Showing papers on "OpenSees published in 2014"

An advanced numerical model of elastomeric seismic isolation bearings

Abstract: SUMMARY The nuclear accident at Fukushima Daiichi in March 2011 has led the nuclear community to consider seismic isolation for new large light water and small modular reactors to withstand the effects of beyond design basis loadings, including extreme earthquakes. The United States Nuclear Regulatory Commission is sponsoring a research project that will quantify the response of low damping rubber (LDR) and lead rubber (LR) bearings under loadings associated with extreme earthquakes. Under design basis loadings, the response of an elastomeric bearing is not expected to deviate from well-established numerical models, and bearings are not expected to experience net tension. However, under extended or beyond design basis shaking, elastomer shear strains may exceed 300% in regions of high seismic hazard, bearings may experience net tension, the compression and tension stiffness will be affected by isolator lateral displacement, and the properties of the lead core in LR bearings will degrade in the short-term because of substantial energy dissipation. New mathematical models of LDR and LR bearings are presented for the analysis of base isolated structures under design and beyond design basis shaking, explicitly considering both the effects of lateral displacement and cyclic vertical and horizontal loading. These mathematical models extend the available formulations in shear and compression. Phenomenological models are presented to describe the behavior of elastomeric isolation bearings in tension, including the cavitation and post-cavitation behavior. The elastic mechanical properties make use of the two-spring model. Strength degradation of LR bearing under cyclic shear loading due to heating of lead core is incorporated. The bilinear area reduction method is used to include variation of critical buckling load capacity with lateral displacement. The numerical models are coded in OpenSees, and the results of numerical analysis are compared with test data. The effect of different parameters on the response is investigated through a series of analyses. Copyright © 2014 John Wiley & Sons, Ltd.

Seismic Vulnerability Assessment of Hybrid Steel-Timber Structure: Steel Moment-Resisting Frames with CLT Infill

Abstract: In this article, seismic vulnerability assessment is carried-out on a novel hybrid structure (steel moment resisting frame (SMRF) and cross laminated timber (CLT) infill panels). For the seismicity of Vancouver, Canada, a three-bay, 3-, 6-, and 9-story height SMRFs are designed for two ductility levels (ductile and limited ductility). To study the seismic vulnerability CLT infilled building, parametric analysis was performed by varying infill configuration (bare frame, one-bay infilled, two-bay infilled, and fully infilled). The structure is modeled in OpenSees and nonlinear dynamic analysis is performed. Peak inter-story drift demand and corresponding FEMA performance limits (capacity) values are used to compute the corresponding fragility curves. From the analyses, it can be seen that as more bays are infilled, the fundamental period and seismic vulnerability is reduced significantly. The results highlight that, within the performance-based earthquake engineering, different objectives can be met with va...

Application of Reliability-Based Robustness Assessment of Steel Moment Resisting Frame Structures under Post-Mainshock Cascading Events

Abstract: This paper proposes a reliability-based framework for quantifying structural robustness considering the occurrence of a major earthquake (mainshock) and subsequent cascading hazard events, such as aftershocks that are triggered by the mainshock. These events can significantly increase the probability of failure of buildings, especially for structures that are damaged during the mainshock. The application of the proposed framework is exemplified through three numerical case studies. The case studies correspond to three SAC steel moment frame buildings of three, nine, and 20 stories, which were designed to pre-Northridge codes and standards. Two-dimensional nonlinear finite-element models of the buildings are developed with the Open System for Earthquake Engineering Simulation framework (OpenSees), using a finite length plastic hinge beam model and a bilinear constitutive law with deterioration, and are subjected to multiple mainshock-aftershock seismic sequences. For the three buildings analyzed herein, it is shown that the structural reliability under a single seismic event can be significantly different from that under a sequence of seismic events. The reliability based robustness indicator shows that the structural robustness is influenced by the extent to which a structure can distribute damage.

Progressive Collapse Mechanisms of Steel Frames Exposed to Fire

Abstract: OpenSees is an open-source object-oriented software framework developed at UC Berekeley. The OpenSees framework has been recently extended to deal with structural behavior under fire conditions. This paper summaries the key work done for this extension and focuses on the application of the developed OpenSees to study the fire-induced progressive collapse mechanisms of steel structures. The implicit dynamic analysis method (Newmark method) is applied and the influences of the load ratios, beam sizes and fire scenarios on the collapse behavior of frames are investigated. Single-compartment fire scenarios in the central bay and edge bay are considered, respectively. A total of four collapse mechanisms of steel frames are proposed by varying the three influencing factors. Most of the collapse of steel frames is triggered by the buckling of the heated columns. The thermal expansion of heated beams at early heating stage and their catenary action at high temperature have great influences on the collapse mechani...

