STUDY ON THE IMPACT OF GAP ON SHEAR PROPERTIES OF SC STRUCTURE (2018)

This paper reports on push-off tests to determine the impact on a stud's shear properties of a gap that has developed between the rear plane of an upper steel plate and concrete due to contraction and subsidence of concrete inside a steel-plate-concrete structure (hereafter, “SC structure”). Gap thickness is set as a parameter. In addition, a shear resistance mechanism in yielding was devised in anticipation of a gap that develops at a stud's elastic limit and during yielding. A method is also proposed for computing shear capacity that takes a gap into consideration. Comparison of test results with computation results confirmed that this method is effective. The method was applied to parametric studies on the impact of a gap on a stud's shear properties. Fig. 3 shows the shapes and dimensions of specimens, while Table 1 lists test cases. The specimens were prepared to test the upper steel plate of an SC structure's horizontal component, concrete around the steel plate, and the stud. The specimens comprised H-section steel members and concrete blocks whose ends are integrated with two studs. The stud-welded H-section flange thickness and gap width were set as test parameters. In the tests, downward loads from 100 kN to 200 kN were progressively applied to the upper part of the H-section steel members until the specimens failed. Relative vertical displacements between the concrete blocks and the H-section steel were measured. After the loadings were completed, the front halves of the concrete blocks were removed in order to observe the damage to the studs. Stud deformations were concentrated at their bases, and some of the studs were even ruptured at their bases. For Specimen A-1, stud deformation was confined to its base. For Specimen A-8, stud deformation extended to is center, while for Specimen A-15, stud deformation extended to approx. 2/3 of its length. Fig. 5 shows load-gap displacement relations for individual test cases and the maximum shear capacities per stud based on the evaluation formula indicated in “Recommendations for Design of Building Foundations” of the Architectural Institute of Japan. Specimen A-1 had a maximum load of 139.5 kN and a deformation amount of 10.3 mm at maximum load, Specimen A-8 had a maximum load of 89.8 kN and a deformation amount of 21.9 mm at maximum load, while Specimen A-15 had a maximum load of 73.1 kN and a deformation amount of 29.1 mm at maximum load. It was confirmed that as the gap thickness increased, the maximum shear capacity of the stud decreased, showing larger deformation. In addition, for case A-1, where a gap of 1 mm was set against a 19 mm stud diameter, the ratio of the computation value based on the existing evaluation formula for the maximum proof stress value of the tests was 0.91. The results based on the existing formula shows a slightly low value for case A-1. “Recommendations for Design of Building Foundations” of the Architectural Institute of Japan gives a computation formula for shear capacity that takes a gap into consideration in reference to a design equation for a pile whose top has popped out of the ground. It was also indicated that lowering of shear capacity due to the impact of a gap relates to the intensity ratio of concrete to stud (σB/σy) and the ratio of gap to stud diameter (h/Bs). Computation values based on the proposed formula conform closely to the test results. Although the number of test cases was limited, the tests have confirmed that this method is effective in assessing shear capacities when gaps have occurred.