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RE: Plwd: Rigid Diaphragm Analysis - Opinions Wanted

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Yeah, that's what my seminar notes say too. The only problem I have is in
the Code definitions.

First of all, whether or not "redundancy factor" rarely becomes an issue,
you still have to calculate it. This is one of my anxieties over the so
called "Simplified" Static approach. If the Code authors really intended to
provide a "Simplified" alternative, albeit with higher design forces, the
method should have accounted for this redunancy factor so we would not have
to determine if it was an issue or not.

Secondly, the only point of being "well behaved" that I'm familiar with is
related to the cap of Na. Big deal. Based on 1629.4.2, we still have to
establish that rho is not greater than 1.0 (it doesn't say you don't have to
calculate it) and we also have to be satisfied that the soil is not type SE
or SF and that there are no vertical irregularities of type 1,4 or 5 (table
16-L) or plan irregularities of type 1 or 4 (table 16-M). I would be
surprised if there are any multiple story wood framed residential "real
world" structures that would qualify.

So far, the two wood framed structures I have prepared calculations for did
in fact have a calculated rho less than one, so maybe it will be a mute
point once we get more familiar with the methodology.


Bill Allen, S.E.
Laguna Niguel, CA


>It is also my interpretation from the ICBO notes (from the
>seminar listed
>above) that most residential structures are considered "short period"
>structures and the base shear will be controled by 0.24 Na. In
>this case the
>redundancy factor rarely becomes an issue as the structure is
>"well behaved".
>Dennis Wish PE