The Second-Order Elastic-Plastic Analysis Research Of Semi-Rigid Space Steel Frames

Conventional analysis and design of steel frame structures are performed using the assumption that the connections are either fully rigid or ideally pinned. However, the connections in practice fall between the two extreme cases of fully rigid and ideally pinned. They are semi-rigid connections. This assumption of connections makes errors of calculating results and gets incorrect conclusions. Although in Chinese Code for design of steel structures the semi-rigid connections were referred to. It isn't specified how to use it in design. At the same time, there are no provisions about second-order analysis of space steel frames. So the second-order elastic-plastic analysis of semi-rigid space steel frames has academic and practical significance.After studying current advanced analysis theory of rigid and semi-rigid steel frames home and abroad, the stiffness matrixes for semi-rigid space steel frame were derived based on the finite-deformation theory of continuum mechanics and stress-resultant yield surface plastic rule by using Kishi-Chen power model to describe the nonlinear behavior of semi-rigid connections. They considered the combined nonlinear influences of semi-rigid connections, second-order, material and shear deformation on the behavior and strength of semi-rigid frames. Finally, two analytic procedures have been designed.The case study indicated that the increment of elastic-plastic force of shank ends could be exactly calculated by the stiffness matrix which including the effects of second-order and semi-rigid connections. Precision of the program was acceptable and reliable. Compare the analytic result of rigid steel frames with the analytic result of semi-rigid steel frames, the conclusion could be concluded that the semi-rigid connections could augment displacement of frame in two orientations, and such effect increased with the number of frame floors increasing. Moment of beam support was lessened, by contraries moment of middle cross section of the beam was enhanced because of semi-rigid connections. Furthermore, the second-order effect and shear deformation of the structures were magnified due to semi-rigid connections, the ultimate load resistance of the structures was reduced simultaneity. Therefore, the characteristics of semi-rigid connections must be estimated and considered in steel structural analysis and design.