
The Design Flaw That Almost Wiped Out an NYC Skyscraper - x43b
http://www.slate.com/blogs/the_eye/2014/04/17/the_citicorp_tower_design_flaw_that_could_have_wiped_out_the_skyscraper.html
======
wallflower
What this story leaves out is that the EVP of Citicorp at the time was a MIT-
trained scientist (physical metallurgy). So when this crisis bubbled up -
there was no hesitation in action since there was a scientist/engineer in top
leadership who was able to communicate to the board the severity of the
situation.

"Together they flew to New York City to confront the executive officers of
Citicorp with the dilemma. "I have a real problem for you, sir," LeMessurier
said to Citicorp's executive vice-president, John S. Reed. The two men
outlined the design flaw and described their proposed solution: to
systematically reinforce all 200+ bolted joints by welding two-inch-thick
steel plates over them."

[http://www.damninteresting.com/a-potentially-disastrous-
desi...](http://www.damninteresting.com/a-potentially-disastrous-design-
error/)

[http://en.wikipedia.org/wiki/John_S._Reed](http://en.wikipedia.org/wiki/John_S._Reed)

~~~
matt_trentini
So I presume the bolts and added welded plates were actually stronger than the
originally specified welded joins?

In the interview with Bill LeMessurier it seemed the problem existed even with
the original joins - the bolted joins just made the issue significantly
worse...

~~~
wallflower
Yes, it is more akin to bridge construction.

[http://en.wikipedia.org/wiki/Gusset_plate](http://en.wikipedia.org/wiki/Gusset_plate)

"The building now stands as one of the safest skyscrapers in New York City,
able to withstand a 700-year[1] storm without the aid of the tuned mass
damper."

[http://www.theaiatrust.com/whitepapers/ethics/study.php](http://www.theaiatrust.com/whitepapers/ethics/study.php)

[1] Approximately 140mph gusts.
[http://civil.unm.edu/classes/content//CE%20491-002/ASCE%207-...](http://civil.unm.edu/classes/content//CE%20491-002/ASCE%207-10.pdf#page=294)

------
Timothee
One point that this article doesn't mention but the video does (starting about
here:
[http://www.youtube.com/watch?v=TZhgTewKhTQ#t=350](http://www.youtube.com/watch?v=TZhgTewKhTQ#t=350))
is that the building wasn't built exactly as designed.

In particular, the 8-story-high diagonal parts were done in multiple splices
that were supposed to be welded together but ended up being bolted together.
It sounds like it made things much worse.

~~~
jzwinck
This reminds me of the 1981 Hyatt Regency walkway collapse [1]. The blueprints
called for continuous suspension rods with walkways attached along their
length. This would mean that the load on any single joint between rod and
walkway would be limited to the load on one walkway. But as built, the rods
were not continuous, rather they connected each walkway to the one below. This
meant the load on the topmost rod-walkway joint was the aggregate of the load
of all walkways hanging below it.

The builders did not notify the designers of the change, and 114 people were
killed as a result.

[1]
[http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse](http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse)

~~~
wiredfool
And not only that, instead of using a box section for the steel piece, they
used two c sections welded together like this: []. A box section is strong,
that built up section, not so much.

The thing is, that design would have been a horrible pain to build as
designed. It's a design failure. To build it, you'd need to slide a large
steel section up two screws, following it by a nut up 30 feet. It needed to be
redesigned by someone who knew more about fabrication and erection, and then
checked closely to make sure that there weren't material changes in the
performance.

~~~
Stratoscope
> To build it, you'd need to slide a large steel section up two screws,
> following it by a nut up 30 feet.

This is fascinating, but I feel that I'm missing some terminology and
concepts. I wonder if you could explain in more detail and clarify the terms?

From the part I do understand, it reminds me a lot of what I've encountered in
a recent software project or two.

A company hires a visual design consulting firm for hundreds of thousands of
dollars, and boy do they get their money's worth. Beautiful images and
designs, complete with high quality videos with things moving all over the
place in the smoothest and most seamless way.

And not a thought toward how this fantastic beautiful design would actually be
_implemented_. No consultation with the programmers to see what could actually
work given the required technology.

Agile? That's for programmers. When it comes to the product design, the visual
designers have spoke, and that is that. It's waterfall time, baby!

On one project the designers decided it would be beautiful to have menus and
controls that would slide out and overlap a Google Earth plugin. Great idea!
Until you realize that it would take three solid months to work out all the
cross-platform bugs in that approach. Three months that could have gone into
building something useful, something that customers actually cared about.

