Comparative Analysis Of Steel Structures In High-rise Office Buildings

With the development the height of modern buildings, steel concrete composite structure system has been widely used in high-rise buildings. Research team leaded by Academician Ma Kejian proposed a new assembly integral spatial steel grid box tube-in-tube structure system. The new structures can effectively overcome the shortcomings of conventional tube structures. However, the integral assembly space steel grid box tube-in-tube structure has not been used in the area with high seismic intensity. Therefore, the analysis of mechanical properties and seismic performance of the new structure system can provide the basis and reference for promotion and application of the new system in those areas.Firstly, the thesis introduces the development process and mechanical characteristics of the high-rise buildings and super high-rise buildings. Then it introduces the basic components of the new system, including collaborative type steel open web plate floor(the basic structure and calculation method) and grid steel frame wall structure(the steel grid wall frame shear and bending deformation formula).Taking a proposed 28 storey building in high intensity region(Kunming, Yunnan Province) as example, a numerical analysis model was established by using finite element software MIDAS. The comparison and analysis of the box tube-in-tube structure and conventional frame structure under frequent earthquake was performed.The response spectrum on box tube-in-tube structure was calcualted based on static elastic plastic analysis and the structure of the system component flexion service order was obtained. The mechanical characteristics of the structure of the system show that the structure meets the large earthquake without collapse fortification standards. By using simplified numerical model, some influence factors on shear lag effects including the corner post setting, the thickness of the floor slab, spandrel beam stiffness, grid frame stiffness were analyzed through the shear lag quantization index.A comparative analysis of the frame core tube structure, tube-in-tube structure,box tube-in-tube structure in high earthquake intensity area was carried out. The basic mechanical characteristics, including the structure self vibration period, the distribution of shear, shear lag effect, overturning moment distribution characteristics and displacement response of structures, structural yield and economy were analyzed.The analysis results show that the basic mechanical properties of the box tube-in-tube structure are better than the other two kinds of structures. The new structure shows higher capacity of energy dissipation, bigger lateral stiffness, better overall ability towork cooperatively and its economic benefit is more significant. The elastic and elastic-plastic processes of box tube-in-tube structure under the action of rare encounter earthquake were analyzed. The time history curve of vertex displacement,the time history curve of base shear force and floor displacement angle were compared with that of conventional structures. Analysis results show that the seismic responses of new structure are smaller than that of conventional structures. Seismic hysteresis curves indicate that the box tube-in-tube structure can fully realize the concept of "based on the performance of the structure design".Finally, a summary on box tube-in-tube structure system is presented and suggestions for future research are proposed.