
Genoa Bridge Collapse: The Road to Tragedy - conroy
https://www.nytimes.com/interactive/2018/09/06/world/europe/genoa-italy-bridge.html
======
acomjean
Bridges have lifespans and need constant maintenance.

One of my first tasks as an intern at the Army Corp Of Engineers was to create
6 inspection packets (copies of every part) of the cape cod canal bridge,
which was being inspected.

I know the tappan-zee bridge was replaced because the old one was just too old
(designed to last 50 years, it was replaced at over 60 years).

[https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_(1955–2017)#...](https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_\(1955–2017\)#Replacement_bridge)

One of the reason I left the engineering profession is no one wants to pay for
it so it gets "deferred". The US's bridges get a c+ according to the American
Society Of Civil Engineers.

[https://www.infrastructurereportcard.org/cat-
item/bridges/](https://www.infrastructurereportcard.org/cat-item/bridges/)

I'm also a little curious why the cables were wrapped in concrete. Steel
cables are common on bridges. stability side to side? Concrete is not great in
tension (steel is very good in tension). As the article indicates, it was
potentially hiding some of the cable corrosion, making the situation worse.

~~~
GuB-42
Beside the (wrong) idea of protecting the cables from corrosion, the concrete,
as you said, was there to improve stability.

It is pre-stressed concrete, it is working in compression against the cable
tension. The idea is that as the load increases, instead of pulling directly
on the cables, it just decompresses the concrete.

You can think of the cable as a spring, with the bridge suspended it. As you
walk on the bridge, it bounces. To prevent the bouncing, you can put the
spring under high tension into a rigid pipe, with the ends of the spring
attached to the ends of the pipe. This way, as you walk on the bridge, the
spring tension will stay constant, only the compression on the pipe will vary.

~~~
jmts
_It is pre-stressed concrete, it is working in compression against the cable
tension._

This seems strange to me.

My understanding is that pre-stressed concrete is concrete with reinforcements
inside that apply a compressive force on the concrete. As mentioned by GP,
this is to mitigate the effect of tensile forces within the concrete since
concrete performs poorly in tension.

Are you suggesting that the cables within the concrete are not just stays, but
also the component of the pre-stressed concrete applying a compressive force?
Or is the reinforcement some other component?

I would assume that if the cables themselves were applying compressive force
to the concrete, then their use as stays releases some of this force since the
stays are in tension. Since concrete itself performs poorly in tension, it's
going to provide a negligible counter to reinforce the cables even if it is
still compressed, since the compression forces are provided by the cables. It
seems to me that putting pre-stressed concrete into tension via its
reinforcements is defeating the purpose of having pre-stressed concrete in the
first place.

Or is concrete in _some_ compression able to respond better in tension by
weight than say, a thicker cable at the same weight as the given cable and
concrete combined?

~~~
geezerjay
> I would assume that if the cables themselves were applying compressive force
> to the concrete, then their use as stays releases some of this force since
> the stays are in tension. Since concrete itself performs poorly in tension,
> it's going to provide a negligible counter to reinforce the cables even if
> it is still compressed, since the compression forces are provided by the
> cables. It seems to me that putting pre-stressed concrete into tension via
> its reinforcements is defeating the purpose of having pre-stressed concrete
> in the first place.

Not quite. High resistance steel is used in prestress applications, which
provides a considerable headroom to determine what cables are used (number of
strands per cable group and number of cable groups per cable) and how to
design a structure (target prestress values, dynamic/vibration properties,
load variation/fatigue design, etc). Therefore, just because a designer
selects a specific prestress cable that doesn't mean the cable will be
designed to be stressed closed o yield or even fatigue limits. The designer
can pretty much design a structure that uses prestress cables loaded at a
fraction of their design limits but subjected to higher loads at construction
to be able to unload the initial prestress load as compression. This strategy
is often used in bridges, as is designing a bridge to e intentionally heavier
so that variable loads are a fraction of the dead load to increase fatigue
life.

------
matant
It's incredible how well documented and rich of information is the article.
I'm Italian and I could not find in any Italian newspapers all the information
that I needed! It makes me aware of how poor is the information in my country!

