internal building wall pressure

[PSF]

What is the point of the second term for internal building pressure in the ASCE7 equation 6-17 for calculating applied wind loads???
Pz = q G Cp - q G Cpi
If I apply all positive (or all negative) pressure to the inside walls, the net result of adding the leeward and windward components is exactly the same as if I never used the term.

 

[JAE]

Not if you have an expansion joint through your building perpendicular to the wind direction. In that case, the internal pressures do affect the overall lateral force on each of the two individual buildings.

The internal coefficient also affects the overall uplift forces on the structure through the roof loads.

 

[chichuck]

You are correct about the horizontal forces, without the expansion joints mentioned by JAE, they cancel out. But the vertical forces, due to roof suction or pressure as applicable, still are a factor.



regards,

chichuck

 

[cap4000]

Typically its for the Roof Loads as walls just cancel out as you indicate. Depending on what wall your "opening" is actually on windward or leeward, will determine the overall + or - Roof Load internal pressure effect.

 

[UcfSE]

Since wind pressures are assumed to act normal to the roof or wall surface, the internal pressures would not cancel out totally if the walls are not parallel to each other in the considered direction. That doesn't happen often though.

 

[Taro]

For the Main Wind Force Resisting System, the internal pressures tend to cancel out as stated above. The major impact of the internal pressures in on Component and Cladding design.