Simulated Analysis on Optimum Scheduling of Outrigger-Brace Connection for Super High-Rise Structure

Super high-rise structure is a hot research issue of large-scale complex structure. Many of its structural systems adopt the hybrid structure system composed of steel structure outer frame tube and reinforced concrete core tube, and are equipped with outrigger truss. Due to the different materials of steel structure outer frame tube and concrete core tube, the vertical deformation during construction is also different. Premature connection of outrigger truss will produce large initial deformation and initial internal force in the truss, and too delayed connection may lead to incomplete structural stiffness and structural safety problems under extreme load conditions.
In this paper, the 33-34 storey truss and 51-52 storey truss in the South Tower of Yinchuan Lvdi Center were taken as the research objects, and the numerical simulation is carried out by using ANSYS software. In five cases, the effects of different connection time on the internal force and deformation of outrigger truss structure were compared. Through the numerical simulation results, the axial force, stress and deformation curves of the most unfavorable member in five cases were obtained. The analysis results show, the later the connection time is, the smaller the axial force, stress and deformation of truss members are. According to the axial force curves of the outrigger truss, it can be obtained that in the five cases, the maximum axial forces of members No.1, No.2 and No.3 are 340 kN, 1 830 kN and 870 kN, respectively. Under case 4, the maximum axial forces are 90 kN, 400 kN and 120 kN respectively, which are reduced by 73.5%, 78.1% and 86.2%. According to the deformation curve of outrigger truss, the maximum deformations of members No.1, No.2 and No.3 are 9.73 mm, 9.82 mm and 9.98 mm in five cases. Under case 4, the maximum deformations are 3.26 mm, 3.43 mm and 3.27 mm respectively, which is reduced by 66.4%, 65.0% and 67.2%.
During the construction of the south tower of the twin towers of Yinchuan Lvdi Center, considering the long period of structural shrinkage and creep, it is difficult to form greater lateral stiffness without the connection of the inner and outer tubes with the outrigger truss for a long time. At the same time, considering the construction period and the ability to resist disaster loads, select the case 4 where the truss response is relatively small, that is, the extended truss is connected after the completion of the outer frame tube construction section. During the connection and closure of the upper and lower outrigger trusses, the on-site outrigger truss construction monitoring system was deployed. The data analysis shows that the strain variation of the outrigger truss is in good agreement with the numerical simulation results, which verifies the reliability of the connection timing optimization algorithm proposed in this paper.