Seismic Design

Abstract

The earthquake that occurred in Northridge, California, on January 17, 1994, greatly affected structural engineers in California and elsewhere. Vertical forces and ground motions induced by the earthquake were greater than had been experienced before. Newly built structures, designed according to then-current building codes, suffered damage severe enough to render them unusable. In one instance, apparently similar structures a block apart came through the quake with far different results. One structure suffered only superficial damage while the other had to be demolished, so poor was its condition. Though not initially evident, not only precast concrete structures, but cast-in-place concrete and structural steel buildings numbered equally among the casualties. Parking structures of all types, with their long spans and large plan areas, were among some of the spectacular failures. Until more evidence was discovered, the seismic performance of concrete parking structures, both precast and cast-in-place, in the Northridge earthquake came under heavy criticism in newspapers and technical journals.