Energy-based fragility curves of building structures equipped with viscous dampers

Abstract

The performance of systems equipped with fluid viscous dampers (FVDs) has been extensively analyzed only by determining the deformations, accelerations, and forces. However, with current analysis and methodology for quantifying structural damage, focusing on energy as an evaluation criterion is conceptually very attractive. The energy concept is able to capture structural characteristics simultaneously as deformation, force, and the number of hysteretic loops. Therefore, the aim of this paper is to introduce a comprehensive investigation to estimate the probability of collapse (P[collapse]) of three steel buildings (3-, 9-, and 20-story) equipped with linear and nonlinear FVDs based on plastic energy demand EPD. To assess the seismic collapse, nonlinear static pushover analyses (NSPA) were utilized to compute the plastic energy capacity EPc with significant contributions of higher modes, and incremental dynamic analyses were performed subjecting 20-pairs of earthquake records to produce a response curve of EPD until it caused collapse. Then, the fraction P[collapse] at a given intensity level was be estimated when the EPD exceeds the EPC; subsequently, the analytical fragility curves were developed. The results demonstrate that the supplemental FVDs can substantially reduce (i.e., by 30–100%) the P[collapse]of steel buildings. P[collapse] based on EPD experiences lower values than those based on inter-story-drift demand (θD). In most cases based on EPD, buildings with nonlinear FVDs have a relatively lower P[collapse] than linear FVDs. Although, in the case of the θD, the linear FVDs are effective than nonlinear ones in reducing P[collapse].