Past ASCE Wind Provisions

[ads0221]

I have what should be a quick question. We have a client that has has an existing 200' flare stack that is going to be going through some restoration to replace in kind some existing rusted out gussets/guy wires. Our only scope of the project is to check to verify that the existing stack will be up to current ASCE 7-16 wind provisions. We do not have any existing vendor drawings but we do have existing foundation drawings that date back to 1990.

Would anybody have handy or know where I can verify what the current wind code would be around this year? We're basically doing a comparison between the two.

Thanks,

 

[canwesteng]

I don't understand. Are you checking for current wind load provisions, assuming 7-16 is in force in your jurisdiction? Or checking against 1990 wind loads? It sounds like the former, so just use the ATC hazard tool online.

 

[Once20036]

"current wind code" around that year will depend on where you`re located.
Are you in the US? Which state?

 

[271828]

Wind speeds from past ASCE 7 editions will probably be apples-to-oranges with ASCE 7-16.

If you're to "verify that the existing stack will be up to current ASCE 7-16 wind provisions" then you'll need to use the wind speeds in ASCE 7-16.

 

[ads0221]

I worded my question incorrectly. We are going to be using ASCE 7-16 to check the stack with the current wind load provisions. I was curious what wind loads one would have used in 1990 to compare the two. Location is in Louisiana.

 

[canwesteng]

You would need a copy of ASCE 7-88 and to do a full wind calc and then make sure to compare either ASD vs ASD or factored vs factored load. Wind speeds between the two can't be compared, and calculated forces can't be compared directly either. Probably not worth the effort.

 

[driftLimiter]

Seems like you might want to do that so you can have some ammunition when someone inevitably asks you why things are changing so much. This I can understand, If I were going to go down this route, I would try to get a reference pressure (maybe at the top of the stack) used in each method. Then be sure you use appropriate conversion factors to scale up the old pressure to be comparable to the new pressure.

TBH although the text of the wind load provisions has changed a lot. The resulting pressures (in ASD for example) used for design of MWFRS remain pretty close. Maybe just look at the design wind speeds and understand the recurrence interval and 3-second gust differences in the wind speed.

I think you wont find a significant difference in the actual wind loading from then to now. But you will find a significant difference on the resistance side of the equations that may not be trivial.

 

[ads0221]

7-88 that's what I'm looking for. Yes, we're not doing any changes at all to the flare stack or the foundations. Simply evaluating if the foundations are fine for the new wind codes. I want to have both compared in my back pocket in case we can't get them to work on paper.

Thanks again for everyone's responses.

 

[WinelandV]

I was still in Kindergarten in 1988, but wouldn't the 7-88 be using the fastest mile method for wind speeds? I think you'll need to hunt down how to do the conversion from fastest mile to 3-second gust, as well as the ASD/LRFD switch.

Also, pretty sure the wind maps got re-drawn for 7-16, so there's a decent chance that wind speeds did increase since 1988, even accounting for the issues above.

Please note that is a "v" (as in Violin) not a "y".

 

[JStephen]

There is an ASME code for stacks, and I don't recall if it has its own wind provisions or not.
Also, ASCE has a book on wind loading in refineries, etc., that may be of use.
Wind loading on stacks is often controlled by vibration issues, and that design may vary considerably, so you may have a lot of variation even if two different people designed the same stack using the same references.

 

[phamENG]

I really don't think looking at the old wind loads will help you at all. As others have said, the loading hasn't changed much. But a big difference on the resistance side is the 1/3 increase for wind/seismic. That used to be really popular. 1500psf soil became 2000psf soil for wind loads. Steel got 'stronger' for these short and transient loads. So while the wind load may be identical to current requirements, it doesn't mean the structure meets code because there's a good chance it lacks the required resistance to those loads.

 

[Bagman2524]

I have a copy of ASCE 7-88 if you need info from a particular section. Whole thing is only about 100 pages long

All I know is P/A and Mc/I

 

[driftLimiter]

Whole thing is only about 100 pages long

Amazing that the buildings from then still stand without 4 chapters on wind loads....

 

[1503-44]

I worry more about today's structures. Everything seems to be getting skinnier, longer spans, fewer columns and farther apart. The old ones are time tested.
(I've never bought a new house. Never will.)

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[ChorasDen]

I've never bought a new house. Never will.

This astounds me. I don't know where you live or are located, but the advancements in understanding, modeling, and building lateral resisting systems for seismic loads has had me always look for a house constructed post Northridge event.

 

[canwesteng]

If you believe ASCE, MWRS loads have gone down in most areas. C+C have shot up though.

 

[HTURKAK]

I am afraid this is more than calculating the wind induced moment as per latest ASCE loading code..

The applicable code in this case ASME-STS -1 -STEEL STACKS and the latest version is ( ASME website

https://www.asme.org/codes-standards/find-codes-standards/sts-1-steel-stacks

) STS-1 - 2021. I have 2006 version and AFAIK, there are mandatory sections and worked example.

My approach would be, consider the dynamic characteristics of the stack , all modes of vibration may occur during wind loading and consider vortex shedding effects .

The vortex induced moment could be much more than Mwind.

I would investigate wind , seismic and vortex induced wind cases to check the foundation ..

My opinion..









If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[ads0221]

https://www.asme.org/codes-standards/find-codes-st...[/URL] ) STS-1 - 2021. I have 2006 version and AFAIK, there are mandatory sections and worked example. My approach would be, consider the dynamic characteristics of the stack , all modes of vibration may occur during wind loading and consider vortex shedding effects . The vortex induced moment could be much more than Mwind. I would investigate wind , seismic and vortex induced wind cases to check the foundation .. My opinion..]

That’s a good point, we have our mechanical group who’s going to be giving us reactions using their MecaStack program of base foundation and guy wires.

I will look into everything you guys referenced. Thanks as always.