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Re: Plywood rigid diaphragms

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In a message dated 98-08-31 03:00:06 EDT, you write:

<< Subj:	 Re: Plywood rigid diaphragms
 Date:	98-08-31 03:00:06 EDT
 From:	jgkorff(--nospam--at)ix.netcom.com (james korff)
 Reply-to:	seaint(--nospam--at)seaint.org
 To:	seaint(--nospam--at)seaint.org
 
 Where does the .005H limitation come from ?
 
 jgkorff
  >>

The .005H is from the Los Angeles City Division 93 Ordinance.  This was the
maximum limit in the 1994 UBC for structures with a period less than 0.7
seconds, which could be even less if  0.04/Rw governed.

I am don't know how this now correlates to the 1997 UBC, so hopefully someone
can explain the comparison, if there is still one.  If you use the 1997 UBC
the maximum deflection limit would be based upon section 1630.9.2.  The
maximum inelastic drift is (delta m) = 0.7R(delta s).  Per section 1630.10.2
the (delta m) drift can not exceed 0.025H for structures with a period less
than 0.7 seconds which most bearing wall wood structures will be (R= 5.5). 

The (delta m) drift is then = (0.7)(5.5)(0.025)(H) = 0.0963H.  The questions I
have are do you somehow still account for the 1.4 conversion (97UBC Rw = 5.5
vs 94 UBC Rw = 8).  Is (delta m) suppose to be similar to the (94 UBC
deflection )(3Rw/8).   

Michael Cochran