Modeling and analysis of cable vibrations in cable-stayed bridges under near-fault ground motions

To represent the cable vibrations of cable-stayed bridges under earthquake actions, this study proposes to model each cable using the multiple nonlinear truss elements with an initial strain and an equivalent number of elastic beam-column elements with a zero cross-sectional area in parallel. The novel method facilitates the bridge model to reach the equilibrium state under the dead loads and enables to take into account the cable nonlinear vi-brations as well as cable loosening under seismic events. Then the seismic responses of a case cable-stayed bridge are investigated under near-fault ground motions. It reveals that both the external vibrations and parametric vibrations might develop in the stay cables, depending on the cable locations and earthquake input directions. The traditional method, using one truss element to represent the cable, would for most cases overestimate the seismic responses of the cable, the tower and the deck. Especially, the overestimation is significant under the longitudinal and vertical earthquake excitations as the stiffening effect significantly reduces the nonlinear parametric vibrations of stay cables. The exception is when the bridge is subjected to the transverse seismic inputs only where the external vibrations increase the cable force vibration amplitudes. The present study highlights the importance of modelling the stay cables with multiple elements and including the bi-directional or tri-directional earthquake inputs when conducting seismic analyses of cable-stayed bridges.