Defines the wind velocity acting on the tank. You should follow Section 5.9.7.1a. The standard is a 120 mile per hour (53.6 m/sec) wind but may be increased to account for additional tank height, wind gust, internal pressure, or open-top tanks.
Several configuration settings control how the wind pressure is computed and applied to the tank. These configuration settings are as follows:
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Roof Projection in Wind Moment?- Turns on and off wind loads on the roof.
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10% Plus 5 psf in Wind Moment- Defines the basic wind moment definition according to Section 5.9.7.
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Section 5.11 Wind Pressure- Defines the wind pressure to be used for Section 5.11 stability.
Notes on Wind Velocity when there is user defined Height versus Wind Wind Pressure
The Wind Velocity is used to determine the design wind pressure PWS per paragraph 5.2.1 k) 1). The design wind pressure is then used to determine the moment MWS which is used in Table 5.21b. Per the Code in Imperial Units:
PWS = 18(V/120)2
The moment in foot-pounds generated by this pressure in lbs/ft2 is then computed as follows:
MWS = PWS * D * H2/2
Where:
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V is the design wind speed in miles/hr
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D is the tank diameter in feet
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H is the tank height in feet
When wind pressure versus elevation is used, there is a disconnect between how the API 650 Code works with its built-in use of the ASCE wind code. With a known wind speed and other ASCE factors entered in, the wind loads and moments are all worked out consistently.
If you have entered in a user wind pressure versus elevation, the wind velocity must match the design wind pressure at the top of the tank. This helps ensure you obtain the desired moment used in the uplift calculation. When the velocity is correctly entered, the value of [Moment] in the output would match the value of [MWS] within reason. However, as with any Code or Standard, the analyst must interpret the Code and use best engineering judgment when selecting an appropriate input value.