Showing papers on "OpenSees published in 2016"

A bridge column with superelastic NiTi SMA and replaceable rubber hinge for earthquake damage mitigation

Abstract: This paper reports a unique concept for resilient bridge columns that can undergo intense earthquake loading and remain functional with minimal damage and residual drift. In this concept, the column is designed so that its components can be easily disassembled and reassembled to facilitate material recycling and component reuse. This is meant to foster sustainability of bridge systems while minimizing monetary losses from earthquakes. Self-centering and energy dissipation in the column were provided by unbonded superelastic nickel–titanium (NiTi) shape memory alloy bars placed inside a plastic hinge element made of rubber. This replaceable plastic hinge was in turn attached to a concrete-filled carbon fiber-reinforced polymer tube and a precast concrete footing that were designed to behave elastically. The proposed concept was evaluated experimentally by testing a ¼-scale column model under simulated near-fault earthquake motions on a shake table. After testing, the model was disassembled, reassembled and tested again. The seismic performance of the reassembled model was found to be comparable to that of the 'virgin' model. A relatively simple computational model of the column tested that was developed in OpenSees was able to match some of the key experimental response parameters.

Numerical simulation of FRP-jacketed RC columns subjected to cyclic and seismic loading

Abstract: This paper presents a numerical model for the cyclic/seismic behavior of reinforced concrete (RC) columns retrofitted with fiber-reinforced polymer (FRP) confining jackets. Such a column model has previously been unavailable despite the popularity of FRP jacketing as a seismic retrofit method for RC columns. The proposed numerical column model is based on a recent stress-strain model for FRP-confined concrete subjected to cyclic axial compression and a hysteretic moment-rotation model to account for the effect of strain penetration of the longitudinal steel bars in the column footing (i.e., effect of fixed-end rotations). This column model was implemented into OpenSees (Open System for Earthquake Engineering Simulation) using its fiber-section force-based nonlinear beam-column element. Predictions of the numerical column model for three FRP-jacketed RC columns subjected to either double-curvature bending or single-curvature bending are shown to be in close agreement with the test results.

Hybrid Simulation of Thermomechanical Structural Response

Abstract: A new thermomechanical hybrid simulation method is proposed that extends the mechanical hybrid simulation method by including thermal degrees of freedom and temperature loads. The thermomechanical hybrid simulation method was implemented in the OpenSees and OpenFresco frameworks. Modifications to enable this new capability centered on incorporating the temperature degrees of freedom in the hybrid model domain, and on developing new OpenFresco objects and a test execution strategy to simultaneously control the structural elements of the experimental setup, the thermal loads, and the mechanical loads. The implementation of the thermomechanical method at the ETH Zurich IBK Structural Testing Laboratory was verified and validated using a simple two-element hybrid model. The responses of the model to a force ramp, applied to the full structure, and a scaled version of the ISO 834 standard fire curve, applied to the experimental element, were obtained in two simulations—one conducted using an explicit a...

Probabilistic Vulnerability Assessment of Horizontally Curved Multiframe RC Box-Girder Highway Bridges

Abstract: Numerous concrete box-girder bridges in California are horizontally curved and also have at least one in-span hinge. The curvature and in-span hinges in multiframe bridges lead to significant differences in bridge dynamic response during seismic excitations. In this article, a set of analytical fragility curves for horizontally curved highway bridges are developed based on nonlinear time history analyses in OpenSEES, focusing on subclasses of seismically designed multiframe concrete box-girder bridges with multicolumn bents and seat type abutments. Component damage levels are explored for joint seals, columns, bearings, abutments, unseating of decks, foundations, and shear keys, and system level damage states consistent with HAZUS-MH definitions. Curvature was identified to be an important factor that adversely affects the fragility of multiframe bridges. Median value modification factors are proposed to scale fragility curves to account for the deck radius effects.

Deteriorating hysteresis model for cold-formed steel shear wall panel based on its physical and mechanical characteristics

Abstract: Shear wall panels (SWP) are the primary lateral load resisting elements in cold-formed steel (CFS) structures. In this paper, smooth hysteresis models that take into account strength and stiffness degradation, as well as pinching effect have been developed and implemented in OpenSees software, as user-defined uniaxial materials named CFSWSWP and CFSSSWP for wood and steel sheathed SWP, respectively. The proposed analytical models are validated using the experimental tests results obtained from the literature, where a good agreement has been achieved. In order to investigate the influence of the CFS SWP parameters variation on the hysteresis characteristics of the response, several non-linear quasi-static analyses have been carried out using different CFS SWP configurations. The key parameters which have most affected the cyclic response were identified and assessed.

