Influence On Response Of Mega Steel-Frame Structures From Hypo-Frame And Floor Stiffness

In this paper, the mega structure and its characteristics are introduced. The mechanical models, analysis methods and the present seismic research condition of the structures are summarized. The main problems and the direction of further seismic research of the structures in future are pointed out.On the basis of these, the paper studies profoundly the influence on response, seismic design method and seismic behavior of the mega steel structures from the floor stiffness and hypo-frame. Three representative mega steel-frame structures are selected. Four calculative modes are hypothesized, which are, mode 1: considering the main-frame, not considering the floor stiffness; mode 2: considering the cooperation of main and hypo frames, not considering the floor stiffness; mode 3: considering the cooperation of main and hypo frames, and the floor stiffness; mode 4: considering the main-frame and the floor stiffness. 5 typical earthquake waves are selected, which represent different site conditions respectively. Using finite element program ANSYS, three-dimensional history time analysis of three mega steel-frame structures with different calculative modes subjected to different earthquake ground motions are conducted. The results of structural period, displacement and internal forces including axial force, shear force and bending moment are obtained. In order to study how the floor stiffnesses influence on the mega steel-frame structures, the results of mode 1 and mode 4 of example 1, and those of mode 2 and mode 3 of three examples are compared. Some conclusions are obtained as follows: compared with beams and columns of the common steel-frame structures, the cross-sectional dimension of mega beams and mega columns in the main-frames of mega steel-frame structures are very large. Because the mega structure system has great lateral stiffness and entirety work behavior, whether or not considering the floor stiffness has less influence on the entirety responses of the mega steel-frame structures and on the displacement and internal forces of columns of the mainframe, but larger influence on the response of columns of hypo-frame. So it is reasonable that mode 1 substituting for mode 4 is compared with mode 3 to study the influence on response, and seismic behavior of the mega steel structures from the hypo-frame. Compared the results of structural period, displacement and internal forces of mode 1 with mode 3, we can know that the hypo-frame can increase the lateral stiffness of the mega steel-frame structures, decrease lateral-deformation of the structures, especially decrease the maximum inter-storey displacement obviously, and get the internal forces and deformation of the whole structure more uniform. From the analysis results, it can be found that the maximum axial force gets lesswith hypo-frame than without it, and the maximum shear force and bending moment get more with hypo-frame than without it. Thus it can be seen that the mainframe can be an independent structure system by itself, but the cooperation of main and hypo frame should be considered for conducting the entire analysis and design, otherwise the mega structure can be unsafe, In addition, from the comparing analysis, it can be found that the shear force and bending moment of inside-row columns are increased much more than those of outside-row ones in a mega column. So this phenomenon should be paid attention during designing of a mega structure.