Bridge Load Rating Practices for Cranes

Oversized and overweight Rough Terrain (RT) and All Terrain (AT) commercial cranes are used extensively at dam projects and continuously cross bridges that serve the requirements of the public agencies or private utilities that own them. Depending on the state jurisdiction, these cranes will be trailered or driven under a variety of local and multistate permit programs. The effects of crane loads on highway bridges are a frequent concern due to the variability in age, design, construction, and condition of the bridges. Currently, the only guidance available for analysis is criteria outlined in AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications and AASHTO Guide Manual for the Condition Evaluation and Load and Resistance Factor Rating of Highway Bridges (LRFR). The information in this presentation will help determine safe loading capacity and placement of three common types of classifications of oversized cranes on a bridge. It is based on vehicular loading and requires an analysis methodology that extrapolates an allowable crane permit loading from the LRFR bridge design or legal loading. The differences between vehicular & crane live and static loads, axle configurations, and load placements are discussed. There are recommendations for making informed decisions on adjustments in impact loads, live load distributions and lane loading based on the Strength II requirements outlined in the evaluation and rating procedures in the AASHTO LRFR and LRFD specifications. This article will also show an outline for planning a crane operation on a bridge that includes consideration of working loads, placement and minimizing risks.