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Fwd: Re: plywood shear transfer detail

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In a message dated 97-04-08 02:52:17 EDT, AnandNene(--nospam--at) wrote:

<< I have told my clients many times that old conventional framing will not
"calc out to code" but performs.>>

One reason this is often the case is that most structural members and
connections do not experience the maximum loads and stresses during their
service life that the code requires they be designed for.  In fact, the
maximum conditions often occur during construction.  We've all seen roofers
stacking bundles of roof tiles and plywood on a few roof rafters.  That
practice will stress the rafters and connections more than any subsequent
loads (other than during a reroof), and surely overstresses further the
nailed connections between rafters and ceiling joists tha Bill Allen
expressed concerns over.

A second reason why buildings perform even though they don't calc out is that
our analyses are fairly simplistic (for wood frame residential buildings).
 In using the ELF analysis for seismic, or simple span assumptions for a hip
roof framing, we make it easier for ourselves, and are comfortable in our
knowledge that these are conservative approximations.  But in reality, a hip
roof needs to be analyzed as a three dimensional, indeterminate system.
 Those strongbacks and kickers perform load redistribution that we ignore in
our simplistic analyses.  The connection calcs ignore the effect of gravity
in providing friction resistence.

<<We need to find a good compromise and a balance between reality and
rejecting what can not be "calced out". >>

This is a good subject for a thread in its own right.  Perhaps other readers
will share their experiences and approaches in dealing with clients on such

Franklin Lew, SE

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Subject: Re: plywood shear transfer detail
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Richard Lewis, P.E.
Missionary TECH Team

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.