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Re: Hyatt Regency

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Thanks (as usual)  :)

for the expanded insight.

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


On 4/9/06, Harold Sprague <spraguehope(--nospam--at)> 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.

Harold Sprague

>From: "Robert Kazanjy" <rkazanjy(--nospam--at) >
>Reply-To: <seaint(--nospam--at)>
>To: seaint(--nospam--at)
>Subject: Re: Hyatt Regency
>Date: Sun, 9 Apr 2006 11:02:56 -0700
>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
>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.
>On 4/9/06, Andrew Kester, PE <akester(--nospam--at)> wrote:
> >
> > Harold,
> >
> > I have never heard of that explanation as a contribution to the failure
> > 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,
> > 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
> > joint where the two channels were welded together.
> >
> > But Salvadori explains the main reason for failure was the original
> > 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,
> > the engineers mistakingly approved (or in my shop dwg stamp, "REVIEWED"
> > took no acceptions....) The result was the fourth floor walkway box beam
> > supported the second-floor walkway hanger rather then the load going
> > directly into the hanger rod. Now it was supporting its own walkway
> > 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
> > column, you move it 2 feet over onto a beam. Now that column load is
> > 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
> > Harold, for someone not familiar with the incident.)
> >
> > I can certainly see how a poor or incorrect weld in this instance would
> > 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
> > 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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