Behavior of TOBs bolted curved T-stubs to steel tube with internal stiffener.

Internal stiffeners can effectively enhance the structural performance of Thread-fixed One-side Bolts (TOBs) bolted steel beam to circular tubular column connection by increasing the out-of-plane flexural capacity of the column wall and the anchorage length of the TOBs. Five TOBs bolted T-stubs to circular steel tube specimens with three different forms of internal stiffeners, substituting the tension zone of beam to column joint, were designed and tested in this paper to determine a reasonable form for the internal stiffener. Test results showed that the strengthened specimen could prevent undesirable plastic deformation of tube wall and hole threads shear failure. The Type-II stiffener consisting of an internal steel tube with a longitudinal rib performed the optimum strengthening effect. Finite Element analysis is conducted to analyze phenomena that could not be directly observed during the test. It is found that the hole threads in the stiffener wall provide considerable anchorage force, which may be larger than that provided by the hole threads in the steel tube in the late loading stage. Parametric studies are also conducted on the wall thickness, rib thickness, and installation gap of the Type-II stiffener. The results show that the stiffener wall thickness is the main factor affecting the strengthening effect and the installation gap should be controlled within 2 mm to ensure the strengthening effect. Finally, design approaches are presented to predict the carrying capacity of the strengthened connection, and the validation against the test and FE results shows reliability and stability. • Five specimens were tested to explore the optimum strengthening method for TOBs bolted circular steel tube joints. • Finite Element analysis is conducted to evaluate the axial bolt forces provided by the tube wall and stiffener wall, respectively. • Parametric analysis is conducted on the connection with Type-II stiffener. • Design methods are proposed to predict the failure mode and the yield strength of the connection. [ABSTRACT FROM AUTHOR]