Internal Pressure in Enclosed Bldg?

[SKJ25POL]

I thought since Enclosed Building is enclosed there will be no internal pressure due to wind load, any body can explain in plain language why there is internal pressure due to wind if the building is completely sealed?

Thank you

 

[jayrod12]

So there are no doors or windows into the building?

 

[KootK]

Even with no doors or windows, buildings still leak significant amounts of air through their envelopes. Even if there was no leakage, there would still be internal pressure. Think of a ballon.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[DaveAtkins]

I always thought internal pressure is due to the mechanical system being unbalanced. Nothing to do with wind.

But the factor for a partially enclosed building is higher, so wind must play a role.

DaveAtkins

 

[JAE]

Big storm comes in. Atmospheric pressure drops suddenly? Not sure of the numbers but wouldn't there be an internal pressure from that?

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[manstrom]

I thought it had to do with a window or door getting knocked out due to a storm.

Maybe it has to do with regular pressure from air leakage. I do recall watching the attic access panel in my house lift up during a hurricane.

If the structure is absolutely, 100% sealed (a steel tank) then you can probably neglect it.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[mike20793]

In a partially enclosed building, wind can enter the structure and cause greater pressure (like a balloon filling up). In an enclosed building,

 

[mike20793]

Internal pressure is developed from wind blowing into and over the structure. In a partially enclosed building, wind can enter the structure and cause greater pressure (like blowing into a balloon). In an enclosed building, wind is assumed to not enter the interior of the structure. The pressure coefficients come from testing. There was a NCSEA webinar about a year and half ago where they described what happens to the wind when it blows over the building (how it detaches and reattaches to the structure) and what causes the internal suction as well as the windward and leeward pressures.

 

[mike20793]

Sorry for the double post. I was trying to elaborate and didn't mean to post the first response.

 

[msquared48]

Mechanical systems can sometimes be designed so that the internal pressure is greater than the outside at all times to avoid contamination from exterior air.

Mike McCann, PE, SE (WA)

 

[KootK]

Further to Mike's point, I worked on a hospital one time where an interior surgery room was kept under positive pressure at all times so that microscopic nasties always got pushed out of the room rather than into it by air leakage. I designed the surrounding light gauge walls for the standard 5 psf. When they turned the system on, two of the wall pancaked out and fell over. Now I don't live in America any more.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[DaveAtkins]

You don't live in America anymore...

Is that because you are afraid of a wall falling over, or you are afraid of microscopic nasties

DaveAtkins

 

[jayrod12]

He's probably running from the law

 

[KootK]

I shall not take the bait.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[msquared48]

Bathrooms should always be designed so that the air pressure on the outside is greater than inside yo avoid contaminating the outside air.

Mike McCann, PE, SE (WA)