Reliability analysis of stiffened tank-roof stability with multiple random variables using minimum distance and Lagrange methods

• Reliability model with multiple random variables was established.
• A method using minimum distance and Lagrange formulae was proposed.
• Key factors affecting reliability include effective and equivalent thickness.
• The inferior quality of welding was equivalent to decrease equivalent thickness.
• Relationship of reliability and effective thickness is positive and near–linear.

Based on the reliability and buckling analysis of the steel tanks with a stiffened dome-roof, a mathematical model with multiple random variables was established and a new method for calculating and analysing the reliability and stability of the tank-roof by minimum distance and Lagrange formulae is provided. The analysis result of the tank as an engineering example by the proposed method shows that the thickness of both dome-roof-plates and stiffened ribs would affect the reliability of the tank-roof under different external loads. It is demonstrated that decisive factors affecting tank-roof reliability may be analysed such as: material thickness and external load. A reliability assessment is also needed performed to prove the correctness of both model and method. The assessment results were consistent with those from the engineering example. A baseline, reference method, for tank design and operation is thus proposed.

Reliability index with different effective thickness and equivalent thickness tank-roof thickness and stiffened plates thickness both have effects on reliability index under external loads. The relationship among reliability index, roof effective thickness and stiffened plate equivalent thickness is positive correlation and nearly linear when the external load is certain as shown in figure.Figure optionsDownload as PowerPoint slide