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1 S U M M A R Y Update of the AASHTO LRFD Movable Highway Bridge Design Specifications There are approximately 1,000 movable highway bridges in the US inventory. The first guide specifications for design of movable bridges were developed in the early 1900s and utilized Allowable Stress Design (ASD). ASD methodology continued to be implemented for movable bridge design until there was a major rewrite in 2000 with the publication of the AASHTO Load and Resistance Factored Design (LRFD) Movable Highway Design Specifications. The 2000 publication incorporated basic LRFD structure, but it essentially employed ASD arranged in LRFD format. It was acknowledged within the guide specification that there was not enough available data to more fully apply the reliability-based LRFD approach, but the basic structure was developed so that future updates could employ such methodology to be more consistent with the LRFD approach utilized for fixed structures. In the current project, our research team gathered additional available data to progress implementation of the LRFD platform where possible. Implementation of reliability design also included an update to wind loading, which is one of the most impactful loads when sizing prime movers and braking for movable bridges. The existing specifications have traditionally employed uniform wind loading regardless of bridge geographic location or function (e.g., local road vs. port of entry). The update allows the owner the option of employing site-specific conditions to develop the design wind speed. This is an adaptation of the Dutch movable code that considers the probability that a particular movable bridge needs to be âavailableâ to operate for certain site-specific conditions. Other general updates have been included that reflect updates to design practice or other referenced standards.
