A rational design approach of intermediate wind girders on large storage tanks

• The design approaches for the wind girders in API650 were presented.
• 3D model is established to simulate the real distribution of wind load.
• The strengthening effects of the tank bottom is considered.
• Based on this design proposed, the material was significantly reduced.

In storage tanks, intermediate wind girders are used to prevent the buckling failure of tank wall caused by wind load. For the design of the intermediate wind girders, two key parameters must be determined: the size of intermediate wind girders and the spacing between the girders. In the code API650, the spacing is expressed as the maximum height of the unstiffened tank wall and the size is referred to the minimum section modulus. In this paper, the design approach for the maximum height of the unstiffened tank wall and the simplified mechanical model for the minimum section modulus adopted in API650 were presented to reveal the simplification regarding the magnitude and action zone of wind load and the negligence of the strengthening effects of the tank bottom. A 3D finite element model was built to study the wind pressure distribution around the tank and strengthening effects of the tank bottom. Optimal analysis to minimize the weight of the wind girders for a given wind load was performed numerically and formulas for the size and spacing of the wind girders according to the optimal results were given. Based on the optimal design proposed in this paper, the material consumed for the winder girders were significantly reduced.