Performance of bridges in the 1989 Loma Prieta earthquake – lessons for Canadian designers

Abstract

Damage to buildings and bridges during the October 17, 1989, Loma Prieta earthquake prompted site visits by the authors. This paper first reviews examples of the severe damage and the collapse of bridges in the 1971 San Fernando and 1987 Whittier Narrows earthquakes. The resulting changes to U.S. bridge design codes and the application of different types of restraining devices used to retrofit existing bridges are discussed. Examples of damage and collapse of bridges in the 1989 Loma Prieta earthquake are illustrated. The important roles played by the presence of soft soil, poor structural systems, and inadequate detailing are highlighted. The observed damage is used to illustrate the need to assess the seismic design provisions of the current CSA standard for the design of highway bridges. Concern over the presence of existing hazardous bridges in significant seismic zones in Canada is emphasized and a checklist for evaluating existing bridges is presented. Key words: seismic design, earthquake, evaluation, Loma Prieta, San Fernando, bridges, codes, retrofitting.