大型LNG储罐外罐长期预应力损失分析

由于混凝土收缩徐变及钢筋应力松弛的耦合作用,LNG储罐外罐预应力系统将产生长期预应力损失,严重影响储罐的安全性能。为此,基于按龄期调整的有效模量法及混凝土结构设计规范中的相关模型,以国内某大型LNG储罐外罐为研究对象,应用ABAQUS有限元软件,建立了多组模型分别模拟收缩徐变损失、应力松弛损失及其耦合作用下的损失,分析了混凝土收缩徐变及应力松弛的相互作用对长期预应力损失的影响规律,并讨论了双向设置预应力对长期预应力损失的影响。研究结果表明:(1)环向、竖向预应力筋长期损失终值(50年)最大值分别达到张拉控制应力的10.97%、17.02%;(2)环向、竖向预应力筋在收缩徐变和应力松弛耦合作用下的损失分别为收缩徐变损失与应力松弛损失代数和的83.59%和86.33%;(3)提出相互作用折减系数,当收缩徐变损失和应力松弛损失大小相近时的折减系数最小;(4)竖向预应力对环向预应力筋长期预应力损失的影响较为明显。结论认为,该研究成果有助于提高大型LNG储罐混凝土外罐的安全性。

Analysis on the long-term prestress loss of the external walls of large LNG tanks

Due to the coupling effect of concrete shrinkage creep and tendon stress relaxation, the prestressed system of the external walls of LNG tanks suffers from long-term prestress losses, which seriously affect the safety performance of the tanks. In this paper, a large LNG storage tank in China was taken as the research object. By using the age-adjusted effective modulus method and the relevant models in the design code of concrete structure, the multiple models were established by using the ABAQUS finite element software to simulate the prestress loss caused by shrinkage creep, stress relaxation and coupling effect. Then, the influence law of the interaction between shrinkage creep and stress relaxation on the long-term prestress loss was analyzed. Finally, the influence of two-way prestress on the long-term prestress loss was discussed. And the following research results were obtained. First, the ultimate (50 years) maximum of long-term losses in circumferential and vertical prestressing tendons reach 10.97% and 17.02% of the tension control stress, respectively. Second, the losses in circumferential and vertical prestressing tendons under the coupling effect of shrinkage creep and stress relaxation are 83.59% and 86.33% of the algebraic sum of shrinkage creep loss and stress relaxation loss. Third, the interaction reduction coefficient is proposed, and it reaches the minimum value when the shrinkage creep loss and the stress relaxation loss are close. Fourth, the effect of vertical prestress on the long-term prestress loss in circumferential prestressing tendons is obvious. In conclusion, the research results are crucial to the design safety of concrete wall of large LNG tanks.