Wind load on a steel stack. IBC2018 or ASME STS-1? who prevails? 1

[banana33]

Good morning from Netherlands!
We're building a chemical plat located in USA and we have to design a steel stack the will be (obviously) placed in USA.
I have a big doubt about the wind speed to consider in the wind load calculation.
IBC 2018 report wind speed maps (regardless the building category) which are significantly different from wind speed map found in ASME STS-1 norm (ASME norm is specific for the design of steel stacks).
In this case which norm prevails between IBC2018 and ASME?
In my modest opinion ASME norms is "in charge" because it is specific for steel stack so wind loads must be obtained from it but i'm not sure about this point, mostly because ASME wind speed is lesser than IBC's one and i don't want underestimate it.

Can someone help me to understand which is the correct (and legal) way?

Thank you so much!

 

[JAE]

I'm not familiar with ASME STS-1 but IBC 2018 wind is an ultimate (factored) wind speed where you use 1.0W for factored design and 0.6W for service (allowable) type designs.
Perhaps ASME is still using the service level speeds???



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[banana33]

Dear JAE,
thank you so much for your kind reply.
I see the difference between factored and allowable wind speed of IBC2018 code.
Asme STS-1 use a basic wind speed based on a 3 second gust velocity and explain how to calculate the force acting on the stack starting from this speed.
I would like to understand "normatively speaking" which is the correct norm that must be applied in order to be compliant to the law.
Which is the "stronger norms" between the general IBC norms (that cover a lot of kind of structure) or the ASME STS-1 (specific only for steel stacks)?

Thanks!

 

[GC_Hopi]

Sounds like a question to the Authority Having Jurisdiction or the Engineer of Record. If they have no requirement/preference then industry standard will rule.

 

[banana33]

Thank you Hopi.
What do you mean about "industry standard"? ASME, IBC or what else?

Regards

 

[JAE]

With stacks you many times have to consider the along wind loads and also the across wind loads due to vortex shedding.
I think the ASME code here would be more applicable and give you more appropriate wind conditions to design from (vs. the IBC-ASCE 7 wind loads, which are mostly for buildings).



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[AskTooMuch]

ASME like other horizontal and vertical vessel.

 

[GC_Hopi]

The important part is to check with the owner to determine what design standard they want or if any code officials will be checking the design and what their requirements are. If you are a specialty engineer and you are submitting to the Engineer of Record then ask them for their requirements. If none of the above apply then it's really engineering judgment on how you want to proceed. Especially if what you are designing will be inside the fence of the plant then ASME is quite valid. If it's outside the fence then you may consider reviewing the website of the county in the US which it will be located. The website should have information on what building code if any they have adopted. Lastly for loading IBC will refer to ASCE 7 for the loading and there is discussion of pipe racks in there. And of course use the best practices and industry standards.

 

[AskTooMuch]

No county official will check this. Structures in refinery, chemical, o&g, etc.. usually don't require it.

OP is not in the US, most likely not licensed in the state this plant will be and most likely not supervised by a licensed engineer in that state. They do their design then submit the drawings to US counterpart with minimal checking from US counterpart. That's how it is in O&G EPC.

I'm in no way saying they do a bad job but I don't think this is acceptable practice in commercial buildings where it requires county official approval.

 

[GC_Hopi]

AskTooMuch; I agree with you that is how things currently happen. Just saying its best to do your due diligence. And in your example, I would say make a request to the US counterpart about design standards. If they say boo then so be it but at least you can check that box and email is cheap.

 

[JStephen]

I would be inclined to use whichever one gave me the higher loading.
The IBC wind speeds would normally be used with ASCE 7, and it'll be kind of a mess to work through the "G" factor equations in there. Don't just plug the IBC wind speed into the ASME design, though.

The old UBC used "fastest mile" wind speeds, if I recall right. Then ASCE 7-05 used "3-second gust" and the wind-speed numbers increased considerably. Then ASCE 7-10 used strength-level wind and incorporated importance factor into the wind speed, and the wind-speed numbers increased even more. However, in all of this, the design loads haven't really changed that much. If the ASME document is aligned with UBC, it may not be off as much as you suppose.

 

[DCBII]

Wind speeds in the latest version of ASCE 7 have dropped significantly due to new wind data being available. I'm surprised ASME is lower. Are they that much different that the entire design will change by using the most conservative value?

 

[JLNJ]

The old ASME STS-1 was rife with errors. Maybe they have cleaned it up by now. I would be a little wary.