Bridge Collapse Genoa - Informed Engineering Perspectives

[epenguin]

The dramatic collapse of a bridge in Italy with many fatalities has been the big item of news all over Europe.
https://www.theguardian.com/world/2...-death-toll-italy-minister-calls-resignations and many other reports.

I just wonder if the qualified people here can throw any light not on the specifics which would be hard for them to know, but in general.

I mean bridges are supposed to stay up. Engineers are famous for knowing how to construct bridges. For doing calculations on bridges, that is something they are famous for. And they are pretty successful because bridges generally stay up.

I realize they cannot be left to themselves to stay up, but require checking and maintenance from time to time. Worrying thing, that does not seem to me at all easy. The temples of antiquity, the Coliseum, I've been told, would still be standing intact if they had been maintained. That what throws them down is plant life, inserting itself between the stones etc (as well as the edifices being used as convenient quarries sometimes), but this can be seen superficially and could be prevented without any advanced technology. Whereas I think of the steel members that might be suffering, corroding or something, as buried deep inside concrete and quite invisible. Difficult.

A distinguished engineer was asked for comments on BBC last evening, and was not particularly comforting. Said that bridge safety was 'a calculus of uncertainties'. Engineers would give an uncertain warning that it would be prudent to close a bridge for investigation, then it was up to someone else to assume the responsibility of the significant economic damage, a lot depends on them, of deciding whether or not to close them pending investigation.

There are many of these often spectacular bridges in Italy, basically a mountainous country. There are a number, in my impressionistic memory a dozen or two in the autostrade into and out of Genoa and in the hundred or two kilometres of coastal autostrada South from there, (Where you are more at risk from the drivers than from bridge collapse, more there than anywhere else I know, but that's another matter). The link on the above article notes that there have been other collapses in Italy, put down to inadequate inspection and maintenance. One may suspect in construction too - cutting corners with the materials etc. relative to those specified. In other words corruption. Often enough in Italy buildings calculated to resist a given strength of earthquake have nevertheless collapsed for this reason. That explains why you see in the headline that immediately there is an assumption someone is to blame and a search for a culprit.

It would be useful to hear from experts here what light they can shed on this, on the state of the art and how things are, can be, managed. The article also states "the bridge was a sort of jewel in Italian engineering, because at that time it was built with new engineering techniques."

They can surely explain the striking way an entire section collapsed, One would expect it to break in one point, but then I suppose as it kind of pivoted, snaps in another?

 

[Astronuc]

For some images - https://en.wikipedia.org/wiki/Ponte_Morandi
and https://www.cbc.ca/news/world/bridge-collapse-genoa-italy-1.4784417

Apparently, there has been some concern expressed regarding the age of the bridge and its design.

The design of the bridge has been criticized in the past. Antonio Brencich, a professor specializing in reinforced concrete construction at the University of Genoa, called the span "a failure of engineering" in an interview in 2016.

"As this reinforced and pre-stressed concrete bridge has been there for 50 years, it is possible that corrosion of tendons or reinforcement may be a contributory factor," said Ian Firth, former president of The Institution of Structural Engineers, a London-based international network. He called the bridge "an unusual design."

Mehdi Kashani, an associate professor in structural mechanics at the University of Southampton in the U.K., said maintenance issues and pressure from "dynamic loads," such as traffic and wind, could have resulted in "fatigue damage in bridge components."

Certainly, modern day methods of bridge design are more robust than they were 50 years ago.

From several images, it seems the western tower (of three) collapsed. That's pretty significant. They'd want to determine the initial failure point, i.e., did the roadway span fail, one of the cables sets, or the tower itself (base or upper portion).

Investigators will have to look at the design, construction and maintenance records, assuming that's possible. They'll look for signs of fatigue and corrosion (environmental degradation) of concrete, rebar and steel structures, as well as the design. With respect to design, they'd look for stress concentrations (both tensile and shear). They'll have to look at the quality of the concrete and steel used in the construction, and if possible, the construction methods.

Static and dynamic loads are part of the design, so they'll want to understand if the design loads were adequate. Dynamic loads include vehicular traffic and weather, and seismic loads. They'll have to look to see if the failed tower had stable footing.

