4 replies to this topic

[hank89]

SERM 6 page 7-27 indicates the Cs value for T<TL be determined by ASCE eq 12.8-3 and the maximum value be determined by ASCE 12.8-2.

I have always used equation 12.8-2 to determine Cs and equation 12.8-3 for the maximum (provided T<TL; which it is for most low rise buildings.

Thoughts?

In addition, Cs min in not 0.01 per 12.8-5, this was changed to 0.044Sds I >=0.01 per asce7-05 supp#2

[McEngr]

Page 7-27 states it correctly. The best thing to do is reference the Sa chart and take out the I/R to determine where you are along the curve based on your period, T or Ta.

[hank89]

Page 7-27 states it correctly. The best thing to do is reference the Sa chart and take out the I/R to determine where you are along the curve based on your period, T or Ta.

Thanks McEngr... following the Sa chart is the way to go, I was just following the text of ASCE7 on page 129. I've learned a bunch while studying for this exam!

BTW the SERMS definition of "wind borne debris region" on 7-42 states "region in Hawaii that is within 1 mi of the coastal high water line and where the basic wind speed is at least 110mph."...
this is not correct.

IBC 2009 states "hurricane prone regions that are within 1 mile of the coastal mean high water line where the basic wind speed is 110mph or greater; or portions....120mph; OR hawaii"

[McEngr]

I've designed buildings in Hawaii and they follow their own rules... they use a Kzt factor, exposure factor, and wind speed on maps produced by the building department locally for the big island. Ultimately the locals overrule whatever the code says, of course. Thanks for the further "errata" updates.

[dakota_79]

Thanks for the catch on the erata, Hank.

Yeah, with that graph McEngr noted in mind, my procedure is usually to calc Ts=Sd1/Sds. If T<Ts, then 12.8-2 controls by inspection. If Ts<T<Tl, then 12.8-3 controls by inspection. Just a minor shortcut / timesaver (on the order of a few seconds, but every little bit counts!).