Evolutionary Spectra-Based Time-Varying Coherence Function and Application in Structural Response Analysis to Downburst Winds

Priestley's oscillatory process theory is widely employed to model nonstationary excitation. However, the underlying coherence function of this theory can only be time invariant. To take into account the time-varying coherence function, the Sigma-oscillatory process theory and Wold-Cramer decomposition model have been introduced in literature. Due to its straightforwardness, the Wold-Cramer decomposition model is used in this study. Based on the Wold-Cramer decomposition model of nonstationary wind excitation, the alongwind response analysis framework of tall buildings to nonstationary winds is presented. The time-varying coherence function models of two downburst events are developed using the measured downburst data. The influence of time-varying coherence of nonstationary winds on the alongwind tall building response is investigated. Numerical examples show that the time-varying coherence function may lead to larger structural response compared with the corresponding time-invariant coherence function model. Considering the large variation of nonstationary downburst winds, the observation drawn from this study should be further evaluated using more measurement wind data. It can be expected that the time-varying coherence function may play an important role in better modeling the nonstationary winds and their load effects on structures.