| With the acceleration of urbanization in China, its city scale is expanding rapidly. Theexisting facilities and space The existing buildings in major cities are either newly built orhave been used for many years,they can not satisfy the requirements of people’s lifeanymore.To increase the building areas either by means of rebuilding after demolition at thesame places or by relocating on other sites would increase the cost and waste the landresources. Therefore, to expand the service areas and utility rate of the existing buildings,priority is given to renovating or storey adding. For such kind of buildings, due to the lowlevel of the original design, some are without earthquake fortification, others are of lowerstandard owing to the lack of consideration of future development. Accordingly, research onthe design of such buildings for storey adding or renovating is of particular importance.Because of its high strength, light weight, short construction period, occupation of smallland area during construction and convenience of construction, steel structure is a preferableand favorite choice in the renovation of old buildings by means of storey adding, which hasbeen well accepted in the trade.The effect of treatment methods of column base for the seismic Performance of thestructures:According to the capacity of transfer moment,the column base of adding storeysmay be divided inio three kinds:hinge column base，semi-rigid column base， rigid columnbase.The semi-rigid column base can better shows the working Performance of the Practicalcolumn base,but some common structure design softwares can not realize semi-rigidmodeling and often use ideal rigid and hinge model.This assumption changes the structureupper and lower stiffness ratio,and may effect the earthquake action of structure.So this Paperanalyzes and compares with the effects of anti-seismic Properties of the structures fordifferent column base mode.In this paper, an actual project was taken as an example. According to the characteristicsof RC structure, the rational design scheme of storey adding was proposed. Then by using thefinite element analysis software SAP2000, three-dimensional models were built. The modalanalysis was conducted for the12-layer frame structure and10+2layer composite structureso as to investigate their changes in the natural vibration periods and modes. Dynamicelastoplastic time history analysis was also carried out for the12-layer frame structure and 10+2layer composite structure and the2layer steel structure as well to study their structuralresponses under intensities of rare earthquakes.The analysis compared with the12-layer frame structure shows that after storey adding,different increases in the maximum sways, the maximum angles of inter-story drift and themaximum inter-story shear forces occur to both the10+2layer composite structure and2layer steel structure, and the adding of steel structure intensifies the seismic response of the10+2layer composite structure; and for different seismic waves imposed at differentdirections, the extent of increase also differs. The RC structure exerts great amplificationeffect on the seismic response of the added steel structure, which cannot be taken intoaccount in the simplified design so that the model of overall structure after storey addingshould be built to conduct the analysis of structural responses.From the observation of the time, sequence and process of the appearance of plastichinges in the12-layer frame structure and10+2layer composite structure, the added storeymakes the plastic hinges occur earlier, more and develop more extensively; the second、third、eleventh of beams are all the weak parts of the structure, to which much attention should bepaid in storey adding, and corresponding measures of strengthening be taken when necessary;under rare earthquakes, some columns may stop working prematurely, which greatly lowersthe seismic performance of structure and effective strengthening measures should be adoptedin this case. |
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