Seismic Performance Analysis Of Steel Frame Storey Adding On Existing Concrete Structures

With the development of our country’s economy and social progress,some old buildings in urban areas have been unable to meet people’s growing use needs.The large-scale demolition does not conform to the concept that the national lucid waters and lush mountains are invaluable assets.The use of adding steel structure storey on the existing concrete frame is a good solution for applicability and economy.Since the damping ratios of steel structure and concrete structure are different,and the lateral stiffness is quite different,how to solve the difference of damping ratios of the two structures,select the steel structure storey’s type,and control the whiplash effect by using buckling restrained braces to ensure that the two structures maintain good seismic performance under seismic action plays an important role in the transformation and reinforcement of existing buildings in our country.In order to solve the problem that the damping ratio of adding steel frame storey-is different from that of the existing concrete structure,the RAF method is proposed in this paper,which regards the existing coccrete structure as the foundation of the steel structure.A total of 108 finite element models are established to analyze the stiffness ratio of the RAF method for the number of layers of the existing concrete structure and the number of steel structure layers,and the empirical formula is fitted.Considering that the cross section of the steel structure is affected by the architectural design and the transportation and hoisting conditions at the construction site,a small column mesh layering scheme is designed,and the seismic performance is compared with the large column mesh and the portal frame scheme.Then obtained the experience of steel structure adding storey selection.In the analysis process,it is found that the whiplash effect of steel structure adding layer is obvious,so the buckling restrained brace is designed based on the stiffness ratio and shear ratio.The economy of the two design methods to control the whiplash effect is compared.Based on 160 finite element models,the influence of the floor arrangement of BRB,the number of existing concrete structures and the number of steel structure adding layers on the control of whiplash effect is summarized.The main conclusions are as follows: the empirical formula of RAF method application premise fitted in this paper has good accuracy;With the increase in the number of layers of existing concrete structures and the decrease in the number of layers of steel structures,the stiffness ratio applicable to RAF method gradually decreases.The seimic performance of small column net storey adding scheme is similar to that of large column net storey adding scheme,and the portal frame storey adding scheme has better protection effect on existing concrete structures.Buckling restrained braces based on stiffness ratio and shear ratio have good control effect on whiplash effect,and the design method based on shear ratio is economical.The arrangement of buckling restrained braces with steel storeys has an adverse effect on the control of inter-story drift angle of bottom concrete structures;The control effect of buckling restrained brace on the whiplash effect decreases with the increase of steel structure layers and the decrease of existing concrete structure layers...