Conditionally simulating nonstationary typhoon winds with time-varying coherences for long-span bridges

Typhoon winds near its external eye wall are not only strong but also nonstationary with time-varying coherences. This study proposes a conditional simulation method for multivariate nonstationary typhoon winds with time-varying coherences for long-span bridges. The Kriging method for conditional simulation and the time-varying wind spectrum and coherence are first introduced. The decomposition of the time-varying spectrum matrix is then discussed in order to obtain the time-varying correlation functions. It is found that the conventional Cholesky decomposition and the proper orthogonal decomposition (POD) are not suitable and only the square root decomposition (SRD) is appropriate for the decomposition of the spectrum matrix with time-varying coherences. Based on the field-measured nonstationary typhoon wind time histories and the time-varying spectrum and coherence models established for the Stonecutters cable-stayed bridge during Typhoon Hato, the proposed conditional simulation method is finally applied to the bridge and validated by comparing the simulated typhoon wind time histories with the measured ones as well as the unconditional simulation results. The comparative results demonstrate that the conditionally simulated wind time histories are similar to the measured ones and that the proposed conditional simulation method can be used to provide a better typhoon wind field than the unconditional simulation method.