Development of a novel self-centering buckling-restrained brace with BFRP composite tendons

Abstract: Buckling-restrained braces (BRBs) have excellent hysteretic behavior while buckling-restrained braced frames (BRBFs) are susceptible to residual lateral deformations. To address this drawback, a novel self-centering (SC) BRB with Basalt fiber reinforced polymer (BFRP) composite tendons is presented in this work. The configuration and mechanics of proposed BFRP-SC-BRBs are first discussed. Then an 1840-mm-long BFRP-SC-BRB specimen is fabricated and tested to verify its hysteric and self-centering performance. The tested specimen has an expected flag-shaped hysteresis character, showing a distinct self-centering tendency. During the test, the residual deformation of the specimen is only about 0.6 mm. The gap between anchorage plates and welding ends of bracing tubes performs as expected with the maximum opening value 6 mm when brace is in compression. The OpenSEES software is employed to conduct numerical analysis. Experiment results are used to validate the modeling methodology. Then the proposed numerical model is used to evaluate the influence of initial prestress, tendon diameter and core plate thickness on the performance of BFRP-SC-BRBs. Results show that both the increase of initial prestress and tendon diameters can obviously improve the self-centering effect of BFRP-SC-BRBs. With the increase of core plate thickness, the energy dissipation is improved while the residual deformation is generated when the core plate strength exceeds initial prestress force.

Seismic performance and collapse prevention of concrete-filled thin-walled steel tubular arches

Abstract: The primary objective of this paper is to investigate the seismic behaviour of concrete-filled steel tubular (CFST) arches using incremental dynamic analysis (IDA). A nonlinear elastic–plastic finite element model is developed using OpenSees software and is verified with a shaking table test. Single-record IDA studies indicate that a CFST arch undergoes global dynamic instability when subjected to ground motions of increasing intensity levels. During this process, either dynamic elastic buckling or dynamic elastic–plastic buckling may occur. Dynamic strength, which is defined as the capacity for preventing global dynamic instabilities of CFST arches, is determined with a series of multi-record IDA calculations. A lower bound equation that takes into account the effect of slenderness ratio, axial compression ratio, and included angle is proposed for the prediction of the dynamic strength of CFST arches.

Response modification factor of the frames braced with reduced yielding segment BRB

Abstract: In this paper, overstrength, ductility and response modification factors are calculated for frames braced with a different type of buckling restrained braces, called reduced yielding segment BRB (Buckling Restrained Brace) in which the length of its yielding part is reduced and placed in one end of the brace element in comparison with conventional BRBs. Forthermore,these factors are calculated for ordinary BRBF and the results are compared. In this regard incremental dynamic analysis (IDA) method is used for studying 17 records of the most known earthquakes happened in the world. To do that, the considered buildings have different stories and two bracing configurations: diagonal and inverted V chevron, the most ordinary configurations of BRBFs. Static pushover analysis, nonlinear incremental dynamic analysis and linear dynamic analysis have been performed using OpenSees software. Considering the results, it can be seen that, overstrength, ductility and response modification factors of this type of BRBF(Buckling Restrained Braced Frame) is greater than those of conventional types and it shows better seismic performance and also eliminates some of conventional BRBF

Evaluation of seismic behavior improvement in RC MRFs retrofitted by controlled rocking wall systems

Abstract: SUMMARY Using rocking wall systems is a recent technique to improve seismic behavior in reinforced concrete structures. This paper compares three 10-story and three 20-story reinforced concrete frames (moment-resisting frames) with intermediate ductility, reinforced concrete frames with shear wall, and reinforced concrete frames with controlled rocking wall (RCRW) by the use of pushover analysis. At the end of the research, the wall in a 20-story RCRW system is post-tensioned then analyzed, and its results were compared with RCRW results. Simulation and numerical analysis were performed with OpenSees software. The results show that plastic hinge formation and inter-story drifts are well distributed in the structure with rocking wall system in comparison with the other systems. Meanwhile, energy dissipation and displacement ductility are increased in RCRW frames. With post-tensioning wall in RCRW, the drift ratios are more uniformed. Copyright © 2013 John Wiley & Sons, Ltd.

