Study On Equivalent Linear Isolation Design Of Gas Duct Based On Linear Elastic Response Spectrum

Gas duct is a vital part of the flue gas system of thermal power station,however the existing gas duct bearing can't meet the demand of seismic isolation.Meanwhile China as a country where the earthquake happened frequently,the seismic requirements for the buildings,structures,infrastructure are gradually increased.Therefore,studying the isolation design of gas duct system could not be hesitated.Based on the linear elastic response spectrum,this paper studies the isolation design of the gas duct by using the equivalent linearization and the finite element method.Furthermore,this paper mainly completes the following works:(1)According to the practical engineering data,the finite element model of isolated and non-isolated gas duct system was established by using the SAP2000 analysis software.According to the spectral characteristics,effective peak and endurance time,suitable seismic waves are selected for zone II and zone III.Through the nonlinear time history analysis of direct integration,the hysteretic loops of different bearings are obtained,and the hysteretic loops of the isolation bearings are three linear.The curves are full and the dissipation of seismic energy is obvious.The shear force,acceleration of the gas duct are extracted,the maximum time response of isolation and non-isolation cases is compared and analyzed.It is found that the dissipation of seismic energy of the double friction pendulum bearing is obvious,and the shear and acceleration of the support and the gas duct can be effectively controlled,so that the damage degree of the gas duct under earthquake can be reduced.(2)Through nonlinear time history analysis of isolated gas duct system,the influence of site motion parameters on seismic isolation is investigated.The dynamic response of the isolated gas duct system in zone II,zone III and 7 degree intensity and 8 degree intensity are compared.The results show that the isolation effect of the gas duct system on zone II and zone III is good.When the site type is the same,the shock absorption effect of the 8 degree rare earthquake is more obvious.In order to investigate the effect of ash loading on the seismic response of isolated gas duct system,the accumulated ash load case and ash free load case are set up.The results show that the isolation bearing has obvious effect in two kinds of working conditions,and the shear force and acceleration are ideal.(3)Using the secant method and equivalent damper energy dissipation method,the formula of equivalent stiffness and equivalent damping ratio of isolated bearing and isolated gas duct system is explored and used.A two-point model of the gas duct system was simplified,and the equation of motion was established.Based on the complex mode damping theory and strain energy theory,the expression of the combined damping ratio of the gas duct system is obtained.Finally,the method of equivalent linearization is verified and the reason of the error is analyzed by finite element analysis.(4)According to the formula of ASCE 7-10,FEMA 368 and the equivalent stiffness,equivalent damping ratio formula what are introduced in this paper,meanwhile,using the linear elastic response spectrum and the designing idea of the isolation bearing,equivalent linear isolation design of gas duct based on linear elastic response spectrum is proposed.Taking a rectangular steel gas duct under a 7 degree rare earthquake in zone III as an example,using the equivalent linear isolation design based on linear elastic response spectrum,a concrete design flow is given.