Probabilistic performance-based evaluation of a tall steel moment resisting frame under post-earthquake fires

Abstract: Purpose This paper aims to develop a framework to assess the reliability of structures subject to a fire following an earthquake (FFE) event. The proposed framework is implemented in one seamless programming environment and is used to analyze an example nine-story steel moment-resisting frame (MRF) under an FFE. The framework includes uncertainties in load and material properties at elevated temperatures and evaluates the MRF performance based on various limit states. Design/methodology/approach Specifically, this work models the uncertainties in fire load density, yield strength and modulus of elasticity of steel. The location of fire compartment is also varied to investigate the effect of story level (lower vs higher) and bay location (interior vs exterior) of the fire on the post-earthquake performance of the frame. The frame is modeled in OpenSees to perform non-linear dynamic, thermal and reliability analyses of the structure. Findings Results show that interior bays are more susceptible than exterior bays to connection failure because of the development of larger tension forces during the cooling phase of the fire. Also, upper floors in general are more probable to reach specified damage states than lower floors because of the smaller beam sizes. Overall, results suggest that modern MRFs with a design that is governed by inter-story drifts have enough residual strength after an earthquake so that a subsequent fire typically does not lead to results significantly different compared to those of an event where the fire occurs without previous seismic damage. However, the seismic damage could lead to larger fire spread, increased danger to the building as a whole and larger associated economic losses. Originality/value Although the paper focuses on FFE, the proposed framework is general and can be extended to other multi-hazard scenarios.

Development of a new deteriorating hysteresis model for seismic collapse assessment of thin steel plate shear walls

Abstract: A new hysteresis model is developed for thin Steel Plate Shear Wall (SPSW) systems which incorporates cyclic and in-cycle deteriorations. The model is implemented into the OpenSees software and is validated against a number of experimental evidences. Seismic response sensitivity of SPSW system to the hysteretic model characteristics is evaluated, afterwards, using three code-conforming SPSWs with different heights. The 15 variant models developed for each frame using different combinations of deterioration parameters are subjected to incremental dynamic analysis. The sensitivity of the derived median collapse capacities, expressed in Sa(T1) terms, to the “cyclic” and “in-cycle” deterioration parameters are finally assessed.

Seismic vulnerability assessment of a Californian multi-frame curved concrete box girder viaduct using fragility curves

Abstract: Seismic response of multi-frame curved viaducts has been proved to be very complex due to typically inherent irregularities identified in this class of bridge structures such as deck in-plane curvature, altitudinal irregularity and deck discontinuity. The discontinuity provided by the expansion joint has made this class of bridges prone to catastrophic damages caused by multiple collisions between adjacent frames during both torsional and translational modes of responses as well as deck unseating at the expansion joints. This paper presents the seismic response of a Californian multi-frame curved concrete box girder viaduct, considering four different radii of curvature and five altitudinal coefficients, using fragility curves. Fragility curves are developed by considering different sources of uncertainties related to earthquakes, structural geometries and material properties. The full nonlinear time-history analyses are performed utilising 3-D numerical bridge models generated in OpenSees finite ...

3D Numerical simulations of elastomeric bearings for bridges

Abstract: Multilayer elastomeric isolation can be considered a well-known solution with many applications in the last 20 years in the infrastructure arena. In particular, isolation has been extensively applied for pier and abutment protection, in order to strengthen bridges against earthquakes. Elastomeric bearings can be subjected to large axial loads and lateral displacements during strong earthquakes, which induce potentially buckling effects. The recent Forcellini and Kelly (J Eng Mech 140(6):04014036, 2014) model allows to take into account large deformation response of a bearing when buckling occurs. This paper aims at verifying this theory using experimental results and numerical simulations. First of all, test results are taken from Nagarajaiah and Ferrell (J Struct Eng 125:946–954, 1999) and compared with the developed theory. Then, numerical simulations have been performed by applying OpenSees.

