C&C roof mechanical louver doors

[MechWang]

Hello everyone, just being stumped with this one, I am trying to replace a mechanical room louver double door located at a 15 story building roof and my structural engineer propose a high negative design pressure (in the hundreds) which is very unusual for louver doors and per calculation using Mecawind, this is a zone 5. My question is why is this mechanical room louver door which is located within the interior area of a flat roof is not part of the roof zone and shouldn’t this be considered not a high pressure zone area, therefore maybe zone 1 or 2 or 3? I would appreciate any inputs.

 

[dik]

I'm not sure I understand the question, but it should be posed to the structural engineer. He may have reasons for using a higher zone value. Is the louvre elevated slightly so that wind blowing across it may cause high suction values? There could be several reasons.

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[MechWang]

I'm not sure I understand the question, but it should be posed to the structural engineer. He may have reasons for using a higher zone value. Is the louvre elevated slightly so that wind blowing across it may cause high suction values? There could be several reasons.

Yes, it is a double door with the louver placed in the cutout middle section of the door, say a foot from the sill and top section of the door. The roof mechanical room dimension where the door to be placed is 15’x19’ and directly in front of the louver door is the roof elevator machine room and adjacent to it is the roof generator room. Would this cause high suction values?

 

[dik]

If elevated above the roof a little, high suction pressures can be created. The 'airfoil' shape of the air flow caused by this slightly elevated surface will create this airfoil effect. The engineer should be able to determine this effect and that may be what he has done. Ask him if there is any manner of mitigating this effect.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Agbsh]

For walls there are zone 4 and 5 (corner) for C&C. The door/wall is not part of the roof pressure (horizontal surface). As you know, C&C is influenced a lot by effective area (max of either tributary area or span*span/3). In your case this is 285 square foot. This area is not small and maybe will reduce your wind pressure.
Ask the engineer for calculations and the area he used. Also, make sure the wind speed he used is the correct one.

 

[jdcollins]

My question is why is this mechanical room louver door which is located within the interior area of a flat roof is not part of the roof zone and shouldn’t this be considered not a high pressure zone area, therefore maybe zone 1 or 2 or 3?

That's not how the wind load provisions work. This is likely being calculated assuming your mechanical room is a "Rooftop Structure" per ASCE, which forces you to use Sec 29.4.1 (ASCE 7-22) which, simply put, takes your design wind pressure at your main roof elevation and multiplies it by 1.9. This multiplier can be reduced if your rooftop structure is large in size compared to your main building footprint. That is likely why the pressure is so high. Not to mention that this roof is 15 stories high. I'm not surprised at all that you're getting these kinds of pressures.