Experimental study on a new-type concrete filled steel tubular column-slab joint subjected to low-cycle reversed horizontal load

For resolving the difficulty that slab-column system can not be popularized in high-intensity earthquake area, a new-type concrete filled steel tubular column-slab joint is presented in this paper. The new-type joint is characterized by forming a hinge joint between the steel tubular column and the concrete flat in interior of building. And it has no use for horizontal loads, which bore completely by the concrete wall or column around the building, but only bore the vertical loads in the structure. For all that, the joint should not be destroyed badly to introduce the collapse of building after suffering a big lateral load such as strong earthquake. In order to prove the performance of the joint in punching shear capacity and resisting lateral displacement, the tests are put up about two 1/2-scale interior column joint specimens subjected to low-cycle reversed horizontal load. And the axis force in steel tubular column was loaded before the low-cycle reversed horizontal load according to the ratio of shearing force bringing from the weight of superstructure and punching shear capacity of slabs(GSR) which includes three case: GSR=0.69, GSR=0.83 and GSR=0.93. The test results are introduced including the whole process, the values of cracking load, maximum load, failure load and the punching shear failure model. Meanwhile the hysterisis loops, skeleton curves and the strain curves of steel bars along the slab width are also given. The experimental study has showed: (1) the joint has the much punching shear capacity than the value calculated by formula 7.7.1-1 of code for design of concrete structures. (2) the relative displacement of the joint can achieve 2% of storey height which is two times of a frame structure´s story drift limit in Code for Seismic Design of Building Structure before the specimens were destroyed even in high GSR case. (3)The new joint with a low additional moment flexion can work well cooperating with column and slab. From the experimental we can- - resulted that the additional moment flexion in joint is enough low to be regarded as a hinge. The structural form of the connection is simple and easy to use, while the seismic behavior of slab-column structures is better than the common slab-column system.