Stiffness degradation-based damage model for RC members and structures using fiber-beam elements

Abstract: To meet the demand for an accurate and highly efficient damage model with a distinct physical meaning for performance-based earthquake engineering applications, a stiffness degradation-based damage model for reinforced concrete (RC) members and structures was developed using fiber beam-column elements. In this model, damage indices for concrete and steel fibers were defined by the degradation of the initial reloading modulus and the low-cycle fatigue law. Then, section, member, story and structure damage was evaluated by the degradation of the sectional bending stiffness, rod-end bending stiffness, story lateral stiffness and structure lateral stiffness, respectively. The damage model was realized in Matlab by reading in the outputs of OpenSees. The application of the damage model to RC columns and a RC frame indicates that the damage model is capable of accurately predicting the magnitude, position, and evolutionary process of damage, and estimating story damage more precisely than inter-story drift. Additionally, the damage model establishes a close connection between damage indices at various levels without introducing weighting coefficients or force-displacement relationships. The development of the model has perfected the damage assessment function of OpenSees, laying a solid foundation for damage estimation at various levels of a large-scale structure subjected to seismic loading.

Finite element reliability and sensitivity analysis of structures using the multiplicative dimensional reduction method

Abstract: Finite element reliability analysis (FERA) has been used to evaluate the reliability of structures. In FERA, approximate methods are commonly used to estimate the mean and variance of the structural response, while its probability distribution is primarily derived based on the Monte Carlo simulation (MCS) method. This paper advances FERA by combining it with the multiplicative dimensional reduction method (M-DRM). The proposed M-DRM allows fairly accurate estimation of the statistical moments, as well as the probability distribution of the structural response. The distribution of the response is obtained using fractional moments, which are calculated from the M-DRM, along with the maximum entropy principle. The variance of the response, based on global sensitivity measures, is obtained as a by-product of the analysis. The proposed approach is integrated with the OpenSees software and is illustrated through examples of nonlinear finite element analyses of reinforced concrete and steel frames. The p...

Seismic response of multi-frame bridges

Abstract: Long cast-in-place concrete bridges are often constructed in multiple frames separated by in-span hinges. The multi-frame system offers lower construction and maintenance costs, fewer adverse effects due to creep, post-tensioning, and thermal deformations as a few of its advantages. However, the seismic response of multi-frame bridges has been uncertain owing to the complexities of their discrete system. This study intends to improve the understanding of the seismic response of multi-frame bridge systems and evaluate the applicability of current design assumptions. Responses of multi-frame bridges and comparable single-frame bridges of the same length are compared. Seismic demands on multi-frame bridge columns, abutments, and in-span hinges were investigated through high-fidelity analytical simulations. Approximately 3400 nonlinear time history analyses of prototype bridges with realistic designs were performed using the OpenSees platform. Analysis of variance was implemented along with a factorial design to study the effect of several independent factors, including the number of frames, substructure system, unequal column heights, soil type, ground motion intensity, and capacity-to-demand ratio. It was observed for elastic dynamic analysis that a 90 % modal mass participation ratio is not adequate to accurately estimate dynamic responses. Seismic demands on columns in multi-frame bridges are typically smaller than those in comparable single-frame bridges. The multi-frame system is seismically more robust than the single-frame system, specifically for bridges spanning non-uniform valleys that include unequal column heights. To prevent longitudinal unseating at in-span hinges, it is critical to consider the interaction of transverse and longitudinal responses. The seismic damage to abutment backwalls and backfills in multi-frame bridges is expected to be extensive owing to small expansion joints.

Experimental and numerical investigation on the behaviour of prestressed high strength concrete pile-to-pile cap connections

Abstract: Six Prestressed High Strength Concrete (PHC) pile-to-pile cap connections were tested to evaluate their damage process and failure modes under low cyclic loading. The hysteretic behaviour, rotation angle, ductility and bearing capacity were observed and analyzed. In addition, the effect of connecting forms and cutting-off piles on seismic performance of pile-cap connections was considered and investigated. The experimental results showed that flexural bending failure occurred in all connections. There were two main failure modes. One was tensile rupturing of prestressed bars and headings, resulting in loss of bearing capacity of the connections. The other type was more severe damage due to anchor bar yield and appearance of plastic hinge. Moreover, bond-slip failure of anchor bars was not observed in the cap, and the length of anchor bars met requirements. The analysis indicated that the bearing capacity and energy dissipation capacity increased along with the rotation capacity of the pile connections. Nonlinear finite element models were established to analyze the mechanical properties of these connections using OpenSees. The load-displacement curves obtained from the numerical analysis agreed with the experimental results. The effects of various parameters on the behaviour of the connections were conducted based on the numerical model.

