The Global Stability Performance Of Stormproof Playground Grid Roof Under Earthquake

Current research on stability issues mostly focuses on reticulated shell structures.In actual disasters,especially earthquake disasters,the grid structure damage occurs from time to time,and grid instability(including member instability and local instability)is more obvious.For this reason,this article conducts an in-depth study on the stable failure mode of the grid roof structure of stormproof playground under earthquake.The numerical analysis methods of static and dynamic stability(seismic action)of the grid structure are discussed,and suggestions for the selection of the element simulation in the stability analysis of the grid structure are given.In the internal force analysis of the grid structure,it is usually simplified to a two-force rod mechanics model.The calculation length method is used to ensure the stability of the members during the design,and the overall stability of the grid is no longer checked.Under the action of earthquakes,the members of the grid will often buckle,and this model of the rod element based on the two-force rod model cannot consider member buckling.The global stability of grid roof cannot be accurately analyzed using this model.In order to consider member buckling for analyzing global stability of stormproof playground grid roof under earthquake and the selection of units to analyze the stability problem is discussed.The main content and conclusions of the paper are as follows:(1)In this paper,the selection of elements and how to consider member buckling are discussed,and the stability of the articulated compression bars and articulated trusses in the structure of the members is analyzed by analytical method and approximate analysis method including the Virtual Displacement Principle,Principle of potential energy,Timoshenko energy method,the Rayleigh-Ritz method,and Finite element method.It shows the importance of displacement function in finite element analysis and provides a theoretical basis for element selection.(2)Based on the obtained selection unit and the method of considering the instability of the members,the eigenvalue buckling analysis of the grid structure and the grid with the lower frame is carried out.If the beam element does not consider segmentation,the instability of the rod cannot be considered,the overall stability of the grid will also be overestimated.Considering the section of the beam element,the instability of the member can be considered,and the linear buckling load coefficient of the lowest order is accurate.When the beam element uses the first-order shape function,the second-order shape function and the third-order shape function,the lower the order of the shape function,the less accurate the linear buckling load coefficient.No matter which shape function is used,if the beam element does not consider the segmentation,the instability of the member cannot be considered,and the lowest-order buckling mode is inaccurate.It is recommended to use segmented beam elements to analyze the stability of the grid.The segmented beam elements are used to analyze the static nonlinear stability of the grid.The results show that the grid may undergo strength failure under static force.(3)Analysis of global stability of stormproof playground grid roof under earthquake,considering the influence of member buckling,and considering the impact of imperfection.The analysis shows that if the grid members are not segmented,the buckling of the members cannot be considered,but the grid structure will be partially destabilized.A multi-segment beam model is adopted,and the buckling of the members is considered,and a more ideal ground motion amplitude-node(the end node of the member and the middle node of the member)displacement curve is obtained.The curve has obvious inflection points and bifurcations.It shows that under the action of strong earthquakes,the grid roof may undergo instability failure,rather than the strength failure mode.