Performance of grouped stud connectors in precast steel-UHPC composite bridges under combined shear and tension loads

Ultra-high performance concrete (UHPC) becomes an innovative resolution for facilitating the construction and structural performance of prefabricated bridges. Head stud shear connectors are commonly applied in pre-fabricated steel-concrete composite bridges and can withstand uplift forces as well as shear forces. In this paper, six standard push-out tests (SP-Test) and ten modified push-out tests (MP-Test) are prepared and tested. In the MP-Test, stud connectors are subjected to shear and tensile forces simultaneously. The stud diameter, stud aspect ratio and the ratio of tension to shear are considered for their effects on shear resistance, shear stiffness and ductility. Besides, the finite element (FE) analysis and parametric analysis are conducted to further investigate the behavior of stud connectors under combined loads. The formulas for predicting the shear-tension interaction strength and shear resistance of stud connectors in UHPC under combined loads are proposed. The results show that the stud connectors exhibit both shear and tension failure characteristics under combined loads. The lower ratio of tension to shear has less effect on the shear resistance and ductility. Meanwhile, the stud aspect ratio is positively related to shear resistance and ductility but has no effect on shear stiffness under combined loads. As the ratio of tension to shear increases, a considerable reduction is observed in the shear resistance and relative slip as well as shear stiffness of stud connectors. However, the attenuation effect of tensile stress on the shear strength of studs can be neglected when the tensile shear ratio is less than 0.17. The unevenness of the force on single stud in stud connectors can be ignored and excessive strength of UHPC has limited effect on improving the strength of studs under combined shear and tension loads. The proposed shear strength reduction factor talees into account the ratio of tension to shear and gives more reasonable predictions of shear resistance under combined loads. Besides, compared with other available equations, the proposed shear-tension interaction model predicts the interaction strength more accurately.