Forced Behaviors And Ultimate Load-carrying Capacity Analysis Of Steel Frame Structural System

Steel frame structures apply rapid development in recent years in our country. This kind of structure has spread greatly span with characteristics of its good stress performance, less weight, good seismic performance, rapid construction, high level of industrialization, capable of recovery and so on, so it has developed spreadly in building structures.For its shortcoming, P-delta effects play an important role in the response of lateral loads to the steel frame structures which Shear forces and bending moments in structural members induced by gravity loads are increasing. Stiffness of the structure is reduced by P-delta effects which lead to an increase in drift. In structural design beams and columns are always in non-elastic stage. Compare to elastic stage, P-delta effects will make the whole building collapsed. Although a simplified method for calculating second-order elastic analysis is adopted in order to consider second-order effect in the book Code for design of steel structure (GB50017-2003). The method adopted by the code is only confine to the stage of elasticity. Really, P-delta effects play a key role in response of structural ultimate bearing capacity.While considering the axle strength of the crossbeam influencing the strength of steel frame steadily, this paper has inferred rigidity reduction coefficient of the crossbeam that the code adopts and revise it.Based on the plastic zone method, this paper has set up the calculation model of steel frame through a software ANSYS finite element procedure in order to analyze ultimate bearing capacity of steel frames. This paper considers it the material nonlinear, geometric nonlinear, residual stress and initial geometrical imperfections to the impact of ultimate bearing capacity of steel frames.To testify the accuracy of this paper's calculation model, it is used to compare with the outcome of quadrilateral steel frames of Hunan University, the results show that the both conform to each other. It proves that this paper's analytical method is reliable and has higher precision and can replace full-scale experiment.This paper simulates the whole process of elastic-plastic behavior of ultimate bearing capacity and is compared with results of defective of Vogel's portal frame and Vogel's six story frame, the analyzed method has been definitely proved practical.Residual stress of steel component section does not influence the rigidity at elastic stage of the structure. But make yield strength of steel structures advanced greatly. To the final ultimate bearing capacity, residual stress influence is not so great. Initial geometrical imperfections obviously make lateral rigidity of steel structures drop, but the final ultimate bearing capacity is not greatly influenced either.Finally, combined with the book Code for design of steel structure (GB50017-2003), this paper analyzes about second-order elasticity in the norm and gets some helpful conclusions.