Research On The Elastic-Plastic Behaviors And Seismic Behaviors Of Plane Steel Frames With Semi-Rigid Connections

People always treat beam-to-column connections as fully rigid or pinned ones to simplify the calculation of the steel frames in traditional designs. In fact, most of beam-to-column connections will be neither pinned nor fully rigid ones. They belong to semi-rigid ones. Extensive studies show that the behaviors of semi-rigid connections would make great effects on the behaviors of steel frames, such as the internal forces, the horizontal deflection, the ultimate load-bearing capacity and the daynamic behaviors, which could not be neglected to design the steel frames.In order to study the nonlinearity performance of steel frames with semi-rigid connections, several key problems on it are studied.1. According to the mechanics performance of semi-rigid connections, a new calculation model of this kind of structure is presented in this paper, which suit to all kinds of analysis methods of plane steel structures, such as the elastic analysis, the elastic-plastic analysis, the time-history elastic analysis and the time-history elastic- plastic analysis. And it simplified the nonlinear analysis procession of structures.2. Based on the theory of beam-to-column, the elastic stiffness matrix and geometrical stiffness matrix of this kind of structures are derived by revising its rotation-displacement equations. According to the superposition principle under small deformation, the moment expressions at two ends of element with semi-rigid connections are inferred under any load. The second elastic analysis and the second elastic-plastic analysis of this kind of structures are made in these ways. According to this model, two corresponding programs of this kind of structures are worked out in FORTRAN language. And the effects of semi-rigid behaviors are analysised in these programes.3. The simplified methods of structural stability and internal forces are presented according to the mechanic performances of semi-rigid connections. The critical gravity load of each floor can be calculated in this way. Meanwhile, the internal forces and horizontal deflections can be obtained under all kinds of loads.4. Revising its rotation-displacement equation, a mass matrix of this kind of structures is derived by virtual principle in this paper. The time-history elastic and elastic-plastic analysis of this kind of structures are made in Rayleigh damping matrix and Wilson-θnumerical integration method. Moreover, two corresponding programs of this kind of structures are worked out in FORTRAN language in this way. The earthquake responses of this kind of structures with braced and unbraced are analysised in these programes. The results show that the unbraced steel frames with semi-rigid connections is sensitive to the semi-rigid behaviors, and it is not suitably to use semi-rigid connections with small rotational rigidity in unbraced high-rise steel frames.5. A new storey model is presented in this paper. Based on the superposition principle under small deformation, the formulas of its lateral stiffness and horizontal deflection are derived. Meanwhile, the formula of height ratio of inflection point of column is derived. The effects of several parameters of structure on its natural period are analyzed, and simplified formula of its natural period is fit in this thesis. The numerical results show that this storey model and simplified formula is reliable and can be used in preliminary seismic design of this kind of structures.