Seismic vulnerability of older reinforced concrete frame structures in Mid-America

摘要

This research quantifies the seismic vulnerability of older reinforced concrete frame structures located in Mid-America. After designing a representative three-story gravity load designed reinforced concrete frame structure, a nonlinear analytical representation was used evaluate inter-story drift demands from simulated earthquake time histories that were representative for the region. Limit state story drift capacities were identified for FEMA 273 guidelines, nonlinear pushover analyses, and incremental dynamic analyses. Integrating these two quantities allowed for the creation of fragility curves which relates the probability of exceeding a particular limit state given an imposed spectral acceleration at the fundamental building period. These curves were then used to evaluate the seismic vulnerability of the representatively designed structure. The structure as originally designed was found to be inadequate to resist large lateral loading that would be typical for the Memphis area. So structural retrofit performed by increasing the column-to-beam strength ratio was evaluated by increasing the strength of the column members in the analytical model. The first retrofit raised the column-to-beam strength ratio to 1.2, which is currently required by the ACI code provisions. The second retrofit raised the column-to-beam strength ratio to 1.8, as suggested in previous studies. The story capacity, demand, and fragility curves were once again created for these retrofitted structures. Comparison of these fragility curves is discussed in relation to the retrofit strategy of column strengthening for older reinforced concrete frame structures in Mid-America.