The American Association of State Highway and Transportation Officials recently released two new bridge design publications: “Guide Specifications for LRFD Seismic Bridge Design, 3rd Edition,” and “Guidelines for Performance-Based Seismic Design of Highway Bridges, 1st Edition.”
[Above image by AASHTO]
AASHTO said the new “Guide Specifications for LRFD Seismic Bridge Design, 3rd Edition,” are for use in the design and construction of conventional bridges to resist the effects of earthquake motions. They have been approved as an alternative to the seismic provisions in the AASHTO load and resistance factor design or LRFD Bridge Design Specifications, 9th Edition, and differ from those provisions in the use of displacement-based design procedures, rather than the traditional force-based R-Factor method.
The guide specifications contain detailed guidance and commentary on earthquake-resisting elements and systems, global design strategies, demand modeling, capacity calculation, and liquefaction effects, AASHTO said, with capacity design procedures underpinning the guide’s methodology – including prescriptive detailing for plastic-hinging regions and design requirements for capacity protection of those elements that should not experience damage.
Meanwhile, the new “Guidelines for Performance-Based Seismic Design of Highway Bridges, 1st Edition,” represents the first implementation of performance-based seismic design for bridges in the United States.
The aim of this guide is to provide bridge designers and owners with a methodology for selecting the appropriate level of performance for a given bridge and implementing a design process that will, reasonably, result in achieving that level of performance under the design ground motions.
AASHTO said that, specifically, the guidelines (a) provide design methodology for performance-based seismic design of bridges; (b) establish three bridge operational categories based on their importance in the transportation system: critical, recovery, and ordinary; (c) establish the performance goals for each of these operational categories for both lower- and higher-level seismic events; and (d) provide fundamentals of direct displacement-based design for bridges.
Concurrently, AASHTO also issued 2023 Interim Revisions to its “AASHTO LRFD Bridge Construction Specifications, 4th Edition,” making several updates the original 2017 publication; including a complete revision of Section 29, Concrete Anchors, which now makes those specifications consistent with the ones found in the “AASHTO LRFD Bridge Design Specifications, 9th Edition.”
AASHTO noted that it is necessary to have these 2023 Interim Revisions, as well as the 2020 and 2022 Interim Revisions, to have all current specification information.
To order a copy of those interim revisions, visit the online AASHTO Store and search by the publication’s Item Code LRFDCONS-4-I3 or click here for a direct link to the web page on the store site for them.