Application and verification of random vibration method for simply supported beam bridge crossing strike slip fault

Abstract

This paper proposes a model for spatially varying fault-crossing ground motions, incorporating pulse effect and permanent ground surface displacement due to directivity and fling-step effect. The model is constructed through a superposition of high- and low-frequency components in the frequency domain. To develop a spatially varying fault-crossing ground motion model, the power spectral density (PSD) of a low-frequency single-pulse velocity is combined with a high-frequency PSD. This model captures the effect of local site conditions, wave passage, and coherence on the structural responses of fault-crossing bridges. A theoretical stochastic analysis scheme based on the pseudo-excitation method (PEM) is then introduced for seismic analysis of simply supported bridges subjected to spatially varying fault-crossing ground motions. The accuracy and efficiency of this PEM are verified through comparative analysis with the nonlinear time history method (NTHM) using the equivalent ground motion inputs. These inputs are derived by transforming the proposed fault-crossing seismic model from the frequency domain into time-domain ground motion time histories. To facilitate the use of the proposed spatially varying fault-crossing ground motion model and efficient PEM in stochastic seismic analyses of complex, critical bridges, the scheme is implemented and verified within a general finite element platform. It is subsequently applied to a fault-crossing simply supported bridge under spatially varying ground motions, accounting for pulse effect and spatial variability. Conclusions are drawn that support applications in the seismic design and analysis of fault-crossing bridges exposed to the high-velocity pulse effect and multiple spatially varying ground motion excitations.