 

[tech99]

The BBC reported that work was being carried out "to shore up the tower foundations". So that will be an area for investigation. They also show pictures of the cables, showing corrosion, and also some strengthening from a previous upgrade. Unusually the tension cables are in concrete, so corrosion and the impossibility of inspecting them must be an issue, especially in a marine area. BBC also report the number of cables is much less than present day practice, but I am uncertain what this means exactly.
On the first suspension bridge across the River Severn in the UK, 1960s, I believe that microphones are installed which listen for wires breaking, and they are heard breaking all the time. Someone has to make a judgement, because such structures have a finite life.

 

[JBA]

It will be interesting to see what they find/decide as the source of the failure.

In the #4 post Wiki... site "Construction" section there is a photo that if you click on it, the last picture selection to the right shows in red what section of the bridge collapsed; and, apart of short tie-in sections at each end, all of components in that section (bridge & tower components),other than the cables, are loaded in compression.

 

[anorlunda]

In the #4 post Wiki... site

Do you mean this? https://en.wikipedia.org/wiki/Ponte_Morandi

If not, please provide a link.

 

[JBA]

Yes, in the section titled "Construction" there is a picture, if you click on that picture, it will open to larger view of that picture with an arrow on the left and right side, if you click on the arrow on the right side twice you will see the picture with the red area.

 

[arydberg]

One of those pictures is https://en.wikipedia.org/wiki/Ponte_Morandi#/media/File:Ponte_Morandi.jpg

It is interesting that the spans between the cables and the 2 ( almost) vertical supports seem unusually thin.

 

[TomBrooklyn]

On the first suspension bridge across the River Severn in the UK, 1960s, I believe that microphones are installed which listen for wires breaking, and they are heard breaking all the time.

I would submit that if wires are breaking, the design was faulty.

 

[JBA]

In response to the above, it is also possible that the wires experienced environmental conditions and loadings that were not anticipated during the design some 50 years ago. Since the wires were breaking was a known problem, then the responsibility for the failure should not be assigned to the designers but to those responsible for seeing the bridge was adequately maintained.

As someone that spent the last 20 years doing new product development of industrial pressure relief valves used extreme services, I can state that, unfortunately, no matter how diligently you design and select materials and how much pre-release testing you perform, the customer is going to be the ultimate test of any new product as to how it will perform and survive under his particular service conditions. That is the reason that we refused to specify any specific maintenance schedule for our valves; as an example, the maintenance schedule for a valve in a corrosive fluid or vapor service or a corrosive environment is drastically different from one in cryogenic service or in an enclosed plant environment etc.

 

[CWatters]

I saw a report n TV that it was struck by lightning just before collapse.

Edit..
http://www.ansa.it/english/news/201...ses_09b3702e-4891-43cb-bba5-70150edab658.html

 

[nsaspook]

I saw a report n TV that it was struck by lightning just before collapse.

Edit..
http://www.ansa.it/english/news/201...ses_09b3702e-4891-43cb-bba5-70150edab658.html

That's interesting as a possible trigger in a weakened structure. The bolt current in the re-bar grid from a strike could have flash vaporized the water that had been absorbed by the concrete and caused it to expand so fast that it pulverized the areas immediately surrounding the re-bar in a shock wave of expanding gas. Similar to the effect when lightning strikes a live tree.

https://www.concreteconstruction.net/how-to/lightning-damage-to-concrete_o
https://www.facebook.com/ScottEvansTV/photos/pcb.1671244362891545/1671243309558317/?type=3&theater
http://www.kwch.com/content/news/Lightning-strike-in-Wichita-creates-hole-in-concrete-417679823.html

 

[256bits]

maybe I wasn't logged earlier and tried to post, and it's lost, but...
Cracking of concrete would accompanied with an electromagnetic field, oscillating, in the vicinity of the crack, as the stress suddenly is reduced along the crack length. Whether the field is strong enough to initiate an atmospheric lightning strike as a precursor to complete failure is something to look at. The lightning strike may not be the originator of the failure, but an indicator that complete failure is imminent.
http://framcos.org/FraMCoS-7/01-12.pdf

It is widely reported that changes in geoelectric potential
and anomalous radiation of geoelectromagnetic
waves, especially in low-frequency bands, occur
before major earthquakes. At the laboratory
scale, similar phenomena have also been observed
on rock specimens under loading. In this case, crack
growth is accompanied by acoustic emission ultrasonic
waves and by redistribution of electric
charges.

 

[alantheastronomer]

It was reported in the news that the load of traffic over the bridge exceeded the load that the designers had planned for. One thing that this event had in common with the Florida International University bridge collapse, is that both bridges were undergoing maintenance at the time of collapse. It seems like common sense that traffic should be halted during maintenance just to err on the side of caution. It turns out that in the case of the FIU collapse, cracks had been much worse than first reported and that a design flaw may have been responsible.

