Study On The Influence Law Of Gymnasium Hung-scoreboard On The Seismic Response Of Spatial Grid Structure

With the development of national fitness and various sports events,the construction of gymnasium has become a major demand to meet people’s sports needs and high-level urban construction.In recent years,the application of hung-scoreboard,a large quality display device which is flexibly suspended in the center of the site,has increased significantly in the gymnasium.After investigation and analysis,the spatial grid structure is the type of gymnasium roof structure mainly used to carry the hung-scoreboard.Spatial grid structure has the characteristics of large span,many degrees of freedom and dense frequency,and the seismic response is more complex.The existing literature on the seismic response analysis of spatial grid structures is mainly aimed at the situation without hung-scoreboard,while the influence law of flexible suspension large mass hung-scoreboard on the natural vibration characteristics and seismic response of spatial grid structures needs to be revealed.The spatial grid structure is mainly divided into reticulated shell structure and grid structure.In this paper,the flexible suspension hung-scoreboard single-layer spherical reticulated shell coupling system model and the flexible suspension hung-scoreboard grid structure coupling system model are established respectively.The natural vibration characteristics and seismic response of the coupling system are analyzed by Lanczos method and explicit dynamic elastoplastic time history analysis method respectively.The differences of the vibration mode and frequency of the coupling system,the peak value of node acceleration and the peak value of rod axial force are compared when the actual hanging hung-scoreboard and the hung-scoreboard are simplified to a fixed mass.The effects of the changes of sling length and hung-scoreboard mass on the natural vibration characteristics and seismic response of the coupling system are discussed.The hanging hung-scoreboard has a great influence on the natural vibration characteristics of reticulated shell and grid.In general,hanging the hung-scoreboard will reduce the natural vibration frequencies of the two structures as a whole.The first three natural vibration frequencies are close to 0 and are not affected by the change of sling length and hung-scoreboard mass.The quality of the hung-scoreboard only has a certain influence on the low-order natural frequency of the two structures,and has little influence on the highorder natural frequency;The length of the sling only has a certain influence on the loworder natural frequency of the reticulated shell,but has little influence on the high-order natural frequency of the reticulated shell and the natural frequency of the grid.When the hung-scoreboard is suspended,the first three vibration modes of the two structures are hungscoreboard swing,and the fourth and later gradually become the common vibration of the hung-scoreboard and the main structure.For the single-layer spherical reticulated shell structure,a platform needs to be set under the center of the reticulated shell to hang the hung-scoreboard.Compared with the hung-scoreboard simplified as a fixed mass,the suspended hung-scoreboard has an obvious amplification effect on the node acceleration peak of the single-layer spherical reticulated shell,and the amplification of the node Z-direction acceleration peak is the most significant,which is mainly due to the small vertical stiffness of the reticulated shell.When the seismic wave is input in one direction,the hanging hung-scoreboard has a great amplification effect on the peak axial force of some ring rods,which can be amplified by 5 times at most;When the seismic wave is input in three directions,it can greatly amplify the peak axial force of the cross bar of individual platforms,up to 130 times.For the grid structure,the hung-scoreboard can be hung on the lower chord of the grid by using the advantages of the structure,avoiding the use of platform and effectively saving space.Compared with the hung-scoreboard simplified as fixed mass,the amplification effect of suspended hung-scoreboard on the peak horizontal acceleration of some grid nodes is more significant,and on the whole,the amplification effect on the peak horizontal acceleration of nodes is greater than that on the peak vertical acceleration.The hanging hung-scoreboard has a great amplification effect on the peak axial force of the outer upper chord and some web members.When the seismic wave is input vertically and in three directions,when the sling length is 9m and the hung-scoreboard mass is 20 t,it will have a great amplification effect on the axial force of more members.In conclusion,the amplification effect of the suspended hung-scoreboard on the peak acceleration of nodes and the peak axial force of members of single-layer spherical reticulated shell and grid structure cannot be ignored.The method of simplifying the hungscoreboard into a fixed mass is dangerous.It is suggested to take the envelope value of seismic response results under the combination of different sling length and hungscoreboard mass as the design basis.