~~~
jaclaz
JFYI (Italian) among many others, these are the more technical ones:

[https://www.ingenio-web.it/20966-il-crollo-del-ponte-
morandi...](https://www.ingenio-web.it/20966-il-crollo-del-ponte-morandi-a-
genova)

[https://www.ingenio-web.it/20925-il-viadotto-sul-
polcevera-e...](https://www.ingenio-web.it/20925-il-viadotto-sul-polcevera-
ecco-larticolo-di-riccardo-morandi-del-1967-con-tutti-i-dettagli-progettuali)

[https://www.ingenio-web.it/20939-ing-camomilla-come-e-
perche...](https://www.ingenio-web.it/20939-ing-camomilla-come-e-perche-
intervenimmo-sugli-stralli-della-pila-11-del-ponte-morandi-nel-1992)

~~~
pb060
True, but those are technical ones. I couldn't find any article explaining
what a "strallo" is, in fact "cos'è uno strallo" (what is a straw) seems to be
a common search based on Google's autocomplete.

~~~
jaclaz
>True, but those are technical ones. I couldn't find any article explaining
what a "strallo" is, in fact "cos'è uno strallo" (what is a straw) seems to be
a common search based on Google's autocomplete.

It's not a "straw", it is a "stay" in English.

Strallo is a term mutuated from boats, a sail boat has a mast (albero) that is
kept vertical and strong by one or more sets of "stays" (stralli):

[https://en.wikipedia.org/wiki/Stays_(nautical)](https://en.wikipedia.org/wiki/Stays_\(nautical\))

[https://it.wikipedia.org/wiki/Strallo_(vela)](https://it.wikipedia.org/wiki/Strallo_\(vela\))

On the sail boat the function of the stay is "opposite" to that of a bridge
stay, it is used to keep the mast pressed to the base and more rigid, on a
bridge they are simply "suspension supports" allowing to carry the weight of
the viaduct deck and transferring the vertical load to the tower or pylon
(torre o antenna).

[https://en.wikipedia.org/wiki/Cable-
stayed_bridge](https://en.wikipedia.org/wiki/Cable-stayed_bridge)

[https://it.wikipedia.org/wiki/Strallo_(ingegneria)](https://it.wikipedia.org/wiki/Strallo_\(ingegneria\))

------
dmurray
> a structural engineering professor at the Politecnico di Milano, Carmelo
> Gentile, found troubling signals of corrosion or other possible damage...he
> has performed his tests on some 300 bridges around the world

It would be very interesting to know what he had to say about the other 299
bridges. After all, you can find someone who will tell you you have a
structural problem with the safest bridge. It's hard to tell if they are a
crank, someone with a vested interest, someone seeking publicity for their new
diagnostic method, or genuinely an expert who is giving you good advice. But
if Professor Gentile mostly says the bridges are fine, but singled out this
one as a danger - then it's really worth listening to his other
recommendations.

~~~
shkkmo
Since he was contracted to do the inspection, I presume they found his
diagnostic method credible.

------
SamuelAdams
Slightly off topic, but they way they changed the info graphic as you scrolled
was _really_ cool! This is one of the rare cases where extra JavaScript makes
sense - it really improves the experience.

~~~
DonHopkins
NYT is famous for their beautiful yet informative scrolling infographics:

[https://www.nytimes.com/interactive/2018/01/27/technology/so...](https://www.nytimes.com/interactive/2018/01/27/technology/social-
media-bots.html)

------
dv_dt
How does this entire article get written without a single mention that much of
the road infrastructure here, bridge included, had been privatized and was
being managed by the Atlantia corporation. The article actually seems to put
the reader on the mistaken impression that Autostrade (former name of
Atlantia) is some sort of media management company.

"Autostrade, which handles media queries on behalf of the subcontractor, Spea
Engineering, declined to comment."

