MWFRS Windward Wall Pressure Calculation
MWFRS Windward Wall Pressure Calculation
(OP)
I was talking with colleagues to see what elevation they use for calculating MWFRS windward wall pressures:
1) Top of wall;
2) Average wall height;
3) Take qz evaluated and top and bottom of wall and take average;
4) Some other variation like qz evaluated at 2/3 the top of wall height.
I can’t find anything that says what the correct way is. Is it stated anywhere how it should be done? What do you guys do. For what its worth, the 1998 wind losd guide by Mehta and Perry uses top of wall.
1) Top of wall;
2) Average wall height;
3) Take qz evaluated and top and bottom of wall and take average;
4) Some other variation like qz evaluated at 2/3 the top of wall height.
I can’t find anything that says what the correct way is. Is it stated anywhere how it should be done? What do you guys do. For what its worth, the 1998 wind losd guide by Mehta and Perry uses top of wall.






RE: MWFRS Windward Wall Pressure Calculation
RE: MWFRS Windward Wall Pressure Calculation
RE: MWFRS Windward Wall Pressure Calculation
RE: MWFRS Windward Wall Pressure Calculation
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RE: MWFRS Windward Wall Pressure Calculation
RE: MWFRS Windward Wall Pressure Calculation
For the windward walls on a building, the wind force is uniformly increasing above 15'. Below 15' the force is uniform with z=15'.
RE: MWFRS Windward Wall Pressure Calculation
When calculating the wind pressures for the windward wall on a multi-story building, you can step the wind loads as you increase height. This is usually done per story level.
So say you have a story in 15 foot increments. For exposure C, Kz for the first 15ft is 0.85.
Story level 2 is from 15ft to 30ft. Kz @ 30ft = 0.98. But that is for calculating the velocity pressure at 30 feet. The average wall height for story level 2 is 22.5 feet. Thus, using 0.98 is conservative, but it is what most people do. I was wondering if other engineers use a more precise calculation of Kz.
Kz at the average wall height of 22.5 ft is 0.92, which is significantly less than 0.98. Even taking Kz as 2/3 the story height, or at 25ft, is 0.94. Which is still conservative, yet significantly less, than 0.98.
This is what I'm talking about.
RE: MWFRS Windward Wall Pressure Calculation
RE: MWFRS Windward Wall Pressure Calculation
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant