Seismic design criteria for transporation structures

Seismic criteria for the design of transportation stuctures have evolved slowly since their inception in the early 1940s. Although seismic design criteria are far more sophisticated than they were in the 1940s, the minimum levels of lateral strength in 1990 are virtually identical to the 1940 levels over a substantial range of fundamental period. Many of the freeway structures in the San Francisco Bay Area were designed in the 1950s and early 1960s. The partial collapse of the Cypress Street viaduct (designed in 1952) during the 1989 earthquake has raised concerns regarding the seismic strength of these freeway structures and therefore the seismic criteria to which they were designed. Furthermore, the damage sustained by freeway structures in San Francisco that were designed after 1971, to strength levels similar to those specified in 1990, has raised serious questions regarding current seismic design criteria for transportation structures.