Tropical Storm-Induced Buffeting Response of Long-Span Bridges: Enhanced Nonstationary Buffeting Force Model

An enhanced nonstationary buffeting force model for calculating tropical storm (i.e., typhoon/hurricane)-induced buffeting response of long-span bridges is presented. The evolutionary power spectral density (EPSD) in the existing nonstationary tropical storm wind model is first revisited and enhanced by taking into consideration the recently-proposed typhoon turbulence spectra. A coherence transfer function matrix and time-dependent aerodynamic admittance function are introduced to eliminate the strip and quasi-steady theory assumptions by way of implementing wind tunnel measured span-wise and chord-wise coherence of aerodynamic forces. Finally, the nonlinearity in the buffeting forces resulting from the variations in the instant effective angle of attack and the nonuniform span-wise profile of the mean wind speed are considered in the enhanced model. The influence of the aforementioned enhancements in the nonstationary buffeting force model on the tropical storm-induced buffeting response of long-span bridges is assessed through the example of the Stonecutters Bridge subjected to Typhoon Dujuan. The results suggest that the enhanced EPSD model of tropical storm winds, nonlinearity due to the instant effective angle of attack, and the variations in the velocity span-wise profile slightly change the buffeting responses. However, introduction of the span-wise coherence of buffeting forces increases nonstationary extreme responses by 25-40%, and the time-dependent admittance function reduces the extreme responses by as much as 70%.