NCHRP Report 458, Redundancy in Highway Bridge Substructures ,contains the findings of a study to develop a methodology for considering substructure redundancy in the design and evaluation of highway bridges. The report builds on the work on bridge superstructure redundancy presented in NCHRP Report 406 and integrates the findings in that report into a single recommended specification for addressing bridge redundancy during design. The material in this report will be of immediate interest to bridge design specification writers and to bridge engineers interested in the quantitative assessment of bridge redundancy.

The AASHTO LRFD Bridge Design Specifications require the consideration of redundancy while checking the strength of all bridge members including substructure elements. The requirements, however, in some cases, are subjective, and the specifications recognize the importance of continued research to provide improved quantification of redundancy in bridge structural systems.

NCHRP Project 12-47, "Redundancy in Highway Bridge Substructures," was initiated to extend the methodology developed in NCHRP Project 12-36, "Redundancy in Bridge Superstructures," to bridge substructures. The research was performed by Imbsen & Associates, Inc. of Sacramento, California. The current report fully documents the methodology used to develop and calibrate a process for quantifying redundancy in bridge substructures and for calculating appropriate adjustment factors to maintain a uniform level of structural reliability. An appendix to the report contains recommended language for introducing the quantification of redundancy for superstructures and substructures into the AASHTO LRFD Bridge Design Specifications.