Studies On Stability Behavior And Design Method Of Grid Tube Structures

Grid tube is a type of structure system that has been widely adopted in high-rise building and TV tower structures.It can be classified into orthogrid tube and diagrid tube according to the arrangement of columns and beams.When the grid structure is adopted in high-rise building and TV tower structures,floors may be removed because of architectural request at certain region in height,which leads to that the grid tube in this region would be prone to buckle under vertical loads because of a lack of lateral support.In this dissertation,the cylindrical orthogrid tube and hyperboloid diagrid tube have been focused on and their elastic and elasto-plastic stability behavior have been investigated extensively to develop a design method.Firstly,it is found that the cylindrical orthogrid tube would likely to fail by two buckling modes under axial compression,namely global longitudinally flexural buckling and circumferential multi-wave buckling.The ring beam's restraining action on the columns in two buckling modes are explored separately,and corresponding elastic buckling loads of three-story cylindrical orthogrid tube are derived by using energy method.Based on these obtained results,the elastic buckling loads of multi-story cylindrical orthogrid tube are obtained by numerical fitting,leading to an explicit expression of the normalized slenderness ratio,a key design parameter.Then,a design method of the cylindrical orthogrid tube under axial compression has been established by the relationship of the reduction factor of strength and the normalized slenderness ratio according to the nonlinear FE analysis.A strength design requirement for the ring beams is also proposed to avoid their premature failure before the buckling of columns.The FE numerical analyses have been conducted on the elastic stability behavior and load-carrying capacity of the cylindrical orthogrid tube subjected to pure bending moments.Then,the normalized slenderness ratio and reduction factor of strength of the cylindrical orthogrid tube subjected to pure bending moments are established for further foming a comprehensive design method.Moreover,the load resistance of cylindrical orthogrid tubes under combined bending moment and axial compressive actions is investigated by using nonlinear FE numerical analyses.The obtained results indicate that the interactive N-M curve for the stability bearing capacity prediction of the cylindrical orthogrid tube can be approximately considered as a linear relationship,hence the stability bearing capacity of the cylindrical orthogrid tube under this combined load actions can be designed by simply adopting a linear equation with two terms of axial compression N and bending moment M.The stability behavior of the hyperboloid diagrid tube is also investigated by FE numerical analyses,especially the effects of the stiffness of the top and middle ring beams on the stability behavior of the hyperboloid diagrid tube are focused on.Based on these investigations,a lower limit of axial stiffness of the top ring beam has been developed.Moreover,the middle ring beams are recommended to be arranged densely in the hyperboloid diagrid tube,which will remarkably improve its stability bearing capacity.A reduced-scale model of the hyperboloid diagrid tube in the China Comic and Animation Museum was tested,which reveals that it fails according to regional multi-column instability mainly on both sides of an opening.The additional numerous FE numerical analyses have been conducted,in which the effects of overall initial geometric imperfection,the ratio of stiffness between the secondary and primary columns,in-plane stiffness of top ring beam,and dimensions of portal columns on the load-carrying capacity and failure mode of the hyperboloid diagrid tube have been investigated.