Behavior of concrete-filled steel tubular planar intersecting connections under axial compression, Part 1: Experimental study

In the innovative structural system known as the diagrid structure, a connection commonly consists of four obliquely intersecting columns and several beams. This paper presents two types of concrete filled steel tubular (CFST) planar intersecting connection, which are applicable to CFST diagrid structures with structural beams mounted on them. An equation to calculate the bearing capacity of the connections is proposed based on the Chinese design code for CFST columns. Eight specimens were tested under monotonic axial loading with the purpose of investigating the performance, bearing capacity, and failure mechanism of the connections under axial compressive load. The parameters in this study were connection detail, intersecting angle between columns, and loading type. The deflection, stress, failure modes, and bearing capacity of the specimens were obtained. The result shows that the angle between the CFST columns has a considerable influence on the failure modes. In addition, lining plates provide a larger confinement effect than flange plates. The loading type has little effect on the behavior of the connections. The ratio of compressive loading capacity to the results calculated by the proposed formula ranged from 0.99 to 1.31, which shows that the calculated bearing capacity is accurate or conservative for structural design. Finally, the behavior of the connections presented here was verified to be similar to that of an CFST stub column.