Altitude wind reduction
Altitude wind reduction
(OP)
How do you calcualte wind pressure reduction based on altitude?
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RE: Altitude wind reduction
Any effects due to lower air pressure would be negligible compared to this.
Also if you are talking about something on top of a mountain, the wind will speed up as it goes over the crest(see topographic factors).
This is all covered in the ASCE7 commentary (assuming your in the US)
RE: Altitude wind reduction
Wind speed increases with alitude above the ground, not necessarily alitude above sea level. So you should see some minor reduction in areas that are flat and elevated as opposed to sea-level areas of equal flatness.
I may be remembering wrong, but it seems like the older ASCE A58.1 actually had density in the equation.
RE: Altitude wind reduction
RE: Altitude wind reduction
John D. Holmes' "Wind Loading of Structures" covers this, if I remember correctly - I do not have my copy handy. You will still be in a boundary layer near the ground, so the wind profile will still be the same as any other location, but you can reduce the velocity pressure according to the ratio of density altitude to air density at "normal" MSL conditions. Forgive me for not remembering the equations, but you'll probably find very little benefit on low rise buildings.
RE: Altitude wind reduction
At one time the Denver(elevation 5,280 feet) building code used the density of air as 85% of that at sea level. I haven't checked lately to see if this is still the case. I once designed a structure at 10,000 feet (Winter Park, Colorado)and I think the density of air is on the order of 70% of that at sea level.
Considering all the guess work that goes into wind design such as wind speed, terrain factors, gust factors, and shape factors, I would be hesitant to take much of a reduction for altitude.
RE: Altitude wind reduction
RE: Altitude wind reduction