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RE: Required wall attachment to a flexible diaphragm.

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Note that the forces in wood members will need to be reduced by a factor of
1.4 for WSD and the 1/3 increase is allowed.  The idea was to keep the
overstrength factor equal to about 2.0 for all materials, i.e., steel,
wood, concrete and masonry etc.

Gerard Madden <GerardM(--nospam--at)> on 08/26/99 03:00:09 PM

Please respond to seaint(--nospam--at)

 To:      "'seaint(--nospam--at)'" <seaint(--nospam--at)>           
 cc:      (bcc: Niaz A. Nazir/EQE)                            
 Subject: RE: Required wall attachment to a flexible          

If you are talking about anchorage to a flexible diaphragm of tilt-up of
masonry wall, then ap = 1.5 otherwise 1.0.
Rp is 3.0 unless you do not meet the shallow anchorage requirement which
is the anchor in the wall must be embedded 8 times its diameter (i.e.
3/4" A.B. must have 6" embedment) otherwise your Rp equals 1.5 and your
force doubles.

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. Soil type D yields the worst

Yes . . . the forces get very high . . . don't use shallow anchors!!!

Confusing Ain't it. We'll get used to it. (hopefully)

Gerard Madden, P.E.
Civil Engineer, Associate
CRJ Associates, Inc.
email: gerardm(--nospam--at)
tel: 650.324.0691
fax: 650.324.0927

> -----Original Message-----
> From:   From the desk of Joe Otto [SMTP:jmo_engineering(--nospam--at)]
> Sent:   Thursday, August 26, 1999 2:36 PM
> To:     Seaint@Seaint. Org
> Subject:     Required wall attachment to a flexible diaphragm.
> The 1997 UBC Section 1633. indicates the values for Rp and Ap
> of 3.0
> and 1.5 respectively should be used for elements of the wall anchorage
> system.
> What are the components of the wall anchorage system that these values
> apply
> to?  Is it the attachment of the wall to the diaphragm.  Or does this
> also
> include the subdiaphragms and cross-ties?
> if hx = hr ==> Fp = ap*Ca*Ip/Rp*(4Wp)
>              = 1.5 * (.44*1.2) * 1.0 / 3 * 4 * Wp  = 1.06Wp
> This seems high to me.  If anyone could take the time to
> clarify/confirm
> this, it would be appreciated.
> Thanks in advance.
> Joseph M. Otto, PE
> Ireland Engineering
> Fremont, CA