The ATC-18 report, Seismic Design Criteria for Bridges and Other Highway Structures: Current and Future, was developed under a grant from NCEER and FHWA. Available through ATC. (Published, 1997, 151 pages)
ABSTRACT: ATC-18 presents the results of one component of the FHWA project DTFH61-92-00112, namely design criteria review. The overall scope of work on the ATC-18 project consisted of a review of current design practice and criteria, ongoing research in seismic design criteria development, and philosophies behind the seismically resistant design of highway structures including bridges, tunnels, and retaining structures. Particular attention was given to foundation design requirements. Roadbeds were excluded, however, because they are generally not the concern of structural engineering practitioners and researchers, the primary intended audience for this report.
The ATC-18 project team initially focused on a review of current design practice and criteria for new bridge design, as well as the philosophies on which they are based. This involved a review of existing U.S. standards along with the latest codes of Japan, New Zealand, and Europe. Guidelines developed for the Transportation Corridor Agencies (TCA) for Orange County, California, and in-progress work such as the new AASHTO Load and Resistance Factor Design (LRFD) Bridge Specifications were also reviewed. Issues that received attention included performance criteria, importance classification, definitions of seismic hazard for areas where damaging earthquakes have longer return periods, design ground motion, duration effects, site effects, structural response modification factors (R factors), ductility demand, design procedures, foundation and abutment modeling, soil-structure interaction, seat widths, joint details, and detailing reinforced concrete for limited ductility in areas with low-to-moderate seismic activity.
The ATC project team also reviewed information emanating from the ongoing ATC-32 project, an extensive effort under which ATC is reviewing and recommending revisions to Caltrans Bridge Design Specifications (Caltrans, 1993), which are a modified version of the 1983 AASHTO specifications and subsequent interim specifications dated 1984, 1985, and 1986. Issues under investigation in the ATC-32 project include performance criteria for bridges that consider the importance of the bridge, life-safety preservation in all earthquakes, and bridge functionality after lesser earthquakes; foundation and abutment design; concrete design; steel design; analysis methods; and bearing design.
The final phase of the ATC-18 project was to develop recommendations for the future direction of seismic code requirements for bridge structures in the United States. This was achieved by developing an outline of a future standard together with issues that need to be developed and resolved. An important part of the recommendations is a two-level design approach.
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