Field Testing and Analysis of a Composite Steel Tee Concrete Deck Bridge System

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 first bridge using this system was placed in service in 2021. This single-span demonstration bridge, consisting of 10 [steel tee concrete deck (STCD)] sections, has a span of 9.75 m and a width (from out-to-out) of 7.93 m. Composite action in the STCD bridge system is provided by an innovative mechanism for shear transfer between steel and concrete, consisting of transverse deck reinforcement bars passing through holes in the steel tee webs. In this study, the STCD bridge responses during controlled vehicular load tests were measured and compared with results from finite-element analysis (FEA) and conventional line-girder analysis, which is often used in typical bridge design calculations. Test and analysis results are used to (1) assess the composite action in the STCD bridge provided by the innovative interface shear transfer mechanism; (2) assess the consistency between measured STCD bridge responses and results from typical bridge design calculations; and (3) understand and quantify differences between measured STCD bridge responses and various analysis results. The test results show that the STCD bridge system exhibits composite behavior consistent with a plane-section transformed-section analysis in regions away from the bearings. Composite behavior is observed near the bearings; however, plane-section behavior over the depth of the composite section is not observed, as a result of interaction with the large concrete end diaphragms of the bridge. In addition, FEA results show the effects of the parapets and the torsional stiffness of the concrete end diaphragms on the response of the bridge. Comparisons of test and FEA results suggest that the semi-integral abutment conditions of the bridge cause notable restraint of the end diaphragms. The vehicular load distribution factors previously recommended for conventional line-girder analysis of the STCD system are shown to be relatively conservative compared to the test and FEA results.