 

[CWatters]

Picture and comment in the UK papers today includes discussion around the cable stays which are steel encased in concrete. One picture shows quite a lot of rust staining of the concrete stays near the top where they meet the towers. Comment says the concrete makes it hard to inspect the steel for rust. Apparently the stays on several towers had been reinforced in this area but not on the one that collapsed. This is also the area most likely to be hit by lightening.

This could be nothing to do with the cause. I understand they were also working on the foundations of at least one tower.

 

[Keith Mackie]

The reports on the collapse gave two pieces of information:
1. They were doing maintenance work on the bridge at the time
2. The collapse happened during an intense rain storm.

These two together lead to a very prosaic but plausible sugestion:

Bridge maintenance often includes the mainenance/replacement of the rubber bridge bearings. Temporary supports must be provided while this is done. Is it possible that the temporary supports were in the process of being secured when the rain squall hit, that some aspect had not been finalised but the workmen doing the job dropped their tools and made a dash for shelter. The rest, as they say would be history. Dropping a main support like that even a mere few inches would be enough to collapse the bridge.

 

[jedishrfu]

While speculation is a natural consequence of disasters such as this, we must remember that only the final analysis counts. I am reminded of the Infamous Tacoma Bridge collapse and how for decades afterward people described the collapse as a consequence of harmonic vibration.

However more modern analysis revealed it to be something more insidious.

https://motherboard.vice.com/en_us/article/kb78w3/the-myth-of-galloping-gertie

 

[Baluncore]

However more modern analysis revealed it to be something more insidious.
https://motherboard.vice.com/en_us/article/kb78w3/the-myth-of-galloping-gertie

Is there a concise abstract or a summary of that long-winded story?

 

[jedishrfu]

Maybe this Journal article from 1991:

http://www.ketchum.org/billah/Billah-Scanlan.pdf

The Motherboard article isn't as long as it appears though as there are roughly 50% pictures and videos too.

 

[anorlunda]

Is there a concise abstract or a summary of that long-winded story?

It is still very contentious. https://www.physicsforums.com/threads/expunging-myths-from-the-classrooom.849853/But apropos this topic, the TWA 800 case is very on point. There were many theories discussed online. The most popular one is that it was shot down by a missile (backed up with eyewitness accounts). The actual cause, empty fuel tank vapor explosion, was too mundane to make the list of speculations.

 

[dragoneyes001]

one look at the footage and you can tell there wasn't enough rebar in the concrete having been on enough sites when solid structures are torn down the volume of steel easily exceeds what's exposed at the bridge after the collapse. I'd bet you dollars to donuts the contractors shorted the amount thinking once the concrete is poured no one will see it.its always possible someone called for less rebar at the design stage but I'd be surprised if that was the case

tension cables inside the concrete is common in concrete highrise construction to adjust the floor so it stays as intended. but they also have all the steel to rely on.as a counter force the bridge looks extremely lacking in that respect.

 

[anorlunda]

I'd bet you dollars to donuts

That's is not the standard that should apply before publicly accusing specific people or organizations of acting badly.

If the participants want to continue this thread, please do not post accusations.

 

[Baluncore]

well short of being on site and being directly part of the investigation this thread is NOTHING but assumptions so you may as well close the thread now. nothing anyone posts here will be anything more than speculative!

Your assertion that everything posted here is speculative denies general comments on bridge design, construction, maintenance replacement and demolition.

I want to know how we can make bridges that fail gradually by plastic deformation, rather than by a catastrophic collapse?

Can a redundant structure allow a significant deflection, one that clearly indicates an approach to failure, but which somehow strengthens the structure as deflection increases.

 

[anorlunda]

I want to know how we can make bridges that fail gradually by plastic deformation, rather than by a catastrophic collapse?

That's a fine ambition, and probably not impossible if it could be done affordably. But I think that would rule out concrete.

I found a nice summary of bridge support types.
https://theconstructor.org/structural-engg/types-of-supports-reactions-uses-structures/16974/

But before going that route, we have to examine the whole topic of bridge safety. We can't just assume that plastic deformation is the best way to improve that. Nor can we just assume that the next incremental dollar for overall safety should be spent on bridges.

