Design of passive control system for seismically excited cable-stayed bridges

Abstract

In this dissertation, the design procedure and guidelines of lead rubber bearing (LRB) are proposed and the effectiveness of designed LRB is investigated for seismically excited cable-stayed bridges. Furthermore, additional control device, i.e. viscous damper (VD), is considered to improve the control performances. The LRB is widely used for the seismic isolation system to control responses of buildings and short-span bridges under earthquakes because these provide structural support, base isolation, damping and restoring forces in a single unit. The most important feature of the seismic isolation system for short-span bridges and buildings is lengthening the natural period of structures. However, the seismic characteristics of long-span bridges such as cable-stayed bridges are different from those of short-span bridges and buildings, and these bridges have very complex behavior in which the vertical, translational and torsional motions are often strongly coupled. For these reasons, it is conceptually unacceptable for long-span bridges to use directly the recommended design procedure and guidelines of LRB for short-span bridges and buildings. Therefore, new design approach and guidelines are required to design LRB for cable-stayed bridges. Considering important responses of cable-stayed bridges, the design index (DI) is proposed to design LRB. The proper LRB is selected when proposed DI is minimized or converged for variation of properties of LRB. The design results show that the damping and energy dissipation effect of LRB are more important than the shift of the natural period of structures for cable-stayed bridges. And the control performance of designed LRB is also verified. The sensitivity analyses of properties of LRB are conducted for different characteristics of input earthquakes. The performance of designed LRB is not changed significantly for different characteristic of input earthquakes and thus the robustness of designed LRB is verified for differen...