Effect of degradation on collapse margin ratio of steel moment frames

Although several studies have investigated the effect of degradation on the behavior of structures, investigations on collapse margin ratios are rare in the literature. In this study, the effect of strength and stiffness degradation on collapse capacity of steel moment frames is investigated. The aim is to determine margin of safety against collapse using a probabilistic approach. For this reason, 14 moment frames are designed including 4 long period and 3 short period models with 5 and 8m bay length. These buildings are representative of common office and residential buildings built in cities. Buildings are designed according to ASCE7-05 specifications. In the first stage, effective seismic parameters are calculated using a pushover analysis. In the second stage, collapse performance levels are determined using incremental dynamic analysis by considering seismic excitation uncertainties. Results show that the overstrength factor that is recommended by ASCE code is not always conservative. Overall, structures designed with common building codes show acceptable margin of safety against collapse.