Moment due to wind load.

[Rich134]

Hello to You All

I am new to this site and I have a question. I am considering an API requirement for achoring vertical storage tanks. They say that a 100 mph wind will create 18 Lbf per square foot of projected surface. If the moment tending to overturn the tank is below a given level, no achoring is required. That seems reasonable, but I have forgotten my calculus. What is the moment tending to overturn the tank?

It seems that it would be the total force times some fraction of the height, but I can't find the answer in any of my reference books.

 

[JAE]

The overturning moment would be the total force on the tank projected area times the distance from the centroid of that projected area to the grade level where you are calculating the overturning.

There would also be a resisting moment taken as the tank weight times the distance between the leading toe of the tank and the centroid of the tank weight.

Whether you include some percentage of the weight of tank contents is a subjective decision depending on the potential for the design wind load and the tank being empty occurring at the same time.

 

[haynewp]

I would ensure a 1.5 safety factor for overturning before deciding that anchors are not required.

 

[JAE]

Yes yes....forgot to mention that..thanks haynewp.

 

[Rich134]

Thanks guys. That was exactly what I needed. The API safety factor is 1.5. Good call.