Analysis And Design Of Ultimate Load-Carrying Capacity For Top-and Seat-Angle Semi-rigid Spatial Steel Frames

Most of beam-to-column connections in steel frames are semi-rigid.Their behavior lies between perfectly-rigid connection and ideally pinned connection.The actual effects of connection behavior must be considered in design of steel frames.A conservative estimation may be provided in conventional design methods using elastic global analysis and the limit state member design.In order to overcome the difficulties of the conventional approach, second-order elastic-plastic analysis and design of semi-rigid spatial steel frames should be directly performed.Top- and seat-angle connections are analyzed to obtain mechanical behavior under static loads.The three-parameter power model proposed by Kishi-Chen is adopted.The practical procedures for determining the initial connection stiffiness and ultimate moment capacity are provided.The results show that the behavior of semi-rigid connections is greatly influenced by the angle's thickness,length, distance between the axes of the bolt which in tension and flange of the beam,the bolt diameter and the height of the beam.Based on the finite-deformation theory of continuum mechanics and stress-resultant yield surface plastic flow rule,stiffness matrixes for semi-rigid spatial steel frames are derived using Kishi-Chen power model to describe the nonlinear behavior of semi-rigid connections.An analytic procedures have been designed.The example is given to show the effects of top- and seat-angle semi-rigid connections to the ultimate load-carrying capacity of spatial steel frames.A overall design method of top- and seat-angle semi-rigid spatial steel frame is first summarized based on the above analysis.A contrast about load combinations and constraint function for design of steel structure between China and USA is given, some concluding remarks are then made.The proposed method achieve the LRFD design requirements without tedious separate member capacity checks,including K -factor calculations,can account for an inelastic moment redistribution and thus may allow some reduction of steel weight.The example also indicates that some stabilization problemes should be noticed for the design of multi-story semi-rigid spatial steel frames.