The Second-Order Elastic-Plastic Analysis And Design Methods' Research Of Space Steel Frames

The traditional designs methods of steel frames can be divided two steps: to analyze whole structure by one-order elastic method and to design individual element by ultimate strength design method in which effective length coefficient is considered. However, the accurate ultimate strength of whole structure cannot be gained by those methods. Furthermore, the valid code for design of steel structures establishes the second-order elastic analysis simplified methods only for plane steel frames. Therefore, it's necessary to research space steel frames about it's second-order behavior.According to the finite-deformation theory of nonlinear continuum mechanics and stress-resultant yield surface plastic rule, the large deformation elastic-plastic analysis of the ultimate strength of space steel frames structure is developed, which can consider the effect of axial force, shear force, moment, torsion and shear deformation.In this paper, the simplified second-order elastic design method, which comes from the code for design of steel structures, is used to analyze space steel frames, and the analytical results is compared to those of the accurate second-order elastic method. In the numerical example, three varieties frames are compared, including 1 bays-1 stories, 1bays-2stories and 1bays-3stories frames, and three kinds of load combinations are considered. The conclusion for the example is that the method of this paper can be used to calculate not only main directional second-order moment, shear force and second-order axial force but also the horizontal displacement of multiplayer frames. The error analyses verify that the method is reliable and can helpful to engineers in structural design.