Showing papers on "OpenSees published in 2023"

Seismic Responses and Damage Control of Long-Span Continuous Rigid-Frame Bridges Considering the Longitudinal Pounding Effect under Strong Ground Motions

Abstract: Continuous rigid-frame bridge (CRFB), a type of bridge adopting the unique form of pier-girder consolidation, combines a T-shaped rigid frame with a continuous girder. CRFBs located in western China are likely to suffer destructive earthquakes, which may result in serious damage to bridges. To study the longitudinal seismic responses and damage control of different structure types of the CRFB under strong ground motions, this work develops three nonlinear dynamic analysis models considering the initial internal force state and longitudinal girder-pier pounding effect based on the OpenSEES (version 3.3.0) platform. Moreover, the present study comparatively analyzes the displacement responses, internal force of piers, pounding force and times, and damage condition of the three models and investigates the effectiveness of tuned inerter-based dampers (TIBDs) in controlling seismic responses of the CRFB. The numerical results show that the longitudinal seismic responses of the main piers in the three models are obviously different, especially when subjected to near-fault ground motions. The peak pounding force at the abutments is much larger than at the transition piers, while the pounding times are the opposite. Under near-fault ground motions with a peak ground acceleration (PGA) of 0.4g, the main piers may be damaged moderately or even more seriously, and the bearings are completely destructive. The TIBDs can effectively control the maximum seismic responses and damage degree of the CRFB under pulse-like near-fault ground motions. Among them, both the tuned viscous mass damper and tuned inerter damper are ideal and useful devices. This study can provide useful references for the seismic design and performance analysis of CRFBs.

Seismic performance of steel braced frames with innovative assembled self-centering buckling restrained braces with variable post-yield stiffness

Abstract: An innovative assembled self-centering buckling restrained brace (ASC-BRB) with variable post-yield stiffness is proposed in this study, aiming to better control structural responses under earthquakes of different intensity levels. The proposed ASC-BRB consists of the buckling restrained brace (BRB) system and self-centering (SC) system, where the SC system provides the variable post-yield stiffness with trilinear elastic behavior. The overall configuration and restoring force model of the brace are first described, and six independent hysteretic parameters are determined to comprehensively describe its hysteretic behavior. A simplified truss model of the ASC-BRB is established using OpenSees, and the experimental and numerical hysteretic curves coincide well with each other, indicating that the simplified model has satisfactory accuracy. The simplified model is then utilized to investigate the effect of the design parameters on the hysteretic behavior of the ASC-BRB. Nonlinear dynamic analyses are also conducted for three 6-story steel frames with different types of braces. The comparison results indicate that the proposed ASC-BRB with high post-yield stiffness can effectively limit the displacement development at the lower floors, but the structural high-mode effect will be further amplified. Finally, system level parametric analyses are performed to study the influence of brace design parameters on the structural responses, and reasonable values for these design parameters are recommended according to the parametric analysis results.

Predicting Seismic Collapse Safety of Post-Fire Steel Moment Frames

Abstract: This paper summarizes a study focused on evaluating the post-fire performance of steel Intermediate Moment Frames (IMFs) following earthquakes. To this aim, archetypes comprising 3-bay IMFs with three different heights were seismically designed, and their two-dimensional finite element models were created in OpenSees software. The post-fire mechanical properties of steel were inserted into the models based on 64 different fire scenarios. The effects of different cooling methods are scrutinized at system level. To develop seismic fragility curves, Incremental Dynamic Analysis (IDA) was performed using 50 suites of far-field and near-field records, according to FEMA-P695. Then, the Collapse Margin Ratio (CMR) of each model was calculated based on the data from the fragility analysis. The results show that the seismic resistance of structures that experienced fire declines to some extent. In addition, the lowest safety level was observed when the structures were subjected to pulse-like near-field records.

