PROBABILISTIC DEMAND ASSESSMENT OF SEISMIC BASE-ISOLATED STRUCTURES IN OMMEDIATE OCCUPANCY PERFORMANCE LEVEL

Evaluation of isolated structures in the form of Performance-Based design framework would make greater understanding of behavior such these structures and give a quantitative idea about regulationʹs adequacy in preparing safety margin under extreme loadings especially in performance objects with lower damage states. Seismic demand analysis of Base-Isolated special moment steel Structures has been investigated in this paper. 4-, 6- and 8-storey of three dimensional designed structures has been modeled in OpenSees Platform. The structures were Analyzed and Designed based on ASCE 7-2010 standard, ANSI/AISC 360-10 and ANSI/AISC 341-10 Specifications and some two dimensional frames were adopted from these archetypes for Evaluation of the performance objective. Various Source of Nonlinearity such as Material and Geometric Nonlinearities have been Intended in Finite Element Models. To consider the uncertainty in one hand and create comprehensive fragility curve on the other hand, Incremental Dynamic Analysis (IDA) using Far Field Ground Motions Set has been utilized. The structure performance would be presented in terms of "fragility curves" and "limit state frequencies" for immediate occupancy performance object. Results show that the mean annual frequency of models are much lower than the Fixed-base ones. It can be observed that the ASCE 7-2010 Standard can provide a uniform risk in models with various type of configuration too.