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NCHRP Web-Only Document 269: Guide Specification for Service Life Design of Highway Bridges 1 S U M M A R Y Development of the AASHTO Guide Specification for Service Life Design of Highway Bridges Consideration of more rigorous approaches to service life design has increased in recent years. The majority of instances of explicit consideration of service life design has been limited to signature bridges and other projects where extended service lives (i.e., greater than 100 years) are specified by the owner. Many state Departments of Transportations (DOTs) and other transportation agencies have recognized the importance of implementing service life design for typical highway bridges; however, no specification or standard has been developed to date in the U.S. This ultimately led to the initiation of NCHRP Project 12- 108. The main objective of this project was to develop a new guide specification on the service life design of highway bridges for adoption by AASHTO, including a set of case studies that demonstrate its application. The goals of the new guide specification were to provide practical guidance to designers of highway bridges on how to implement service life design during the design phase, utilize available data together with bridge owner experience to tie design practices to service life, and to allow for the future incorporation of probabilistically calibrated limit states. Information was gathered from a literature review, a survey of transportation agencies, and members of the research team. The Guide Specification itself was developed around a three-tiered approach of âgood-better-bestâ practices tied to three categories of service life: Normal, Enhanced, and Maximum. Definitions of exposure classes are included to aid the designer in categorizing the severity of the environment surrounding a bridge. Material and component specific design specifications are provided as a function of service life category and/or exposure class, most of which take the form of deemed-to-satisfy or avoidance of deterioration approaches. The exception to this is the limit state of chloride-induced corrosion of reinforced concrete, for which design concrete cover values were probabilistically calibrated. An appendix provides the background to this probabilistic approach to chloride-induced corrosion, which was adopted from fib Bulletin 34 and is intended for use with project specific requirements. This appendix also provides a framework for the future inclusion of additional limit states. The Guide Specification concludes with a set of case studies demonstrating the use of the developed service life design provisions. A number of knowledge gaps were identified over the course of the project, including limitations to the current service life prediction models and a lack of supporting data needed to develop deterioration models for additional service life limit states. The Guide Specification is formatted such that updates based on new information may be implemented into the document, when available.
