Manual de diseño de puentes

U.S. Department of Transportation Federal Highway Administration

Publication No. FHWA HI-98-032 May 2001

NHI Course No. 132068

)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) )))))))))))))))

Load and Resistance Factor Design (LRFD) for Highway Bridge Substructures
Reference Manual and Participant Workbook

National Highway InstitutePREFACE For many years, engineers have designed foundations, walls and culverts for highway and other applications using allowable stress design (ASD) methods. In ASD, all uncertainty in loads and material resistance is combined in a factor of safety or allowable stress. For most highway design, the American Association of State Highway and Transportation Officials (AASHTO) StandardSpecifications for Highway Bridges represents the primary source document for ASD of substructures. In 1994, AASHTO approved Load and Resistance Factor Design (LRFD) in the LRFD Highway Bridge Design Specifications. In LRFD, the uncertainty in load is represented by a load factor and the uncertainty in material resistance is represented by a resistance factor. Due to the fundamental differences between thesubstructure design process by ASD and LRFD, this course has been developed to present the fundamentals of LRFD for the geotechnical design of highway bridge substructures. Because this document was prepared for engineers and others who are already familiar with the design of substructures using ASD, it is intended for use in conjunction with other documents describing standard geotechnical designprocedures. The objectives of this reference manual are to provide the basis for an understanding of the:
• • • • • • • •

Differences between ASD and LRFD for substructure design Benefits of LRFD for substructure design Importance of site characterization and selection of geotechnical design parameters Process for design of substructure elements by LRFD using the AASHTO LRFD Specifications as aguide Process for selection and application of load factors and load combinations Methods available for calibration of resistance factors Basis for calibration of the AASHTO LRFD resistance factors for substructure design Procedures available for modifying or developing resistance factors to achieve designs comparable to ASD

This Reference Manual is intended principally to serve as asupplement to the Participant’s Workbook for the FHWA’s National Highway Institute Course on Load and Resistance Factor Design for Highway Bridge Substructures. The Reference Manual can also serve as a primary reference for engineers in modifying or developing resistance factors to achieve designs comparable to ASD and for designing foundations, earth retaining structures and culverts through the numerousdesign examples included throughout the design chapters in the manual. The authors acknowledge the efforts of the project technical managers, Mr. Jerry DiMaggio and Mr. Richard Cheney, FHWA Senior Geotechnical Engineers who provided constructive guidance and input for this document, and Mr. Chien-Tan Chang, FHWA’s Contracting Officer’s Technical Representative who provided administrative oversightand guidance.

i

The authors also wish to acknowledge contributions of the following members of the Technical Working Group listed in alphabetical order:
• • • • • • • •

Chris Benda - Vermont Department of Transportation James Cuthbertson - Washington State Department of Transportation Richard Engle - Ohio Department of Transportation Ashton Lawler - Virginia Department ofTransportation James Lyons - Federal Highway Administration Paul Passe - Florida Department of Transportation Tom Saad - Federal Highway Administration James Schluter - CONTECH Construction Products

Lastly, the authors wish to thank the following employees from D’Appolonia for their vital contributions and significant effort in preparing this document: Ms. Tara Heyer, Mr. Robert Whitaker, Mr. David Mudry,...