Loss Of Prestress Analyses On External Walls Of LNG Storage Tanks

As storage of liquefied natural gas(LNG)main pressure vessel,the large-scale LNG storage tank is not independent designed in domestic.The effect of creep,loss of prestress,and prestressed tendon design issues are the problems to be solved Urgently in the process of design.Due to the larger loss of prestress and creep effect,the outer tank will produce cracks,which will seriously affects the security and durability of this tank.This article adopts the method of theoretical analysis and numerical simulation.In a case study of a large LNG storage tank in Shandong province,The author mainly does the following research:1.The writer proposes a new method for calculating the partial tensioning prestress loss.By adopting ADIN A finite element software,we established a finite element model,simulated the stress and deformation distribution of the outer tank,analyzed partial tensioning prestressed loss.2.We established the outer tank's creep finite element model.Under the influence of concrete creep,analyzed stress and strain distribution of the tank.The long-term loss of prestress control equation was deduced.The control equations was verified by using literature's experimental data.The long-term loss of prestress of shandong LNG tank is forecasted.3.By adopting ADINA finite element software,we established a LNG storage tank numerical model.Under normal operating conditions and inner tank leakage conditions,we analyzed the distribution regularity of stress and cracks.Based on the elastic-plastic mechanics of cylindrical shells theory and related references,On the basis of fully considering the loss of prestress,we deduced vertical and circular prestressed tendons control equation,and then optimized design of prestressed tendon.The following findings are achieved: The bottom of the wall was the most dangerous place in the process of tensioning prestressed reinforcement.The best tensioning sequence was that first tensioned circumferential prestressed tendon and then tensioned vertical prestressed tendon.Partial loss of prestress distribution is non-uniform along the wall height,the wall's partial prestress loss from 0.2 H to 0.3 H height was greater than the standard value.Due to the creep effects,it will produce cracks at the bottom of the tank,which will seriously affect the durability of the tank and safe use.In the first two years,the long-term loss of prestress changes quickly,and then changes slowly,the biggest loss of prestress is 11.2% of the tension control stress.Walls prestressed reinforcement design must fully consider the loss of prestress.The circumferential and vertical prestressed tendon optimized design method can improve the bearing capacity of the wall.