Study On Story-increasing Design Of Existing Frame Structures

With the decelopment and progress of the times and the shortage of land resources,the demand for storey-adding and transformationg of existing buildings was increasing,and the application was becoming more and more common.People had also greatly improved the technology of storey-adding and renovation.According to the continuous exploration of predecessors,the progress of technology and the continuous improvement and progress of new building materials,the technology of storey-adding and renovation was also diversified.Economic,reliable,easy to construct,less impact on existing buildings,better seismic performance,was the direction to be pursued in storey-adding renovation.Adding energy dissipation devices in the process of building upgrading could not only increase the seismic performance of existing buildings after adding stories,but also protect the internal structure and decoration of buildings more effectively,so as to reduce the damage degree of buildings under earthquake and had better stability.In this paper,three different design schemes were adopted for the storey-adding renovation of existing frame structures on the premise of meeting the use requirements.Three kinds of storey-increasing schemes were steel frame direct storey-increasing scheme,steel frame-shear wall scheme and inner tube cantilever sub-truss scheme.Firstly,through the Yingjianke structural design software,the original structure and three storey-increasing schemes were calculated under the frequent earthquakes and the rare earthquakes.Then compared and analyzed the results.The results showed that:(1)The bearing capacity of the lower structure would be insufficient when the direct storey-adding scheme of steel frame is adopted,and the "whiplash effect" would occur on the upper steel frame,which could not meet the requirements of the code under rare earthquakes and need further strengthening and transformation.(2)The scheme of steel frame-shear wall had very good overall stability.The shear wall could improve the lateral stiffness of the whole structure.It could effectively improve the seismic performance of the whole structure under frequent and rare earthquakes,but the amount of engineering was large and the economy was poor.(3)Under the condition of guaranteeing the effective connection between the upper and lower structures,the more innovative design scheme of the inner cantilever sub-truss scheme was adopted.This scheme could effectively control the displacement of the whole structure after adding stories under frequent earthquakes.Under rare earthquakes,it could also met the standard of "large earthquake can not collapse".This scheme had less influence on the original frame structure and was the best of the three schemes.This scheme could be further optimized for overall seismic design.Subsequently,in order to reduced the seismic effect on the structure,the energy dissipation method was adopted to optimize the seismic design of the inner cantilever sub-truss scheme.Viscous fluid damper device was used in inner cantilever sub-truss scheme,and SAP2000 finite element software was used for analysis and calculation.The contents of the analysis were divided into two steps:(1)Firstly,studied on effevtive damping coefficient of viscous fluid damper.The results showed that with the increase of the damping coefficient,the seismic action of the structure would decrease proportionally.The damper could greatly reduce the external load on the structure and improve the seismic performance of the structure.(2)Then the elastic-plastic time history analysis of inner cantilever sub-truss scheme under rare earthquakes was carried out by using non-linear viscous fluid dampers,and the placement positions of viscous dampers were compared and analyzed in two different ways.The results showed that the increase of viscous dampers under rare earthquakes could effectively control the maximum displacement and the displacement angle of the structure.And the effect of viscous dampers on the inter-story acceleration and the relative inter-story velocity was very obvious.Moreover,under the condition that the upper and lower structures had sufficient connection stiffness,the viscous fluid dampers could play a more full role of damping and achieve the optimal seismic design of the whole structure,which achieved the purpose of the project.