[https://www.cbsnews.com/news/italy-bridge-collapse-genoa-
atl...](https://www.cbsnews.com/news/italy-bridge-collapse-genoa-atlantia-
autostrade-concession-with-causes-unclear/)

[https://en.wikipedia.org/wiki/Atlantia_(company)](https://en.wikipedia.org/wiki/Atlantia_\(company\))

The technical specifics of the bridge collapse are interesting, but the
privatization of multiple road systems should have in theory let the company
be cognizant of the systemic issues of the design practices of various eras,
but how was this missed? The company was managing the bridge since 1999,
almost twenty years now. This is as much or more of an organizational question
as well as a private vs public ownership question as it is a technical one.

~~~
aboodman
You read a different article than me:

> He warned the company that manages the bridge, Autostrade per l’Italia, or
> Highways for Italy, but he said that it never followed up on his
> recommendation to perform a fuller computer study and to outfit the bridge
> with permanent sensors.

> For reasons it has not fully explained, Autostrade, which took over
> management of the bridge in 1999, did not carry out the same operation on
> the supports of the other two towers — including the tower that collapsed.

> Autostrade won the concession to run nearly half of Italy’s highways from a
> cash-strapped Italian government, starting in 1999. After that, there were
> no major renovations of the Morandi bridge.

... etc ...

~~~
dv_dt
Why are they using the wrong name of the company? I think I missed it because
I was looking for the Atlantia name. Looks like I did miss quite a few
references that way!

~~~
aboodman
Looks like Atlantia is a conglomerate that has a large controlling interest in
Autostrade per l'Italia and similar businesses. Autostrade per l'Italia is
still a business entity, so it seems appropriate to me for the article to
refer to it.

[http://www.atlantia.it/en/operations/italian-motorway-
operat...](http://www.atlantia.it/en/operations/italian-motorway-operations)

 _edit_ softened snarky language.

~~~
dv_dt
But why then treat Autostrade like a pr management entity?

"Autostrade, which handles media queries on behalf of the subcontractor, Spea
Engineering, declined to comment."

I guess that's what bothers me a bit - is that there is a somewhat in depth
investigation regarding the technical explanation, but a big shrug at hitting
the wall on explanation of management failures, which IMHO should go all the
way up thru the ownership conglomerate.

~~~
9935c101ab17a66
I feel like you formed a conclusion based on your incorrect knowledge of the
name of the company. Now that's been corrected, and your error highlighted,
you're doubling down rather than admitting you made a mistake.

------
dmix
> by using investigators’ descriptions of a central piece of evidence — video
> footage captured by a security camera.

Whenever I read about these incidents, with only one camera angle, I almost
want to buy a camera and point it outwards from my apartment just in case I
catch something like this happening in my city.

~~~
tlb
An artist in New York took a picture out his window almost every day for 11
years with a large-format film camera. He indeed caught something notable.
[https://www.amazon.com/Window-Septembers-1995-2005-Reiner-
Le...](https://www.amazon.com/Window-Septembers-1995-2005-Reiner-
Leist/dp/3791336797)

~~~
benchtobedside
For anyone wondering what he caught: "The resulting bulk of around 2,200
photographs documents both the every-day life and change of Manhattan,
including the historic event of the destruction of the World Trade Center on
September 11, 2001"

\--
[https://en.wikipedia.org/wiki/Reiner_Leist](https://en.wikipedia.org/wiki/Reiner_Leist)

------
mc32
Not a civ engineer... But the way things cascaded and experienced a domino
effect seems troubling. Contrast with the ‘89 SF quake caused one upper deck
section of the then cantilevered section of the SF-OAK bridge to collapse. It
fell into the lower deck, but did not cause the lower deck to give way. This
seems to indicate they had better tolerances (higher safery factor). But that
may be a very naive take.

~~~
Filligree
The article mentions this. Common engineering practice today is to avoid any
single points of failure, but back when this was built, the profession was
high on precision engineering based off modern finite element models and other
ways to more exactly determine the capacity of a bridge.

It was deliberately built without redundancy, because they thought they could
achieve perfection. In fact the models they used were correct -- it was the
underlying assumptions about the long-term behaviour of the materials used
that were wrong.

