Experimental research on the connection node of square steel tube column and T-shaped piece

To study the mechanical performance and failure mode of the square steel pipe column-T-shaped connection joint, the unidirectional static loading test was conducted. The study involves the unilateral high strength bolt connection – The tensile bearing capacity and failure mode of T-piece square steel tubular column connection joints are analyzed as bolt type and bolt diameter. The size of the T-shaped member and other mechanical properties of the stiffener in the column determine that the steel tube column and T-shaped member is a connection node. The results show that plastic deformation is mainly distributed at the junction of flange and web of T-shaped steel tube, and the deformation develops most rapidly with the increase in displacement. Bolt type and bolt aperture have little influence on the ultimate bearing capacity of specimens. The welded stiffeners in the column enhance the stiffness of the column and reduce the plastic deformation capacity of the specimen. By increasing the thickness of the flange and web of T-shaped parts, the bearing capacity can also be improved obviously. The steel structure is a natural prefabricated structure. Its material has the advantages of lightweight, high reliability, and good seismic performance. The construction process of steel structure buildings is fast and involves less wet construction. It is easy to implement industrialization with standardized construction in steel-structured buildings (Qu 2020). The use of steel structures is becoming more extensive and the joint is an important stress-bearing part connecting beam-column members in the structure. Its structural form and mechanical performance affects the safety of the entire structure, hence the study of joint performance is of great significance. In the previous research on the square steel tube column-H-beam joint, there was no operating space while using ordinary high-strength bolts to fasten, and it was necessary to open installation hand holes, which reduced the construction efficiency. The unilateral high-strength bolts have the characteristics of unilateral tightening, reliable connection, and convenient construction. This new type of fastener can effectively solve the problem of difficulty in the application of ordinary high-strength bolts to closed-section members (Li 2015). In recent years, scholars at home and abroad have studied the steel tube column-T-joint joints, mostly steel beams are simplified by connecting the joints with flush end plates or overhanging end plates, and focusing on exploring 129the influence of self-locking unilateral bolts on the joints. Z.Y. Wang (2010) et al. found that, compared with ordinary bolts, unilateral bolts increased the plastic deformation capacity of joints by using unilateral bolts and ordinary bolts to pull out T-shaped pieces. Wang Yan et al. (2018) studied the self-locking unilateral high-strength bolt T-joint joints and conventional high-strength bolted joints, and found that the failure modes of unilateral high-strength bolts and conventional high-strength bolts are different, and the ultimate tensile load of the two is also different. The force and initial stiffness are the same. The edge distance and bolt distance of unilateral high-strength bolts have little effect on their ultimate tensile capacity, and the bolt distance has little effect on the tensile capacity of T-shaped joints. Walid Tizani (2010) et al. simplified the steel beam and end plate part of the CFST column-steel beam flat end plate joint into T-shaped pieces, carried out the tensile test of the T-shaped joint of the CFST column, and studied the common high-strength bolts, common unilateral tensile capacity of bolts, and unilateral bolts with nuts in square steel tubes with and without concrete. Studies have shown that joints have the greater bearing capacity with concrete, and unilateral bolts with nuts have greater tensile properties. J. Lee (2010) et al designed the square steel tube column to connect the test piece with the T-shaped piece in the tension zone and used the unilateral screw Ajax ONESIDE connection to conduct monotonic tensile and compression tests on the test piece. The test results are consistent with the existing theoretical model of the yield line. The maximum load that the flex cylinder can bear in the tension zone before yielding is compared, and a good agreement is obtained. In the experiments with more simplified models, Jia Shushuo (2020) et al. studied the seismic performance of the unilateral bolted connection between the rectangular steel tube column and the H-shaped steel beam, and found that the seismic performance of the self-locking unilateral bolt can meet the requirements of the joint design. Currently, many scholars at home and abroad have done little research on the connection joints between steel pipe columns and H-beams by splitting T-section steel as connectors and unilateral bolts as fasteners. The foundation is laid by the in-depth study of the connection nodes of steel beams through T-pieces. In this paper, the unidirectional static loading test was carried out on the square steel tubular column T-shaped joint connected by a nested unilateral high-strength bolt. The failure mode and tensile capacity of T-type joint of square steel tubular columns connected with single side high strength bolt are studied. The effects of different bolt types, bolt diameters, T-piece sizes, and stiffeners in the column on the mechanical properties of the T-piece joint are analyzed. The research content can provide a reference for the engineering application of square steel tubular T-shaped joint.