Research On Seismic Behavior Of Separated Structural System Based On Variable Cross-Section Braces

With the rapid development of national economy and technology, the steel structures are playing important role in modern buildings. The research on seismic behavior of steel structures is particularly important for the development of national society, economy and disaster prevention as steel structures are challenged by the irresistible natural disasters, such as earthquakes. Under the effects of strong earthquakes, the steel structures have an advantage to prevent seismic collapse due to lighter weight, good ductility. But the deformation resistance, joints ductility and economy of the steel structures should be further improved. Improving the structure system of steel building is one of the most direct and effective measure to improve the bearing capacity, seismic capacity and the economy. According to the stress characteristics of axial forced components and high-rise steel buildings, this paper proposes a new hinged steel frame system, which based on the variable cross-section braces. The seismic behavior of this structure system, including the research on the stability behavior and hysteresis behavior of variable cross-section braces, were analyzed in this thesis.As part of this work, the elastic stable theoretical analysis has been carried out for I variable cross-section braces, by employing the effective inertial moment and effective length while the variable cross-section brace has the same overall buckling load as the constant cross-section brace. The finite element method(FEM) model was developed with finite element software ANSYS to analyze the elasto-plastic stability for I variable cross-section braces. The practical approach for checking the overall stability of I variable cross-section braces was showed based on a large number of examples. Compared to the constant cross-section braces with the same steel quantity, the stability behaviors for rectangular hollow variable cross-section braces and circular hollow variable cross-section braces were analyzed respectively. Different slenderness ratio and wedge ratio were considered in the analysis to evaluate how these parameters influenced the ultimate bearing capacity of elasto-plastic stability of variable cross-section braces.A parametric analysis was conducted to investigate the influence of the slenderness ratio and wedge ratio on hysteresis behavior of axially forced variable cross-section braces under low-cycle load using the FEM model. The bearing capacity, stiffness and energy dissipation capacity of three kinds of variable cross-section braces were analyzed by comparing with the constant cross-section braces. The FEM model for two cases of the separated structures based on rectangular hollow variable cross-section braces were created to analyze structural responses under a number of ground motion records. The time-history of the structural vertex displacement, acceleration, interstory drift and base shear were analyzed by comparing with the steel framework with rigid connections.