Analysis And Assessment Of The Vibration Responds Traffic-Induced Of Xi'an Bell Tower

Xi'an Bell Tower is a key cultural relic under the state protection.The growing vibration induced by ground traffic and the future subway will exert a serious impact on the Xi'an Bell Tower.In this paper,based on vibration monitoring,the impact of ground traffic on the Bell Tower is studied;the impact on Bell Tower of the vibration induced by subway around the Bell Tower is thoroughly analyzed;in addition,according to the national standards (GB/T50452),the impact of the superposition of ground traffic vibration and subway vibration to Bell Tower is comprehensively evaluated.The main contents include:(1) The ground traffic vibration response of Xi'an Bell Tower was continuously monitored in 24 hours for the first time.The probability statistics method is employed to analyze the monitor vibration signal,and the statistical values of velocity and acceleration with degree of confidence of 95%are used as the assessment index of vibration.(2) The free vibration response of the monitored signal is obtained by Random Decrement Method.ITD is adopted to get dynamic parameters of Bell Tower within traffic vibration amplitude for the first time,on this basis,the stiffness of mortise and tenon joint calculation model is derived through inversion,the questions of dynamic parameters unable to be identified with the traditional methods in environmental noise and the similar timber structure is unreasonably calculated due to tenon and mortise connection stiffness cannot be accurately determined are solved.(3) The formula for calculation of ground vibration attenuation induced by the parallel vehicles on a ring road is established,and the computed results are better agreement with the measured value.(4) Regarded the rail as a continual Euler-Bernoulli beam in Winkler ground,the train-track-roadbed model is established,with the consideration of pseudo-static load of train and dynamic contact force between wheel and rail.According to by the time series estimate power spectral density's periodogram law principle,the research adopts five level of orbital power spectra which US Federal railway Administrative bureau FRA proposed;then,through the Fourier inverse transformation,the orbital not smooth time domain samples are obtained, which determine the track irregularity peak-to-peak value and the corresponding wave length; on the basis of the research,the influence of the wheel track dynamic contact force are considered.Based on the orbital roadbed coefficient's definition,computation model is established to solve the roadbed equispaced spring constant,and the roadbed uniform spring stiffness is obtained by using the numerical simulation method.Finally,based on the Matlab procedure platform,the computational procedure is established,and the load time interval caused by the moving train acts on the roadbed is obtained.(5) Taken loading time delay into consideration for the first time,the impact of the vibration on Bell Tower,induced by double row train movements on subway No.2 and No.6 lines,is numerically analyzed,and then the dynamic responds and the vibration dissemination rule of Bell Tower is obtained;the dynamic responds of Bell Tower induced by vertical vibration in two different propagation directions is superposed by ways of SRSS superposition,as a result,the dynamic response of Bell Tower is obtained when several trains are simultaneously moving.(6) It is proposed and verified that under the traffic vibration,the dynamic response of building can not be calculated by single particle import similar to earthquake response analysis method,moreover,the impact of vibration wave phase difference and vibration rapid attenuation during the propagation must be take into consideration.(7) In order to solved the practical problem of the limitation about vibration observation point arrangement on Bell Tower,a key cultural relic under the state protection,the timber structure analysis model under traffic vibration has been established,and then the Bell Tower two-story building floor's vibration velocity is transformed into vibration velocity at top column.(8) The analysis model for the high-station base of Bell Tower is established based on wave theory,and the basic expression for solving vibration velocity of high-station base is derived. The allowable value of panicle vibration velocity at bottom of high-station base is given,in line with empirical formula and the protection grade of Bell Tower,which fill the appraisal standard blank of the historic building with high-station base under traffic vibration.(9) According to the national standards(GB/T50452) and the allowable value of panicle vibration velocity at bottom of high-station base,the impact of the superposition of ground traffic vibration and subway vibration to timber structure of Bell Tower and its high-station base is comprehensively evaluated.