Experimental study on grouped stud shear connectors in precast steel-UHPC composite bridge

Headed studs in the group arrangement are usually used to connect the precast slabs and steel beams in composite bridges. Ultra high-performance concrete (UHPC) as an innovatory solution to improve the performance of bridges has been adopted for manufacturing slabs. To investigate the shear behavior of grouped stud connectors (GSC) embedded in UHPC, seven series of push-out tests were performed with varied parameters including stud diameter, the aspect ratio of stud and stud spacing. The test results revealed that the failure of push-out specimens was governed by stud fracture while no cracks in slabs. Shear behavior was improved with the increase of stud diameter. Reducing stud spacing below the threshold of design codes resulted in a decline in shear performance, and aspect ratio lower than the minimum recommendation of design regulations was feasible for grouped studs in thinner UHPC slabs. The curves of load-stud strain were divided into two stages corresponding to different critical loading points for specimens with different stud diameters. Finally, an empirical model was proposed by regression analysis to predict the load-slip behavior of GSC embedded in UHPC, and the calculation models of shear capacity in design codes and literature were also assessed by the experimental data.