Improved Nonlinear Cyclic Stress–Strain Model for Reinforcing Bars Including Buckling Effect and Experimental Verification

Abstract: Buckling is an important nonlinear behavior of steel reinforcing bars subjected to repeated compression and tension strain reversals, which significantly affects the overall cyclic behavior of reinforced concrete (RC) elements and impairs their load-carrying and energy-dissipation capacities during strong earthquakes. The accuracy of numerical assessment of the seismic performance of RC elements can be much improved if the buckling effect is effectively included in the stress–strain model of reinforcing bars. In this paper, modified Gomes–Appleton cyclic steel stress–strain relationship intended for improved accuracy is presented, which is suitable for inclusion in programs based on Opensees platform for the nonlinear analysis of RC elements. The modification is developed to improve the simulation accuracy of the inelastic buckling stress–strain path by a simplified model based on the equilibrium of a plastic mechanism of buckled bar consisting of four plastic hinges. Then an adjustment coefficient is introduced to further modify the developed buckled bar stress–strain model. A comparison of the numerical simulated results with experimental results of 36 steel bars subjected to reversed tension-compression loading is performed to verify the accuracy and effectiveness of the proposed model.

Preparing Pressure-Impulse Diagrams for Reinforced Concrete Columns with Constant Axial Load using Single Degree of Freedom Approach

Abstract: In this paper, moment-curvature behavior of reinforced concrete column with constant axial load is determined using finite element method and then it is introduced to a single degree of freedom (SDOF) model based on Euler- Bernoulli theory. Using this SDOF model, dynamic response of the RC column under the blast loading is estimated. The introduced SDOF includes secondary moments (P-δ) effects, nonlinear behavior of the material and effects of strain rate on concrete and steel materials through the time calculation of the model. Results obtained from SDOF model for transverse displacement of RC column under blast loading is compared to analysis by finite element software OPENSEES. Then, introduced SDOF method is used for drawing Pressure-Impulse (P-I) diagram of the column with considering the presence of axial compressive load. According to the results, introduced SDOF model has simple and quick computations and accuracy of predictions is acceptable.

Performance-based evaluation of strap-braced cold-formed steel frames using incremental dynamic analysis

Abstract: This study is an effort to clearly recognize the seismic damages occurred in strap-braced cold formed steel frames. In order to serve this purpose, a detailed investigation was conducted on 9 full scale strap-braced CFS walls and the required data were derived from the results of the experiments. As a consequence, quantitative and qualitative damage indices have been proposed in three seismic performance levels. Moreover, in order to assess seismic performance of the strap- braced CFS frames, a total of 8 models categorized into three types are utilized. Based on the experimental results, structural characteristics are calculated and all frames have been modeled as single degree of freedom systems. Incremental dynamic analysis using OPENSEES software is utilized to calculate seismic demand of the strap-braced CFS walls. Finally, fragility curves are calculated based on three damage limit states proposed by this paper. The results showed that the use of cladding and other elements, which contribute positively to the lateral stiffness and strength, increase the efficiency of strap-braced CFS walls in seismic events.

Axial elongation in ductile reinforced concrete walls

Abstract: Axial elongation has been observed during tests of reinforced concrete (RC) members subjected to either monotonic or cyclic loading. The implications of elongating plastic hinges in beams on the seismic performance of RC frame buildings, and in particular the floor systems, has been extensively studied. However, few investigations have addressed axial elongation of RC walls. To expand on the existing knowledge of axial elongation in RC members, the measured axial elongations of 13 previously tested RC walls were investigated. These tests included a wide range of vertical reinforcement ratios, vertical reinforcement layouts, and axial loads. The procedures to estimate wall elongation that were proposed in the Public Comment Draft Amendment No. 3 of the New Zealand Concrete Structures Standard (NZS 3101:2006) were also evaluated and compared against the measured elongations from the tests. The experimental results showed that elongation magnitudes in the analysed walls were between 0.4-0.8% of the wall length at 1.5% lateral drift, and that the elongation equations proposed for NZS 3101:2006 provided an acceptable estimation of the expected elongation in RC walls. Additionally, numerical models were developed using distributed-plasticity fibre-based elements in OpenSees and membrane elements in VecTor2 to verify the ability of these commonly used modelling techniques to capture wall elongation. The numerical simulations were able to represent the global and local behaviour with good accuracy and both models were able to capture the peak elongations. However, the more sophisticated concrete material models in OpenSees allowed the fibre element models to more accurately represent the experimental wall elongations, especially when considering residual elongations.

