Push-out behavior of headed stud shear connectors in FRP-UHPC-steel double-skin tubular members (DSTMs)

The FRP-concrete-steel double-skin tubular members (DSTMs) have attracted worldwide research due to their excellent mechanical performance. However, the limitation of these DSTMs lies in the low strength and crack resistance of normal concrete. To further improve their mechanical performance and durability, a solution by replacing the normal concrete in DSTMs with ultra-high performance concrete (UHPC) is proposed. This research focused on the shear behavior of headed stud shear connectors in DSTMs, a crucial component in their overall performance. Through rigorous testing of sixteen push-out specimens, the effects of parameters including the compressive strength of concrete/UHPC, the steel fiber volume ratio in UHPC, and the diameter and layout of headed studs on the interfacial shear behavior of DSTMs were investigated. The test results not only proved that the application of UHPC in DSTMs resulted in a different failure mode and a higher interfacial shear performance, but also revealed that the investigated parameters obviously effected the interfacial shear load-slip responses of DSTM push-out specimens. Subsequently, the shear capacities of push-out specimens predicted by four of the existing theoretical models were compared with the test results. The comparison results indicated that a more accurate model for predicting the interfacial shear capacities of headed stud shear connectors in FRP-UHPC-steel DSTM is needed in future research.