A Practice-Oriented Approach for Probabilistic Seismic Assessment of Building Structures

Abstract

A relatively simple probabilistic approach for the seismic performance assessment of building structures combines the SAC-FEMA method, which is a part of the broader PEER probabilistic framework and permits probability assessment in closed form, with the N2 method, which is based on the pushover analysis of a multi-degree-of-freedom model and the response spectrum analysis of an equivalent single-degree-of-freedom (SDOF) model. In the probabilistic approach the most demanding part of the PEER probabilistic framework, i.e. the Incremental Dynamic Analysis (IDA), is replaced by the much simpler Incremental N2 (IN2) analysis which requires less input data and less effort but, nevertheless, generally provides an acceptable accuracy. The incremental N2 (IN2) curve is intended to approximate a summarized IDA curve. Predetermined default values for dispersion measures are needed for the practical implementation of the simplified approach. In the paper, the simplified approach is summarized and applied to the seismic performance assessment of two variants of an asymmetric three-storey reinforced concrete frame building. The first variant represents a building designed for vertical loads only, without consideration of seismic codes (the “SPEAR building”, tested and analyzed within the European project SPEAR), whereas the second variant represents a building with the same geometry but designed according to Eurocode 8 (EC8) considering design ground acceleration on rock of 0.25g and soil type C. The probabilities of exceedance of the near collapse (NC) limit state are estimated and discussed. The results of the analyses indicate that the building designed according to the EC8 is able to survive a ground motion which is about 3.1 times stronger than in the case of the SPEAR building, while the probability of the exceedance of the NC limit state is about 25 times smaller.