Added Internal Pressure to Wind Load

[jesvelt]

I am working on the review of a building with an added internal pressure on the building from fans. There are exhaust louvers that classify the building as partially enclosed. I am looking for a code reference or any information on adding the internal pressure from the fans to the internal pressure from wind.

 

[dlew]

jesvelt,

I do not know of any code that cover that case,but some questions come to mind:

1) Do the louvers have shutters?
2) Will the fans be off and the shutters be closed during high winds?

If the answer is yes to both questions, will the buiding still be classified as partially enclosed?

Do the fans increase/decrease the internal pressure in the building significantly? One-inch of water is equivalent to 5 psf?

Regards

 

[jesvelt]

The exhaust system has weighted doors. The doors are never locked closed. The component I am concerned about designing is a suspended ceiling and am primarily concerned with internal pressure load combinations.

The building was designed for a minimum of 1.5" water pressure or about 7.8 psf. If the internal wind pressure is added to the water pressure the ceiling would need to be designed to resist a much larger force. The internal pressue for an 85 mph Exposure C is approx 17 psf. By adding the loads together the internal pressure is significantly higher.

The UBC and ASCE7 include a self-straining force in the reference, but in the commentary this is described as stress caused by dimensional changes. I am not sure that internal forces would be concidered dimensional changes.

We did some small scale rough tests and found that it appeared the forces were added together. The tests were very rough though, and I thought it would be helpful to have a code reference to refer to when discussing the findings with the client.

 

[quark]

Sorry Guys! If I am out of the way. By internal pressure do you mean pressue of inside air.

If it is so, then 1.5" wc is hell lot of a pressure and I never heard of. Generally 15 pascals or 1.5mm is standard. I have worked with areas where the area pressure was 8mm of wc and that was in extreme cases. Even 8 mm corresponds to 1.69 psf approximately. Perhaps 1.5"wc is the static pressure of fan.

Regards,

Repetition is the foundation of technology

 

[jesvelt]

The building is a potato shed. The industry standard is 1.5" of static fan pressure minimum. The building is pressurized when the fans start. If the wind held the doors closed or open and increased the internal pressure, what would be a reasonable assumption as to what happens?
Thanks for the replies.