~~~
chiph
_This is fascinating, but I feel that I 'm missing some terminology and
concepts. I wonder if you could explain in more detail and clarify the terms?_

So, the atrium was (say) 80 feet tall, with the sky bridges every 20 feet. So
one at 20, 40, and 60 feet. If the continuous rod that had been specified in
design was used, it'd be a little longer than 60 feet long (80 foot ceiling,
lowest bridge 60 feet below that, plus a another foot or so to make room for
fasteners).

That would mean that the middle bridge would have to have had the nuts spun
along 40 feet (either from the top or bottom) and the nuts for the topmost and
bottom-most bridge would have to be spun along 20 feet of thread. But before
you could put the topmost nut on, you'd have to support the rod as you placed
it through the box-section beams for the middle bridge. And then do the same
for the topmost beam. And then lift it all so that the top end of the rod
could be secured to the ceiling.

And this wouldn't have been one rod at a time -- you'd have to do the same for
all dozen or more rods _at the same time_. Nightmare from a construction
schedule standpoint.

~~~
vonmoltke
My understanding of the incident also is that 60+ foot rods didn't, and still
don't, exist as regular items. They would have needed to be custom-made,
further hitting cost and schedule.

~~~
joeframbach
Could something like this be used (at a large scale) to "extend" multiple
shorter segments of rod?
[http://www.pl-259.com/nuts%20adapt%203%208%20to%201%204%20x%...](http://www.pl-259.com/nuts%20adapt%203%208%20to%201%204%20x%2020.JPG)

~~~
wiredfool
Yes. Couplers would work(1). You'd probably want jam nuts as well, just so
things don't back out on you.

1\. There may be problems with that approach. IANAPE. They would be different
problems than actually caused the failure.

------
ot
Reminded me of the design flaw of the Millennium Bridge in London, where the
engineers accounted for all resonance modes but one, the one that can be
caused by pedestrians:

> Resonant vibrational modes due to vertical loads (such as trains, traffic,
> pedestrians) and wind loads are well understood in bridge design. In the
> case of the Millennium Bridge, because the lateral motion caused the
> pedestrians loading the bridge to directly participate with the bridge, the
> vibrational modes had not been anticipated by the designers. The crucial
> point is that when the bridge lurches to one side, the pedestrians must
> adjust to keep from falling over, and they all do this at exactly the same
> time.

[http://en.wikipedia.org/wiki/Millennium_Bridge_(London)](http://en.wikipedia.org/wiki/Millennium_Bridge_\(London\))

~~~
abduhl
Accounting for "all resonance modes" is physically impossible as there are an
infinitely many number of resonance modes.

It's more precise to say "accounted for most dominant resonance modes".

~~~
sp332
"Accounting for" means they made sure it was strong enough for the expected
loads.

------
sitkack
"But what I found out at that meeting were that all factors of safety were
gone."

Many catastrophic "accidents", and I use quotes because they could have been
averted had people not cut corners w/o knowing the full context.

    
    
      * Chernobyl (after hours test by an untrained crew with an inverted fail safe design)
      * http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse (design change in the field, very similar to the citicorp flaw)
      * 3 Mile Island (indicator that triggered on switch rather than valve)
      * Fukashima (cost cutting on seawall and generator snorkels)
      * Ariane-5 (code reuse, dead code)
    

If you want to look at good engineering, look at the Brooklyn Bridge[5] and
the DC-3[6].

Too many people don't design with proper safety factors. You build it, you
test it, you test it till it fails and you understand those failures. I would
trust another citicorp wouldn't happen because we can do realistic wind model,
we can do an earthquake model, an anything model. Maybe we can get to a safety
factor of 1 when everything is automated, when everyone has an off-site backup
of their own brain but until then. Safety factor 6.

[5] [http://www.asce.org/People-and-
Projects/Projects/Landmarks/B...](http://www.asce.org/People-and-
Projects/Projects/Landmarks/Brooklyn-Bridge/) [6]
[http://en.wikipedia.org/wiki/Douglas_DC-3](http://en.wikipedia.org/wiki/Douglas_DC-3)

~~~
Someone
The Brooklyn bridge is over-engineered. Proof of that is that it handle
today's loads.

