New Seismic Guide Specification Adopted for LRFD Design of Highway Bridges
At their annual meeting, held in July 2007, the AASHTO Subcommittee on Bridges and Structures voted to adopt a new seismic specification for the LRFD design of highway bridges. The new specification is largely based on the materials originally developed by the ATC-MCEER joint venture under Project NCHRP 12-49: Comprehensive Specifications for the Seismic Design of Bridges in 2003. The Subcommittee chose not to accept the 2003 recommendations as is. In 2004, MCEER initiated two exploratory tasks as part of its FHWA Highway Project to develop a road map for development and implementation of new criteria. Dr. Roy Imbsen, who is also an MCEER Advisory Panel Member, acted as PI on the tasks and subsequently led the consensus building and technical revisions that resulted in the new guide specification.
The approved two part ballot item updates the current force-based design specification to reflect the use of a 1,000 year return period and also presents a newly developed seismic guide specification that uses a displacement based approach. The vote was 47 states Yes, 1 state No, and 0 states abstaining. It was submitted to the full Subcommittee by Technical Committee-3 (T3) with unanimous support from T3 member states.