ABSTRACT
California has approximately 1500 steel girder bridges and 400 steel truss bridges on the public highway system. Of these, 769 have been identified as possessing either fatigue prone or fracture critical details. Fatigue cracking is becoming evident on our high ADT steel bridges. Most of this cracking is associated with out-of-plane bending predominately occurring at fatigue prone connections that are subject to high cycle rotations and displacements. Code based fatigue analysis gives little guidance for these situations. Repairing or retrofitting a specific location seems to drive the cracking to other locations. Once cracking occurs, widespread cracking seems to quickly initiate at similar details. Retrofits are difficult to effectively design as structural behavior and driving forces are not well understood and are difficult to model. In some cases, reliable retrofits are not clear or evident. Environmental and health concerns associated with lead based paints are making repairs of steel bridges costly; a definitive strategy before work begins should be determined to reduce these costs.
CALTRANS would like to present current ideas and information on inspection programs, effective NDE methods for early crack detection, case studies, fatigue analysis strategies, effective retrofit designs, ideas as to the cost effectiveness of rehabilitation vs. replacement, and other related topics. The purpose of this presentation is to exchange ideas and information with engineers, researchers and transportation officials in the United States to better understand the best strategy to take in tackling fatigue cracking problems.
