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Re: Hyatt Regency

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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 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.


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 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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