ASCE7 Minimum Wind Load definition
ASCE7 Minimum Wind Load definition
(OP)
I don't understand the definition of the minimum load on the ASCE7-05.
The minimum wind load (10psf or 480 N/m2 )needs to be applied horizontally to the entire vertical projection of the building.
I know that the preassure is proportionally to the V^2, but i want to know how did the ASCE7 determine this 480 N/m2. The minimum wind velocity in USA is 85mph (38m/s) and if I follow the equation for the preassure:
q=0.613*Kd*Kzt*Kz*I*V^2
q=0.613*0.85*1*0.705*1*38^2=530 N/m2
Kd=0.85
Kzt=1
Kz=0.705 for exposure B and heights < 9.1m
V=38 m/s
This 530 N/m2 does not match with the minimum load of 480N/m2
Please help me, I will apreciate that ;)
The minimum wind load (10psf or 480 N/m2 )needs to be applied horizontally to the entire vertical projection of the building.
I know that the preassure is proportionally to the V^2, but i want to know how did the ASCE7 determine this 480 N/m2. The minimum wind velocity in USA is 85mph (38m/s) and if I follow the equation for the preassure:
q=0.613*Kd*Kzt*Kz*I*V^2
q=0.613*0.85*1*0.705*1*38^2=530 N/m2
Kd=0.85
Kzt=1
Kz=0.705 for exposure B and heights < 9.1m
V=38 m/s
This 530 N/m2 does not match with the minimum load of 480N/m2
Please help me, I will apreciate that ;)






RE: ASCE7 Minimum Wind Load definition
Also, this is the basic wind pressure. You need to use the figures in ASCE 7 to apply it. Some of the figures increase the pressure (like in corners) and other reduce the pressure.
There's also internal pressures, depending if the building is enclosed or partially enclosed.
You've also cherry picked a very low wind pressure. 85 mph is not the usual wind pressure for the vast majority of the USA, 90 mph (or more) is.
Finally, your case is the reason they have a minimum wind pressure. The code wants to make sure even under unusual wind combinations, no one ever uses less than 10 psf.
RE: ASCE7 Minimum Wind Load definition
RE: ASCE7 Minimum Wind Load definition
I really wanted to know if this "10 psf" are some kind of conventionally number tipically or if it has a scientific meaning.
I'm studing to implement this standard in Chile ( with other velocities, the minimim is 30m/s) and thats why i'm asking for. If i have a low velocity obiously the minimum preassure needs to be a lower value than 10psf.
Other standards (equal to asce7) used different numbers for the minimum load, but there's no more literature to obtain this values ..
RE: ASCE7 Minimum Wind Load definition
The reason for inclusion of the 10 psf minimum lateral load is simply to ensure that there is no odd combination of factors that would lead to unexpectedly low design pressures. It ensures a minimum lateral capacity for the structure.
RE: ASCE7 Minimum Wind Load definition
Any of these occurrences may result in negligible net pressures for C&C, MWFRS, or global stability. I think the 10 psf is intended to assure some minimal integrity and global stability of the building. Again it cannot possibly have any rational basis other than educated engineering consensus.
RE: ASCE7 Minimum Wind Load definition
I'm trying to understand how can a define a minimum load for my country (Chile). We have 67 mph as wind speed in our maps ...
other countries like Colombia, Venezuela changed the minimum load:
Colombia has 38 mph and 8.4psf
Venezuela has 43mph and 6.3psf (smaller than Colombia)
USA has 85 mph and 10psf
It seems that the pressure arent proportionally to the V^2.
RE: ASCE7 Minimum Wind Load definition
Alternatively, you could select a trial pressure and check it against examples of conventional construction that you do not wish to prohibit.
RE: ASCE7 Minimum Wind Load definition
And yes- the pressure is proportionate to the square of the wind speed (everything else being equal), but the wind speed has little to do with the minimum pressure. As others have noted, it's just a "feel good" number to ensure a minimum amount of lateral capacity.
RE: ASCE7 Minimum Wind Load definition
Example:
Take a monoslope open roof structure, freestanding, like a picnic pavilion or carport. You would apply the ASCE wind pressures perpendicular to the roof surface for your basic design. But when considering MWFRS lateral forces for overall stability of the structure, you take the horizontal component of this force. In the case of the wind direction going "up slope", this horizontal component would actually be in the opposite direction of the wind (which to me is a bit counter intuitive).
However, the magnitude of this force may very well equate to less than 10psf applied horizontally to the vertical projection of the roof depending on the wind speed and roof slope. Therefore, you use the minimum 10psf.
Another very similar case would be the same structure, with a traditional two sloped gable type roof. If you take the pressures perpendicular to each slope of the roof, if the slopes are the same, the horizontal components would cancel each other out. Therefore, you have the 10 psf minimum.
I think I have this right....
RE: ASCE7 Minimum Wind Load definition
Have you made any progress in implimenting ASCE7-05 in Chile yet?
If not what is the current standard for windloads on signs?
RE: ASCE7 Minimum Wind Load definition
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: ASCE7 Minimum Wind Load definition