Wind load calculation 2

[LTRN]

I need to perform a calculation for minimum wall thickness required, in terms of wind load for a simple vent stack. I am interested in the proper formula and any additional comments as well. Thank You.

Stack dimensions
36 inch diameter
90 feet height
.375 nominal
100 MPH wind

 

[kstaylor]

Use a structural Code like IBC (e.g. International Building Code, the old UBC) or ASCE 7 for determining external loads on structures due to wind, seismic, snow, ice, etc. Your local jurisdiction may specify which Code they require for this type of structure.

 

[meca]

LTRN,

For a slender stack you have to consider the along wind loads, but you also have to consider the across wind loads due to vortex shedding. I have ran the stack that you provided in my stack analysis software (

http://www.mecaconsulting.com).

Here are the results:

Wind Code : ASME STS-1-2000 'Steel Stack Design' (much of this is taken from ASCE 7-98)
Wind Speed: 100 mph
Exposure : C
Importance: 1.15
Corrosion Allowance: 1/16"
Material: A-36 Carbon Steel
Thickness: 3/8"
Max Temp: 250 Deg. F

The wind pressure at the top is 47 psf and at the bottom of the stack is 13 psf, the pressures change along the height of the stack due to Kz. The stresses are acceptable for the along wind loads, however this stack could have a vibration problem. The critical wind speed is 12 mph, which is very low. This means that at 12 mph vortex shedding could occur producing large deflections. As I have it modelled, the stack is unacceptable per ASME STS-1-2000 'Steel Stack Design'.

If you contact me at chris@mecaconsulting.com, I will email the analysis output to you.

Regards,

Chris

http://www.mecaconsulting.com