Performance assessment of innovative seismic resilient steel knee braced frame

Abstract: Buckling restrained knee braced truss moment frame (BRKBTMF) is a novel and innovative steel structural system that utilizes the advantages of long-span trusses and dedicated structural fuses for seismic applications. Steel trusses are very economical and effective in spanning large distance. However, conventional steel trusses are typically not suitable for seismic application, due to its lack of ductility and poor energy dissipation capacity. BRKBTMF utilizes buckling restrained braces (BRBs) as the designated structural fuses to dissipate the sudden surge of earthquake energy. This allows the BRKBTMF to economically and efficiently create large span structural systems for seismic applications. In this paper, a prototype BRKBTMF office building located in Berkeley, California, USA, was designed using performance-based plastic design procedure. The seismic performance of the prototype building was assessed using the state-of-the-art finite element software, OpenSees. Detailed BRB hysteresis and advanced element removal technique was implemented. The modeling approach allows the simulation for the force-deformation response of the BRB and the force redistribution within the system after the BRBs fracture. The developed finite element model was analyzed using incremental dynamic analysis approach to quantify the seismic performance of BRKBTMF. The results show BRKBTMF has excellent seismic performance with well controlled structural responses and resistance against collapse. In addition, life cycle repair cost of BRKBTMF was assessed using the next-generation performance-based earthquake engineering framework. The results confirm that BRKBTMF can effectively control the structural and non-structural component damages and minimize the repair costs of the structure under different ranges of earthquake shaking intensities. This studies conclude that BRKBTMF is a viable and effective seismic force resisting system.

Computer-based evaluation of design methods used for a steel plate shear wall system

Abstract: Summary Vertical boundary elements (VBEs) play a key role in seismic performance of steel plate shear wall (SPSW) system and consume major part of the steel material in a structure. The different methods allowed by design standards for computing the force demands exerted on the VBEs yield in widely varied results and are evaluated in this study through a computer-based approach. After elaborating these methods, development of a versatile and user-friendly program is presented that implements various SPSW design algorithms. The program relies on component object model technology and interactively communicates with a component object model supporting program, etabs, as the analysis core. It also benefits from an object-oriented structure. At the next phase, the developed program is utilized to design SPSWs with different heights and extract VBE demands using different methods. Nonlinear time history analyses of the structures, performed in opensees software using a bin of seven ground motion records, have been ultimately used for assessing the precision of different demand estimation methods. The AISC 341-10 capacity-based design method was shown to provide overestimations that reached 90% and 1888%, respectively, for axial and flexural VBE demands of 17-story building. Lower overestimation ratios were found for shorter structures. Copyright © 2016 John Wiley & Sons, Ltd.

Probabilistic seismic assessment of Buckling Restrained Braces and Yielding Brace Systems

Abstract: The current paper investigates the effectiveness of using an innovative structural fuse named YBS over the Buckling Restrained Brace (BRB) within the context of performance-based earthquake engineering. To this end, two groups of structures equipped with BRB and YBS braces are modeled by OpenSEES platform. In the first part of the paper, simplified procedures including pushover and Incremental Dynamic Analysis (IDA) are utilized for seismic performance evaluation. In the second part, two EDP-based and IM-based probabilistic frameworks are employed to gain a more comprehensive assessment. On this basis, fragility analysis is carried out for different performance levels. Also, limit state frequencies are calculated to compare collapse capacity of both systems. Finally, confidence levels are estimated to study reliability of the structures against collapse. Results show that both systems can achieve the expected performance objectives. However, YBS represent superior performance beyond the sideway collapse performance level.

A multi-mechanical nonlinear fibre beam-column model for corroded columns

Abstract: Purpose – A new modelling technique is developed to model the nonlinear behaviour of corrosion damaged reinforced concrete (RC) bridge piers subject to cyclic loading. The model employs a nonlinear beam-column element with multi-mechanical fibre sections using OpenSees. The nonlinear uniaxial material models used in the fibre sections account for the effect of corrosion damage on vertical reinforcing, cracked cover concrete due to corrosion of vertical bars and damaged confined concrete due to corrosion of horizontal tie reinforcement. An advance material model is used to simulate the nonlinear behaviour of the vertical reinforcing bars that accounts for combined impact of inelastic buckling and low-cycle fatigue degradation. The basic uncorroded model is verified by comparison of the computation and observed response of RC columns with uncorroded reinforcement. This model is used in an exploration study of recently tested RC components to investigate the impact of different corrosion models on the inelas...