In this paper, a probabilistic framework for constructing a dynamic modified model for RC columns was developed based on dynamic loading test results and the Bayesian updating method. The influences of strain rate on the mechanical behaviors of RC columns were investigated by analyzing the experimental data obtained from dynamic loading tests. The basic equations of dynamic modified models for RC columns in terms of yielding strength, ultimate strength, pre-yielding stiffness, and ductility coefficient were established based on the Bayesian updating theory. Posterior distributions of the unknown model parameters were estimated using the Markov chain Monte Carlo (MCMC) algorithm, which provided insight into the mechanism of the dynamic effect on RC structural members. By comparing the predicted results with available experimental data, the accuracy and effectiveness of the proposed models were verified. It was found that the Bayesian-based models can obtain more-accurate predictions of the skeleton curve of RC columns under both uniaxial and biaxial dynamic loadings. Moreover, the superiorities of the Bayesian-based models over the non-Bayesian models were presented through quantitative comparison. The presented approach provides a valuable assessment of the dynamic behaviors of RC structural members, which can be used to improve the accuracy of the seismic response predictions of RC structures.

The fragility of concrete-filled steel tubular (CFST) frame structures with buckling-restrained braces (BRBs) subjected to multiple earthquakes is studied in this paper. First, a fiber beam element model with rate-dependent concrete and steel material properties is developed for CFST members and, then, the effect of the strain rate on the seismic response of the CFST frame structure is investigated numerically. The influence of BRBs on the seismic response of the CFST frame structure is then comparatively analyzed. The seismic responses of the CFST frame structure with BRBs under single mainshocks and earthquake sequences are investigated, and the fragility curves are generated using probabilistic seismic demand analysis. The obtained roof displacement and inter-story drift ratio (ISDR) of the structure decreased by 10.2% and 6.9%, respectively, when obtained while considering the strain rate effect, compared with those obtained without consideration of the strain rate effect. BRBs can effectively improve the seismic performance of the CFST frame structure in that the maximum roof displacement and ISDR can be reduced by 45.1% and 43.9%, respectively. Compared with those under single mainshocks, the maximum roof displacement and ISDR of the structure with BRBs under earthquake sequences significantly increase. The fragility of the BRB structure under earthquake sequences is more severe than that under single mainshocks. Therefore, the influences of the strain rate effect and earthquake sequence should be considered to realistically evaluate the seismic fragility of CFST structures.

This paper presents a comprehensive assessment method of the fragility of low‐rise cold‐formed steel (CFS) framed wall structures subjected to wind hazards considering the fragility of both the main structure and the cladding system. The effects of wind directions on the fragility of CFS framed wall structures were also studied. For the main structure, the fragility curve is established using the maximum interstory drift ratio (ISDR_max) as the performance index for assessing the wind fragility of the structure. For the cladding system, the probabilistic models of the wind load and the cladding component resistance are established based on Monte Carlo simulation, and then methods for the fragility assessment of single cladding components and the cladding system under wind hazards considering the influence of the number and arrangement of the cladding components are proposed. The results indicated that, under strong wind, the cladding system may be damaged before the required wind resistance capacity of the main structure is exhausted. In particular, the roof sheathing is the most prone to damage, followed by the stud wall. That is, before the main structure is severely damaged or collapses, the cladding systems may be severely damaged, rendering the structure unusable. Therefore, the comprehensive assessment of the fragility of this type of structure subjected to wind hazard considering the fragility of both the main structure and the cladding system is more accurate. This study is of great significance for the improvement of the wind resistance performance of CFS structures and the popularization of this type of structure.