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Re: collectors & omega

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Jeff Smith wrote:
> I have a 112'x60' two story wood framed building with partially grouted cmu
> exterior walls. (roof, second floor over slab on grade). In the short
> direction I have two 10' sections on each side of the building, of stacked
> double sided plywood shearwalls spaced every 20'. (Evenly spaced, very
> redundant.)
> Can I use the collector element exceptions of section 1633.2.6 or do I need
> the omega 2.8x increase/1.4ASD. The exception is for "structures or portions
> thereof braced *entirely* by light framed wood shear walls...". However, I
> have six lines of equally spaced plywood shear wall resistance between the
> exterior cmu walls. The omega seems a bit severe for this application, I
> already have a near fault increase, my collectors are almost as big as my
> holdowns.
> Now for some complaining....Who's Idea was section 1633.2.9 item 3? We use R
> of 4.5, then this paragraph states that flexible diaphragms with
> concrete/cmu walls must use design forces from section 1630.2 using R of
> less than or equal to 4? Why not make it 3.1415927....
> Regards,
> Jeff Smith

I was told at an ICBO seminar that the reason for the exception is
twofold.  First: the additional number of fasteners due to Omega would
more than likely split the wood, therefor the member would actually be
weaker.  Second: there in natural redundancy in "light frame"
construction.  Typically this means residential.  If I were you, I would
first ask the reviewing agency (or municipality) that will approve the
plans.  If you can't get a straight answer from them, use the exception
if you feel you have a redundant enough structure.

Just my two cents....	Jake Watson, E.I.T.
			Salt Lake City, UT