空间管桁架结构卸载方法的有限元仿真模拟分析

Finite Element Simulation Analysis of Unloading Method of Space Tube Truss Structure

钢结构建筑因其强度大、韧性好、可塑性强、施工周期短、绿色环保等优势,得到了现代设计师们的青睐。在钢结构现场安装中,当钢结构整体吊装完毕并将荷载全部施加完后,需要进行卸载处理。大跨度空间管桁架结构在卸载中,由于其管件数量众多,节点形式各不相同,造成结构整体内力复杂多变,各杆件之间的受力难以确定,若盲目地选定其卸载顺序可能会造成结构局部受力过大,从而导致结构产生塑性变形甚至结构破坏,所以确定合理的卸载顺序就变得尤为重要。以石药健康城项目为研究对象,给出了一种空间管桁架结构的卸载方法,并进行了有限元仿真模拟。在卸载过程中,首先进行初级卸载,即将非主要受力支架进行一次性拆除,然后进行二级卸载,即再对主要受力支架进行分步卸载。整个过程采用MIDAS/Gen有限元分析软件对结构和主要受力支架进行仿真模拟分析,考虑到仿真模拟的目的即确定卸载顺序,所以支架用?219×10的钢管来代替,且设置为只受压单元,卸载时采用钢管两端施加强制位移的方式。经确定,卸载顺序以模拟出来的支架支反力大小为主要依据,对支反力大的支架进行优先卸载,具体以最大支反力的两组支架为当前卸载步,每次卸载量为10 mm,每个卸载步都进行一次受力计算,根据当前支反力的大小确定下一次的卸载顺序,以此往复模拟卸载,直至最后卸载完毕,并将模拟出来的具体卸载顺序应用于实际施工中作为指导。另外,在整个模拟过程中,对于出现支反力为0且不再发生变化或变化不大的支架直接进行拆除,不再进行模拟计算。在模拟分析过程中,记录结构杆件的应力变化情况,并标记出发生最大应力的杆件,通过杆件应力的大小及变化情况来证明此卸载方法的可行性,在现场实际卸载过程中也可以对这些杆件进行应力监测,确保卸载过程中整体结构的稳定性。经模拟分析,整体卸载完毕共需19个卸载步,在卸载过程中并未出现变形及应力超限的情况,模拟过程中的结果分别为:支架的最大支反力为1033 kN,结构的最大挠度为59.27 mm,最大应力为236.40 MPa。

Steel structure buildings are favored by modern designers because of their advantages of high strength,good toughness,strong plasticity,short construction period,and green environmental protection.In the on-site installation of the steel structure,after the overall hoisting of the steel structure is completed and all loads are applied,unloading treatment is required.For the unloading of the long-span space tube truss structure,due to the large number of pipe fittings and different node forms,the overall internal force of the structure is complex and changeable,and the force between each member is difficult to determine,so blindly selecting the unloading sequence may it will cause the structure to be overstressed locally,resulting in plastic deformation or even structural damage of the structure,so it is particularly important to determine a reasonable unloading sequence.Taking the CSPC Health City project as the research object,an unloading method of the space tube truss structure was given,and the finite element simulation was carried out.Specifically,in the unloading process,primary unloading was performed first,that was,the non-main stress-bearing support was removed at one time,and then secondary unloading was performed,that was,the main stress-bearing support was unloaded step by step.In the whole process,MIDAS/Gen finite element analysis software was used to simulate and analyze the structure and main stress-bearing supports.Considering that the purpose of simulation was to determine the unloading sequence,the supports were replaced by?219×10 steel pipes,and were set as compression-only units,when unloading,the forced displacement was applied at both ends of the steel pipe.It was determined that the unloading sequence was mainly based on the simulated support reaction force of the support,and the support with large support reaction force was preferentially unloaded.Specifically,the two groups of supports with the largest support reaction force were the current unloading step,and the unloading amount was 10 mm each time,each unloading step was subjected to a force calculation,and the next unloading sequence was determined according to the size of the current support and reaction force,and the unloading was simulated reciprocally until the final unloading was completed,and the simulated specific unloading sequence was applied to the actual construction as a guide.In addition,in the whole simulation process,for the supports whose support and reaction force was 0 and did not change or change little,the support was directly removed,and the simulation calculation is no longer carried out.In the process of simulation analysis,the stress change of structural members was recorded,and the member with the maximum stress was marked.The feasibility of this unloading method was proved by the magnitude and change of the member stress.Stress monitoring of these members could be performed to ensure the stability of the overall structure during unloading.According to the simulation analysis,19 unloading steps were required to complete the overall unloading.During the unloading process,there was no deformation and stress exceeding the limit.The extreme values of the results in the simulation process were:The maximun support reaction force of the bracket is 1033 kN,the maximum deflection was 59.27 mm,and the maximum stress is 236.40 MPa.