Abstract: A long-span circular truss structure with a steel structure roof span of 66 m in a theater was considered to be divided into four unit structures due to construction conditions, and the unit structure is assembled on the ground and hoisted as a whole. Each unit structure is an irregular steel truss. MIDAS was used to calculate and analyze the changes in the stiffness and strength of the steel structure unit during the lifting process to determine whether it met the construction requirements. In order to find the best position of the lifting point of the shard unit, the center of gravity position of the shard unit was calculated by the definition method of the center of gravity position. The unit structure was selected four ears arrangement points, and the quadrilateral geometric center formed by the arrangement points was close to the center of gravity of the unit structure. According to the setting principle that the average distance between the point and the center of gravity of the unit structure gradually, three kinds of hanging point arrangement schemes were determined and simulated by MIDAS. The lifting lug node was restrained by node elastic support, which imposed small stiffness constraints. The truss was simulated by rod elements, considering the influence of the hoisting process, and the dynamic effect coefficient was 1. 4. The structural element stress, node vertical displacement and stress ratio were considered to determine the rationality of the plan, and to choose the optimal hanging point layout plan.
After 4 unit structures were hoisted in sequence, the welding connection between units was carried out. After the hoisting and installation of connecting beam were completed, the unloading work of the supporting structure started. The long-span spatial structure was complicated. The process of internal force redistribution of structural members required calculation and analysis, so the unloading method of the support system was very critical. Due to the small number of tire frames in this project, the order of unloading individual tire frames was adopted. The unloading plan was divided into four working conditions, and the unit cooling and unloading method was used to simulate the unloading process through MIDAS model. During the unloading process of the supporting structure, the temperature unit was set to be 50 mm long, and the material linear expansion coefficient was 1 mm/℃. A compression-only elastic connection was adopt between temperature unit and supporting point. After the unloading was completed, the temperature unit and supporting point were automatically separated, and the value of stress and vertical displacement of roof members during the unloading process of construction were calculated.
The research results showed:1) the design section of the roof structure met the safety of the construction process; 2) the structure unloading process has sufficient rigidity and strength, and the structural force was stable to meet the construction requirements; 3) the vertical displacement curve of the support point of the removed tire frame showed a linear upward trend. It was judged that the structure was stable under force, and the vertical displacement curve of remained support points was S-shaped. The closer to the position of the first removal point, the more obvious the vertical displacement curve of the observation point was. Therefore, the structural points with the S-shaped vertical displacement curve need to be set up for the limit and anti-overturning of the supporting nodes, and construction monitoring should be carried out. Based on the simulation calculation results, the implementation of the unloading plan was deterrmined.