Report on Techniques for Bridge Strengthening. Design Example \u2013 Stringer Retrofit - Composite Action and Continuity Changes.

2018PDFTech ReportFHWA-HIF-18-044DTFH61-11-H-00027BridgesStrengthening (Maintenance)RetrofittingBridge designComposite materialsUnited StatesUnited States. Federal Highway Administration. Office of InfrastructureAhlskog, C.United States. Federal Highway Administration. Office of InfrastructureModjeski and MastersFederal Highway AdministrationThis example involves the replacement of stringers during re-decking on an existing truss/floorbeam/stringer bridge. The existing stringers are non-composite rolled W24x76 beams, that were designed for HS-20 live loads. The design criteria is to provide new stringers to obtain a HS-25 live load rating factor equal to or greater than 1.0, while minimizing the weight of the new stringers. The flexural live load ratings of the new stringers were significantly increased by both making the stringers composite with the new deck and changing the continuity of the stringer spans. This example only involves a study of the flexural resistance of a typical interior span for the new and existing stringers using the Strength-I Limit State. This example is based on AASHTO LRFD Bridge Design Specifications, 7th Edition.84