Shear Connectors For Hybrid Composite FRP-Concrete Bridge Girders

In the fiber-reinforced polymer (FRP)-concrete bridge girder system developed at UMaine, composite action between the concrete deck and the FRP is necessary for the section to work efficiently. The degree to which the two materials act compositely is heavily reliant on the effectiveness of the shear connectors that positively connect them. The connection system must be able to withstand the maximum shear flows developed between the girder and deck while permitting little or no relative slip, but also have sufficient fatigue capacity to remain effective over the lifespan of a bridge. In a conventional steel and concrete section, composite action is achieved with shear studs welded to the top flange of each girder and embedded in the concrete deck. Shear studs have been extensively tested for both strength capacity and fatigue resistance. Welded studs are not an option for an FRP girder and a new type of shear connection system is necessary. This research was conducted in two phases: experimental testing and numerical modeling. Strength, stiffness and fatigue resistance properties were assessed in the experimental phase, with two unique types of shear connector systems being evaluated. The first relied entirely on SAE J429 fasteners in bearing to transfer shear. These were found to meet the AASHTO specifications for infinite fatigue life as well as have sufficient strength and stiffness. The second system, a novel shear transfer mechanism that relies on a roughened FRP surface, and a minimal number of mechanical fasteners has been developed. Experimental results indicate that this connection meets design criteria as well and provides near perfect composite action. Based on experimental results, numerical modeling to assess the effectiveness of the bearing connection system has been conducted. The model utilizes a layered moment curvature analysis that incorporates the non-linearity in the load-slip response of the shear connectors and the uniaxial constitutive properties of the concrete. Parametric studies were carried out with this model to gain important insights into girder design and limiting values of partial and full composite action