Research on effective length of bar of space steel structure of the Shenzhen Universiade Sports Center

A new type of structural system named as single-layer folded-plane latticed shell structure was adopted for the steel roof of the main stadium of the Shenzhen Universiade Sports Center.The whole structure was composed of numerous triangle grids bent in different angles with subordinate triangle grids inside.The subordinate triangle grids were connected to the quarter point of the intersecting line of two surfaces by the subordinate bar of the welded combined box section.The stability of the major bar in the intersecting line was affected by many factors,such as the border,the subordinate bar in the surface,and the angle between the two surfaces.Currently,there is no code specifying the calculation of the effective length of the major bar.In order to calculate the effective length of the major bar,the instability model of the structure by linear method was analyzed first.Second,based on the results from the linear analysis,the instability model of the structure was analyzed with geometric nonlinear method.Then the critical loading capacity of the major bar was obtained.At this step,the effect of nonlinear deformation of adjoining bars was considered.Third,the effective length of the major bar was calculated according to the formula of instability capacity of varied-axial-force bar with pinned joint.The research shows that: 1) the effective length of the major bar is greatly affected by the angle between two surfaces and the stiffness of the two ends;2) the coefficient of the effective length of most major bars is less than 1.0 or close to 1.0;3) the coefficient of the effective length of vertical bar is more than 1.0 due to the influence of horizontal displacement.Both the unloading test of the main stadium and the overall stability analysis justified the research results.