
Are we underestimating the vulnerability of bridges? - smb06
https://engineering.stanford.edu/news/when-bridges-collapse-are-we-underestimating-risk
======
Spooky23
That's the beauty of facts and engineering.

We may overestimate or underestimate. Nobody has built the vast network of
bridges that we have before to the same standards, so operating experience
should result in changes in our understanding of what and how we assess them!

If we look at the bridges that have survived 100, 150 or more years, they are
mostly massively overbuilt due to limitations of the era they were built in.
Perhaps some of the more modern spans are less overbuilt and are thus more
vulnerable to environmental or other changes?

~~~
knz
The biggest threat is politicians (and voters) who don't understand that
"structurally deficient" means we need to invest in inspections, repairs, and
replacement.

The I-35W collapse was near my house at the time and the fact that Governor
Pawlenty had long pushed for reduced government spending (inspections in
particular) was not lost on many people. His replacement, Governor Dayton, was
partly elected due to promises to rebuild/repair even if taxes had to be
raised to fund it (what a radical theory!).

~~~
afpx
If I build a big tower, and it falls down and injures or damages, I'm liable,
right?

If government-owned infrastructure falls down (because of lack of funding) and
injures or damages, is anyone liable?

Not a rhetorical question

~~~
jdavis703
The government can be sued. If they loose the suit they (or rather) taxpayers
have to pay. So in theory if you vote for politicians and policies that cause
these kinds of failures you the voter are held liable.

~~~
Arizhel
Maybe we should have a system where we no longer have secret ballots, and
instead your votes are recorded, but in an encrypted way so that only a proper
impartial investigation board (perhaps at the federal level) can have access
to it, in cases where it's decided that the voters for bad politicians need to
be punished personally for their contribution to the problem. So when the
government is sued, everyone who voted for those politicians gets to pay. I
really don't see why those who voted against the negligent or criminal
politician should be on the hook for it.

------
niftich
As of writing, this links to university news release.

The actual paper is doi:10.1061/(ASCE)IS.1943-555X.0000354 [1].

 _Abstract_

 _Predictions of the risk to built infrastructure posed by climate and land-
use change have suggested that bridge collapses may increase due to more
frequent or intense flooding. Assessments of the United States often assume
that bridges may collapse when the 100-year flood (i.e., a flood with 1%
annual frequency of exceedance) occurs, but this assumption has not been fully
tested because of a lack of comprehensive collapse records. Thirty-five
bridges for which a stream gauge on or near the bridge recorded the flow
during total or partial collapse were identified and used to test this
assumption. Flood frequency analyses, other statistical analyses, and
structural reliability methods were used to quantify the return periods of
collapse-inducing flows, identify trends linked to event and site
characteristics, and evaluate the potential importance of collapse return
period variability in assessing the impact of climate and land-use change on
hydraulic collapse risk. The results indicate that the collapse-inducing flow
return periods varied considerably (range: 1 to >1,000 years) and were
frequently lower than values considered in many climate impact assessments: 23
of the 35 bridges were estimated to have collapsed during flows with return
periods of lower than 100 years. Annual failure probabilities computed using
the full distribution of return periods of the collapse-inducing flows, as
opposed to central values (e.g., means), were more sensitive to an assumed
increase or decrease in the underlying frequency of flooding. These results
suggest that linking bridge collapse to only the 100-year flow does not
capture significant variability associated with collapse return periods,
potentially reducing sensitivity to flood frequency changes and reducing the
robustness of assessments of the impact of climate, land-use, and streamflow-
regulation change on hydraulic bridge collapse risk._

[1]
[http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IS.1943-555...](http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IS.1943-555X.0000354)

------
dockd
What exactly are "modern design standards" required by bridges? When did the
modern era start? Is there really a major moment in bridge design where the
standards changed? Is there even broad agreement on what these standards are?

(Side note: the bridge pictured in the article is the Bridge of the Gods, just
upstream of Bonneville Dam on the Columbia River. There's going to be more
than bridge problems if the flow of the river takes out that bridge.)

~~~
WatchDog
As a layman, the difference I notice between "modern" and older bridges is,
less exposed steel and more concrete.

