Effect On Seismic Spatial Variability Of Subsupported Plate Space Trusses

Large span space structure mainly includes grid structure,shell structure,suspended cable structure,thin film structure,aeration structure and other structural forms.This kind of structure form is flexible and changeful,and its shape is either shocking or beautiful,so it becomes the preferred structural form of various large public buildings.As one of the members,the flat grid structure is widely used in our daily life due to its many advantages,such as reasonable stress,light weight,low construction difficulty,rapid construction period,low cost and environmental protection of materials.As the urban population becomes more and more concentrated,there will be a larger scale and larger span of plate and grid structure constantly appearing in our life.This kind of large-span structure faces many unique engineering design problems.Earthquake is a common natural phenomenon and one of the main factors to be considered in a structure.In the past,people often think that statically indeterminate number of large-span spatial structure,light weight,seismic performance is good,so when considering earthquake action is often a consistent input for the earthquake response of structure,but along with the continuously deepening perfecting theory research,we found that for large span space structure building size is larger,the influence of the spatial variability of earthquake effect on structure is very significant,considering seismic spatial variability of multi-point inputs than consistent input adverse effect on building more and more close to reality.Based on the above reasons,this paper considers the influence of the lower support structure and conducts a study on the seismic spatial variability effect of the large-span flat-bed frame structure.The following specific research results are obtained:1.The plane size,respectively,set up to 60 m×60 m,90 m×90 m and 120 m×120 m is put four cone plate grid structure finite element model of the upper space truss rods hinged on both ends of the bar element are adopted to simulate and calculate,satisfied the bar under the action of static design load,the section size of trigonometric series synthetic method based on spectral representation considering traveling wave effect and coherent effects of earthquake ground motion field,space truss structure by finite element analysis software ANSYS and considering the effect of the ground motion spatial variability time history analysis.2.Taking into account the changes of roof load,seismic acceleration and apparent wave velocity parameters of the flat grid structure,as well as the travelling wave effect and coherent effect,the structural response of the flat grid structure with no lower support structure with uniform input and multi-point input under three-dimensional seismic input was investigated.Comparative study shows that for long-span flat space truss structure are not the lower bearing,when considering the earthquake action of multipoint input,axial force of the structure of the node displacement and bar will be amplified,especially network frame around the bar and the node,if in seismic design of structure seismic action is not taken into account when more input,the design result be unsafe.At the same time,the factors influencing the calculation results are analyzed.3.A 60 m and 90 m lower support span quadrangular plate grid structure model is established.Considering the traveling-wave effect and coherence effect,the dynamic time-history analysis method of the whole load domain is used to analyze the structural response of the above models with consistent input and multi-point input under 3d seismic input respectively.The results show that,when considering the influence of the lateral stiffness of the lower support structure on the upper grid structure,the vertical displacement of the node of the lower grid structure with multi-point input will increase or decrease according to a certain rule,and the axial force of the bar will obviously decrease.