Stadiums Wind Category as per Asce

[Mohamed Maher]

Dear All,

Regarding stadiums canopy design is it should consider as per ASCE 16 category 2 or 3 for wind speed (as risk 3 is higher in wind speed).

Best regards,
Mohamed Kamal

 

[phamENG]

Depends on the usage and the governing building code (note that ASCE 7 is a standard, not a code). Where I practice, ASCE 7 is referenced in the code (which is a locally edited version of the IBC). IBC and ASCE 7 have slightly different criteria for selecting a risk category. Since the IBC is the building code, I have to use that. It's nice because it breaks it down based on use category and occupant capacity. If you don't have to use the IBC or a variant of it, then you can use the definitions in ASCE 7 which are a bit more vague and require the application of engineering judgement.

To exercise proper judgement, you have to consider lots of things. Is the stadium open or enclosed? If it's enclosed, then it's reasonable to assume it could be used an emergency shelter - go with the higher risk category. If it's open, then it won't be a shelter. But could people be there during a design event? Where I am, the answer is generally no - our design wind events are hurricanes. But in other areas the design wind event can occur suddenly and unexpectedly. If that's the case, then I'd go with III since you could have several thousand people there. If the answer is no and the place will be empty, then risk category II may be appropriate if damage or debris originating from your structure won't endanger any place that is a risk category III.

Or you can take the conservative approach (which is what I recommend) and just use risk category III.

 

[Mohamed Maher]

Thanks ..but based on what the asce divide the building categories..is it consider that buildings can be empty during the wind load..or deal with the building depend on its function for example hospital will be occupied..stadium will be empty ..shops will be empty ...is that the concept
Or the concept that the stadium have too much people in the match accordingly it will be same during the wind.

Thank for your replay

 

[phamENG]

The definition of a Risk Category III structure, according to ASCE, is: "Buildings and other structures, the failure of which could pose a substantial risk to human life." It further mentions economic impact or mass disruption of daily life and hazardous materials. I don't think the last two sections really apply - unless of course the owner wants it built to be a bit more stout to protect his investment.

So...what is a significant risk to human life? If my house collapses while I'm in it, my life is at substantial risk and I'm a human, so it could qualify, but we design houses for Risk Category II. So the application of II and III for anything that doesn't fit into the significant economic/daily life disruption or hazmat is usually based on the number of occupants. That's part of the reason I brought up the IBC - it breaks it down pretty nicely. The commentary in ASCE 7 also has a diagram indicating the relationship between risk category and the number of people at risk.

Trying to make a decision about will it be empty during a design event is usually not a good idea. I've only done it once, and that was because the contractor screwed up and the only way to finish (oddly enough it was a canopy on a stadium) without ripping half the back wall down and rebuilding was to design the canopy connection for Risk Category II wind loads. Before going that route, we had an in depth discussion with the architect, the owner, and the building official to get buy in all around and explain what we were doing and why. But again - where we are a Risk Category II wind event is at best a powerful Cat 1 hurricane, maybe a minor Cat 2. If anyone is watching high school football outside in a hurricane...well...Darwin. The other concern is with surrounding buildings. There was no concern of adding to the amount of debris in the event of a Risk Category III event, so the AHJ approved it. Again - this was a FIX. I would never design it like this from the outset.

It's a stadium with hundreds if not thousands of people in it. Design it for Risk Category III.

 

[Mohamed Maher]

I have another question please regarding cp factor in ACSE 7-16 FIGURE 27-3-4 DO WE SHOULD CONSIDER the cp according to clear wind flow or obstructed wind flow and how can i calculate the blockage ratio?
I'll attach one photo for the stadium elevations and it have two shapes

I attach also pdf file contain the stadium shape

 

[phamENG]

What do you think and why?

 

[Mohamed Maher]

It should depends on blockage ratio but the how to calculate the blockage ratio? I'm not sure about it for example if I took the farthest point for the canopy to the the height of first seat it will not consider obstructed..that will be same till I reach middle of seats ..and after ratio will be turn into obstructed so what is the one I should follow

 

[phamENG]

If you cover 50% of the end of a garden hose, do you consider the garden hose 50% blocked? Yes. So if you cover 50% of the airflow outlet under your stadium canopy, the flow of air under your canopy is 50% blocked.

It's important to think about wind loads as what they are - aerodynamic forces on a rigid body caused by fluid flow against and around its surfaces. In this case, between two surfaces.

 

[Mohamed Maher]

So which section I should consider ..if the seats height increased every step I should take the higher one and calculate the blockage ratio depend on it or combine all the different seats
levels and its crossponding level

 

[HTURKAK]

ENG. Mohamed Maher (Structural);

I will suggest you to look the following document ( UEFA GUIDE TO QUALITY STADIUMS )

https://www.uefa.com/MultimediaFile...ions/General/01/74/38/69/1743869_DOWNLOAD.pdf

If this is a real question, the wind tunnel test is necessary to determine the pressure coefficients.

GOOD LUCK..