Seismic Collapse Risk Assessment of Low-Aspect-Ratio Reinforced Concrete Shear Walls Using the FEMA P695 Methodology

Abstract: Several recent research studies have demonstrated that the seismic performance of low-aspect-ratio reinforced concrete (RC) shear walls (i.e., defined herein as walls with height-to-length ratios less than 2) has not been yet adequately quantified to allow for robust risk assessment. This is mainly attributed to the complex nonlinear flexure/shear interaction behavior of such walls, along with their wide spectrum of possible design parameters, leading to major discrepancies in their seismic performance. Despite this unique behavior, most building codes and design standards do not assign distinctive seismic performance factors for such walls. To address this, the main objective of the current study is to propose seismic performance factors for low-aspect-ratio RC shear walls when different wall geometrical configurations and design parameters (e.g., aspect ratios, axial load levels, and seismic design categories) are adopted. These factors are evaluated against the acceptance criteria of the FEMA P695 methodology for Quantification of Building Seismic Performance Factors. In this respect, a numerical model was developed and experimentally validated to simulate the seismic response of 36 low-aspect-ratio RC shear wall archetypes. The model was utilized to perform nonlinear static and dynamic analyses, and collapse fragility curves were then generated to assess the collapse risk of such wall archetypes following the FEMA P695 methodology. According to the methodology, the proposed seismic performance factors were assessed by quantifying the ratio between the median collapse intensity and the intensity of the maximum considered earthquake (MCE). The results showed that R factors of 2.0 and 3.0 for special low-aspect-ratio RC walls with low and high axial load levels, respectively, can limit the probability of collapse under the MCE and are subsequently able to meet the FEMA P695 acceptance criteria.

Evaluation of rocking motion on the seismic performance of a linked column frame system

Abstract: A linked column frame (LCF) is a seismic-load-resisting system with ductile behaviour. In this system, the link beam, operating as a shear fuse, reduces or eliminates damage to other components of the structure under various hazard levels. In this study, by combining rocking motion and changes in the linked column pattern, an innovative seismic-resisting system was developed. The aim was to improve the performance of the LCF system by reducing damage to the flexural beams and columns and to concentrate damage in the link beams. For this purpose, a three-storey model based on the SAC building was designed based on storey drift demands. The model was evaluated by incremental dynamic analysis (IDA) according to Fema P-695 instructions using OpenSees. Results of changes in the linked column pattern from the IDA indicated a 20% increase in the structural capacity of the LCF model. Compared with the model without rocking motion, the model with rocking motion resulted in reduced structural capacity, shear and horizontal acceleration of the storey, and maximum drift. This novel LCF seismic system provides self-centring and damage control by using features such as rocking motion.

Experimental and numerical response of unbonded post-tensioned rocking wall under lateral cyclic loading

Abstract: This study examined the experimental behavior of three unbonded post-tensioned (PT) single rocking wall (SRW) specimens with varied initial prestressing levels and cross-sectional areas of PT strands subjected to a series of quasi-static cyclic lateral loadings. To investigate the cyclic performance of the specimens, the damage patterns, force-displacement relationship, stiffness degradation, stress of PT strands, and neutral axis depths were compared and evaluated. In addition, the prestress losses of the PT strands experienced in the test were also measured and estimated using a theoretical equation. The test results show that the SRW specimens exhibited low damage, good self-centering, and large deformation capacity with a minor residual drift. Moreover, the low energy dissipation capacity indicates that the SRWs without damping elements cannot be recommended in high seismic zones. In addition, the experimental and predicted results demonstrate that the prestress losses of PT strands in SRWs resulted from wedge seating before they achieved the proportional limit. Finally, a multi-spring model based on the idea of a nonlinear macro element was adopted to simulate the rocking walls in OpenSees software, and the calculated results were consistent with the experimental results.

INSPECT-SPSW: INelastic Seismic Performance Evaluation Computational Tool for Steel Plate Shear Wall Modeling in OpenSees

