Wind and Earthquake Design
The potential wind and earthquake loadings on a pressure vessel are specific to the geographic location where the vessel is installed. Design parameters for the United States can be obtained from maps published by API. Refer also, to the Civil and Structural Manual. Section 440 of this manual describes how these design parameters are used to determine the maximum potential loads for design of the vessel.
Both wind and earthquake loads create overturning moments that develop longitudinal stresses in the shell of vertical vessels. The weight of the internal contents of a vessel will amplify the overturning moment resulting from earthquake loading, and must be taken into consideration when calculating the longitudinal stresses. It is not necessary to design a pressure vessel for the simultaneous occurrence of maximum wind and earthquake loads.
The longitudinal stresses developed in the vessel’s shell by the wind and earthquake loads must be added to the longitudinal stresses attributable to the internal pressure. However, the longitudinal stress attributable to the internal pressure is nominally one-half of the hoop stress, which is the maximum principal stress that governs the design of the vessel for internal pressure. Furthermore, the combined stresses for wind or earthquake and internal pressure are allowed to exceed by 50% the maximum allowable design stress for the material of construction given in the Code.
Higher stresses are permitted because a vessel is only intermittently subjected to severe wind and earthquake loads. Consequently, wind and earthquake loads will not usually affect the design of a pressure vessel shell. The major exceptions would be vessels designed for low pressures with relatively thin shells and a high weight of internal contents. Wind and earthquake loads can have a very significant effect on the design of the support and anchoring for a vertical vessel.
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