Unveiling shear performance and structural integrity of studs in steel-concrete composite structures

Advancements in modern bridge engineering have led to the development of thinner and lighter steel-concrete composite structures. Ultrahigh-performance concrete (UHPC) has emerged as a cutting-edge solution to enhance performance and expedite construction. This research investigates the failure modes and load-slip relationships of short studs shear connectors in steel-thin UHPC composite structures (STUCs) through push-out testing. Experimental results demonstrate that fracture of the stud shank and local concrete crushing are the primary failure modes observed in all specimens. Increasing the stud diameter enhances shear strength, while dense arrangements of short studs and reduced stud height decrease the shear capacity of individual studs. The D19 and D22 studs exhibit significantly higher elasticity moduli (237.7 GPa and 221.4 GPa, respectively) compared to the UHPC layer (45.67 GPa) and the steel girder made of Q235B (216.2 GPa), indicating greater stiffness. The ultimate tensile strength is highest for the D19 stud (487.16 MPa), followed closely by the D22 stud (453.29 MPa) and the steel girder (425.03 MPa), while the UHPC layer shows a considerably lower ultimate strength of 129.01 MPa. All metal components (D19 and D22 studs and steel girder) have a uniform poisson ratio of 0.3, suggesting similar deformation characteristics under stress, in contrast to the UHPC layer's lower ratio of 0.216. Comparisons with existing construction specifications indicate conservative predictions of shear capacity for short studs in thin UHPC layers.