Revision and Upgrading of Seismic Design Specifications
Richard V. Nutt
Appears on pages(s):
bridges (structures); building codes; dynamic tests; earthquake-resistant structures; structural design; Design
Applied Technology Council (ATC) is conducting a California Department of Transportation (Caltrans) sponsored project to review and revise existing standards, performance criteria, specifications, and practices for the seismic design and construction of new bridges structures within California. The goal is to provide standards and criteria that will insure that California bridge structures of all types perform well in earthquakes. Specifically, as affirmed by the Governor following the 1989 Loma Prieta earthquake, all transportation structures must be seismically safe and important transportation structures must maintain their function after earthquakes. The project builds on developments in bridge seismic design that have been made over the past 20 years. It uses results from current research plus observations made in recent earthquakes to identify several significant improvements that can be made to the current Caltrans Bridge Design Specifications (BDS). At the present time, a draft revised BDS and Commentary have been developed. The revised BDS is based on new performance criteria that was developed by Caltrans, its independent Seismic Advisory Board, and ATC. Specific improvements to design procedures are made in several areas, including seismic loading, foundation design, dynamic analysis, and concrete and steel design. The project is ongoing and the draft BDS will continue to be evaluated and, most likely, revised as the project continues. In addition to an overall review by the panel of 13 technical advisors selected for this project, independent external reviews will be conducted by selected experts in various aspects of seismic design. Several trial designs will also be performed using the draft provisions. The results of these trial designs will help point out deficiencies in the draft specifications that can then be improved prior to their being adopted for general use. In the end, this project will produce bridge seismic design criteria that reflect a consensus of expert opinion and provides a uniform approach to bridge seismic design in California.