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Re: "Apparent Rigidity"

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Apparent Rigidity is the EI value required for a simple span live load
deflection meeting the criteria specified in the table. In other words the
rigidity (EI) required to limit the deflection to say l/240.

HTH,

Rand

----- Original Message ----- 
From: "Bill Polhemus" <bill(--nospam--at)polhemus.cc>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, September 14, 2004 4:30 PM
Subject: WOOD: "Apparent Rigidity"


> I have come across this term in perusing the WFCM, and I cannot figure out
> exactly what it means.
>
>
>
> It occurs in particular in Tables 2.13A-B (CEILING FRAMING CAPACITY
> REQUIREMENTS). Footnote (1) to this table states:
>
>
>
> "Apparent rigidity capacities shall include the effects of both bending
and
> shear deflections. Apparent rigidity capacities have been adjusted for
> solid-sawn lumber to account for these effects. Contact the I-joist
> manufacturer for apparent rigidity capacities to be used for I-joists in
> this table."
>
>
>
> And Footnote (2) says:
>
>
>
> "Tabulated apparent rigidity requirements assume single span conditions.
For
> continuous span conditions, tabulated apparent rigidity requirements shall
> be permitted to be multiplied by 0.75."
>
>
>
> The units of "apparent rigidity" are in.^2/lb., and a typical value is
> between 5 and 30 MILLION.
>
>
>
> So not sure how to use this information.
>
>
>
> Interestingly, the rafter span tables give you selection values in f-sub-b
> for load and E for deflection. Don't know why the difference.
>
>



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