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Re: Hyatt Regency

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Of the specimens we tested, failure occurred with a load of 20.5 kips on the rod. (The NBS estimated the failure load to be 20.2 kips.) Plastic deformations were observed in our specimens at 13.5 kips. By comparison, the factored ultimate load should have been about 64 kips for the as built 2 rod configuration.

There was a noticeable buckle in the web when the rods were just snug tight (no measurable load) .

Our estimates of dead load were 8.768 kips for each of the 2 walkways (slightly higher than the NBS study). Assuming the rupture load at 20.5 kips, DL of 2 x 8.768 kips, and 2 walkways of 120 sf trib area each results in a failure live load of about 12.4 psf on each walkway. That is about 19 people averaging 160 pounds occupying 240 square feet.

When weighing various proposed strengthening scenarios Dr. George Hauck observed in his 1983 ASCE paper. "... It is ironic, and indeed frightening, to conjecture what the possible result of such modifications might have been: The walkways could have collapsed under a much greater but still reasonably probable live load, with a yet more devastating effect."

Regards,
Harold Sprague





From: "Robert Kazanjy" <rkazanjy(--nospam--at)gmail.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Re: Hyatt Regency
Date: Sun, 9 Apr 2006 18:41:09 -0700

Harold-

Thanks (as usual)  :)

for the expanded insight.

Do you have any idea of the actual live load on the structure?

cheers
Bob

On 4/9/06, Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote:
>
> I participated in one of the many studies following the collapse.  It is
> true that the capacity of the connection was cut in half by the change of > the original one rod vs. the 2 rod configuration. But the connection was
> grosely inadequate for even the original single rod connection.  I would
> have to dig out my research, but the FAILURE load was somewhere about a 30
> psf load for the design as originally configured.  Note that is the
> FAILURE
> load not a service load. The FAILURE live load on the configuration that
> was constructed was about 12 psf.  The design service live load was
> supposed
> to be 100 psf.  As you can tell even the original configuration was well
> in
> excess of normal margins.
>
> The constructability change was noted on the shop drawings and approved by
> the structural engineer.
>
> The weld failure due to combined bending and tension was the initiation of
> the collapse but the connection was doomed for a lot of reasons.
>
> Regards,
> Harold Sprague
>
>
>
>
>
> >From: "Robert Kazanjy" <rkazanjy(--nospam--at)gmail.com>
> >Reply-To: <seaint(--nospam--at)seaint.org>
> >To: seaint(--nospam--at)seaint.org
> >Subject: Re: Hyatt Regency
> >Date: Sun, 9 Apr 2006 11:02:56 -0700
> >
> >Adrew-
> >
> >My understanding of the KC failure is the same; in the original design
> the
> >hanger rods were supposed to take the entire load with each floor level
> >system only taking that floor level load.
> >
> >For constructablility, separate hanger rod sections were substituted such
> >that the top floor level system took it's own load AND the load from
> below.
> >
> >The welded channel sections that made up the floor level details were not
> >originally meant to be part of the series load path.
> >
> >When the overall design concept change was made, the channel detail was
> >not
> >a strengthened to take increased localized load.
> >
> >A detail that was adequate for it's own load failed under the increased
> >series load
> >
> >at least that's what I recall of the info I've read about the failure.
> >
> >cheers
> >Bob
> >
> >
> >
> >On 4/9/06, Andrew Kester, PE <akester(--nospam--at)cfl.rr.com> wrote:
> > >
> > > Harold,
> > >
> > > I have never heard of that explanation as a contribution to the
> failure
> >of
> > > that walkway... Is that something recent that has come out? It made me
> > > curious, because until 9-11 it was considered the most deadly
> structural
> > > disaster in US, and probably still is in the category "due to engineer
> > > error". So I pulled out Salvadori's book "Why Buildings Fall Down"
> (yes,
> >it
> > > is written for the layperson but still a good historical ref), and the
> > > diagram showing the failure does show the hanger rod nut pulling
> through
> >the
> > > joint where the two channels were welded together.
> > >
> > > But Salvadori explains the main reason for failure was the original
> >design
> > > called for a single long rod to support two walkways, which was more
> > > difficult to construct then if you use two shorter rods. The shop dwgs
> > > showed two rods connecting to the 4th floor box beam instead of one,
> >which
> > > the engineers mistakingly approved (or in my shop dwg stamp,
> "REVIEWED"
> >and
> > > took no acceptions....) The result was the fourth floor walkway box
> beam
> >now
> > > supported the second-floor walkway hanger rather then the load going
> > > directly into the hanger rod. Now it was supporting its own walkway
> >weight
> > > and live load, so the load could have been 2x the design load in
> theory,
> > > causing the fourth floor box beam to fail by allowing the nut to pull
> > > through the joint between the channels.
> > >
> > > Hard to explain without a dwg, but imagine a two story bldg where you
> > > take a second story column, instead of being continuous to the first
> >story
> > > column, you move it 2 feet over onto a beam. Now that column load is
> >going
> > > into the beam and the connection between the beam and column, and the > > > connection was not designed for that, so it fails. (Not explaining for
> >you
> > > Harold, for someone not familiar with the incident.)
> > >
> > > I can certainly see how a poor or incorrect weld in this instance
> would
> >be
> > > a huge contributing factor to the failure.
> > >
> > > Sounds like Salvadori may have glazed over the weld issue for
> > > simplification purposes. Either way there were shop dwg coodination
> > > mistakes. I also wonder why they did not just use a HSS section rather
> >then
> > > build their own? Were HSS just not that popular in the late 70s? Or
> >throw a
> > > PL 1/4 on the bottom of the channels to reinforce that area...
> > >
> > >
> > > Andrew Kester, PE
> > > Structural Engineering Consultant
> > > Lake Mary, FL
> > >
>
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