Seismic Response Analysis of Long-span Cable-stayed Bridges Subjected to Multi-support Excitation

A long-span cable-stayed bridge often has multiple supports separated by certain distances. If a long-span bridge is located in a complex terrain with different local soil conditions, the spatial variability may result in quantitative and qualitative differences in seismic response as compared with those produced by synchronous motion at all supports. Therefore, how to simulate the ground motion propagating in the field soil becomes imperative and crucial. The conditional simulation method proposed by Vanmarcke et al (1993) is adopted in this study for simulating properly correlated earthquake ground motions at an arbitrary set of closely-spaced points. The absolute ground displacements at the different supports are then used as the essential seismic loading in the dynamic equilibrium equation which is solved by the Newmark direct integration method. The Stonecutters cable-stayed bridge located in Hong Kong is finally taken as an example to illustrate the conditional simulation of seismic ground motion and seismic effects on the bridge. The results show that the conditional simulation of seismic ground motion, considering wave-passage effect, incoherence effect and site-response effect, is important to reflect the spatial variability of ground motion. The computed seismic responses, including bending moment, stress, and displacement responses, also show that the spatial variability of ground motion shall be taken into consideration for the seismic response analysis of long-span cable-stayed bridges with multiple supports.