API 650 design uplift pressure on the roof

[Emiliano87]

Hello, I'm trying to do some calculations on Wind overturning stability on a self supported cone roof tank with internal pressure. The thing is that when I look at the design code in the point 5.2.1(k)2 it states the maximum design pressure on roof. My struggle is to understand the meaning of this. Say I have some wind speed that results into an uplift pressure on roof per 5.2.1(k)1 .And internal pressure such that it exceeds the 1.6 times the design pressure P per F 4.1, does it mean that I need to reduce the allowable internal pressure in tank so I dont exceed the max design pressure on roof cap? .If this point states that I need to take into account only 1.6 P per F 4.1 if the sum of design and internal pressure exceeds that value, how can I make the wind overturning stability check since it's made with load combination cases?

 

[JStephen]

I think in most cases, for a self-supporting roof, the allowable pressure per F4.1 is going to be higher than any wind pressure.

I think the point of the section being referenced is that if the roof is going to peel off the tank in a hurricane, then you can't develop the same amount of uplift as you could if it stayed on.