NCHRP Report 489, Design of Highway Bridges for Extreme Events, contains the findings of a study to develop a design procedure for application of extreme event loads and extreme event loading combinations to highway bridges. The report describes the research effort leading to the recommended procedure and discuses the application of reliability analysis to bridge design. All appendices to the report are included on CRP-CD-30.

The magnitude and consequences of extreme events such as vessel collisions, scour caused by flooding, winds, and earthquakes often govern the design of highway bridges. If these events are considered to occur simultaneously, the resulting loading condition may dominate the design. This superpositioning of extreme load values frequently increases construction costs unnecessarily because a simultaneous occurrence of two or more extreme events is unlikely. The reduced probability of simultaneous occurrence for each load combination may be determined using statistical procedures. The AASHTO LRFD Bridge Design Specifications developed under NCHRP Project 12-33 cover the basic design combinations with dead load and live load. Extreme load combinations were not considered in the LRFD calibration because of the lack of readily available data concerning the correlation of extreme events. Nevertheless, a probability-based approach to bridge design for extreme events can be accomplished through incorporation of state-of-the-art reliability methodologies.

The objective of NCHRP Project 12-48 was to develop a design procedure for the application of extreme event loads and extreme event loading combinations to highway bridges. This objective has been achieved with a recommended design procedure consistent with the uniform reliability methodologies and philosophy included in the AASHTO LRFD Bridge Design Specifications. Four new extreme event load combinations are included to maintain a consistent level of safety against failure caused by scour combined with live load, wind load, vessel collision, and earthquake, respectively.

Download: Complete NCHRP Report 489 (1.7 MB) or Report Parts; Front Matter, Chapter 1, Chapter 2, Chapter 3, Chapter 4, Appendix Intro, Appendix A, Appendix B, Appendix C,, Appendix H, Appendix I, Glossary & References, or Unpublished Appendixes; Appendix D (10.7 MB), Appendix E (5.2MB), Appendix F (5.1 MB), Appendix G (11 MB)

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