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Effects of in‐cycle strength degradation on collapse capacity of steel moment frames

In this study, the effects of in‐cycle strength degradation of steel moment connections are investigated on global behavior of multiple degree‐of‐freedom structures. Two types of degrading connection models are defined and compared with a bilinear non‐degrading model. Due to dispersion of the experimental test results on connections performance, two models are considered for each type. A probability assessment is carried out by implementation of incremental dynamic analysis to find the capacity of the structures for various performance levels. A sensitivity study is conducted on hysteresis parameters of connection models to investigate the effect of these parameters on global behavior of the structures. Due to increased dispersion of displacement demands observed in degrading cases, a reliability analysis is carried out to consider the effect of uncertainty on confidence level of the structures. Results show that in‐cycle strength degradation can lead to abrupt dynamic instability and as a consequence decrease in reliability of the system against collapse. Copyright © 2013 John Wiley & Sons, Ltd.