Seismic Evaluation of Older Concrete Frame, Frame-wall, and Bearing Wall Buildings for Collapse Potential-ATC 78

摘要

The seismic life safety risk from older concrete buildings, particularly frames, is well known. Current evaluation methods based on component performance are reasonable to measure damage, but conservative to predict global collapse. For several years, FEMA, through ATC (ATC 78), has sponsored development of a simplified method to estimate the probability of collapse that can be used to rank older concrete buildings for the purpose of setting priorities for mitigation and identifying the truly dangerous ones. A probabilistic collapse evaluation method for frame buildings was completed in early 2015 and tested by 15 engineering firms. Based on those tests on real buildings, improvements have been made and the methodology has been extended to consider the presence of structural walls and further tests of the methodology on real buildings have been completed. The methodology estimates the probability of story collapse based on story drift demand and gravity load carrying capacity and associated uncertainties. The goal was to develop an evaluation methodology that is comparable in effort to ASCE 41, Tier 2, but yields gradations of risk, rather than pass/fail results. Building jurisdictions (or owners of large inventories) are expected to be able to use the evaluation results to prioritize mandatory mitigation, or to select a subset of high risk buildings for mandatory mitigation.