Are we underestimating the vulnerability of bridges?
engineering.stanford.edu
engineering.stanford.edu
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?
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!).
If government-owned infrastructure falls down (because of lack of funding) and injures or damages, is anyone liable?
Not a rhetorical question
http://www.mprnews.org/story/2012/11/14/law/i35w-bridge-sett...
"After the structure fell into the Mississippi River during rush hour Aug. 1, 2007, killing 13 people and injuring 145 more, Minnesota lawmakers set up a compensation fund for victims. As part of that legislation, they nullified a statute of limitations that would have prevented the state from seeking damages. In May, the nation's highest court declined to hear Jacobs' challenge to that law, and the company had little recourse.
State Sen, Ron Latz sponsored the legislation that set up the compensation fund. While the state recovered from Jacobs and another firm less than half of the nearly $37 million paid out in compensation to victims, Latz said it was the right thing to do, not just for the victims and their families but also for Minnesota taxpayers."
From Wikipedia "URS Corporation [...] settled for $52.4M [...] URS had performed fatigue analysis consulting on the bridge for the Mn/DOT."
and "Jacobs Engineering Group, the successor of Sverdrup & Parcel, the firm that designed the bridge [...] paid $8.9 million in Nov. 2012 to settle the suit"
The real fault is with the government, and especially the elected politicians who don't run the government properly and get these things inspected and fixed (and worse, run on platforms of shrinking government). Why aren't they ever personally liable? They should be.
To me that feels lacking, unless the government bodies responsible for infrastructure maintenance get proper resources and time and expertise to do this on a large scale. Can people today really expect to understand how things were built a 100 years ago? (honest question, imagine the same for IT)
Yes. This can be done.
The same as today, 100 years ago designs were based in calculations of the bridge response to the expected loads. Today, we know better what are those loads and how to calculate the response of the structure, but it is the same process.
Construction itself has also changed with the years. We have ways to asset materials and machine them that are way ahead of what we had 100 years ago, we can assembly the bridge with much more precision, and the efficiency of our tools has vastly improved, but the principles are the same.
The issue seems to be that despite having extremely detailed blueprints a lot of the actual assembly was left to skilled welders and technicians on site, and they used techniques which were not documented. So You can look at the blueprint, you can look at the actual remaining Saturn-V rocket, and still have no idea how two elements were welded together to withstand launching into space, because it's just not documented anywhere. The person who did the weld is long dead, so in a way, an extremely important element of assembly is lost and has to be replicated by experimentation.
I'd imagine it's the same with bridges - blueprints might say that a column of specific durability was used, but it won't say how it was made, and therefore you won't know what can break inside it.
Edit: corrected Atlas to Saturn V
Modern engineers can understand them in theory, but they'd just use a micro-controller for anything that complicated, so they don't have the same fluency in those systems as the original engineers.
Also, the private engineering firm likely had nothing to do with the maintenance of the bridge after construction -- That's the job of the state DOT and whoever they contract out to.
There's a lot of knowledge and experience in State DOTs, they'll do some bridges in house, some they contract out for. (WA state, states may vary, depends on budgeting conditions and workload.) The older engineers there are generally really smart, and have been doing it for a long time. In stark contrast to the computer industry, experience really does mean something.
I don't think engineers are being prosecuted for criminal negligence in cases like this - rather, the firms have civil liability. As far as holding politicians personally liable, they can be prosecuted if they break the law. Other than that, I envision it would be chaos if individuals could sue politicians for how they do their job.
Specifically for I-35W, "photos from a June 2003 inspection of the bridge showed gusset-plate bowing" but apparently the inspectors didn't realize they needed to be watching for that.
"...inspectors did not routinely check that safety features were functional."
https://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge...
I drove over that bridge not long before it collapsed, and marveled at how they had concrete and trucks lined up from one end to the other in a closed lane.
yeah that's what scares me most, infrastructure is built to the cheapest bidder that can satisfy safety requirement that often don't account for aging
I've recently passed under two (!) overpass that failed at different times due to lack of maintenance, and every time I'm in queue on top of a bridge it scares the heck out of me watching everyone tailgating each other instead of leaving some margin to the car ahead.
Could we use neural nets to help the inspectors?
Have drones with webcams circle the bridge. It would surely speed up the process and may alert to something the humans overlooked.
24% were classified struct def in 1990 vs 10% in 2015.
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...
(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.)
In the case of bridges, you're going to get the basic Steel or Concrete code, maybe some federal guidelines if it's an interstate, definitely state DOT standards.
As for modern vs not -- There are definitely classes of bridges that I'd not consider modern. Anything with rivets, or sections that are built up by lots of little pieces (like the old style riveted trusses). Those aren't done anymore for several reasons: onsite labor is more expensive than shop labor, rivets are inconsistent and weak compared to bolts or welds, and the ongoing painting to control corrosion is a nightmare. In places like the West Coast, the older bridges are not built to current seismic standards, which have been evolving as quickly as the rest of the codes (e.g. tiedowns, base isolation, column jacketing). A lot of the older bridges also have details that aren't terribly good for fatigue performance.
There was definitely an inflection point, probably in the 80's where precast prestressed concrete started being the go-to design for more than just a plain old girder bridge over the interstate.
That will be heavily spalled 50 years from now. Almost as dumb as building thin flexible skyscrapers with reinforced concrete.
There are thousands of slender concrete structures that have been in service (thus far) without issue.
https://commons.wikimedia.org/wiki/File:Forth_Replacement_Cr...
Three bridges built in 1890, 1964 and 2017 respectively (from right to left in the picture above).
"The AASHTO LRFD Bridge Design Specifications are intended for use in the design, evaluation, and rehabilitation of bridges, and are mandated by the Federal Highway Administration for use on all bridges using federal funding."
It is over 2000 pages long without errata. It is updated yearly with major updates less frequently.
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.
I'm not blaming the designers of the freeway though. My house has a giant plate glass window right next to my deadlocked front door. Our entire society is built around trusting that most people don't want to destroy the nice things we've collectively built. But if someone smashed my window and stole my TV, I'd probably make sure that window was a little more secure. Incremental improvements.
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
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.
They are fast when the situation is dire enough that the politicians don't care what it costs and the NIMBYs and nit-pickers shut their mouths.
I think the result was a reduction in what was permitted to be stored under bridges and viaducts, in common with a similar restriction that was already implemented on major railways. I can't find a source for that.
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.
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... (Dutch, sorry, no English source)