Shear performance of the epoxy-bolt interface between UHPC slabs and GFRP girder

The shear performance of the epoxy-bolt interface between ultrahigh-performance concrete (UHPC) slabs and glass fibre-reinforced polymer (GFRP) girder was evaluated via push-out tests. A total of thirteen GFRP-concrete push-out specimens, including eleven GFRP-UHPC specimens with an epoxy-bolt interface, one GFRP-UHPC specimen with a bolt interface and one GFRP-normal-strength concrete (NSC) specimen with a bolt interface, were compared. Experimental parameters included the concrete strength, interface type, bolt spacing (sbolt), bolt-embedding length (hbolt), bolt number (nbolt), bolt diameter (dbolt) and bolt strength (σbolt). The test results revealed four failure modes, i.e., debonding of the epoxy layer, bolt shank shear failure, GFRP flange shear-out failure and concrete failure. Compared to the GFRP-UHPC specimen with a bolt interface, the bearing capacity and shear stiffness of the GFRP-UHPC specimen with an epoxy-bolt interface were approximately 10% and 40% higher, respectively, and the ultimate slip was approximately 3.5% lower. The employment of the UHPC slab substantially improved the shear stiffness by 19% compared with the GFRP-NSC push-out specimen. The nbolt, dbolt and σbolt showed a positive influence on the bearing capacity, whereas the hbolt showed a negative influence. The epoxy-bolt interface was recommended in the GFRP-UHPC hybrid beams to improve the composite action. Finally, the bearing capacities of the GFRP-UHPC push-out specimens with the epoxy-bolt interface were predicted.