Earthquake ground motion spatial variation effects on seismic response control of Cable-Stayed Bridges

Abstract

The spatial variability of the input ground motion at the supporting foundations plays a key role in the structural response of flexible long span bridges such as cable-stayed and suspension bridges, therefore the spatial variation effects should be included in the analysis and design of effective vibration control systems for such horizontally extended structures. The control of long-span bridges represents a challenging and unique problem, with many complexities in modelling, control design and implementation, since the control system should be designed not only to mitigate the dynamic component of the structural response but also to counteract the effects of the pseudo-static component of the response. The feasibility and efficiency of seismic control systems for the vibration control of cablestayed bridges are investigated. The spatial variability effects of the ground motion in the analysis of seismically controlled long span bridges is considered based on the decomposition of the total structural response into a dynamic component and a pseudostatic component. The assumption of uniform earthquake motion along the entire bridge could be unrealistic for long span bridges since the differences in ground motion among different supports due to travelling seismic waves may result in quantitative and qualitative differences in seismic response as compared with those produced by uniform motion at all supports. Comparison of the seismic response of the controlled cable-stayed bridge due to non-uniform input of different wave propagation velocities with that due to uniform input demonstrates the importance of accounting for spatial variability of excitations.