Sensitivity of The Response of Box-Girder Seat-Type Bridges to the Duration of Ground Motions Arising from Subduction Earthquakes

The design practice of Box-Girder Seat-Type (BGST) bridges in Western U.S. has significantly evolved due to the advances in modeling and analysis techniques. These advanced procedures help engineers and researchers to better understand the behavior of BGST bridges during seismic excitations. Within this setting, the combined effect of the duration of ground motions and the spectral shape on the response of bridges has not been exclusively studied. This study investigates the effect of duration of ground motions on the response of BGST bridges through a series of comprehensive statistical analysis. Three-dimensional finite element models of two real BGST bridges are analyzed using a set of 100 ground motions obtained from subduction sources. Through the statistical procedure of Step-wise nonlinear regression-and other statistical measures-the sensitivity of Engineering Demand Parameters (EDP) of bridges to various Intensity Measures (IM) including Arias Intensity (I0), RotD50 spectral acceleration at the bridge's natural period (Sa), Significant Duration (D5-95), mid-frequency () and derivative of the mid-frequency (') are evaluated. Specifically, the impact of Significant Duration (D5-95) of the ground motions is studied. Results indicate that the Significant Duration (D5-95) of the ground motions ascending from the subduction sources is significantly associated with the response of bridge structures and can increase the accuracy of bridge response characterization if considered alongside Sa or I0. Furthermore, it is concluded that the duration of subduction zone ground motions has a noteworthy impact on the behavior of BGST bridges under seismic excitations and must be given proper consideration in the design and analysis of such bridges particularly during the ground motion selection process.