban Environments

Abstract: The interactions between a structure, its foundation, and the surrounding soil during an earthquake are referred to as soil-foundation-structure interaction (SFSI). The interactions between multiple structures, and their foundations, through the surrounding soil are collectively known as structure-soil-structure interaction (SSSI). Modern design codes in use in the United States, and abroad, provide guidance for considering SFSI during the seismic design of structural systems. However, these same codes do not provide any guidance for considering SSSI. This situation is a direct result of the current paucity of research into the effects of SSSI on structural performance. This dissertation describes the results of four centrifuge experiments designed to study the influence of SSSI on the seismic performance of building- foundation systems. Following these experiments, numerical models were developed and their efficiency at reproducing measured response evaluated. The experimental program involved two pairs of tests. During Test-1 and Test-2, the SFSI and SSSI-influenced responses of two three- dimensional inelastic frame structures were recorded. During Test-3 and Test-4, the interactions between an inelastic frame structure and an elastic rocking wall arranged in a variety of orientations were recorded. In each of the pair of test series, one configuration was devoted to the evaluation of the response of the model frame structures far from any neighboring structure. Ultimately, the experimental results demonstrate that when structures are placed next to each other, the seismic demands in inelastic frame structures can increase. As such, seismic structural performance may be negatively impacted by SSSI. The tests reveal that footings of buildings placed nearest to other buildings can be physically restrained when loaded towards the other building -- a physical mechanism that had not previously been observed. This asymmetrical physical restraint resulted in a stiffened hysteretic response of footings nearest to adjacent buildings and nominal increases in seismic demands to superstructure elements. It is also demonstrated that wave-based analytical solutions to the SSSI problem alone are not adequate for modeling the interactions between building-foundation systems with highly nonlinear foundation responses. During the numerical phase of this research, available tools for modeling SFSI effects (i.e., absent the effects of neighboring structures) in OpenSees were first refined. The shallowFoundationGen command was redeveloped to give the user greater flexibility. Subsequently, it was demonstrated that the updated modeling technique provides an adequate means to model the experimentally observed coupling of the vertical footing force and overturning moment load combinations for shallow foundations attached to inelastic frame structures. Finally, an available methodology for modeling wave-based SSSI effects was implemented in OpenSees and its capability to predict the experimentally measured seismic demands of an SSSI- influenced inelastic structure was evaluated. Ultimately, it is concluded that the use of foundation-to-foundation connection springs, which are based on wave-based solutions, is insufficient for capturing the seismic response of adjacent structures with highly nonlinear individual SFSI responses

Design and Analytical Evaluation of a New Self-Centering Connection with Bolted T-Stub Devices

Abstract: A new posttensioned T-stub connection (PTTC) for earthquake resistant steel moment resisting frames (MRFs) is introduced. The proposed connection consists of high strength posttensioned (PT) strands and bolted T-stubs. The post-tensioning strands run through the column and are anchored against the flange of the exterior column. The T-stubs, providing energy dissipation, are bolted to the flange of beam and column and no field welding is required. The strands compress the T-stub against the column flange to develop the resisting moment to service loads and to provide a restoring force that returns the structure to its initial position following an earthquake. An analytical model based on fiber elements is developed in OpenSees to model PTTCs. The analytical model can predict the expected behavior of the new proposed connection under cyclic loading. PTTC provides similar characteristic behavior of the posttensioned connections. Both theoretical behavior and design methods are proposed, and the design methods are verified based on parametric studies and comparison to analytical results. The parametric studies prove the desired self-centering behavior of PTTC and show that this connection can reduce or eliminate the plastic rotation by its self-centering behavior as well as providing required strength and stiffness under large earthquake rotations.

Shake Table Testing of a Full-Scale Five-Story Building: Pre-test Simulation of the Test Building and Development of an NCS Design Criteria

Abstract: This paper is one of five within a session discussing the findings from a full-scale, five-story building test program conducted at the NEES-UCSD Large High Performance Outdoor Shake. This paper focuses on the pre-test simulation of the test building with the objective of predicting its seismic response and thereby; (i) guiding the selection of earthquake motions for the test program and (ii) providing guidance for the design of various nonstructural components and systems (NCSs) to be installed in the test building. Two nonlinea,r finite element models were developed independently in this effort: 1) a macro-element based model was implemented in the OpenSees platform, and 2) a detailed finite element model was prepared using the general finite element software package DIANA. In this paper, the description and assumptions adopted for each of these two models are first provided, and then the simulation results for selected test motions are presented and compared. Utilizing these models, a procedure is developed to define project-specific NCSs design criteria. The developed design criteria are compared with the current code provisions and their implications discussed.

