| In recent years,there are many engineering cases where steel storeys are added onto high-rise reinforced concrete structures,which have caused many scholars to study the seismic performance of such buildings.However,most of the research objects focus on masonry structures or frame structures.There are few studies on the seismic performance of steel storeys added onto frame-shear wall structures.At present,there is no clear way to do this in China.The requirements of seismic design codes make the actual engineering design lack of reasonable design reference.Based on an engineering example of a high-rise frame-shear structure in Xi'an,this paper uses two finite element software ETABS and SATWE to model the structure,and analyses the seismic performance before and after adding stories,which provides a reference for the future design of this kind of engineering.The main contents of this paper are as follows:1.By summarizing and analyzing the damping ratio of the frame-shear storey structure system,it can be seen that for the steel structure with fewer storeys and more regular structural layout,the damping ratio is greatly influenced by concrete structure,and the constant damping ratio is 0.045.Using ETABS model,the seismic performance of the frame-shear storey system with different column footing stiffness is analyzed,and for the unbounded steel structure,the seismic performance of the frame-shear storey system with different column footing stiffness is known.The rigid joints should be adopted as far as possible in the steel structure with additional storeys.For the steel structure with supporting storeys,the advantages of hinged column footing are more obvious.In this paper,the scheme of hinged column foot and supported column footing are adopted in the steel structure with additional storeys.2.Two finite element analysis software ETABS and SATWE are used to establish the calculation model of the structure before and after adding storeys.The results of the two software are consistent,which verifies the accuracy of the model.The results of modal analysis before and after adding stories show that the period of the structure becomes longer,the maximum increment is 0.029 s,and the whole structure becomes more flexible.The response spectrum analysis results before and after adding stories show that the displacement,the displacement angle and the shear force of the stories increase in varying degrees.The maximum increment of the displacement of the stories is 8.6%,and the maximum increment of the displacement angle is 11%.The increase of shear force at the top of the original structure is about 30%,and that at the bottom is less than 5%.It can be seen that the addition of steel structure increases the seismic response and is unfavorable to earthquake resistance.3.El-Centro wave,Borrego wave and artificial wave are selected to analyze the elasto-plastic time history of structures before and after adding stories under rare earthquakes by using ETABS software.The maximum floor displacement,maximum inter-story displacement angle and maximum floor shear force of the structure after adding stories are obviously larger than those of the original structure,in which the maximum increment of floor displacement is about 15%,the maximum increment of inter-story displacement angle is about 20%,the maximum increment of shear force of the top floor of the original structure is about 30%,and the maximum increment of shear force of the bottom floor is less than 10%.The addition of stories in steel structure makes the appearance of plastic hinges in the whole structure earlier and more in number;the frame beams directly connected with shear walls and the shear walls with openings at the bottom of the structure are weak parts,which should be strengthened.At the end of the earthquake,only plastic hinges appear at the end of the beam,and neither the columns nor the shear walls have entered the plastic stage.The structural design realiges the seismic design concept of "strong column and weak beam". |
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