Comparisons of Seismic Performance of Fully-Bolted Column Joints of Steel Tubular Columns with Built-in Cross-Shaped Core Barrels and Built-in Octagonal Core Tube

There are some problems such as low construction efficiency, high labor cost and environmental pollution in the traditional full penetration welding joints of square steel tubular columns. In order to solve the above problems, the research group proposed the full-bolted connection joint of square steel tubular column with built-in octagonal core barrel. The joint connects the upper and lower columns by setting the core tube and high-strength bolts to realize the complete assembly on site. At present, a series of quasi-static, pseudo-dynamic and shaking table tests have been completed. The results showed that the joint form had the same mechanical properties as the welded joint, and could also realize the efficient assembly of the construction site. Furthermore, to enhance construction convenience and economy, as well as reduce the amount of steel and welding labor, a cross-shaped core barrel was suggested. The barrel was designed to have the same elastic bearing capacity as the octagonal core barrel. The finite element software ABAQUS was used to create a finite element analysis model for fully-bolted joints of square steel columns with built-in octagonal core barrels and built-in cross-shaped core barrels. The whole process of stress of the two connection joint members was analyzed, and the plastic development and final failure mode of the whole specimen and local members at the stress characteristic points were compared respectively. On this basis, the seismic performance of the two connection joints was further compared and analyzed, including hysteresis curve, skeleton curve, stiffness degradation, energy dissipation performance and residual deformation.
The results of finite element analysis showed that the two types of joints damage under reciprocating loading were relatively similar, and both were plastic hinge section damage at the bottom of the column.The hysteresis curves of the forms of the two joints were full and there were no obvious pinching phenomenon. The equivalent viscous damping coefficients were between 0.25 and 0.28, and the seismic performance of the two was good. The elastic interlayer displacement angle ranged from 1/36 to 1/22, and the elastic-plastic interlayer displacement angle was 1/15, both of which met the requirements of Code for Seismic Design of Buildings(GB/T 50011—2010). Compared with the form of the joint with built-in octagonal core barrels, the yield bearing capacity of the form of the joint with built-in cross-shaped core barrels was reduced by 7.5%-16.3%, the peak bearing capacity was reduced by 7.8%, and the ductility performance was improved by about 66.7%. When the displacement angle was 1/100, 1/50 and 1/15, the stiffness of the joints with built-in cross-shaped core barrels was 0.94%, 2.05% and 8.43% higher,respectively. When the negative load was loaded to the displacement angle of 1/100,1/50 and 1/15, the stiffness of the joints with built-in cross-shaped core barrels was 0.91%, 1.85% and 8.51% higher, respectively. After loading, the residual deformation of the joints with built-in cross-shaped core barrels was 4.9% lower than that of the the joints built-in octagonal core barrels. The above research results showed that the joints with built-in octagonal core barrels had higher bearing capacity and energy dissipation capacity, and their hysteresis curves were fuller ; the stiffness degradation of the joints with built-in cross-shaped core barrels was gentle, the residual deformation after the earthquake was small, and the ductility performance was better. Both joint forms have good application prospects.