| With the rapid development of economy and maturity of seismic isolation technology in our country,the number of buildings using isolation technology is increasing.For some buildings with early construction and commemorative significance,the seismic performance of them are obviously insufficient due to low design standards at that time,the seismic strengthening is urgently needed to be solved.Traditional method of seismic strengthening is to increase the ‘resistance’ of structure to resist earthquake action.However,this method of increasing stiffness of components will lead to an enlarged section of the members and cause increase of earthquake effect on structures.The use of isolation technology has become a new and effective seismic strengthening idea,which has been deeply studied and widely applied.However,from existing research results,there is a lack of research on the seismic performance of existing buildings under construction of seismic isolation retrofitting.It is of great theoretical significance and engineering practical value to study the seismic performance of structures under construction and ensure the risk of seismic damage of structues from construction period to completion of isolation retrofitting.In this paper,seismic risk of the structure during construction period of isolation retrofitting is analyzed.The base isolation design of existing buildings,the seismic response of the structure under construction,and the construction process of isolation retrofitting of existing buildings are studied.The main research results are as follows:(1)The displacement transfer functions of single-degree-of-freedom and multi-degreeof-freedom systems are derived based on the frequency domain motion equations of them.With the additional damping ratio and stiffness of isolation bearings as constraints and minimum sum of transfer function values as objective,the optimum design of damping and stiffness of isolation devices is carried out.The results show that the displacement transfer function can significantly reflect dynamic characteristics of structure in frequency domain,and can well show the influence of system parameter on system response,and optimize isolation parameters.(2)The finite element model of the structure under the construction of seismic isolation retrofitting is established by using the beam-column plastic hinge element,Gap element and bearing element.Under the action of the target earthquake intensity(8 degrees),the seismic performance of structures of two construction schemes and different construction stages is studied.The results show that with the change of construction schedule,the horizontal stiffness of the structure is continuously reduced due to the increase of isolation bearings,and some of the structural beams enter into plasticity,but the development degree is relatively light.Under the action of frequent earthquakes,both construction schemes can protect structures from collapse.(3)The elastoplastic analysis of the structure during construction period is further carried out by continuously enhancing the strength of ground motions.The ability to resist earthquake risk and seismic failure mode of structures under different construction schemes and stages are studied.The research results show that the horizontal displacement of frame columns in isolation storey is too large to destroy the structure during construction period,and with the progress of construction(increase of the number of bearings),earthquake intensity that the structure can resist is small.Through comparative analysis,it is found that the seismic performance of structures under construction scheme two is better than that under scheme one,and the risk of earthquake damage is smaller. |
