huangyhg

wind sways/deflection critera, aisc dg#3 & 'pre-eng' metal b
aisc design guide #3 (dg#3) suggests a 10 year return period wind pressures (~75% less) for checking element
deflection and building sway/drift. this seems like a effective 鈥?/3 allowable deflection鈥?increase, contrary to overall structural engineering practice.
the 鈥楢isc code鈥?is not prescriptive, the 鈥楢ci code鈥?is a bit more but still lacks definition as far as drift is concerned. it seems like the 'pre-engineered' metal building industry (mbma) had a lot of input into dg#3.
it points outs that a lot of 鈥榮pecial detailing鈥?is required to accommodate deflections/sways, but does not address solutions to critical areas like corners. 鈥楽pecial detailing鈥?for large movements will not done by architects unless they are made aware that it is required. in addition, i do not think that they would like 1+鈥?masonry control joints at building corners to accommodate sway movements etc by flexible frames.
also most criteria are significantly less than sway / deflection values mandated by 'seismic' codes that accept
'damage鈥?to non-structural elements as a criteria vs. 'wind' codes that are based on a 'no damage' basis to elements. a lot of the listed values are also less than the few 鈥楥ode鈥?mandated requirements that do exist. 鈥楥odes鈥?apparently do not allow 鈥?0 year鈥?pressures to be used.
鈥楥odes鈥檃re mandated, while 鈥楥ommentaries鈥?鈥楻ecommendations鈥?and 鈥楧esign guides鈥?are not.
asce 7-98 'standard' also now clearly (rather than hinting as a in previous editions) says that allowable stresses should not be increased for 鈥榙ead + wind鈥?load conditions unless it is based on the materials characteristic (e.g. wood) for taking short term loads, since combinations are based on probabilistic theory of simultaneous loading. steel, masonry and concrete do not quailfy here.
why are 鈥楥odes鈥?not more prescriptive in wind deflection / sway?
building owners and the public need to be protected in what they 鈥榖uying鈥?when they get a building designed to dg#3 vs an 鈥楨ngineered鈥?building designed to 鈥楥ode鈥?
it also seems like people who use & reference dg#3 are not 'playing on a level field' with the rest of the structural engineering profession.
any feedback/thoughts?

seeing even a 15 m tall traffic light pole swinging under gusts is a sobering enough experience. much more if you see panels for ads doing the same, and then whole deck metal factory buildings shaking under wind.
it is my opinion that more than h/400 drift at probabilistic level 50 years windstorm should not be allowed, and that the need of special detailing and corners, ridges etc should be clearly detailed in codes.

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]