On June 1-5, 2003, the American Association of State Highway and Transportation Officials (AASHTO) Subcommittee on Bridges and Structures held their 2003 Annual Meeting in Albuquerque, New Mexico. Rick Land, State Bridge Engineer from Caltrans, chaired the Technical Committee session for Seismic Design (T-3).
The formal agenda included a presentation by Ian Buckle, Technical Director of MCEER’s Highway Project, sponsored by the Federal Highway Administration (FHWA). He gave an overview of the new “Seismic Retrofitting Manual for Highway Structures” which is to be published later this year. The manual consists of two parts: Part 1- Bridges and Part 2 – Retaining Structures, Slopes, Tunnels, Culverts, and Pavements.
Chairman Rick Land gave a presentation on the technical committee’s effort to update the national guidelines for the seismic design of highway bridges. He summarized the discussions and consensus of eleven states represented at a workshop sponsored by FHWA earlier in the year. Issues to be resolved relate to the selection of return period, the apparent complexity of the existing draft guidelines, and the area of influence, complexity and availability of ground motion maps. T-3 heard a proposal for moving ahead with the “NCHRP 12-49 Guidelines for Seismic Design Highway Bridges” and another that would model the guidance on the format recently adopted by South Carolina.
Rick suggested that until new guidance is adopted by AASHTO, states have three alternatives for seismic design:
Continue to use the specification in AASHTO Standard Specification Division 1A. He cautioned that in this case, the 1998 USGS maps must be used.
Use MCEER’s “Recommended LRFD Guidelines for Seismic Design of Highway Bridges” available later this summer from MCEER or the Applied Technology Council (see "ATC/MCEER Joint Venture Publishes New LRFD Guidelines for Bridges").
Use the version of the guidelines that was proposed as agenda item #3 at the 2002 AASHTO Bridge Engineers’ meeting. This is available to states upon request. Inquiries should be made to Rick Land.