Most bridges in the U.S. are designed to resist seismic demands in accordance with either the AASHTO LRFD Bridge Design Specifications or the AASHTO Guide Specifications for LRFD Seismic Bridge Design. These documents are intended for conventional highway bridges. Long-span, non-conventional structures, such as cable-supported superstructures, bridges with truss tower substructures, and arch bridges do not typically respond to earthquakes in the same manner as conventional highway bridges. These bridges are not directly addressed in the AASHTO specifications.
When provisions of existing AASHTO seismic specifications and guidelines are applied to non-conventional bridge structures, the resulting design may not address the intended performance objectives effectively and economically. Accordingly, bridge owners and their design teams typically develop their own project-specific seismic design criteria for non-conventional bridges. Numerous bridges have been developed with unique project specific criteria, but these criteria are outside of the current national standards. Owners and designers recognize this challenge and have approached AASHTO requesting that this issue be addressed in the national seismic standards.
The objective of this synthesis is to document current seismic design criteria for non-conventional bridges. The report will synthesize and present the information documented in a framework that will be useful to bridge owners and to aid the development of national guidelines. Knowledge gaps and research needs will also be identified.
This synthesis will address the following areas (but is not limited to):
• Criteria from a representative sample of non-conventional bridges addressing a range of seismic hazard, site response characterization, bridge type, bridge design standards (e.g., AASHTO, Euro code, state agency), bridge design performance objectives including intended behavior of the seismic resistance systems, and structural analysis techniques;
• Competing load cases or other extreme events that influenced or controlled the design;
• Design considerations related to uncertainty in seismic loading and response of the bridge (e.g., consideration of events exceeding the design event, meeting performance objectives for smaller events);
• Common approaches, challenges, and lessons learned in developing seismic criteria and performance objectives; and
• Agency policies and guidelines for seismic design of non-conventional l bridges.
Information will be gathered through literature review, a targeted survey, and case examples. A survey must achieve an 80% response rate. The principal investigator will describe the methodology to be used for identifying the representative sample of bridges mentioned above, and for collecting the relevant data, in the project work plan. The report will identify knowledge gaps and suggested research to address those gaps.
• AASHTO Guide Specifications for LRFD Seismic Bridge Design (2011)
• AASHTO LRFD Bridge Design Specifications (2014)
• Caltrans Seismic Design Criteria (SDC) Version 1.7 (2013)
• South Carolina Department of Transportation Seismic Design Specifications for Highway Bridges Version 2.0 (2008)
• Recommended LRFD Guidelines for the Seismic Design of Highway Bridges MCEER/ATC-49 (2003).
• AASHTO Seismic – Applicability to Towers and Arches - a presentation to AASHTO SCOBS seismic committee T-3 by David Goodyear, TY Lin International (2014)
• NCHRP 12-06
Jo Allen Gause
First Panel: October 19, 2017, Washington, DC
Teleconference with Consultant: November 9, 2017, 3:00 p.m., ET
Second Panel: July 24, 2018, Washington, DC
Ian Buckle, University of Nevada - Reno
Xiaohua Hannah Cheng, New Jersey DOT
Lee Marsh, BergerABAM
Lucero E. Mesa, South Carolina DOT
Thomas A. Ostrom, California DOT
Richard A. Pratt, Alaska DOT and Public Facilities
Anne M. Rearick, Indiana DOT
Sheila Rimal Duwadi, Federal Highway Administration
Dayi Wang, Federal Highway Administration-Office of Bridges & Structures
Stephen F. Maher, Transportation Research Board