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RE: Required wall attachment to a flexible diaphragm.

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The way I see it is since deflection criteria typically governs in
determining the published values of stout premanufactured hardware, like
Zone4 CTs or Simpson, and most of the deflection derives from the bolts in
the wood, the 1.4 factor for steel elements is not necessary, but rather the
0.85 factor for wood elements (bolts in wood) would actually be the more
correct factor.  As further evidence of this, look in the Simpson catalog
and compare the HD6A, HD8A and HD10A.  They all have the same body and base
material, all have the same anchor bolts and all have the same stud bolts.
The only thing that varies is the number of stud bolts.  Intuitively, this
shows that the bolts in wood govern, and therefore, the 0.85 factor could be

The other option is to remain a little on the conservative side and not
apply the 0.85 factor, but rather use 1.0 when selecting this hardware.

Mike O'Brien, PE

> The force (Fp) applies to Anchor bolts, prefabricated HD's &
> CT's etc..,
> and all elements of the wall anchorage system (Struts, cross-ties,
> chords, and subdiaphragms.) Note that Steel elements must be
> designed to
> resist 1.4 times the force generated by the Fp equation (In ASD & LRFD
> steel design). That means anchor bolts, metal straps (steel only, not
> nails in wood- [that's the way I read it]), and simpson/kc
> metals/zone 4
> hardware must be selected to meet this increased force. But the wood
> elements, i.e. struts, bolted and nailed connections, and
> subdiaphragms
> need only be designed to resist 0.85Fp.
> Gerard Madden, P.E.
> Civil Engineer, Associate
> CRJ Associates, Inc.
> email: gerardm(--nospam--at)
> tel: 650.324.0691
> fax: 650.324.0927
> web: