Equivalent Static Wind Loads for Buffeting Response of Bridges

In current design practice, the dynamic wind loads are described in terms of the equivalent static wind loads based on the gust response factor. This approach results in a distribution of the equivalent static loading similar to the mean static wind load distribution, which may not always be a physically meaningful and realistic load description. In this paper, the equivalent static load representation for multimode buffeting response of bridges is formulated in terms of either a weighted combination of modal inertial load components, or the background and resonant load components. The focus of the present study is on the determination of weighting factors of equivalent static load components in which the correlation among modal response components due to structural and aerodynamic coupling effects is taken into consideration. It is noteworthy that the equivalent static load distributions vary for each response component. The proposed approach particularly helps in extracting design loads from full aeroelastic model test results by expressing the dynamic loads in terms of the equivalent static loads. This facilitates in drawing useful design input from full aeroelastic tests, which have been employed mostly for monitoring the response of bridge models at selected locations. A simplified formulation is also presented in a closed form when wind loading information is available and coupling in modal response components is negligible, which can be very attractive for the preliminary design application. Examples are presented to illustrate modeling of the equivalent static loading and to demonstrate its effectiveness in bridge design.