Research On Mechanical Performance And Seismic Failure Mechanism Of High-rise Primary-secondary Structures

Primary-secondary structure system is a new structure system of super high-rise building. The primary structure is the main supporting system and the lateral loads resisting system, and the secondary structure is only responsible for bearing its own vertical loads and transmitting the forces to the primary structure. The primary structure and secondary structure work together. As the structure has good architectural adaptability and efficient structural performance, it was attracting attention of construction. Yet there were few systematic researches on the seismic performance of the primary-secondary structure, especially the failure mechanism under strong earthquakes was still unclear. In order to solve these problems, mechanical characteristics, seismic failure mechanism and seismic concept design were studied in the thesis:Mechanical performance of high-rise primary-secondary frame structure was studied. Considering different number and location of the main frame beams to establish multiple primary-secondary frame analysis models, its mechanical properties under vertical and lateral forces were researched. For the internal force mutations in the joints between the primary and secondary frame, the effect of different connection ways between two kind structures to the whole structure was analyzed. The influence degree of each component stiffness, secondary frame stiffness and structural arrangements to the whole structure lateral stiffness were discussed. Analysis results showed that the primary structure is the main bearing and the lateral loads resisting system. For the primary structure lateral stiffness is much larger than the second frame, different connection ways has a little influence on the mechanical properties of the structure. But the secondary frame lateral stiffness has a certain contribution to the whole structure.Mechanical performance of high-rise primary-secondary frame-brace structure was studied. Considering different brace forms to establish single brace and X-shaped brace two type analysis models, its mechanical properties under vertical and lateral forces were researched. A nd a primary-secondary frame was established as a contrast model. The influence degree of each component stiffness, secondary frame stiffness and structural arrangements to the whole structure lateral stiffness was discussed. Analysis results showed that by adding the large-scale brace, the primary-secondary frame structure transformed into primary-secondary truss structure. So the moment and shear of the main columns and main beams under horizontal force substantially reduced. The larger brace is the key factor of overall lateral stiffness of structure, and the contribution from secondary frame was greatly reduced.Seismic failure mechanism of high-rise primary-secondary structure system was studied. The primary-secondary frame-core tube structure and primary-secondary frame-brace-core tube structure were analyzed by Pushover method. The component yield order and the outer tube failure path of the two structure systems plastic development process were summarized. The force distributions of primary frame and core tubes were studied and the reasons of force redistributions between them were illustrated base on the component yield order and force transmission. The reason of structure lateral stiffness degradation was explained by the change process of primary frame and core tubes lateral stiffness. Finally, according the characteristics and advantages primary-secondary structural system, and combining the mechanical analysis and nonlinear static analysis results, the reasonable yield order of the structure was discussed. The seismic concept design of primary secondary structure system was proposed proposal. The results showed that the reasonable components yield order of the structure is coupling beams, braces, secondary frame beams, secondary frame columns, walls, primary frame beams, and primary frame columns. Changing the main force member may cause the changes of the yield order of. To satisfy the structural seismic fortification goal s, the relative relationships between each component should be pay attention to when design the structures.