Stairway Tower Wind Load: Corner Zone 1

[eheiberg]

I have a 300 foot long 5 story building (200 feet deep). A 50 foot wide stairway tower projects 20 feet from the front and extends the full height of the building. Does anyone have experience with corner wind load zones for a similar projection? Should the corner zone extend 10% of the projection length (10% * 50 = 5 feet) or 10% of the complete building length (10%*300 = 30 feet), or something else?

Baffled by codes.

 

[JAE]

Typically I use the full building widths. I may be wrong but I think the pressures are more affected by the overall wind flows around the global building rather than smaller projections.



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[DaveAtkins]

I also use the full building dimensions for determining "a." And I only use the corner wind load at the corners of the overall building, not at corners that are away from the main corners.

DaveAtkins

 

[eheiberg]

Dave,

Two questions:

1: Why don't you use the corner wind load at corners that are away from the main building corners; surely there is turbulence there...
2: Are you Dave Atkins from Morristown NJ?

Eric

 

[DaveAtkins]

1. My interpretation of the Code is the turbulence is near the overall building corners. Otherwise, there are buildings where the entire building would see corner wind load, and I don't believe that is the intent of the Code.
2. No, I am the Dave Atkins from Green Bay, WI

DaveAtkins

 

[SAIL3]

the bldg has it's own turbulence zone with or without the stair tower....my concern would be how does the presence of stair tower add/modify the length and intensity of this zone...not knowing this without a wind tunnel test, I would assume the stair tower is entirely in the turbulence zone for a wind load case ....a nagging question would be for me does the tower increase the severity of this turbulence?......

 

[eheiberg]

Thank you all for your replies. I chose to take the conservative route and consider the corner zone to extend 1/10 of the building length along the stair tower. My client will be upset, but not as upset as he would be if a non conservative interpretation caused a failure and components and cladding flew off the building.

 

[jayrod12]

On my drawing, I always designate end-zone component and cladding design wind loads. I also typically design all of my components and cladding for the end zone value. It is not generally a large difference in design pressures and lends to easier design (less members to check) and better piece of mind.

End zone versus non-end zone comes into play only in overall building design, not the components and cladding.

 

[eheiberg]

Jayrod12, I am not sure what you mean by "End zone versus non-end zone comes into play only in overall building design, not the components and cladding" Can you explain?

 

[jayrod12]

I mean, when designing components and cladding, I only use end zone values.

When determining overall building stability I account for end-zones and middle zones.

 

[jayrod12]

For components and cladding, the increase is no more than 15% for end zone pressures compared to middle zone. Seems a waste of my time to run two separate calculations and have two different specs on the drawings, etc.

It does however make a more significant impact on overall building loading (50% increase in end-zones)

 

[eheiberg]

Jayrod12,

Where do you get the 15% increase maximum from. Is there a particular code or standard that you are using? If so please let me know.

 

[jayrod12]

NBCC (Canadian building code)

That 15% is just a rough estimate but basically our pressure/gust coefficient is 2.05 for end zone and 1.8 for middle wall. 2.05/1.8=1.138, 15% increase.

I'm not familiar with ASCE procedures but I imagine it should be relatively close? All of our other design methods are very similar across borders.

 

[eheiberg]

There are so many coefficients!!! However, the ASCE value of 1.8 that I am aware of is for the corner zone (zone 5) and the flat wall zone (zone 4) is usually closer to 1.0 (0.9). So the difference between flat wall and corner zone can be considerable.