Experimental study on edge cell partially-replaced joint for I-beam to multi-celled CFST walls under cyclic loading

The multi-celled concreted-filled steel tubular walls (MCCFSTWs) are widely used in practice, especially in apartment constructions. The use of thin steel tubes in MCCFSTWs makes it weak at the joint zone, therefore the connections between the MCCFSTWs and steel beams become an important issue for the application of MCCFSTWs. A novel joint for the connection between the MCCFSTWs and I-beams is proposed in this study. The main feature of the proposed joint is that the edge cell of the MCCFSTW is partially replaced using a welded C-section, where two partial internal diaphragms are set to transfer the bending moment from the I-beam. With this treatment, the edge cell of MCCFSTWs near the joint zone can be significantly strengthened to satisfy the requirements of the seismic design, while the compactness of concrete at the joint zone can be guaranteed by using the partial internal diaphragms. The design philosophy of the proposed joint is first introduced in this study. Three specimens are then designed and tested under the cyclic lateral loading. Subsequently, the behaviors of the proposed joints are discussed based on the test results, including the failure mode, the hysteresis curve, the ductility, the ultimate load and the initial stiffness. The stress states at the joint zone obtained from tests are also analyzed and compared with those using simplified analytical model. According to Eurocode 3, all tested specimens can be classified as rigid and full-strength joints. Moreover, the rotation capacity of this novel joint meets the requirements of GB50011. The investigation of this paper is believed to be meaningful for the application of the novel joints in the practice.