Of course, the advantage of that is that it hasn't collapsed yet, like a few
under-engineered bridges built way later ([http://www.washingtonpost.com/wp-
dyn/content/article/2007/08...](http://www.washingtonpost.com/wp-
dyn/content/article/2007/08/04/AR2007080401439.html))

But I doubt the ones paying for the Brooklyn Bridge would have chosen this
design if they could have had something for half the price that would last for
75 years.

~~~
m_mueller
As a European this argument is a bit strange to me (since we have so many
structures that are hundreds of years old and are still in use today). Don't
people sometimes just want something that works and keeps on working? A
monument of engineering to be proud of? Something to show to visitors? And on
the economic side of things I'm not at all convinced that rebuilding every
century would be cheaper for something like a bridge, considering the cost of
closing it down.

~~~
Someone
Want? Yes, but want to pay for? I like it that I can see a 600+ year old
church from my living room, too, and that affected the price of my apartment,
but I don't think I would be willing to pay much to have a new building that
will be considered iconic in 500 years time in my view.

Most modern bridges (and buildings, for that matter) get designed for 75,
maybe 100 years of life. I don't think that is different in Europe. Older ones
that still stand typically are sturdier, partly due to the use of larger
safety margins by engineers who (according to today's knowledge) didn't know
much about materials science, partly due to natural selection (bad designs
collapsed or were taken down decades ago)

For every centuries old bridge, scores have been demolished because they
couldn't handle increased traffic or just became too expensive to operate. And
that happens in Europe, too, even in old-stuff loving Great Britain
([http://en.wikipedia.org/wiki/London_Bridge](http://en.wikipedia.org/wiki/London_Bridge))

Looking at bridges, I think the only ones that will stand for centuries are
stone and masonry ones, and those rarely are built anymore. It is way easier
to get large spans using reinforced concrete or steel. Both contain metal that
rusts. Preventing that is expensive; fully preventing it probably
prohibitively so. Even for landmarks bridges such as the Firth of Forth the
Brits do not aim for eternal life
([http://en.wikipedia.org/wiki/Forth_Bridge#Maintenance](http://en.wikipedia.org/wiki/Forth_Bridge#Maintenance):
_" Network Rail has estimated the life of the bridge to be in excess of 100
years. However, this is dependant [sic] upon NR’s inspection and refurbishment
works programme for the bridge being carried out year on year"_)

~~~
m_mueller
If masonry is able to withstand the weather an order of magnitude longer than
steel - wouldn't it make sense to reinvent masonry building techniques for
building stuff that's expensive to close down? I get that labor cost is
prohibitive for this kind of stuff - maybe we will see a renaissance of
masonry once we have flexible enough robots to handle it?

~~~
Someone
I'm not an expert on this, but I wouldn't know of _" stuff that is expensive
to close down"_ relative to the extra costs of a masonry bridge.

Let's consider the Golden Gate Bridge as an extreme example (extreme because
lots of traffic across it has no reasonable alternative routes). If we needed
to replace it, we could build a replacement bridge next to it, connect roads,
and then open them over a weekend with little disruption.

If we chose to shove the new bridge in place of the old one in a week or so,
that would have to disrupt traffic, but I doubt it would be more expensive
than building _and_paying_for_ 20+ piers instead of the two we have _now_
(looking at
[http://en.wikipedia.org/wiki/List_of_longest_masonry_arch_br...](http://en.wikipedia.org/wiki/List_of_longest_masonry_arch_bridge_spans),
we cannot build masonry spans over 100m. The arch bridge is the best we can
hope for when using stone because stone isn't strong in tension).

Also, such a disruption, announced years in advance, need not be that much of
a disruption. People will take a few days of, stay with friends or family,
maybe a temporary camp will be set up, etc)

On the other hand, that Wikipedia page mentions that many 50m+ stone arches
have been built in China since 1950.

~~~
duskwuff
The Golden Gate Bridge is actually a lot less critical than you might imagine.
For a really critical bridge, consider the neighbouring San Francisco/Oakland
Bay Bridge, which carries about twice the daily traffic. And in fact, the
eastern span of the Bay Bridge _was_ replaced last year.

------
gkop
The original source is at [http://99percentinvisible.org/episode/structural-
integrity/](http://99percentinvisible.org/episode/structural-integrity/)

~~~
matthewmcg
Joe Morgenstern's 1995 _New Yorker_ article "The Fifty-Nine Story Crisis" is
also an excellent telling of this story.

