Bridge System Safety and Redundancy (2014)

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116 Conclusions This report calibrated system factors that can be used to account for the presence (or the lack of) redundancy in common-type bridge configurations subjected to distributed lateral loads and vertical live load. The system factors can be used during the design and safety assessment of bridges sub- jected to lateral loads being evaluated using the displacement- based approach specified in the LRFD Seismic Design provisions or the traditional force-based approach. Also, the report pre- sented system factors calibrated for application with orig inally intact as well as damaged bridge systems subjected to vertical vehicular overloads. The proposed system factors are consolidated into equations and fewer tables than those presented in NCHRP Report 406 and NCHRP Report 458. This was achieved by establishing simple relationships between the system factors and relevant geometric properties of the systems or material properties of the primary bridge members. The consolidation of the sys- tem factors into fewer tables is meant to simplify the process of applying the system factors in actual bridge engineering practice. The equations and tables proposed in this study are developed following extensive sensitivity analyses to account for bridges with members that may be overdesigned compared to the minimum design requirements of current and previous specifications and for bridges with deficient member strengths. This makes the proposed system factors applicable for the design of new bridges and the safety evaluation of existing bridges. The proposed equations are necessarily designed to provide an approximate evaluation of the redundancy of bridges as they are meant to cover a wide range of bridge parameters. The proposed sets of system factor equations are presented in a format suitable for inclusion in the AASHTO LRFD Bridge Design Specifications and the manual for bridge evaluation in Appendix A.1 and Appendix A.2 of the contractor’s final report (available on the TRB website). Appendix A.3 (also available on the TRB website) gives three examples illustrating how the system factor equations can be used during the design or the rating of I-girder and spread box-girder bridges under vertical loads and the design of a multi-column bridge system under lateral load. These examples complement other examples pro- vided in the body of the report. For more accurate evaluations of the redundancy of specific bridges, a direct redundancy evaluation involving the non- linear analysis of bridge systems is required. Appendices B.1, B.2, and B.3 of the contractor’s final report (available on the TRB website) describe the analysis process through three examples. These examples consist of the analysis of a multi- cell prestressed concrete box-girder bridge under vertical and lateral load, a steel truss bridge and a continuous steel two-box-girder bridge under vertical load. C H A P T E R 6

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation