Redundancy in Highway Bridge Superstructures: Phase 2
City University of New York
Michel Ghosn and Fred Moses
The product of this study is a proposed methodology for quantifying redundancy in highway bridge superstructures. A proposed specification to account for redundancy in design and evaluation is included
Both the AASHTO Standard Specifications for Highway Bridges and the AASHTO LRFD Bridge Design Specifications require consideration of redundancy when designing highway bridges. These specifications provide limited guidance for determining when a structure is, or is not, redundant. The lack of guidance has led to a large variation in the interpretation of the specification.
The objective of this study was to develop procedures for quantifying redundancy in highway bridges. A direct calculation method and a simplified method using tabulated "system factors" were developed, and a framework for explicitly including measures of redundancy in design and evaluation was proposed. The complete system factors tables are applicable to steel and prestressed concrete bridges comprised of I-beams or box girders. The introduction of system reliability may prove to be particularly advantageous for evaluating the load capacity of older bridges. The findings of this study are fully documented in NCHRP Report 406: Redundancy in Bridge Superstructures. The unpublished appendices A-F are available here.