[http://people.duke.edu/~hpgavin/cee421/citicorp1.htm](http://people.duke.edu/~hpgavin/cee421/citicorp1.htm)

~~~
lexcorvus
Use asterisks for emphasis, like this: _New Yorker_

------
salem
This fantastic validation for a person's undergraduate thesis. It's a real
shame that she wasn't given proper credit at the time.

------
rajacombinator
That's really scummy that the student did not receive appropriate credit at
the time or after. That should have been a career maker story.

~~~
malcolmwhy
The 99% Invisible story covers that a bit if you're interested.
[http://99percentinvisible.org/episode/structural-
integrity/](http://99percentinvisible.org/episode/structural-integrity/)

------
dm2
Reminds me of:
[http://en.wikipedia.org/wiki/File:CCTV_Beijing_April_2008.jp...](http://en.wikipedia.org/wiki/File:CCTV_Beijing_April_2008.jpg)

I'm sure the CCTV building is safe, but I get a small panic attack just
thinking about walking or jumping up and down in that overhanging corner of
the building.

How did they fix it? The article says they "welded" but doesn't say what was
added to increase the strength of the building.

~~~
salem
The documentary is interesting. Some of the steel structure held together by
bolts were welded together with some extra steel braces.

------
bayouborne
This has always been a fascinating story - I can't believe Slate's just now
discovering it. There's a much longer, more detailed account somewhere.

~~~
marklabedz
There's a pretty good one in the New Yorker (paywall, though I've seen scans
of the article floating around):
[http://www.newyorker.com/archive/1995/05/29/1995_05_29_045_T...](http://www.newyorker.com/archive/1995/05/29/1995_05_29_045_TNY_CARDS_000370292)

~~~
mkarr
A full text of the article can be found here:

[http://people.duke.edu/~hpgavin/cee421/citicorp1.htm](http://people.duke.edu/~hpgavin/cee421/citicorp1.htm)

This is much more comprehensive and interesting than the source linked in OP
and elsewhere.

I discovered this a few years back while doing some reading for an ethics
class, and was fascinated by it.

------
smoorman1024
Yeah. I work in this building and it terrifies me everyday. It does sway in
the wind. You can hear the walls creek when the winds are high. Besides the
complete fear that is instilled in my heart because this building was built in
a flawed way it also has an absolute terrible elevator design.

The elevators are double-deckers. So the elevator actually has two rooms that
move together. In the morning if you want to go to an even floor you have to
enter from the basement level and if you want to go to an odd floor you have
to enter from the lobby level. This results in the weird sensation that if you
are going to a higher floor the elevators often stop but the doors do not
open. Probably related to the weird design the elevators break down often and
with or without an elevator set out of commission there are high queue times
during peak hours. This is a building that could REALLY benefit from an
elevator call system where you enter a floor and it assigns you which elevator
to get into to. Why they haven't installed a relatively simple fix like this
is beyond me.

My final gripe about this building is its sheer ugliness IMHO. The steel
facade pegs it as one of those buildings that was built in a particularly
time. It's not timeless like the Empire State Building or perpetually modern
like the Willis Tower or One World Trade center.

I guess its only redeeming factor is the very nice public plaza it has both
inside and outside, its direct access to the E and 6 trains (super convenient
for me), and the fact that it has not fallen down yet.

------
cratermoon
If only software flaws in large commercial proprietary/closed source systems
were subject this kind of discovery and mitigation _before_ things break.

~~~
CaveTech
The flaws in computer software cause damage because people are quick to
exploit them. Mother nature is not quite as driven by money and corruption.

~~~
rdl
A terrifying thing is that one could hack a building management system or the
controls for the tuned mass damper specifically and essentially "self
destruct" the building, or at least make it much more vulnerable to mother
nature.

------
stillsut
I'm curious: since this flaw was pointed out in 1977, has NYC had such winds?
How many times? Would Sandy have done it?

------
sea6ear
I think there was an episode of Numb3rs that was based on this. Maybe Season 1
episode 4 (Structural Corruption)?

It was fun to see the premise turn up in the show and go, oh, I think I know
where they got this idea from.

------
morley
Maybe this is covered in the New Yorker article marklabedz linked to, but I'm
curious what their solution to quartering winds was. (They mention welding as
a part of the solution but don't go into more detail.)