Abstract: Modeling Steel Plate Shear Wall (SPSW) behavior can be computationally demanding. This is especially true when high-fidelity modeling is carried out via shell or 3D solid elements. It has been shown that SPSW behavior can be captured with adequate accuracy through the strip method via nonlinear truss elements idealization. The widely accepted and reliable analysis platform, OpenSees, requires text-based input (.tcl) files created by a skilled programmer. Hence, a Pre/Post-processing User Interface (UI) software package (INSPECT-SPSW) is introduced herein. With basic input, the INSPECT-SPSW package allows the user to create the OpenSees (.tcl) input file, run different nonlinear analyses, and retrieve and visualize the output. In addition, the UI includes illustrated wrappers for several OpenSees commands for various material definitions, plasticity modeling options, modal analysis, and nonlinear analysis types. Validation and verification were conducted against published results of experimental and numerical cyclic loading specimens. The user-friendly interface successfully created accurate models that capture the SPSW nonlinear behavior, including the various possible failure mechanisms. e.g., beam or column plastic hinging, web plate yielding, etc. With demonstrated performance and intuitive UI, INSPECT-SPSW is expected to facilitate the broad adoption of the strip method for Performance-Based Earthquake Design (PBED) of SPSWs.

Comparative study of alternative equivalent frame approaches for the seismic assessment of masonry buildings in OpenSees

Abstract: The equivalent frame (EF) idealisation of masonry structures is widely used in engineering structures. Despite its simplifications, reliable numerical models can be produced to calculate the seismic behaviour of unreinforced masonry (URM) buildings. Different EF modelling approaches have been implemented in commercial software specifically conceived for performing nonlinear analyses on URM buildings (such as 3Muri, adopted in this study). Furthermore, the adoption of such an approach is also possible in general-purpose structural analyses software packages, such as OpenSees, through an ad hoc implementation of analysts. The aim of this paper is to compare various EF modelling approaches by adopting alternative nonlinear beam-elements in OpenSees belonging to the distributed and the lumped plasticity. To this aim, the responses of some benchmark cases study available in the literature from the “URM nonlinear modelling-benchmark project” within the context of ReLUIS projects have been adopted to preliminary test the reliability of the alternative approaches considered. In particular, they consist of some single panels and a trilith, for which the results of various software are already available. In the paper, the results obtained with OpenSees have been more in-depth compared with 3Muri, which is assumed as representative of a larger set of EF models adopted in engineering-practice (having already verified in previous works that it provides a reasonable scatter with other software package options). Then, the analyses have been extended as well to a 3D building representative of the neighbourhood of ‘El Plantinar’ in Seville. An accurate comparison has been carried out in terms of generalised forces, drifts and damage at an element and at a global scale. The results have shown that the method proposed in this manuscript allows using OpenSees to calculate masonry structures with the EF approach with a good agreement to other engineering-practice oriented tools. Thus, this outcome may constitute, in future research, the basis for exploiting the potential and versatility of OpenSees in accounting for other tricky phenomena: the soil-foundation-structure interaction.

Theoretical Study and Nonlinear Finite Analysis of Four-Line Restoring Force Model for Double-Superimposed Slab Shear Walls

Abstract: This paper is concerned with the seismic behavior of a superimposed slab shear wall. Based on the test results of the specimens under low cyclic reversal loading, the formulas with respect to the top displacement and capacity of a shear wall in the consecutive loading process are derived. The concrete grade differentiation between the prefabricated layer and the cast-in-site layer of the shear wall is considered to improve the calculating precision. With the help of these equations, the extent of participation of the prefabricated concrete layers in the different loading stages is revealed, demonstrating a great confirmation of the test results. Two ideal conditions, utterly with and without connective effect between a combined interface, are considered to investigate the action of the bond–slip effect. On this basis, the finite element analysis is completed in the framework of OpenSees. Its quadrilinear restoring force model, with the consideration of the stiffness degradation and pinching effect, is established in this paper by various feature points from the theoretical derivation of capacities in different loading stages. The rationality of the restoring force model of the shear wall is testified by the satisfactory agreement of the test results and simulation results.

Effects of modelling uncertainty on the seismic fragility of frame piers in double-deck viaducts

Abstract: Frame piers of double-deck viaducts (DVFP) have been widely studied and applied due to their high levels of space utilisation and significant engineering benefits, but the uncertainty of their information on modelling significantly affects the accuracy of calculation results for structural seismic demand and seismic capacity, which leads to challenges regarding the accuracy and reliability of seismic fragility analysis. In this paper, an accurate non-linear finite element model of DVFPs was established based on the OpenSees open platform. The seismic fragility analysis of DVFPs is carried out by introducing the endurance time method, and the tornado diagram and central point methods were performed to investigate the sensitivity and uncertainty of a seismic fragility of DVFPs to nine modelling parameters, respectively. The results show that the logarithmic standard deviation of fragility when slight damage, moderate damage, significant damage, and collapse occur on DVFP after considering modelling uncertainty will increase by 6.4%, 16.1%, 13.3%, and 20.1%, respectively. Therefore, it is necessary to consider the influence of modelling uncertainty in seismic fragility analysis.