This isn't the first such collapse, and it likely won't be the last, but it's
safe to say that engineers have learned from their failures. Modern standards
generally maximize redundancy. Precision is used to reliably achieve a high
margin of error, rather than to get away with the minimum possible.

~~~
mc32
So in some respect older bridges were overengineered to compensate for the
lack of good modeling. Then good modelling came along and gave engineers
overconfidence, now this is being corrected with better understading of
materials science?

And thanks for pointing out that reliance on precision engineering might have
led to safety factor reduction due perhaps to overconfidence...

~~~
pfdzm
Modern calculations are usually multiplied with several 'security factors'[0],
anywhere between 1,1 and 1,5 as far as I can remember now (at least in Germany
through a DIN [norm], and now Europe-wide via EN). These design factors come
in at many different stages of the calculations, from materials to static load
distribution (not sure if these are the correct terms in English)

[0]
[https://en.wikipedia.org/wiki/Factor_of_safety](https://en.wikipedia.org/wiki/Factor_of_safety)

~~~
jaclaz
Well, it is not like "earlier calculations" didn't take into account such
safety factors, but the debate is not about existance of safety factors or
their amplitude (1.3 to 1.5 has been used as far as I can remember in concrete
constructions) but rather on redundancy.

To give a different example elevators/lift (those using rope cables) have
usually cables that have a factor of safety 5, but they have nonetherless
additionally at least one set of independent brakes.

Back to bridges and more generally reinforced/pre-stressed concrete
structures, in my experience modern methods of calculation are more precise
than old ones, and allow usually - given the same loads/hypothesis - to save
(i.e. there is less rebar steel and cable steel) between 5% and 10% steel
and/or concrete.

In practice with old methods of calculation there was a 1.05/1.10 "implied"
and "hidden" additional safety factor.

------
lqet
Given that the collapse happened during a thunder storm, and given that there
are reports of a lightning strike prior to the collapse [1]: how likely is it
that water accumulated inside the prestressed concrete hull was suddenly
evaporated by a lightning strike, effectively blowing the cable stay up? I
remember reading about this theory in some interview, but never heard anything
about it since.

[1] [https://www.dw.com/en/speculation-mounts-over-genoa-
bridge-c...](https://www.dw.com/en/speculation-mounts-over-genoa-bridge-
collapse/a-45084494)

~~~
jaclaz
IMHO not more or less unlikely, simply impossible.

~~~
heimdall
Lightning Strike Energy == 1,000,000,000 Joules

1 Joule heats 1g water 0.24 C

1 L water == 100g

1 cu.meter water = 1000L

Room Temp == 23 C

Thus:

(77/0.24) = 320.8 Joules raises 1g water from 23 C to 100 C (boiling).

(1E9 Joules / 320.8 Joules) lightning strike with no losses along the way
heats 3,116,883g of water.

3,116,883g of water == 31,168 L of water == 31 cu.meters of water. This is a
block of water 1m x 3m x 10m.

Steam volume is 1600x liquid water volume. So even if we say that 90% of the
energy is lost in the transfer, that's still 3 cubic meters of water that
flash-boils into steam, quite possibly causing damage to the bridge.

So: perhaps unlikely, but quite possible.

Edit: 3,116,883g of water == 3,117 L of water == 3 cu.meters of water. Damn
math errors, always creeping in. Still unlikely, still possible.

~~~
UnFleshedOne
1L of water is 1000g, then you need additional 2261 joules per gram to
evaporate. So 1E9j will evaporate 384 liters of water, so 0.384 cubic meters
(unless I lost a degree of magnitude here or there myself :)).

~~~
heimdall
[https://www.smbc-comics.com/comics/20130616.png](https://www.smbc-
comics.com/comics/20130616.png)

------
vlehto
This would have been perfect situation for some destructive testing.

During night time block all traffic. Then drive radio controlled, overloaded
trucks over the bridge every six months.

If the bridge fails, you just saved human lives. If it doesn't, the cost of
that project is relatively small compared to pre-emptive repairs. The
likelihood of regular load destroying the bridge in the meantime could be
managed to be negligible.

It's already used with pressure vessels, because hydraulic testing of them is
very safe. Now you would no longer need suicidal truck drivers to do it on
bridges.

