Theoretical Analysis And Shake Table Test Research On Dynamic Response Of Three Dimensional Isolation Storage Tank Under Near Field Earthquake

LNG storage tanks are basic equipment for storing liquid natural gas.In case of damage in an earthquake,it is easy to cause secondary disasters such as fire,explosion,and environmental pollution,causing major losses to the national economy.Although the base isolation technology has been proven to be effective in lowering the seismic effect of storage tanks,most isolation currently used in storage tanks have only horizontal isolation.In addition,due to the different fault mechanisms,some near field earthquakes contain velocity type pulse effects,which is harmful to long period flexible structures such as isolated structures.Therefore,considering the velocity type pulse effect,the dynamic response of150000m~3 chunky storage tank with a height to diameter ratio of 0.402 under near field seismic excitation was studied.The main research and conclusions are as follows:(1)Based on the theory of horizontal and vertical isolation,three dimensional isolation is proposed and designed,which is composed of LRB and disc spring or LRB and thick rubber bearing in series.Besides,with the help of finite element analysis method and test results,a correction formula for the vertical stiffness of the thick rubber bearing is given based on the traditional vertical stiffness formula of the linear nature rubber bearing.(2)Based on the existing theory of tank isolation,the horizontal isolation motion equations considering the nonlinearity of isolation and the vertical isolation motion equations without considering the nonlinearity of isolation are established.And the seismic dynamic response of 150000m~3storage tank was studied by compiling Matlab program.The results show:The damping effect of base shear force,overturning moment,vertical earthquake force,and hydrodynamic pressure of the isolated tank can be reduce by velocity type pulse effect of near field earthquakes.The motion of the sloshing particles in the storage tank can be exacerbated by the horizontal velocity type pulse effect of near field earthquakes,and causing the sloshing wave height increase significantly.In the design of the horizontal isolation,it is recommended that the post yield isolation period is 3-6s,the damping ratio is 0.1-0.2,and yield to weight ratio is 0.01-0.03.While design the vertical isolation,it is recommended that the isolation period is 1-2s and damping ratio is 0.1-0.3.(3)A three dimensional isolation consisting of a lead rubber bearing and disc spring is produced,and scale model with 1:5 similar ratio to that of 1000m~3 storage tank was selected for a shake table test.The results showed that:This test isolation has a good damping effect,whether it is horizontal or vertical.For example,under the three way excitation of Taft and TCU068,the damping ratio of horizontal acceleration of three dimensional isolated storage tank with 2/3 tank height are 87.18%and 81.82%,the damping ratio of vertical acceleration are 93.46%and 74.21%.Compared to other seismic excitations,the horizontal velocity pulses of near field earthquakes can cause large base shear force,while the vertical velocity pulses produce large vertical earthquake effect for three dimensional isolated storage tank.This three dimensional isolation has no obvious damping effect on the sloshing wave height,and even appears wave height amplification phenomenon in some working conditions.(4)The finite element model is established by ADINA,and the correctness of the finite element model is verified by comparing the results of finite element and shaking table tests results.In addition,the dynamic response of the 150000m~3 storage tank under three way seismic excitation was analyzed.The results show:Under the far field and near field three way seismic excitation,three dimensional isolation can effectively reduce the hydrodynamic pressure,radial,hoop,and axial stress of the tank.Among them,the damping ratio under Taft of far field excitation are 55.34%,34.81%,27.03%,27.89%,and the damping ratio under TCU068 of near field excitation are 12.80%,34.30%,20.29%,15.58%.Horizontal velocity pulses for near field earthquakes can reduce the damping effect of hydrodynamic pressure,while vertical velocity pulses can reduce the damping effect of hydrodynamic pressure and axial stress.Under three way seismic excitation,the radial stress and hoop stress reach the maximum near the tank bottom,and the axial stress reaches the maximum at the tank bottom or the remaining tank wall above the liquid surface.It is recommended to pay attention to the reinforcement of the tank bottom and the remaining tank wall during tank design.(5)Taken the 150000m~3 tank as research object,a design response spectrum suitable for a three dimensional isolated chunky tank is proposed,which is base on the standard response spectrum given in Chinese seismic design code.It is also recommended to multiply 2-3 when using the design response spectrum to calculate the dynamic response of a three dimensional isolated tank under near field velocity type pulsed seismic excitation by comparing the results of theoretical analysis and response spectrum calculations.