BS 6399-2 Wind Loading on Cylindrical Silos

[fred2002]

Has anyone tried to use this standard to calculate the wind load on a cylindrical silo. I have got as far as getting the dynamic pressure, qs, but have no idea how to use Table 7 to get the overall pressure coeffient. Do I have to sum all the coefficients for every angle on the periphery and resolve them parallel to the wind direction? In which case I get an overall Cpe of about 5.

Should I use the maximum coefficient in the table i.e. ~70 deg?

Should I use the two diametrically opposed pressure coefficients with the greatest distance?

Should I use the pressure coefficient at 0deg?

BTW, I have seen thread 194-76172 which unfortunately hasn't helped me.

Thanks in advance.

Fred.

 

[Ussuri]

I have tried it a couple of times in the past, but as you know there really isn't any guidance associated with it.

What I have done is to use the coeffs given and plot the pressure distribution around the structure, and from there work out the net overall pressure.

Because it is cylindrical you can check what figure your get using standard drag force equations to see if you get a similar figure.

There is also a publication called "The designers guide to wind loading on building structures" by NJ Cook which gives some guidance.

 

[chichuck]

Ussuri,

Do you know where one could get a copy of the book by Dr. Cook?

regards,

chichuck

 

[pba]

I assume you are trying to determine foundation forces rather than the forces of the actual tank itself?

I don't have the code to hand so can't give you specific direction. - Ussuri's method of determining the net pressure is ok but quite involved. I've always assumed that the pressures given are normal to the face so that way involves a lot of trigonometry.

Unless it's critical try using the combined coefficint for 0 and 180 degrees (about 1.0 and -0.4 giving 1.4 overall if I remember correctly). This should be worse than the worst case...

Elsewhere in the code it deals with forces on individual members and gives a coefficient of 1.2 for the force on a cylinder - That may also be of help.

 

[Ussuri]

http://www.brebookshop.com/details.jsp?id=189997

The link above is for part 2, static structures. There are other parts.

I notice the BRE say its out of print and there are only a few copies remaining.

 

[pba]

Just for the 'fun' of it. I calculated the overall pressure coefficient based on the Table 7 values. Overall it is about 1.2...

 

[fred2002]

Thank you for all your contributions.

I am at a complete loss as to how a fairly useful standard like CP3 V-2 (in that it gave alternatives to square blocks) turned into BS 6399-2. CP3 gives force coefficients for different non-rectangular sections whereas 6399-2 gives the pressure coefficient table for a circular section without giving the reader any idea as to how to use it.

pba, I'd be grateful if you could give a brief outline as to how you came to a value of ~1.2.

 

[slipstick50]

Take a look at the midwest plan service information on winds on tanks,, gaylord and gaylord books on tanks and safarian and harris on tanks........ AISC has stuff too...

the pressure on the tank front and remember the suction on the back,, could email or send more info too..