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storage racks with partially restrained moment connections - wind frame analysis in high seismic zones

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With regard to the partially restrained moment connections, the basic
theory requires that:
1) The beam be able to support the load without any support from the end
connections (i.e. be designed as simply supported)
2) The connection have sufficient ductility to rotate more than the end
angle the beam will have if simply supported without loss of strength
3) The connector have sufficient strength to resist the lateral load.

If the above are satisfied, then the structure will simply distribute out
any fixed end moments under design lateral loads into the beams, leaving
the connections to resist lateral loads alone. While not convenient, you
can verify this in the computer by computing the end moment rotations in
the
beams and input them as initial displacements before running the lateral
loads analysis. You will see that the connections then resist lateral loads
alone.

This is a very neat analysis trick which greatly simplifies the design of a
partially restrained frame. It has been used for decades, and was
particularly
popular in the pre computer days. [The first time I saw such a building, I
panicked and ran to my chief engineer (an old salt if ever there was
one)who was
very understanding about it, gave me the theoretical references, and then
gently reminded me that the building I was so worried about had been there
over
30 years, was clad in "Barker Board" (a very brittle ceramic tile which
some of you may remember), and was showing no signs of displacement, let
alone
distress under some very harsh environmental conditions in northern
Alberta]

As for Home Depot racks, I am biased since I serve as engineer of record
for virtually all of them in the higher seismic zones. There was no
Northridge damage in the
properly loaded racks. One old store did have about 30% of its racks
damaged, sometimes severely, but it had been overloaded due to an oversight
(the merchandising
scheme changed, but they forgot to retrofit the racks). For an unbiased
view, you might contact Andre Filiatrault of the UCSD Powell Laboratories.
He has shaken fully
loaded Home Depot racks on his table. At first he was extremely skeptical,
but has since changed his mind I believe (last statement to me was that in
an earthquake he's
getting under the racks). However, he should speak for himself, and you
might give him a call.

In Seattle, there was essentially no damage, even in Olympia where the
ground did shake very hard (probably exceeding 0.4g PGA). We inspected all
of the stores within 30 hours
of the event. Same was true for Costco, Sam's Clubs, and Office Depots
(which I also design). I'd like to think we're doing at least some things
right.

Regards,

Peter Higgins