Modelling of Steel-Concrete Composite Structures in Fire Using OpenSees

Abstract: This paper presents the extension of the structural analysis software framework OpenSees for modeling steel framed composite structures subjected to fire including the development of a geometrically nonlinear shell element. The new shell element is formed by a combination of membrane elements and Mindlin plate bending elements using a general total Lagrangian formulation. The MITC technique (Mixed Interpolation of Tensorial Components) is applied to alleviate shear locking problems and the addition of drilling degrees of freedom is included. A new thermal load class was created to define the temperature distribution through the thickness of the shell section. The two-dimensional OpenSees material, DruckerPrager, was modified to model the concrete in the composite deck slab at elevated temperature with temperature-dependent material properties according to the Eurocode 2. A three-dimensional finite element model of a composite structure was built in OpenSees, consisting of a flat reinforced concrete slab m...

Seismic performance of reinforced concrete shear wall frames considering soil–foundation–structure interaction

Abstract: SUMMARY A practical application of ‘beam on nonlinear Winkler foundation’ approach has been utilized in this paper for a case study on seismic performance of concrete shear wall frames to assess the soil–foundation–structure interaction effects. A set of 3-, 6-, 10- and 15-story concrete shear wall frames located on hypothetically soft, medium and hard soils were designed and modeled using the OpenSees platform. The numerical model of each frame was constructed employing the distributed and lumped plasticity elements as well as the flexure–shear interaction displacement-based beam–column elements incorporating the soil–footing interface. Pushover analysis was performed, and the results were studied through two code-based viewpoints: (a) force-based design and (b) performance-based design. A comparison was made afterwards between the frame behaviors in the fixed-/flexible-base conditions. The results indicate some degree of inaccuracy in the fixed-base assumption, which is regularly applied in analysis and design practice. The study emphasizes on how the fixed-base assumption overestimates the design of the wall element and underestimates the design of the connected moment frame. Copyright © 2012 John Wiley & Sons, Ltd.

Steel concentrically braced frames using tubular structural sections as bracing members: Design, full-scale testing and numerical simulation

Abstract: This paper presents the results of experimental and analytical studies carried out on two full-scale, one-bay, two-story steel concentrically braced frames. Square hollow and round hollow structural sections were used for the bracing components. The specimens were designed and detailed according to the 2005 AISC Seismic Provisions, and tested cyclically under displacement control but with a fixed lateral load distribution over height. Numerical computational models including the brace components, gusset plate details and frame members were implemented in OpenSees. Numerical simulations were then performed to investigate the cyclic behavior of brace components, brace failure mechanisms and overall system response. Satisfactory agreement was obtained in comparisons of experimental and numerical results. Premature failures observed suggest that beamto-gusset plate connections could be pinned to accommodate large rotational demands at this location without the need to form plastic hinges. Test results also showed that for the braced frames having the same configuration, designed for similar base shear capacities, and subjected to the same roof level displacement history, the braced frame specimen using round tubular sections as diagonal braces was able to sustain larger story drifts without brace fracture than the specimen employing square tubular sections. Fracture of the column base in the second specimen, although inconclusive from a single test, suggests more study is needed of design requirements for column to base plate connections where large variations of axial, bending and shear load are expected.

Hybrid Simulation of Bridge Response to Three-Dimensional Earthquake Excitation Followed by Truck Load

Abstract: A hybrid simulation approach is used to evaluate the traffic performance of a typical California highway overpass bridge after a major earthquake. The prototype bridge used in this study is a five-span single-column-bent reinforced concrete overpass. A hybrid model, composed of the physical column specimen and the OpenSees model of the remainder of the bridge, was assembled using the OpenFresco framework. Two hybrid simulation tests were performed on the same bridge for the same recorded ground motion scaled to represent two levels of seismic intensity: moderate and high. After the earthquake, loads corresponding to a heavy truck placed in the most critical positions on the bridge were applied on the hybrid model. The data obtained from these tests show that a typical California overpass bridge has the capacity to carry heavy truck loads immediately after a major earthquake event.

Experimental and numerical studies on seismic behavior of hollow bridge columns retrofitted with carbon fiber reinforced polymer

Abstract: Seismic behavior of reinforced concrete hollow rectangular bridge columns retrofitted with carbon fiber reinforced polymer (CFRP) was carried out under constant axial loading and lateral bending. The failure characteristics, flexural ductility, dissipated energy, and hysteretic behavior were analyzed based on cyclic testing of eight specimens retrofitted with CFRP. A simplified CFRP-confined concrete model is developed by considering effective strength coefficient and area distribution ratio of CFRP sheets. The hysteretic behavior and its influencing parameters were studied using fiber element model in the OpenSees program. The results indicate that the failure modes and damages region would be changed and the ductility and dissipated energy of the rectangular hollow bridge columns with CFRP were improved greatly, but the lateral load capacity was not improved obviously. The simplified analytical method presented in this paper is effective for analyzing lateral force and deformation hysteretic behavior of...

