FRP-Concrete Hybrid Composite Girder Systems: Web Shear Strength and Design Guide Development

UMaine has recently developed an FRP-concrete hybrid composite girder (CT girder) bridge that shows great promise. Work to-date has verified critical aspects of girder strength and FRP-concrete shear connector performance. Ongoing, separately funded research is focused on refining shear connector design to simplify construction and allow the use of fully-threaded, stainless steel (SS) connectors. In parallel, this technology is being commercialized and implemented by AIT Bridges of Bangor, Maine. AIT has designed a new CT girder bridge to be built on US Rt. 1 in Hampden in 2020, and is extending the concept to incorporate longitudinally pre-cast decks with double CT girders to speed construction (the girder also accommodates transversely pre-cast deck panels and CIP decks). UMaine will load-test the new Hamden CT girder bridge and perform 3D FEA to assess as-built performance and facilitate future load ratings with funding from the UMaine Transportation Infrastructure Durability Center. However, there are two topics that require additional research: the assessment of web shear strength and the development of a design guide. The foam-core webs of these girders have complex fabric layups and web-to-flange transition zones that make their shear strength difficult to accurately estimate with conventional engineering calculations. Because of this, web shear design to-date has been purposely conservative. The topic of web shear is close linked to the development of a design guide, which is essential for widespread acceptance and implementation of the CT girder system. There are three main girder strength design aspects that must be addressed in every design and that are vital components of a future design guide: bending strength, shear connector strength, and web shear strength. Research conducted to-date has reinforced the ability to accurately predict bending and shear connector strength, but web shear strength must be better quantified to permit the development of a design guide.