Nearly ten years have passed since the disastrous Loma Prieta earthquake and over nine years have passed since the Governor's Board if Inquiry into the cause of highway structure failures during that earthquake issued its final report with the warning title Competing Against Time. It is the purpose of this paper to discuss the Seismic Design Specifications and Construction Details that have been developed in California as lessons were learned from the 1971 San Fernando earthquake and subsequent seismic events; and to discuss the unprecedented research program that has provided the bridge design community the assurance that the new specifications and details perform reliably. The Calilfornia Department of Transportation (Caltrans) staff engineers, consulting firms, independent Peer Review Teams, and university researchers have cooperated in this program of Bridge Seismic Design and Retrofit Strengthening to meet the challenge presented in the Board of Inquiry report. The nine-year old Seismic Advisory Board has been an invaluable asset in reviewing the performance criteria, design specifications, and design procedures for both new design and retrofit strengthening of older, non-ductile bridges. In many instances, the Advisory Board positively influenced management decisions to continue financial support of a strong research program to support seismic design and retrofit through its recommendations to the Director of Transportation.

The success of the Bridge Seismic Design and Retrofit Program and the success of future seismic design for California bridges is based, to a large degree, on the accelerated and "problem-focused" seismic research program. That program has been supported at a level more than ten times the pre Loma Prieta level of financial support for all bridge research. The Department has been able to sustain the necessary high level of research support over the past ten years and has adopted a commitment for that level of funding for the foreseeable future. To date, over $40 million U.S. have been expended in this research and proof testing program.

Until recent years, most other states in the United States have not been concerned with seismic design for bridges. However, some 37 states in the U.S. have some level of seismic hazard. The American Association of State Highway and Transportation Officials (AASHTO) is the agency responsible for development of bridge design specifications for nationwide use. AASHTO has typically adopted seismic design criteria modeled after those developed in California. Understandably, there are hundreds of bridges in these other states which have been designed to seismic criteria that are not adequate for seismic forces and displacements that we know today. The seismic retrofit details designed by the California bridge engineers can be of great benefit tothose states who are faced with seismic threats of lesser magnitude, with little financial support for seismic retrofitting, and much less for research and seismic detail development.

The greatest number of large scale tests have been conducted to confirm the calculated ductile performance of older, non-ductile bridge columns that have been strengthened by application of structural steel plate, prestressed strand, epoxy-fiberglass, and carbon fiber composite jackets to provide the confinement necessary to insure ductile performance. Since the spring of 1987 the researchers at UC San Diego have completed more than 100 sets of tests on bridge column models.

The two major considerations in seismic design of foundations are ground motion and foundation and substructure interaction. Caltrans adopted a site specific seismic design philosophy shortly after the 1971 San Fernando earthquake. For the average smaller freeway structures we use the Maximum Credible Earthquake (MCE) for determining the seismic design forces. For major structures we use a site specific probabilistic hazard analysis to determine the most probable design earthquake spectra.

Procedures have been developed to provide for large ground movements in the deck joints and hinges. These details are designed to prevent superstructure elements from collapsing, even though joints may open as much as three feet.

Much research has gone into the development of joint shear, torsion, and moment reinforcement for the large joints common in bridge superstructures.

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