PRACTICE OF BRIDGE DESIGN BEFORE LOMA PRETA AND AFTER NORTHRIDGE EARTHQUAKES

The state of seismic analysis and design before and after the Loma Prieta (۱۹۸۹) and Northridge (۱۹۹۴) events is presented from the viewpoint of a practicing bridge engineer in the State of California, Department of Transportation (Caltrans). The comparison of the analyses and designs performed before ۱۹۸۹ event versus those of Summer ۹۴ is a good indication of the changes brought about because of these particular carthquakes.The traditional approach is presented first, followed by improvements to different aspects of the design procedures in approximate chronological order. Improvements in strength, ductility, and detailing of bridge systems are explained. Solutions are proposed for seismic design of new bridges and retrofit of existing bridges.