Numerical simulation of shaking table tests on 3D reinforced concrete structures

Abstract: The current paper presents the numerical blind prediction of nonlinear seismic response of two full-scale, three dimensional, one-story reinforced concrete structures subjected to bidirectional earthquake simulations on shaking table. Simulations were carried out at the laboratories of LNEC (Laboratorio Nacional de Engenharia Civil) in Lisbon, Portugal. The study was motivated by participation in the blind prediction contest of shaking table tests, organized by the challenge committee of the 15th World Conference on Earthquake Engineering. The test specimens, geometrically identical, designed for low and high ductility levels, were subjected to subsequent earthquake motions of increasing intensity. Three dimensional nonlinear analytical models were implemented and subjected to the input base motions. Reasonably accurate reproduction of the measured displacement response was obtained through appropriate modeling. The goodness of fit between analytical and measured results depended on the details of the analytical models.

Seismic response and simulations of reinforced concrete bridge using OpenSees on high performance computing

Abstract: Nonlinear seismic analysis is becoming increasingly significant to grasp the performance of structures under earthquake. A nonlinear finite element model of existing bridge at Karad, India, including the bridge structure, pile groups, and the supporting foundation soil, is developed under 2D and 3D conditions in Gid (a pre and postprocessor software). The computational model is analyzed using Parallel OpenSees. OpenSees is open source software for carrying out earthquake engineering simulations, developed by Pacific Earthquake Engineering Research Centre, USA. The earthquake simulations were carried out using C-DAC’s high performance computing facilities. The ground motion selection and modification technique-predicting median interstory drift response of building, ground motions are selected by M and R and scaling to Sa(T1), is used for seismic response of combined large scale soil-structure interaction of Karad bridge. The idealized model properly represents the actual geometry; boundary conditions, gravity loads and mass distribution. Nonlinear modeling and analysis allows more accurate determination of stresses, strains, deformations and forces of critical components. The present work involves the effects of specially varying input excitation (earthquakes) at an existing bridge site. A nonlinear finite element model of this bridge site including the bridge structure, pile group and supporting foundation soil is developed in 2D plane strain conditions and in 3D 20 noded brick element. Carefully calibrated nonlinear stress–strain models are employed for both bridge and soil materials, in order to realistically reproduce actual site conditions. Seismic input motions are defined as forces using the boundary layer force method (zero length element approach). The earthquake simulation of bridge structure includes large scale interaction between structure–foundation–soil system and deformations at various locations of the bridge. The results include deformations at base of piers and at various spans of the bridge. Performing the bridge simulation on C-DAC’s Param Yuva facility results in accuracy and saving in computing efforts.

Multiplatform Analysis Seismic Evaluation of a Non-Seismically Detailed Nonlinear RC Structure Retrofitted With Magneto-Rheological Dampers

Abstract: In prior research, the MR damper's dynamic characteristics are typically modeled in the MATLAB/Simulink environment Creating a structural model with nonlinear material properties, however, may be challenging in the MATLAB/Simulink environment without approximating the material behavior and neglecting effects such as P-∆ or panel zone behavior More behaviorally accurate models of these structures can be produced using nonlinear finite element analysis tools such as Abaqus, OpenSees or ZuesNL These analysis tools, however, are not traditionally used to model the complex nonlinear and controllable behavior of MR dampers, nor their associated control algorithms One solution is to facilitate communication between these two tools, a MATLAB/Simulink model of an MR damper and an Abaqus, OpenSees or ZuesNL finite element model of a building structure In this manner, each component is able to be modeled in its preferred environment and these components are able to communicate the necessary information throughout the simulation This solution enables a Multiplatform Analysis (MPA) to test control strategies using MR dampers This thesis describes the formulation of a communication protocol between the MATLAB/Simulink MR damper model and a finite element building structure model This thesis demonstrates, for seismic applications, the application of this MPA technique to a small scale MR damper model and simple linear structure, validates the MPA technique with experimental results from a real-time hybrid test of a 2kN MR damper and two-story small-scale building, and finally applies the MPA technique to a large scale MR damper model and a more complex, nonlinear reinforced concrete structure