Research On Ultimate States And Design Method Of Cold-formed Steel Portal Frame Structure

Bearing capacity ultimate state, normal use ultimate state and design method is studied by using nonlinear finite element method (FEM).Firstly, test samples of cold-formed steel portal frame involving materials nonlinear and geometric large deformation are simulated by FEM. The influence of wall of bolt-hole slipping and initial imperfection on the ultimate load-bearing capacity and deformation of cold-formed steel potal frame is studied. The method of adopting spring replacing the wall of bolt-hole is presented. Based on these studies, the results of test confirm the accuracy and reliability of the results of FEM.Secondly, variable parameter analysis to cold-formed steel portal frame is used through changing height of web, width of flange, rigidity of column-foot, sizes of eave and apex brackets, linear rigidity of components, frame slope, etc. The results of finite element analysis show that the width of flange and frame slope have a little influence on the ultimate load-bearing capacity of the cold-formed steel portal frame. With the increasing of height of web, rigidity of column-foot and sizes of eave and apex brackets, the ultimate load-bearing capacity raises obviously. However, with the increasing of height or span of frame, the ultimate load-bearing capacity decreases.Thirdly, the deformation of a three-dimensional cold-formed steel portal frame mode is analysed. The influence of shear diaphragm action to deformation of cold-formed steel portal frame including vertical deformation and lateral deformation is studied. It also indicates that the structure of cold-formed steel portal frame is controlled by bearing capacity ultimate state on its designing. In addition, research on ateral deformation of the portal frame through varying vertical load shows that second-order effect of lateral deformation is markable in cold-formed steel portal frame. Based on these studies, some suggestions are promoted, such as definite of eave and apex brackets sizes, influence coefficient of diaphragm action, deflection limits of structures or components, etc.Finally, referencing above research achievements, current design codes or documents, simplified design method of cold-formed steel portal frame system is promoted. It includes calculated method of bolt-hole elongation stiffness, simplified calculated method of joint-rigidity, design method of components, design method of joints, etc. Based on the design method, this text has done a trial design to cold-formed steel portal frame, and compares its economic with light-weight portal frame. The results show that cold-formed steel portal frame structure has a better economy in the field of without crane and little-span building.