Development of internally redundant steel box straddle caps
Steel box straddle caps are an efficient solution for bridges located in congested urban environments when using a conventional pier is not possible due to the presence of intersecting roads beneath the bridge. Using steel box girders offers fabrication and erection advantages and high structural performance due to the high torsional stiffness of the box. However, steel box straddle caps are classified as Fracture Critical Members, requiring stringent design, fabrication, and in-service inspections to comply with the provisions of the Fracture Control Plan. Providing internal redundancy to steel box straddle caps to remove the Fracture Critical inspection requirements is highly desirable. It renders a higher degree of safety due to a reduced probability of failure, reduces traffic disruptions necessary for hands-on inspections, and produces significant savings for bridge owners. The research outlined in this dissertation explores two possible design approaches to provide internal redundancy to steel box straddle caps by (i) adding high-strength bars as a secondary tension element and (ii) providing cross-boundary fracture resistance between the components in tension. After completing the preliminary studies, a full-scale experimental program was conducted and complemented with finite element modeling. The results of the experimental testing and analytical studies are discussed, and design recommendations and examples for internally redundant steel box straddle caps are provided.
Redundancy, Steel box straddle caps, Internal redundancy, Nonredundant steel tension member, Fracture critical, Fracture
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