Rounded corner wind load

[hi5chenchen]

Hi guys,
I am tying to work out the wind load for a 100 meter tall building by using AS1170.2. The building has no shape edges(corner radius very large compare to the building's width and length), Just wondering should I apply Kl=3 to the side wall negative wind load in this case? If yes, is there a corner shape modification factors for me to take into consideration within the AS?

thanks

 

[Retrograde]

For a building of that height I would want a Wind Impact Assessment study to be undertaken, which should give the answers you want.

In the absence of such a study I would not use Kl=3 as I feel this is too conservative given you should not expect high suctions to develop on a rounded corner. Section C5.2.1 does not specify any local factors for circular tanks, which is a similar situation to yours.

 

[hi5chenchen]

Thanks Retrograde,
According to your recommendation, if there is a rounded shape building, its wind load should be carried out by the section C5.2.1, circular bins then. Am I correct?

 

[Trenno]

Correct me if I'm wrong, but I was under the impression local factors only really play a dominant role in the design of cladding and immediate supports, ie purlins/girts.

Are you looking at the global stability of the building? Or just a small area of cladding?

 

[Retrograde]

Correct me if I'm wrong, but I was under the impression local factors only really play a dominant role in the design of cladding and immediate supports, ie purlins/girts.

I believe that you are correct Trenno. I assumed that hi5chenchen was looking at the cladding design.

 

[hi5chenchen]

Trenno and Retrograde, you are right, I am looking at window cladding design.
thanks

 

[Retrograde]

According to your recommendation, if there is a rounded shape building, its wind load should be carried out by the section C5.2.1, circular bins then. Am I correct?

C5.2.1 is for a circular tank. Table 5.6 is for a rectangular building. You are not really either of these situations - you are somewhere in between. Therefore you are going to have to use engineering judgement to come up with a solution. I'm sure different engineers will come up with different solutions. If you don't get a satisfactory answer here I would phone up some local wind engineers and try to pick their brains.

 

[hokie66]

Not sure what design stage you are in, but if the building has been or will be subject to wind tunnel testing, you should request advice about cladding loads from the wind consultants.

 

[hi5chenchen]

hi Retrograde. My original solution was to use kl=2 for local pressure factor, sort of use a intermediate value, not so conservative(ie. Kl=3) . But I just found hard to convince myself with a more proper engineering explanation.
If you are able to give me some tips from other professionals, I'd be much appreciated.

 

[hi5chenchen]

Hi hokie, the project has been just started. I don't think the building will be taken through a wind tunnel test unless AS specified so. Also I don't have a access to CFD software either, so just hoping there is a way I can get a good estimation out of the AS1170.2.

 

[Trenno]

What's the difference between using a local factor of 2 or 3? Put it into a dollar value... Does it come close to ~$30k for a wind assessment?

Google is also your friend... Relevant discussion

Also why don't you download the Autodesk Robot Free Trial and give the wind simulation a whirl (yes, pun intended). Test pressures on a rectangular Vs cylindrical model.

 

[racookpe1978]

Well, consider.

EVERY building which has cladding (windows or panels) that have failed has required months - sometimes years! - of very, very expensive repair and re-design efforts and trials-and-errors rework. Ugly, failed solutions in every case. ALL of them required tens of millions, sometimes hundreds of millions, of repairs that taint the building, the designer (the company and architects) years later.

So, you have started with a "lesser problem" than some cases: slightly rounded corners and a sligthly more modest height than a few problem cases. That will push you towards lower failure rates, but you are not out of the envelope yet since the prying and vibrating forces are "local" and may happen anyway as winds get exaggerated by swirls and flows from nearby buildings and nearby plazas and open spots.

With that risk, without a specific wind analysis, I'd use the rounded edges only to buy the greater safety margin from failure, and "sell" it to the project team that way, rather than to try to justify a theoretically smaller (and thus slightly cheaper) joint and tie-back and connection system. Greater reliability.