Wind Load/ Shape Factor For Circular Steel Tanks

[ZIO4]

Hello,
Working to British Standard BS6399 does anyone know a good shape factor to use for a circular steel tank 13.8m diameter?
I've calculated my dynamic pressure qs to be 1.13kPa. Once I have applied a shape factor, over what area do i apply this?
Please Help!
thanks
John

 

[vandede427]

If the British use metric units, then why is what Americans use called English units?

 

[JStephen]

In the older US tank standards, wind load on a cylinder was taken as 60% of that on a flat surface, with the load being applied to the projected area. In the current ASCE 7, wind loading varies depending on shape and roughness of the surface, with roughness being undefined for actual tanks.

In the current API-650, that load is applied, but also uplift on the roof is used as well. But also, load combinations have been revised, and some allowance made for the fact that tanks are seldom completely empty.

It helps if the wind loading and the overturning criteria are all taken from the same standards.

 

[apsix]

Only Americans call them English units.

The correct term is Imperial units.

 

[apsix]

Australian code method attached.
It's not a simple shape factor, but rather a pressure coefficient which varies around the perimeter.

 

[ZIO4]

Thanks Apsix and JSteven, your advide has been pretty helpful. I also continued the search myself yestered and evenetually found the answere in the Britich design Code 6399. Section 2.4.6 is for wind loading to Circular Plan buildings including silo's Tanks stack and chimneys. It uses Table 7 indicating varying pressure given the winds position on the periphery. It is very similar to the graph in the OZ code apsix.

Thanks for your help peeps! Great forum, its the first time i've used it. i'm sure i'll be back.

 

[GalileoG]

I live in a non-seismic area but seismic has always governed my design for cylindrical water/fuel tanks. For wind load, I have taken the cylinder tank as a box-shape. I would think the cylindrical shape of the tank makes it more aerodynamic (ie. less wind load.) so my assumption would be conservative. Someone correct me if I'm wrong.

Clansman

If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.