~~~
morley
I found the answer in the Wikipedia article[1]:

> For the next three months, a construction crew welded two-inch-thick steel
> plates over each of the skyscraper's 200 bolted joints during the night,
> after each work day, almost unknown to the general public.

[1]
[http://en.wikipedia.org/wiki/Citigroup_Center](http://en.wikipedia.org/wiki/Citigroup_Center)

------
drewsears
DRTA, but I listened to the podcast. In it, they say that if the Citicorp
tower fell, it would topple nearby skyscrapers like dominoes.

Out of morbid curiosity, what's the worst case scenario for something like
this? Let's assume terrorists could detonate a bomb large enough to knock over
any one skyscraper in the world. Where should they put it to maximize the
chain reaction of destruction?

~~~
billmalarky
I think most skyscrapers fall straight down under the load rather than topple.
Similar to what happened to the WTC towers. Not that I have any credibility in
this area, but according to that documentary people seemed especially
concerned that this particular building would topple instead of collapse
straight down.

------
n6mac41717
I wish the author had referenced "Why Buildings Fall Down," the book that
first made me aware of the Citicorp Building problem:
[http://www.amazon.com/Why-Buildings-Fall-Down-
Structures/dp/...](http://www.amazon.com/Why-Buildings-Fall-Down-
Structures/dp/039331152X)

------
paul_f
Maybe this is a dumb question, but why couldn't they have found another
location for the new church? Why did it have to be on the same plot as the
Citicorp building?

~~~
mimiflynn
It was an old church. The chuch allowed the Citicorp building to be built
around it, which ended up being above it.

EDIT: spelling

~~~
paul_f
They tore down the old church and built a new, modern one on the site. This is
what makes this whole story so absurd to me.

~~~
Jtsummers
Churches are parts of their community. Moving them isn't always an option. In
NYC the Catholic churches are particularly tied to their neighborhoods,
historically, so there really aren't many places to move to and still provide
a place for that same community.

~~~
mapt
The church could have been established as floors 2 through 10 (or indeed,
floors 70 through 80) of a conventional rectangular box skyscraper, instead of
building what is effectively a large shack at ground level, and designing a
risky skyscraper without corner supports because one of those corners would
pierce the shack.

[http://www.saintpeters.org/your-church/the-
building/](http://www.saintpeters.org/your-church/the-building/)

~~~
jeffdavis
That makes logical sense in the same way as turning central park into a "park
skyscraper" makes logical sense.

~~~
mapt
Why?

Where in the Bible do they demand masonry construction and a lack of
elevators?

------
stillsut
A bug that would make even Heartbleed blush.

------
nashashmi
This sort of story never gets old.

------
philgr
This podcast is fantastical.

------
sscalia
More interesting reading around "Tuned Mass Dampers"
[http://en.wikipedia.org/wiki/Tuned_mass_damper](http://en.wikipedia.org/wiki/Tuned_mass_damper)

~~~
jwise0
The first I had heard of a tuned mass damper was in the installation on Taipei
101. There's a good video of it moving that gives you an idea of just how
colossal these things are:
[https://www.youtube.com/watch?v=NYSgd1XSZXc](https://www.youtube.com/watch?v=NYSgd1XSZXc)

~~~
tapia
What I also find very interesting are the "tuned column liquid dampers", which
applies the same idea of "tuning" the period of the liquid system to one
period of the structure. They are found to be very effective in dissipating
energy after seismic events or constant wind. I'm a civil engineering student
(currently writing my thesis) and I just loved this systems when I learned
from them.

------
happyscrappy
The first Tuned Mass Damper was in the John Hancock Tower.

[http://en.wikipedia.org/wiki/John_Hancock_Tower](http://en.wikipedia.org/wiki/John_Hancock_Tower)

From an engineering standpoint that is a pretty depressing read.

------
cmapes
That was a great read, I usually HATE stories that come from Slate but this
partially redeemed them in my mind.