Macromechanism Approach for Vulnerability Assessment of Buildings on Shallow Foundations in Liquefied Soils

Abstract: The damage caused by seismic shaking and liquefaction-induced permanent ground deformation has conventionally been assessed as two separate problems often by different engineers. However, the two problems are inherently linked, since ground shaking causes liquefaction, and liquefaction-induced soil softening affects ground shaking. Modelling both problems within a single numerical model is complex for both the engineer and the software, and most finite element software only have the capabilities to address one of them. To improve the estimates of the seismic performance of buildings on liquefiable soil, a new sub-structuring approach is proposed called the macro-mechanism approach. This approach allows the soil-liquefaction-foundation-structure interaction to be considered in a series of sub-models accounting for the major nonlinear mechanisms of the system at a macro level. The proposed approach was implemented in the open-source finite element software OpenSees and then applied to a case study of a building where significant liquefaction- and shaking-induced damage was observed after the 1999 Mw 7.4 Kocaeli Earthquake. The case study building was also simulated using two different commercial software programs, the finite difference software FLAC, and the finite element software PLAXIS, by two different research teams. A comparison between the results from the macro-mechanism approach compared to full numerical models shows that the macro-mechanism approach can capture the extent of the foundation deformation and provide more realistic estimates of the building damage than full approaches since the FLAC and PLAXIS models consider elastic elements for the building.

Preliminary study of a seismic-resilient steel pilot building equipped with low-damage connections

Abstract: According to current seismic design codes, structures are designed to exhibit an elastic behaviour or slight damage in case of frequent (low intensity) seismic events. Conversely, in the case of rare (high intensity) seismic events, more widespread damage is allowed. In fact, according to the latter case, structures are typically designed to concentrate the seismic damage into dissipative fuses, whose ductility and energy dissipation capacity is properly designed through the adoption of specific detailing rules. This approach allows the achievement of the safety requirements, with considerable damage to the structural components and large residual drifts, which can significantly compromise the building's reparability. To overcome these drawbacks, recent efforts are aimed at developing innovative seismic resilient structures to reduce structural damage and repair time. Among others, steel Moment Resisting Frames equipped with friction devices in beam-to-column joints have emerged as a promising and effective solution that simultaneously ensures the seismic input energy dissipation capacity and the damage-free behaviour of the system. In this direction, relevant research studies have been carried out within the RFCS-FREEDAM research project, demonstrating the high potential of friction joints in drastically reducing the seismic damage of steel structures. Within this context, the free-from-damage technology developed within the FREEDAM research project is going to be implemented in a demonstration building to be erected at the University Campus of Salerno. The present paper illustrates the preliminary design and results of the numerical simulations in OPENSEES. Non-linear static analyses and Incremental Dynamic Analyses are performed to obtain the engineering demand parameters of interest while accounting for the record-to-record variability.

Seismic performance assessment of a multi-story bamboo frame structure

Abstract: As a building material, engineered bamboo has caught attention around the world due to its advantages in energy conservation and environmental protection. The seismic performance of bamboo buildings needs to be evaluated to further promote the use of bamboo materials in building construction. We studied the seismic response of a 3-story bamboo frame structure numerically using nonlinear dynamic time history analysis. A simplified modeling method for bamboo column-beam joints was proposed in the numerical model. The hysteresis behaviour of the joint was simulated by Pinching 4 material in OpenSEES, with the parameters calibrated through test results. Comparative analysis shows that the proposed modeling method could reasonably reflect the pinching effect and the degradation of the joint hysteretic behavior. A total of 20 ground motions with three intensities were involved in the nonlinear dynamic analysis. The results demonstrate that the frame meets target performance levels, providing evidence for the further popularization of engineered bamboo structures.