~~~
Ndymium
You forget that there are houses below the bridge, that could have been
crushed. Not exactly a place for destructive testing.

~~~
vlehto
If the bridge is fine, there is no problem.

If the bridge is rotten, you have lot fewer victims.

You want to do pre-emptive repairs? OK, the bridge ought to be fine. We can
then proceed with the destructive testing.

You could do the testing with something like 110% of the typical max traffic
load. A rotten bridge would then collapse within 6 months of it's "natural
collapse". Only things you do is to make the collapse more predictable and you
save lives.

~~~
Ndymium
I don't think a testing method where there is a risk of a lot of innocent
people dying is going to be accepted anywhere. I guess that is the dilemma
with these situations.

~~~
vlehto
Would not be the first time saving lives ends up being less important than
avoiding responsibility. So I agree on your prediction.

------
PunchTornado
And the Interior Minister says that the EU is to blame because it doesn't
allow them to invest in infrastructure.

When the EU encourages investments in infrastructure.

Go figure.

~~~
Nasrudith
The EU is clearly valuable to many of its partners as a domestic scapegoat.
The problems come when people actually believe them and try to 'solve' the
problems 'caused' by them and find a stack of disasters that makes being the
prime minister a position competed /against/ becoming instead of /for/.

------
DonHopkins
In the last drone video at the end of the article, the sun is quite low in the
sky, making the shadows of people and tractors stretch out and play against
the shapes. A horrible scene, but the scale and depth and shadows are visually
stunning!

------
stcredzero
For the prudent, form follows function. Doing things because you can, because
it's "neat" is courting folly. There is an analogy here for coding.

------
lqet
Are there any experts here who can elaborate on whether Professor Gentile's
acoustic testing of the bridge's cable stays may have had any negative effect
on its stability?

I found this paper on the method:
[https://www.ndt.net/article/jae/papers/20-083.pdf](https://www.ndt.net/article/jae/papers/20-083.pdf)

E: as mentioned below, the method is completely passive.

~~~
throwaway5752
Be super careful with that line of thought: it is precisely what they will use
to deflect blame from the construction, engineering, and maintenance issues.
"The bridge wouldn't have failed if it weren't for that pesky diagnostic
procedure that also happened to raise all sorts of problems about corrosion
and structural integrity"

edit: also - not an expert but interested and somewhat informed - this is a
very common structural engineering technique and should under no
circumstances, ever, lead to this kind of outcome on a sound structure.

~~~
SolarNet
Also Italy has a (recent) history of prosecuting scientists who attempt to
give their opinion (even if it isn't listened to). If I was an Italian
scientist I would stay far away from predicting anything to or for the
government.

[http://www.sciencemag.org/news/2015/02/why-italian-
earthquak...](http://www.sciencemag.org/news/2015/02/why-italian-earthquake-
scientists-were-exonerated)

------
stillsut
What I find unusual is - according to the infographic - _both_ southern cables
broke in the initial stage. And then that was followed by the northern cables
breaking in response to the load shifting.

I presume the two southern cables are independent components and support
independent platforms. Why would they both break at the same time, if not for
some exogenous event?

------
sonar_un
It’s amazing to me in this day in age that there are no actual videos of the
collapse. Not even from a car camera. I’ve searched everywhere and it would
really be a very useful piece of information to have in order to diagnose what
really happened.

~~~
jpatokal
Per the article, the collapse was recorded by a security camera and the
footage is being analyzed by the investigators, but it has not been made
public yet.

------
gesman
Use stainless steel cable instead?

It cost ~4-5x times more than regular (today, not sure decades ago) but total
cost of bridge build for it's majority was probably (overpriced) labor
anyways.

~~~
AceyMan
In machinery stainless steels have universally poorer mechanical properties vs
non-stainless alloys - a reduced corrosion rate is about the only benefit, and
even so, it's still just "stain-less" — not "stain-free" — over the timescales
of civil infrastructure, it would likely suffer damaging corrosion at some
point.

