A design algorithm used for the roof frame and liner system of extra-large LNG storage tanks

The design of roof frame is one of the most important parts of LNG tank design. In China, however, the calculation of roof frame system of extra-large LNG tanks is currently faced with a series of problems. For example, there is no united yardstick on buckling characteristic value, the calculation is based on many assumptions, and the calculation is inconsistent with domestic specifications and stipulations. In view of these problems, the material non-linearity and structural non-linearity were introduced and the initial defect was taken into consideration. Then, the large non-linear finite element calculation software ABAQUS was adopted to carry out modeling on the roof frame and liner system of extra-large LNG tanks and calculate and analyze the force applied on them and their stability. Finally, a complete set of design algorithm for the roof frame and liner system of extra-large LNG tanks was established and applied to the design of a certain LNG tank (20 × 104 m3) in China. It is indicated that this design algorithm can simulate the actual situations accurately. This design algorithm is structurally composed of shell units and beam units, and it is connected in the pattern of common node. Besides, force calculation is conducted in 10 operational modes and the buckling calculation in 7 operational modes, including all operational modes in the construction process of roof frame and liner system of LNG tanks. It is also revealed that the maximum stress on the roof frame is 125.7 MPa, that on the liner is 101.4 MPa and the minimum safety coefficient used for buckling calculation is 2.57. Under this system, the force and stability of the roof frame of LNG tanks are satisfactory. The research results can be used as reference for relevant design and calculation.