Evaluation of mechanical behavior of shear studs and flexural stiffness of steel-concrete composite girders under negative moments

The primary objective of this paper is to investigate the mechanical behavior of shear stud connections through flexural tests and to assess the flexural stiffness of steel-concrete composite girders under negative moments. To accomplish this, five steel-concrete composite girders were tested under both negative and positive moments, with a particular emphasis on their behavior under negative moments. The test parameters included the spacing of shear connectors, the longitudinal reinforcement ratio in the concrete slab, and the type of concrete. Detailed measurements of the steel-concrete interface slip and the strain along the stud shear connections were conducted to evaluate the local moment distribution along the connectors and to identify the underlying load transfer mechanisms. The results showed that the use of high-performance concrete reduced the slip in the hogging moment zone, thereby enhancing the beam’s flexural stiffness. During negative moment testing, it was observed that the local moments exerted on the connector reached their maximum hogging values near the root and maximum sagging values near the mid-height. Finally, by considering the slip effect at the steel-concrete interface and the tension-stiffening effect in the reinforced concrete slab, a design equation for the effective flexural stiffness of composite girders under negative moments was proposed.