BS 6399 - Cpe pressure coefficient for Circular plan buildings

[sajk14]

Hello all,

I am currently trying to working out the external surface pressure on a circular storage tank ( 15m dia x 12m High ) using the formula....

pe = qs x Cpe x Ca (cl 2.1.3.1 in BS6399-2)

I have obtained values for qs and ca however I am not sure what value to use for Cpe.

Looking at Table 7 (for smooth surface and H/d < 2.5 ) it gives various Cpe values at particular angles in degrees. It is not clear what method to adopt in order to find an overall/single value of Cpe. Please can anyone give me some guidance.

Once I have the Cpe value and substituted it into the above formula for pe, to obtain the windload force on the tank should I multiply pe by the 'projected area' i.e 15m x 12m.... or the total surface area of the cylinder i.e 15m x pi x 12m ?

Another point to mention is that the tank has a conical shaped roof ( less than 12 degrees slope ). How do i apply loads to this as BS6399 does not address cone roofs? I was thinking of a very conservative approach of using the surface area of the cone multiplied by the same pe value above or can I use a projected 'triangle cross section' roof area multiplied by pe?

Thanks for your help and advice.

 

[sajk14]

Can anyone help or comment on the above query please?

 

[patswfc]

skn4

You could sum up the pressure coefficients for each 10 degree segment and resolve the wind pressures to obtain the overall pressure on the tank. This is quick to do on a spreadsheet.

Alternatively use the following which is taken from page 83 of "Wind Loading a practical guide to BS6399-2 Wind Loads on Buildings" by Cook.

"You may estimate the overall drag force on a cylindrical building by taking a net pressure coefficient of Cp = 0.6 acting on the area in elevation (This value is compatible with the factor of 0.85 in Equation 7)"