Load and Resistance Factor Design (LRFD) For Highway Bridge April 2007 Superstructures - Design Manual
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Summary
This document serves as a comprehensive design manual for the Load and Resistance Factor Design (LRFD) of highway bridge superstructures, developed by the Federal Highway Administration (FHWA) and authored by Michael Baker Jr., Inc. The manual is grounded in the AASHTO LRFD Bridge Design Specifications, Fourth Edition (2007), and aims to guide structural engineers in implementing these specifications for both steel and concrete bridges. It addresses the transition from older design philosophies, such as Allowable Stress Design (ASD) and Load Factor Design (LFD), to the probability-based LRFD method, which targets a specific reliability index to ensure uniform safety levels across different materials and limit states. The manual is organized into four volumes covering general considerations, steel superstructures, concrete superstructures, and detailed design examples. Volume 1 outlines the theoretical foundation of LRFD, explaining how load factors, resistance factors, and load modifiers (accounting for ductility, redundancy, and importance) are applied to manage uncertainties in loads and material resistance. It also covers preliminary design constraints, including alignment, clearance requirements, environmental impacts, and life-cycle cost considerations. Volume 2 focuses on the construction and design of steel bridges, detailing girder design, connections, splices, bracing, and specific configurations like curved or tub girders. Volume 3 addresses concrete superstructures, providing methodologies for precast pretensioned girders, continuity via reinforced concrete joints or post-tensioning, and cast-in-place post-tensioned systems. Volume 4 provides practical application through four specific design examples: a straight steel girder bridge without skew, a straight steel girder bridge with skew, a steel tub girder bridge, and a concrete I-girder bridge. These examples illustrate the integration of the theoretical principles and specifications discussed in the preceding volumes. The manual presents all content in both US Customary and Standard International units, ensuring broad applicability. By providing detailed commentary, structural analysis methods, and step-by-step design procedures, the document facilitates the consistent and efficient implementation of LRFD specifications, promoting safer and more reliable highway bridge construction.
Key finding
The manual provides a structured framework for implementing LRFD specifications for highway bridge superstructures, detailing design considerations for steel and concrete components through theoretical explanations and practical examples.
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