~~~
kevin_thibedeau
> more concrete

That will be heavily spalled 50 years from now. Almost as dumb as building
thin flexible skyscrapers with reinforced concrete.

~~~
ggcdn
I fail to see what's dumb about using concrete for skyscrapers. Tall buildings
have been built this way for over 50 years without issue.

~~~
kevin_thibedeau
It's fine for skyscrapers. The Empire State Bldg isn't going anywhere. It's
dumb for thin flexible skyscrapers that will accumulate microfractures in a
relatively short time span and whose steel structure is insufficient to
support the building in the face of significant concrete degradation.

~~~
ggcdn
Microfractures =/= global strength loss. Additionally, the concrete itself
tends to strengthen over time. I guess I just don't understand what failure
mode you are worried about.

There are thousands of slender concrete structures that have been in service
(thus far) without issue.

------
VLM
Lured in for a spanning tree protocol CVE, left with an equally important
civil engineering discussion.

It would be interesting to see an evolution of the concept of 100-year event
over the few decades that its existed. Given the crazy rate of change compared
to more stable engineering challenges like the national bureau of standards
definition of the second or length standard, the endlessly changing definition
of 100 year events look barely more scientific than rolling DnD dice.

------
dpeck
Atlanta checking in
([https://en.wikipedia.org/wiki/Interstate_85_bridge_collapse](https://en.wikipedia.org/wiki/Interstate_85_bridge_collapse)),
yes.

~~~
Shivetya
Most Georgia bridges have fifty years before rebuild or replacement. We had
our 1000 year flood not to long ago and some were replaced quicker. It is not
uncommon to be traveling country roads and come across a recently rebuilt or
new bridge.

Now this I85 debacle is purely in the camp of mismanagement and vandalism. The
vandalism of course being that a person set a fire sufficient to ignite
supposed non flammable building materials that should never have been stored
under a bridge. Doubtful anyone in the State will suffer consequences due to
sovereign immunity.

What many of us who watched all this unfold is to find out exactly what was
stored there and in what quantity. While not flammable doesn't mean it won't
burn it should not have been this simple to ignite.

Credit the contractors rebuilding the bridges, damn they are fast when they
need to be. Of course another contractor managed to buckle the I20 interstate
by filling pipes improperly

~~~
BatFastard
As some one who lives very close to the bridge in Atlanta, it is hard to
believe how disruptive it has been.

While I thought traffic in the past was bad, it recently took me an hour to go
1.5 miles. A trip that usually takes 10 minutes at most. People don't go to
restaurants or out at all, anytime close to rush hour. I use to pop up to
corner to grab a pizza, now it takes me 20 minutes just to get to the end of
my street! Glad I can bike places.

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elihu
How many bridge collapses are caused by floods versus other kinds of failure?

In the Northwest, we're pretty worried about the next big earthquake, whenever
it happens. I also assume that bridges sometimes just fall down on their own
due to corrosion, metal fatigue, low quality materials, improper construction,
or uneven thermal expansion of various materials.

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peterwwillis
The thing is, we've been underestimating bridge failure potential for decades.
At least with reinforced concrete bridges, corrosion is deadly and silent, and
some substances took decades to slowly corrode the steel. It took unexpected
catastrophic failure for us to understand how to build them better.

~~~
jacquesm
The real killer here is salt on the concrete in winter. It slowly leaches
through the top level of the concrete and starts eating away at the steel.
Very effective, totally invisible. Also lots of balconies at risk because of
this.

~~~
ggcdn
Do people salt their balconies? I've never seen nor heard of this.

~~~
jacquesm
Balconies and galleries in apartment buildings to avoid falls in winter.

There's a huge flap around that theme here in NL right now with 1000's of
apartment buildings having to be inspected before mid-june because a building
shed it's balconies.

[https://www.nrc.nl/nieuws/2015/12/22/ministerie-laat-
vloeren...](https://www.nrc.nl/nieuws/2015/12/22/ministerie-laat-vloeren-van-
alle-flats-van-voor-1975-onderzoeken-a1410616) (Dutch, sorry, no English
source)

