Analysis on the Hysteretic Behavior of Special Truss Moment Frame Connections

The brittle failure of traditional beam-to-column connections in moment resisting steel frame was found in the investigation reports of Northridge earthquake (1994) and Kobe earthquake (1995), which led to the poor ductility and deformation capacity of moment resisting steel frame. Therefore, the behavior of beam-to-column connections became a key factor that affected the seismic behavior of moment resisting steel frame. To adapt to the characteristics of large-span public buildings (such as hospitals, shopping malls, stadiums, etc.), the Special Truss Moment Frame (STMF) was attempted to use in some large public building. The STMF structure had the large lateral stiffness, high lateral bearing capacity, and great energy dissipation capacity, which had a wide application prospects. However, the beam-to-column connection between steel column and truss beam was easy to break, especially at the joint weld of chord and steel column, which led to the poor overall ductility and deformation ability of STMF structure. At present, the relative researches on the STMF connections were still small, which was not conducive to the engineering application of STMF structure. In order to clarify the hysteretic behavior of STMF connection, the side beam-to-column STMF connection was selected as the research object. The mechanical characteristics of STMF connection was analyzed through the finite element method, and the effects of the main relative design parameters on its hysteretic behavior were systematically evaluated that could provide reference for its engineering application.Firstly, the BASE specimen of STMF connection was designed in this study, and the three dimensional geometry models were established and meshed by CAD and HyperMesh program, respectively. The ABAQUS program was adopted to build the micro finite element model and to conduct the cyclic analysis. Secondly, the three series STMF connections were designed on the basis of BASE specimen, and the main design parameters, such as chord section, truss height, and end diagonal web member section, on its hysteretic behavior, moment resisting capacity, deformation capacity, yielding mode, and Mises stress distribution, were considered.The analytical results showed that the Mises stress was considerably high at the bottom chord member in STMF connection. The bottom chord member of end segment occurred the overall and local buckling at the nonlinear stage. With the increase of chord section, the moment resisting bearing capacity, and initial rotation stiffness of STMF connection took on the increasing tendency, but had the slight influence on the hysteretic loop shape. With the increase of truss height, the moment resisting bearing capacity and initial rotation stiffness, and energy dissipation also exhibited the increasing tendency except that the energy dissipation had a slight influence, but had the little effect on the failure mode. Under the consideration of non-weaken inclined end web member, the section of inclined end web member did not produce any obvious effect on the hysteretic behavior of STMF connections.