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

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 1 033 kN, the maximum deflection was 59.27 mm, and the maximum stress is 236.40 MPa.