EVALUATION OF COLLAPSE MARGIN FOR RC FRAMES DESIGNED BASED ON IRANIAN SEISMIC CODE

One of the main goals of the seismic design philosophy is to design structures so that the structural collapse to be prevented under intense ground motions. Therefore it is important to quantify the margin of safety against structural collapse. Nonetheless due to high level of nonlinearity involved in vicinity of structural collapse the analytical modeling and assessment is complex and demanding, and includes several sources of uncertainties. Although this issue has attracted considerable interest among seismic engineers and researchers during several past decades no standard method has been introduced. During the past few years FEMA has published a guideline for quantification of the building Seismic Performance Factors, i.e. response modification factor, overstrength factor and displacement amplification factor (FEMA, 2009). As part of the proposed methodology one can assess the structural collapse potential. The approach includes a combination of incremental nonlinear dynamic analysis (Vamvatsikos and Cornell, 2002) and suggested criteria based on semi-probabilistic method to evaluate Collapse Margin Ratio (CMR). The main objective of this research is to study the collapse margin ratio for reinforced concrete frame buildings designed according to Iranian seismic standard (Standard 2800). Incremental dynamic analysis (IDA) is carried out using 22 scaled natural ground motion records. The study includes RC moment resisting frames with 3, 6 and 10 stories considering two types of soil classifications (Type II and III) and two alternatives of ductility levels (Intermediate and high ductilties), according to standard 2800. It is concluded that the RC frame structures designed based on the Iranian Seismic code generally have sufficient margin against collapse based on the FEMA P695 approach. However the actual margin of collapse varies depending on the characteristics of the structures