LNG储罐混凝土外罐稳定工况载荷及应力分析

Analysis on the load and stress of the concrete external walls of LNG storage tanks in stable working conditions

LNG储罐结构复杂,构件种类多,受力复杂,分析极限工况下储罐各部位的应力分布,对于研究全容式混凝土LNG储罐失效具有重要的意义。为此,通过对储罐的罐顶结构简化,在考虑储罐受到的可变载荷的基础上,对罐体受力荷载系统进行了分类计算和等效处理,建立罐体承载能力极限状态下的罐顶结构载荷、预应力载荷及其他各类可变载荷的组合工况,并采用ANSYS软件建立简化后预应力混凝土外罐的1/4部分的有限元模型,通过结构化网格处理和易发生应力集中处网格加密处理,对罐体各类荷载进行了等效处理,分析了储罐在承载能力极限状态下的罐体温度和应力分布。结果表明:(1)空罐工况下罐顶处最大受压受拉应力发生在储罐承压环处,最大应变位于最大拉应力-2.81 MPa处;(2)空罐工况下承台最大压应力、最大拉应力均位于罐底部与承台连接处外缘,应变最大值也位于承台与罐底接触外缘,此部位易开裂;(3)空罐工况条件下只有罐顶部与承压环应力达到混凝土破坏极限,而储罐其余部位应力均在材料安全极限范围内;(4)满罐风载/雪载工况下,罐体混凝土墙在各部位均达到混凝土材料强度极限;(5)满罐风载/雪载工况下承台与罐底连接部位处于混凝土材料受拉应力状态,且拉应力强度远远超过强度极限,该部位小裂纹在一定条件下易发生裂纹扩展;(6)罐体在热角保护部位的压应力达到混凝土抗压强度极限。结论认为,该研究成果为全容式混凝土LNG储罐失效分析提供了理论参考。

LNG tanks are structurally complex with many kinds of components and complicated forces, so to analyze the stress distribution at each part of a tank under extreme working conditions is of great signifcance to studying the failures of full-containment concrete roof （FCCR） LNG storage tanks. In this paper, classifed calculation and equivalent treatment were conducted on the force load system of the tank body by taking the variable load on the tank into consideration after the roof structure of the tanks was simplifed. Then, the combined work-ing conditions of tank roof load, pre-stressed load and other variable loads in the ultimate limit state of bearing capacity were established, and the fnite element model for 1/4 part of the simplifed pre-stressed concrete tank was developed by using the ANSYS software. Finally, various loads on the tank were equivalently treated by conducting the structured mesh processing and the grid encryption processing in the stress concentration area, and the temperature and stress distribution on the tank in the ultimate limit state of bearing capacity were analyzed. And the following research results were obtained. First, in the working condition of an empty tank, the maximum compression and tension stresses on the tank roof are located at the bearing ring of the tank and the maximum strain lies at the position of maximum tension stress -2.81 MPa. Second, in the working condition of an empty tank, both the maximum compression stress and the maximum tension pressure on the cap and the maximum strain are located at the outer edge of the connection position between the tank foor and the cap, where cracking tends to happen easily. Third, in the working condition of an empty tank, only the stress on the tank roof and cap reaches the failure limit of concrete while the stress on the other parts of the tank is in the limit range of material safety. Fourth, in the working condition of a full tank with wind load or snow load, the whole concrete wall of the tank reaches the strength limit of concrete material. Fifth, in the working condition of a full tank with wind load or snow load, the concrete material at connection position between the tank foor and the cap is in the state of tension stress which is much higher than the strength limit, so the small cracks in this position tend to propagate easily in a certain condition. Sixth, the compression stress on a tank at the position of hot angle protection reaches the compressive strength limit of concrete. In conclusion, the research results provide a theoretical reference for analyzing the failures of FCCR LNG storage tanks.