Title: Upgrading Seismically Vulnerable Bearings With Lead-Filled Elastomeric Bearings
Author(s): Ronald L. Mayes, Trevor E. Kelly, and Lindsay R. Jones
Publication: Symposium Paper
Appears on pages(s): 49-70
Keywords: base isolation; bridge bearings; earthquake-resistant structures; energy dissipation; plastics, polymers, and resins; renovating; Structural Research
Bridge failures in past earthquakes have indicated three major problems with existing bridges. The first is the vulnerability of existing rocker and roller-type bearings, and this is coupled with inadequate supportlengths for superstructure girders. The third problem area is the inadequate strength and ductility capacity of supporting superstructures. By replacing vulnerable rocker and roller bearings with lead-filled elastomeric bearings, an effective and economical solution to all three deficiencies can be obtained by utilizing the base isolation and energy-dissipating characteristics of the bearings. The paper discusses the basic concept and philosophy of the base isolation design concept and outlines its application to a recently completed project--the Caltrans Sierra Point Overhead seismic retrofit project. This is an eight-span skewed bridge that has recently been retrofitted using base-isolation concepts. In its "as-built" condition, it was capable of resisting less than 25 percent of the Caltrans design ground motion for the site. Replacement of the existing pot bearings with lead-rubber bearings reduces the forces transmitted into the weak columns by a factor of 6--thus enabling the bridge columns to respond elastically to the design ground motion.