huangyhg

wind design pressures
design pressures at wall corners and roof edges calculated per asce 7 are to be applied over a distance a. this is listed as 0.1 x width, 0.4h, minimum of 3 feet. in the 1997 ubc this used to be limited to a maximum of 10 feet. is ther a similar maximum now in asce 7?
there is not a maximum limit. only those three criteria.
rather over an area with "2a" as a width.
i think the guys that made asce 7 looked at the ubc and decided that calulating wind pressures with it was just way too easy and made too much sense. i think there goal was to make it as confusing as possible.
asce7 is not that complicated, its presentation is just badly set out.
it would be a whole lot easier if you didnt have to flick back and forth to get values from tables.
i think i can settle this argument by saying that it's both complicated and poorly presented.
i asked at a seminar about six years ago why the code changed wind design so much since it didn't appear to be a problem. the answer was this was more accurate (?) and since everyone had computers, there would soon be a computer program that would take care of it for us.
for a small fee, of course.
amen!
asce 7 is bad, and the wind provisions are abominable. there was an article in structural engineer magazine recently where they compared wind load calcs using asce 7 and ubc 97. the author made the point that the results were practically the same, with the ubc yielding slightly higher results. however, the asce 7 calculations were admitted as being far more complicated and taking far longer to perform.
so where's the benefit? i have trouble with any claim that the increased complexity of asce 7 is justified by increased accuracy. definitley a case of false precision.
in these environs, there is a simple and a complex manner of determining wind pressures... the use of either is discretionary. if asce 7 is less conservative, they maybe they should consider a simplified and detailed approach.
dik
getting all these factors and formulas down to the gnat's eyebrow doesn't really mean you are being more accurate, either. how many perfectly rectangular buildings are they building these days anyway?
the wind loads derived from these codes are not a real representation of what happens in nature, but rather produce expressions that work. i think asce 7 has lost site of this.
bjb is exactly right. in fact, i will start using ubc 97 and forget about the white coated lab rats and their holier than thou over complicated wind analysis.
ghosh's articles, (2 articles) written in the structual engineer magazines are well written and it is the first grenade launched during this war to simplify the wind provisions.
excuse my rant, but as structural engineers, who have to deal with this everyday, should scream from the highest mountain that these current provisions are b.s. and we should not have to rely on the computer just to get the forces. it is insane.

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