Research On The Combined Sliding Seismic Isolation Of LNG Storage Tank In Soft Site

With China’s economy changing from high growth to high quality development,the demand for energy is more focused on green,low carbon and environmental protection.Liquefied natural gas(LNG),as a high quality clean fuel,is fueling the development of China’s low carbon economy.As the important equipment for storing LNG,the number of LNG storage tanks is increasing.LNG storage tanks are urban lifeline projects,and it is important to use seismic isolation technology to reduce their seismic impact.For this reason,the group proposed a combined slip isolation scheme and a new type of tensile slip bearing for the seismic isolation study of large LNG storage tanks in coastal soft soil sites,the details of the study are as follows:(1)A combined seismic isolation scheme which can be self-centering,energy dissipation,resistance to large deformation formation and has a damper reaction wall is proposed for a 160,000 m~3 LNG storage tank,and a simplified model of the LNG storage tank is established based on the theoretical model.The performance indexes of the lead rubber bearing isolation tank,friction pendulum bearing isolation tank and combined isolation tank are compared and analyzed under the action of operating basis earthquake(OBE)and safe shutdown earthquake(SSE)to verify the seismic isolation effect of the new combined seismic isolation scheme.The results show that the three seismic isolation schemes have obvious seismic isolation effects on the external tank wall shear force,impulse shear force and monopile shear force,among which the combined seismic isolation scheme has the best effect;the combined seismic isolation scheme has the ability to dissipate the seismic energy and control the horizontal displacement,so that the tank can meet the demand of large horizontal displacement under the SSE earthquake,and has better control on the LNG tank sloshing wave height under the OBE and SSE earthquakes.(2)In order to solve the problem of insufficient tensile capacity of the seismic isolation device of the storage tank structure under the action of large overturning force,a new type of sliding bearing with wedge-shaped separated track was proposed,and the theoretical friction calculation model of the bearing is established.The numerical model of the bearing is established by ABAQUS software,and the mechanical properties are studied by numerical simulation and optimized design,while the influence of the change of wedge angle on the mechanical properties of the bearing is considered.The results show that the new bearing has good compression and tension resistance in the vertical direction and can be optimized by changing the size of the components and improving the material strength;the simulated hysteresis curve of the bearing under the action of compression shear and tension shear is in good agreement with the theoretical value,which proves that it has good horizontal energy dissipation capacity and can adapt to large horizontal displacements;the compressive capacity of the bearing is less affected by the wedge angle,and the tensile capacity increases with the decrease of the wedge angle.When the angle decreases to 60°,the weak point appears between the wedge slider and the upper part of the connection,which leads to the tensile capacity of the bearing begins to decrease.(3)A three-dimensional model of the LNG storage tank was established by using finite element software,combining the combined seismic isolation scheme with the new type of bearing,and the seismic isolation arrangement was carried out in the model to compare and analyze the seismic response of the storage tank before and after seismic isolation in soft soil sites and the seismic isolation effect of the new type of bearing.The results show that the new combined seismic isolation scheme can significantly extend the vibration period of the external tank and reduce the self-oscillation frequency of the structure;the combined seismic isolation layer can effectively reduce the transfer of seismic energy to the superstructure and lower the acceleration peak at the apex of the tank wall,at the same time,the structure can avoid the excellent frequency of the site and prevent resonance;the new bearing has good horizontal energy dissipation capacity and can provide tensile force when the structure generates large overturning force to prevent the structure from overturning.