Base Isolation Concepts for Seismic Bridge Retrofitby Ronald L. Mayes, Dynamic Isolation Systems, Berkeley, CA, USA,
Lindsay R. Jones, Dynamic Isolation Systems, Berkeley, CA, USA,
Trevor E. Kelly, Dynamic Isolation Systems, Berkeley, CA, USA,
Martin R. Button, Dynamic Isolation Systems, Berkeley, CA, USA,
Abstract: Failures in past earthquakes have indicated three major problem areas with existing bridges. The first is the vulnerability of existing rocker and roller type bearings and this is coupled with inadequate support lengths for superstructure girders. The third problem is inadequate strength and ductility capacity of supporting substructures. Lead-rubber bearings provide both base isolation and energy dissipation characteristics that decrease superstructure displacements and provide a force-limiting mechanism for the supporting substructure. In the three-span bridge example the impact of different seismic zones was assessed and it is shown that bearings designed for one seismic intensity are satisfactory for other levels. The Sierra Point Overhead bridge is capable of resisting less than 25% of the CalTrans design ground motion for the site which is close to a major fault. Incorporation of lead-rubber bearings reduces the forces transmitted into the columns by a factor of 5.
Subject Headings: Base isolation | Seismic tests | Bridge design | Rehabilitation | Seismic effects | Bridges | Energy dissipation | Rubber | Superstructures | Substructures | New Zealand
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