Development of fragility curves in adjacent steel moment-resisting frames considering pounding effects through improved wavelet-based refined damage-sensitive feature

Fragility curves present useful information related to earthquake-induced probability assessment of steel moment-resisting frames (MRFs) and determine the probability of the damage exceedance at different floor levels of MRFs. The review of the literature shows that most of the previous studies dealing with the fragility curves were based on conventional measures, such as spectral acceleration at the first mode period, peak ground acceleration, and/or engineering demand parameters (e.g. maximum story drift ratio (max SDR)) to estimate the structure's damage state. In this article, a new approach is developed to map the fragility curves in adjacent MRFs including effects of pounding through improved wavelet-based refined damage-sensitive feature (WB-rDSF) which considers contributions of the upper modes. Morlet and complex Morlet (cmorf(b)-f(c)) wavelets, which is known as extremely precise rDSF, were extended to map the fragility curves. The correlation coefficient between rDSF and max SDR is evaluated as a criterion to determine the efficiency of wavelets-based damage index (WB-DI). The steel MRFs with six and nine stories are selected to implement the proposed approach concerning adjacent MRFs prone to structural pounding during earthquakes. Acceleration responses recorded at the roof of both colliding and non-colliding MRFs were determined using incremental dynamic analysis (IDA) including different seismic ground motion records to formulate the damage index. Moreover, the first mode structural period, used in assembling the WB-rDSF, is estimated via auto-regressive moving average with exogenous input method along with a stabilization diagram. The results show that the fragility curves, derived from cmorf(b)-f(c) WB-rDSF for both colliding and non-colliding MRFs due to higher correlation coefficient, have lower damage probabilities and are more efficient than the estimated fragility curves based on Morlet WB-rDSF which consider only the structural period of the first mode. Furthermore, due to the pounding phenomenon, the lower MRF experiences more damages with a larger probability.