Subject: Re: Seismic Upgrade.... Blue Book Commentary on wood diaphragm
Date: Mon, 24 May 1999 18:45:02 EDT
In a message dated 5/24/99 12:46:38 PM Pacific Daylight Time,
<< Dennis, Yes a custom home with differing roof diaphragms at different
elevations may act as a simple span, hinged (almost) at the supporting
wall, but the shearwalls should be checked for drift for compatible
Williston "Bill" L. Warren, IV - S.E.
Newport Beach, California >>
No argument - I do as normal practice design my shearwalls for deflection. I
will go so far as to admit that any damage associated with wall stiffness in
the Northridge earthquake is, in my opinion, due to the acceptance of a
prescriptive aspect ratio (ie, 3.5:1). Engineers rarely designed wood
shearwalls to deflection standards and had they done so would have found that
highly loaded walls approaching 3.5 to 1 will generally deflect in excess of
the code allowable story drift.
Neglect to check the wall deflection was, in my opinion, the problem
associated with open front damage - not the action of the diaphram in itself.
Therefore, why complicate the design method when one possible answer is to
mandate deflection analysis to prove as close to reality that the expected
deflection does not exceed code allowable story drift.