Composite Steel Tee Concrete Deck Bridge System: Performance of Interface Shear Connection

A new short-span highway bridge system composed of inverted steel tee sections embedded in a concrete deck slab was developed for the Pennsylvania Department of Transportation. The interface shear connection between the concrete deck slab and steel tee sections is nontraditional and is fabricated by drilling holes near the top of the steel tee stems, placing transverse reinforcement bars through the holes, and casting the top of the steel tee stem into the deck. This paper discusses the mechanism and design of this interface shear connection between the concrete deck and the steel tee section to create composite action. The research approach is based on push-out tests conducted on full-scale subassemblies and validated with destructive tests on a full-scale prototype bridge module. The test program and the resulting design equations are discussed. The test results indicate that the response of this interface shear connection between the concrete deck and the steel tee section is dominated by shear yielding of the reinforcement bars passing through the holes in the tee section stem. After shear yielding of the bars, there is local crushing of the concrete and strength recovery as the bars develop catenary action. At larger relative deformation between the deck and steel tee (shear slip), a concrete breakout failure occurs on the bottom of the concrete deck. The use of a stem hole with no bar creates a brittle concrete shear dowel; the strength of this dowel can be estimated using a concrete shear strength formulation. Because the concrete dowels are brittle and the reinforcement bars passing through the stem holes have a ductile response, the recommended interface shear connection utilizes bars in all holes. The results of the full-scale bridge module test indicate that the interface shear connection and associated design equations provide effective composite action in the bridge system.