Wind load on Stacks 1

[SKJ25POL]

Does anybody has expereince on wind load on Stacks (smoke stacks)?
Do they follow AISC7 or there is another standard giving more detailed calculation?
If ASCE 7 methods apply which one?

Any article or document or reference will be greatly appreaciated.
Also would like to know where I can find the deflection limits for the top of the stack.

Thank you for assisting your fellow freshman structural engineer.

Regards.

 

[delagina]

Wind Load for Petrochemical Facilities.

You need to check frequency, etc..

 

[XR250]

I used to engineer these about 20 years ago. We used wind tunnel modeling.
They were very difficult to design - especially at the opening near the base.
Glad I don't do those anymore.

 

[DaveAtkins]

I think ASCE 7 does a nice job of providing wind load provisions. You should check natural frequency, as mentioned above, to determine if it is a "rigid" or "flexible" structure.

DaveAtkins

 

[dcarr82775]

We designed some segmental stacks a while back. ASCE7 gives guidance on the overall wind loads, but not the local distribution on the stack itself, which we found was the much larger issue. We used an old ASCE paper from 1972 that provided a pressure distribution consisting of pressure on the windward face, very large suctions at 90 and 270 from the wind and a smaller suction on the leeward side. I am sure something newer must also provide guidance

 

[BAretired]

Don't neglect vortex shedding. I have never been involved in that type of design myself, but thread794-372072 in the Boiler and Pressure Vessels Engineering Forum may be worth a read and in particular, you should view the video:

https://www.youtube.com/watch?v=hvg0QQt8Ifk&feature=youtu.be

BA

 

[theonlynamenottaken]

Skip ASCE 7 altogether. You need ASME STS-1.

Stacks are so susceptible to vibrations arising from vortex shedding that the "simple" pressures determined in ASCE 7 can be very misleading. When you use STS-1 you'll find a lot of similarities to ASCE 7, with the qz and G (gust factor) calcs being the same, but from there you'll want the vortex shedding-specific coverage of STS-1. You'll find it all but unavoidable to implement some kind of damping to the stack, anything from mass dampers to helical strakes and/or bearing pads.

ASCE 7 - C26.9, "The gust effect factor accounts for the loading effects in the along-wind direction due to wind turbulence-structure interaction... It does not include allowances for across-wind loading effects, vortex shedding, instability due to galloping or flutter... For structures susceptible to loading effects that are not accounted for in the gust effect factor, information should be obtained from recognized literature."

The last stack I had my hands on I did a quick analysis without any damping measures on the stack:
Overturning moment from ASCE 7 wind (inline with the direction of the wind) = 330 k-ft
Overturning moment from STS-1 wind (perpendicular to the direction of the wind, from vortex shedding) = 1150 k-ft

Also, with vibrations from vortex shedding you'll need to evaluate fatigue... Have fun!

 

[BAretired]

SKJ25POL:
If you are a freshman engineer, you really should be getting some assistance from your boss in determining design loads. It is not an area familiar to the average structural engineer. If you are not sure, seek assistance from someone experienced in this type of design either inside or outside your firm.

BA

 

[SKJ25POL]

Dear theonlynamenottaken,

What's the full name of STS-1? Where I can find a copy of that?
I thought for all stacks you do a tunnel analysis? Is STS-1 a tunnel analysis?
I apprecaite for your vast knowledge and information. I like to learn it but my hands are tied.

Thank you

 

[theonlynamenottaken]

Vast knowledge? Flattery will get you nowhere in this forum. Actually, it never hurts

Great links from BAretired. Take his warning seriously (in fact, always take BA's advice seriously) - this subject just isn't as straightforward as a cantilevered beam in a building structure, even though it looks like it from a first glance. I applaud you if you want to dive into this, but you'll need substantial oversight, assistance and collaboration from a senior engineer in the long run.

Wind tunnel testing isn't required as far as I know, but wind tunnel testing will usually result in lower design forces/pressures. The problem is getting a client to commit to the design cost and schedule associated with wind tunnel testing.

ASME STS-1 Steel Stacks
latest edition is 2011

Here is the cover page and table of contents:
Cover Page & Table of Contents

Here is the page where you can order a copy:
ASME Product Page for STS-1

You may be able to find a PDF of the old 2006 edition floating around on the web somewhere...

 

[oldrunner]

You might also look as AASHTO's Luminaries/Pole code and consider vortex shedding and especially fatigue in the revised or new (can't remember now) Chapter 11. A lot of good commentary in this code.