Multielement Hybrid Simulations for Performance Assessment of Multistory Special Concentrically Braced Frames

Previous studies have underlined the importance of establishing a database of high‐fidelity benchmark experimental test results under random loading histories such as earthquake excitations for both existing structural systems as well as newly proposed ones. Such experimental results are useful for understanding the limitations of previously developed numerical models, proposing new numerical models for more recently developed structural systems, better assessing the ultra‐low cycle fatigue (ULCF) life of energy dissipative components, and improving the loading protocols used for element assessments or developments of numerical model. This paper presents experimental results from pseudo‐dynamic hybrid simulations on steel eccentrically braced frames (EBF) equipped with novel cast steel replaceable modular yielding links. The first set of experiments are carried out on a four‐story EBF, with the first‐floor yielding link physically tested in the laboratory. The second set of experiments are performed on a two‐story EBF where the second‐floor link is physically tested in the laboratory, while considering axial loads due to the imbalanced distribution of the seismic weight in the building. Each building structure is subjected to three Maximum Credible Event (MCE) level earthquakes. A framework for performing hybrid simulations on EBFs is proposed where the response of the yielding link is physically captured in a single degree of freedom control system, with or without axial loads. A substructuring strategy is proposed in conjunction with a modeling approach in the integration module. The results confirm the effectiveness of the hybrid simulation framework, which can be adopted in similar studies. Two numerical models are proposed for capturing the response of cast steel links using a simplified and a more advanced approach. The models are first calibrated using incremental reversed‐cyclic experimental test results, and then refined using the hybrid simulation test results. The effects of this calibration improvement are quantified through critically comparing the response prediction for different response parameters before and after improving the calibration with the experimental results. The numerical model which captures the physical mechanism of the cast steel links provides a more accurate response prediction compared to the simplified numerical model using a phenomenological truss with calibrated force‐deformation. The remaining ULCF life of the tested yielding links is experimentally investigated after having sustained three MCE level earthquakes, which indicates a large reserve ductility capacity which is more than twice the required plastic rotation capacity for cast steel links after seismic events.

Section: Evaluation Of Numerical Modelsmentioning

confidence: 93%

Section: Four-story Structure Without Axial Loadsmentioning

confidence: 99%

Section: Evaluation Of Numerical Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

See 3 more Smart Citations

Pseudo‐dynamic hybrid simulations of steel eccentrically braced frames equipped with cast steel replaceable modular yielding links

Mortazavi

Kwon

Christopoulos

2023

Hybrid‐simulation‐based model calibration method for nonlinear seismic analysis

Zhang,

Kwon,

Christopoulos

2023

Self Cite

The calibration of parameters of hysteretic models that simulate the hysteretic behavior of key structural components is a crucial task in the nonlinear seismic analysis of structures to ensure accurate analysis results. For complicated systems, a direct calibration of model parameters at the system level is almost impossible due to the lack of test data. Consequently, the calibration is usually conducted using test results with lower levels of complexity. Currently, a widely accepted practice in calibrating hysteretic model parameters in structural models is to utilize standardized cyclic tests of a single component. However, due to the simplified and unrealistic loading profile of standardized cyclic tests, the relevance between the calibration and the system‐level prediction capabilities can be weak. In other words, a well‐tuned hysteretic model that matches the standardized cyclic test results very well may not be able to produce the same level of accuracy in estimating the system‐level structural dynamic response where the calibrated components will experience more random and complicated loadings. In this paper, a method is proposed to calibrate hysteretic models in a test method with more realistic loading histories through hybrid simulations. The proposed calibration method is then validated by conducting a large number of hybrid simulations on a type of small‐scale buckling‐restrained brace (BRB) specimen. A framework is also proposed to evaluate the relevance between the calibration and the system‐level response considering uncertainties in hysteretic model parameters. The results demonstrate the superiority of the hybrid‐simulation‐based calibration method over the conventional cyclic‐test‐based calibration method.

Mitigation of residual deformations in eccentrically braced frames through a low‐cost re‐centering mechanism

Mortazavi,

Christopoulos,

Kwon

2024

Previous studies have demonstrated that the response of stable yielding systems to random excitations such as earthquakes is inherently accompanied by residual deformations. Stable yielding systems with highly enhanced ductility capacity are more prone to residual deformations. Steel eccentrically braced frames (EBFs) are designed to sustain significant localized inelastic deformations in the segment of the beam referred to as the yielding link, which results in much larger link rotations when compared to inter‐story drift ratios (SDR). Recent experimental and numerical studies on the response of EBFs have demonstrated that even with moderate residual inter‐SDR (less than 0.5%), severe link residual rotations could be expected, which could render the structure difficult to repair. For replaceable yielding links, which were developed to expedite the repair and recovery process in EBFs after major seismic events, large residual link rotations will hinder the link replacement process or at times make it impossible. Therefore, mitigation of residual deformations is of greater importance in EBFs with replaceable yielding links than in conventional EBFs with a continuous beam. This paper provides a brief review of past research on residual deformations and methods for their mitigation. A low‐cost re‐centering system for use in EBFs is proposed to work in parallel with the yielding link, in order to mitigate residual deformations. The proposed system is adopted for two prototype structures designed with EBFs equipped with cast steel replaceable modular yielding links. The effectiveness of the re‐centering strategy is evaluated by means of pseudo‐dynamic hybrid simulations, as well as numerical simulations. The hybrid simulations and numerical studies both demonstrate that not only the proposed system is highly effective at mitigating the residual deformations, but also it is effective in reducing the peak deformations in EBFs.