Tank Wind Loads 1

[cdter]

I'm brand new to wind loading. I have been assigned to analyze wind loads on storage (water and oil)tanks. Don't worry guys, I'm not designing the tanks. I'm basically learning on my own. The two types of tanks I deal with are fixed-dome roof and fixed-cone roof. I have access to the ASCE 7-02 and API-650 standards. I also have access to past wind load calcs on tanks. I have three questions?

1. How is the effective area calculated for each wind zone?
2. How do you calculate the effective area for a dome or cone roof?
3. What equation is the period of vibration derived from to determine the stability of the tank?

 

[JoeTank]

Per API-650...

1 and 2 - There are no wind zones in the current edition of API-650. Basic wind loads are based on a 100 mph wind speed with noted adjustments. A varying wind speed, other than 100 mph, is specified by the purchaser.

The effective area is the projected area of the tank onto a vertical surface. A drag coefficient of 0.5 is applied to cones and domes. For a cylinder, use 0.6.

3 - API does not base wind loads on the frequency of vibration of the tank.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[cdter]

Thanks for the answer Steve. Does anyone else have any input?

 

[tincan]

AWWA D-100 Section 3 basic 100 mph wind

 

[PEStructural]

Per AWWA D100-96; Section 3.1.4, Eq 3-1:

P = 30 * Cd * ( v / 100 )^2 >= 30 * Cd
where

Cd = Drag factor: 0.6 for cylinders, 0.5 for double curved (for the roof)

v = Wind speed in mph

P = Wind pressure applied on the horizontal projection of the tank (for the tank walls = Diameter * Height)

So, the wind pressure on the tank walls = 18 psf for 100 mph.

Hope this helps.

Mike Florio
Superior Tank Company, Inc.