| Since the beginning of the 21st century,the world's super high-rise buildings have developed into a blowout type,and the use of buildings has become more and more complicated.As an effective structure that can resist horizontal loads,the cylinder structure is widely used in high-rise buildings and super high-rise buildings.The frame-core tube structure has unique advantages in the layout of use.As one of the main disasters in buildings,fire is a threat to the safety of the structure.When a building is exposed to a fire,the overall structure will cause proper damage under high temperature and the safety will be reduced.In this paper,the reinforced concrete(RC)frame-core tube structure is taken as the research object,and the fire resistance of the whole structure and the seismic performance under fire are studied.This article mainly does the following work1.The beam members and floor members in the high-rise structure have large deformations after fire,which affect the normal use after fire.Since the strength values of concrete and steel(ribs)have decreased after the fire,the beam members and the plate members cannot meet the bearing capacity design requirements after the fire.Additional fire protection measures are recommended for these two components and reinforced after fire.2.Through modal analysis,analyze the changes of the structure under the first 5 modes,and analyze the different torsional modes and vector displacement changes of each mode.Under the action of the first 5 modes,the column undergoes vertical or torsional motion,and there are different directions of column displacement,which leads to complex deformation of the beam Especially due to the torsion of the two ends of the beam,the beam is prone to large displacement deformation.3.Based on the harmonic response analysis,the original structure before fire and the structure after fire in different regions are subjected to simple resonance action,and multiple peaks appear in the range of 0-100 Hz.The structure after the fire has multiple displacement changes in the same frequency range under the simple resonance action.The structure mainly changes in displacement in the horizontal direction,and the displacement change in the vertical direction is almost maintained at zero.4.Based on the seismic harmonic response analysis under the response spectrum theory,the initial frequency and the termination frequency of the displacement of the original structure before the fire are higher than the frequency after the fire,and the frequency span is large.After the fire,the structure undergoes the same number of displacement changes in the narrow frequency range and the wide frequency range of the original structure.Under the seismic harmonic response analysis,the seismic performance of the structure is reduced after the fire.Moreover,the area of the fire-receiving area occupies a small area,the overall structure is mutually restrained,and the overall performance of the frame-core tube structure is strong.For the barrel portion,its own stiffness,strength and cross-sectional area are large,and considering the simplified single-sided fire condition,the barrel portion can maintain a stable state in the horizontal plane.5.Based on the transient dynamics analysis under seismic waves,the strength of the surface concrete after the fire is reduced,and the cross-sectional area of the member becomes smaller.Under the action of seismic waves,more vibrations occur in the fired area during the same period of time.And because the fire zone is different,the closer the distance to the fire zone,the greater the displacement and frequency changes.Considering the change of the displacement angle between the layers before and after the fire,the fire in the bottom layer has a greater influence on the overall structure and easily exceeds the standard value. |
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