A novel modal combination rule under multi-component ground motion

Abstract

Traditional earthquake-resistant design philosophy involves estimation of peak elastic response for a specified seismic hazard, which in turn requires a modal combination rule for multi degree-of-freedom systems. Commonly used modal combination rule CQC3 estimates just the largest response peaks, while the other higher-order peaks are assumed to be of no significance. The CQC3 rule is based on use of white noise idealization of excitation and is therefore inappropriate for application when the dominant frequencies of the system are outside the frequency-band of significant energy in the excitation. Considering the possibility that structural damage in the post-yield regime can be correlated with the higher-order peaks, a new modal combination rule is developed for the ordered peak response of multi-storied buildings excited by the multi-component ground motions. The proposed rule is formulated using the stationary random vibration theory without any assumption regarding the cross-correlation between different modes and the nature of the input excitation. Results show that the proposed rule outperforms the CQC3 rule, and in addition, estimates the higher-order peaks in a simple way with a significant level of accuracy comparable to that for the largest peak. © The Society for Experimental Mechanics, Inc. 2012.