Abstract:Performance-based seismic design theory has received considerable attention from scholars since its proposition in the 1990s. Collapse evaluation is an important part of performance-based seismic design. In this respect, although current Chinese seismic design codes for building structures have particular requirements and analytical approaches are used to prevent building collapse, they do not provide a quantitative index for the collapse-resistant capacity. Therefore, the collapse-resistance performance of structural systems, the seismic fragility, and collapse capacity of a reinforced concrete(RC) frame structure were investigated based on incremental dynamic analysis. A five-story and three-bay reinforced concrete frame structure, which was designed based on the current Chinese codes, was selected as a study case to conduct a seismic fragility assessment and collapse evaluation. Considering the uncertainty of ground motion, a mass incremental dynamic analysis was conducted for an existing building based on the current codes. In the incremental dynamic analysis, the intensity of a single motion was increased according to a series of intensity measures, under which an elastic-plastic dynamic analysis was performed. The relationship between the engineering demand parameters and the intensity measures was thus obtained, and on the basis of incremental dynamic analysis curves, the seismic demand probability and seismic capacity were then established. Furthermore, collapse evaluation was quantitatively performed based on fragility curves, which enable an estimation of the possible damage to buildings that could occur during an earthquake and have important significance in the improvement of seismic capacity and disaster prevention mitigation work. Finally, a comparison was made between a fiber model and a plastic hinge model based on PERFORM-3D. The fragility curves provide a quantitative evaluation under a specific ground motion intensity, and results show that RC frames designed in accordance with the current code have a small collapse probability during a rare earthquake, and that they meet the requirements of a 3-level design. The fiber and plastic hinge models have similar performance at a low spectral acceleration of motion; however, differences between the two models were evident with an increase in the spectral acceleration. Based on the fiber model, a nonlinear simulation of the RC frame in a collapse evaluation was relatively conservative and had a higher safety margin compared to the plastic hinge model. Therefore, in consideration of efficient modeling, the fiber model provided by PERFORM-3D is a better choice as compared to the plastic hinge model.
