ULTIMATE SHEAR STRENGTH OF INCLINED HEADED STUDS

Abstract

 Headed studs are widely used as shear connecters between steel and concrete. Usually, headed studs are vertically welded in a steel surface. However, if we expect the shear resistance in headed studs, the resistance mechanism is changed such that the headed stud is subject to a force (either tensile or compressive) along the axial direction of the stud, which is predicted to produce considerable resistance. Therefore, it is hypothesized that composite beams using inclined headed studs would improve shear stiffness and strength.

 We proposed an appropriate arrangement and direction of inclined headed studs for beams subjected to unidirectional loading and for girders subjected to a positive–negative cyclic load. In addition, the parallel-inclined type was considered desirable for the beam and the cross-inclined type for the girder. Moreover, we proposed an evaluation method of the ultimate shear strength for the headed studs with positive and negative inclination. The ultimate shear strength was determined on the basis of the assumption that the shear force in a composite beam connection using positive-inclined headed studs is brought into equilibrium with the bearing force of the concrete and the tensile force of the headed stud. In addition, it was assumed that the bearing force of concrete carries the shear force of composite beams using negative-inclined headed studs. The bearing strength of concrete is obtained by multiplying modified coefficients κ_p and κ_n for inclined headed studs in the J. W. Fisher design formula. The tensile strength of headed studs is thus the smallest allowable stress as limited by the yielding of the headed stud or concrete cone failure.

 In this research, first, we confirmed the mechanical behavior of parallel-inclined and cross-inclined headed stud steel and concrete connectors by conducting a structural test under a cyclic shear force. The direction, arrangement, diameter, and length of the headed stud as well as concrete strength were used as experimental parameters. A total of 58 specimens were tested. For the shear tests, the cone failure of the concrete from the stud head, the splitting crack of the concrete from the stud base, the bearing failure of the concrete at the stud base, the shaft fracture at the stud base, and the stud welding part fracture were observed. From the test results, the modified coefficient κ_p used for determining the ultimate shear strength of the headed studs with positive inclination was identified. Second, to identify the modified coefficient κ_n used for determining the ultimate shear strength of the headed studs with negative inclination, we tested four specimens in additional experiments for the parallel-inclined headed stud.

 Finally, we confirmed that the results of the proposed evaluation method for the shear strength are consistent with the test results.