Research progress on innovative earthquake-resilient structural systems

Abstract: In recent years,earthquake-resilient structure has become a research focus in the international earthquake engineering field.This paper presents the study and practice of the innovative earthquake-resilient structure systems keeping up with the international research trends.In the earthquake-resilient frame systems,the end constraints of column were released and the prestressed tendons provided the self-centering capability.An angle steelrubber connection with local rotation was developed and the shaking table test with the finite element simulation based on OpenSees was conducted to evaluate the resilience.In the earthquake-resilient shear wall systems,the shear walls with replaceable foots and the replaceable coupling beam were proposed.Cyclic loading tests and refined finite element analysis were conducted to investigate the seismic performance of earthquake-resilient shear wall systems.The design method was proposed and the replaceable coupling beams were applied in a high-rise building in Xian,China.It can be concluded from series research that earthquake-resilient structures with clear structural system,proper designed connections,collaboration of strength and damping will exhibit desirable resilience under earthquakes and present the broad prospect of real engineering projects.

Nonlinear analysis and test validation on seismic performance of a recycled aggregate concrete space frame

Abstract: SUMMARY Three-dimensional recycled aggregate concrete (RAC) nonlinear finite element models are developed by OpenSees software to investigate the seismic responses of a 1/4-scaled six-story, two-bay and two-span RAC space frame, which has been tested on a shaking table subjected to various earthquake scenarios. The simulated natural frequencies and vibration modal shapes, the acceleration amplification factors, the maximum story displacements and the inter-story drifts are carefully validated by and compared with the test data with overall good agreement. The simulated seismic responses of the RAC frame and the natural aggregate concrete (NAC) frame are also compared. The aseismic capacity of the NAC frame structure is better than that of the RAC frame structure in the early stage, and they behave almost the same in the severe stage under strong earthquake excitations. Both tested and simulated results indicate that not only the peak ground acceleration and duration and frequency of ground motion but also concrete material properties play a prominent role in the overall seismic performances of frame structures. Copyright © 2014 John Wiley & Sons, Ltd.

Multi-Layer Shell Element for Shear Walls in OpenSees

Abstract: Reinforced concrete (RC) shear walls is one of the most widely used lateral force-resisting members of high-rise buildings. This research developed a multi-layer shell element on an open-source FE code of OpenSees for shear walls. The multi-layer shell element can simulate the coupled in-plane/out-of-plane bending as well as the in-plane shear and coupled bending-shear behavior of RC shear walls, and it comprehensively reflects the spatial mechanical behavior of the shell structures. The simulation of rectangular walls, flanged walls and coupled walls under pseudo-static loading was conducted. The simulated results agree well with the experimental results, which validates the rationality and reliability of the proposed model. The nonlinear seismic analyses of a super-tall building, namely Shanghai Tower with a height of 632 m, were conducted based on the fiber beam and multi-layer shell elements, and good agreement was achieved between the analytical results of OpenSees and MSC.Marc. The outcome of this study provides an effective tool and a useful reference for the simulation of high-rise buildings using OpenSees.

Design-Oriented Model for Capturing the In-Plane Seismic Response of Partition Walls

Abstract: Using data generated from experiments, a numerical model is developed for capturing the in-plane seismic response of full-height cold-formed steel framed partition walls. The behavior of the partition wall is captured using a lumped nonlinear material model localized within a zero-length spring. The lumped material is developed with a pinching material used in a parallel configuration within the Open System for Earthquake Engineering Simulation (OpenSees) modeling platform. A simple, lumped model is utilized to facilitate ease of implementation in beam-column type finite element analyses commonly adopted in design of building structures. Importantly, its characteristics are determined by analyzing a large suite of experimental data on institutional and commercial type metal stud walls. Two error metrics based on calculation of the maximum force and half-cycle hysteretic energy are introduced to assess the model’s robustness. The model’s predictive capabilities are demonstrated via simulation of in...

Behavior of composite rigid frame bridge under bi-directional seismic excitations

Abstract: Pushover analysis and time history analysis are conducted to explore the bi-directional seismic behavior of composite steel-concrete rigid frame bridge, which is composed of RC piers and steel-concrete composite girders. Both longitudinal and transverse directions excitations are investigated using OpenSees. Firstly, the applicability of pushover analysis based on the fundamental mode is discussed. Secondly, an improved pushover analysis method considering the contribution of higher modes is proposed, and the applicability on composite rigid frame bridges under bi-directional earthquake is verified. Based on this method, an approach to predict the displacement responses of composite rigid frame bridge under random bi-directional seismic excitations by revising the elasto-plastic demand curve is also proposed. It is observed that the developed method yield a good estimate on the responses of composite rigid frame bridges under bi-directional seismic excitations.