I'm reminded of safety debates when I was an undergraduate. A professor argued that all expensive and spectacular safety measures should stand in line behind the mundane $1 anti-slip strips in bathtubs. His point was that the engineer's approach should be to gather all the safety risks in the world, and rank them by the cost of reducing the risks. Then we would make sure that #1 on the list is fixed all over the world before spending one penny on #2. If we did that, the smallest, simplest, least expensive things would likely rank highest on the list.

 

[dragoneyes001]

Your assertion that everything posted here is speculative denies general comments on bridge design, construction, maintenance replacement and demolition.

I want to know how we can make bridges that fail gradually by plastic deformation, rather than by a catastrophic collapse?

Can a redundant structure allow a significant deflection, one that clearly indicates an approach to failure, but which somehow strengthens the structure as deflection increases.

Not when a staff member makes the statement that a previous post was out of order because they thought it was accusatory for pointing out the lack of structural steel in the video of the collapsed bridge maybe having near forty years of on site experience with concrete and structural building might give me some experience with the industry also considering the majority of catastrophic failures in concrete structures lead back to bad building practices such as the Shopping mall collapse in Asia the massive amounts of deaths when clay and waddle houses flatten during earthquakes ..etc... its not simple speculation to note that a structure torn apart which should look like a massive mesh of exposed rebar has almost no steel showing at all and the few strands which are splayed all over are in fact the tension cables which have pulled out during the collapse.
unless this particular bridge was some revolutionary new building practice the lack of steel is a huge red flag.

 

[epenguin]

Well it would be a pity the thread were blocked for any reason. It may be that we can only have near certainties after official investigations and reports. However that is not a good reason in my opinion to not have reasonable and reasoned conjectures from qualified engineers here because otherwise we are dependent on the general press, and on talk on less qualified sites. I had seen in these sources assertions about lightning, but had no idea whether this was to be taken seriously or not. I learned here that it is at least not outside the bounds of possibility as immediate or contributory cause. (If I understand, the earthing may have been interrupted at a bad moment during the repairs.)

( Engineers might be surprised at the ignorance not only of the public but of relatively qualified scientists from other fields. It may be only me but I but I had not even a vague idea a couple of weeks ago and that prestressed concrete takes trensile loads ( this right?), I thought it was mere protective cladding for the steel cables. I.e. we take for granted this fairly obvious seeming technology many of us are using directly daily more than we do things with moving parts, that light up, get hot, stay up supported only by air, or depend on mysterious relatively new forces like nuclear energy, all of which have risks obvious to us. )

Of the general press talking about the issues talking about the issues at a level accessible to general public the one that I know that I would trust most would be the Economist.The August 18 issue had three useful articles, One on the general world situation, telling us that there is a general world situation (more acute in Italy than in many other places, being an essentially mountainous country with many vertiginous bridges, though maybe fortunately no others contracted on the principles of Morandi Bridge.)
The Economist | The bridges of decay https://www.economist.com/node/21748198?frsc=dg|e

Another on the technology pointing out some known unknowns, but many advances that should help make the problem manageable
https://www.economist.com/science-a...umbling-infrastructure-is-a-worldwide-problem
Despite which "The Genoa bridge is not the first to fall down...And unfortunately it will not be the last.”

And then on the politics.
The Economist | Structural weakness https://www.economist.com/node/21748179?frsc=dg|e
Immediately there is a search for somebody to blame. The city government - of the Five-Star Party, Genoa being one of the few cities it controls - and now one of the two party alliance that constitutes the national government - has a strong motive for this, namely it draws attention away from the unnecessary amount of economic damage this disaster will cause due to their having earlier blocked construction of a relieving bypass (the 5-star movement or parts of it, has a 'dedevelopment' ideology similar to what you hear from no-globalists). But suspicions would have been practically automatic anyway. After every earthquake modern buildings collapse which if they had been built according to the legal and contractual specs should have resisted that degree of quake. Cause - cutting corners fraudulently and criminally with materials etc. not to spec as explained. However these policians are hounding not the original constructors (I think the State was ultimate rresponible!) but the company running it now and on the maintenance issue. I'm guessing, also from the recent update below, that they may not get much out of them and that the point is rather to pressure them and to make a noise now.

https://www.economist.com/business/...eaves-a-european-infrastructure-giant-on-edge

One of the effects not mentioned that I would not be surprised to see is a lot of closures by excess of precaution . Nobody will want to be blamed for an accident, thus if engineers can't give 100% guarantees which I guess they often can't, if their language sound the least bit doubtful, frightened administrators and politicians may prefer the (certain but diffuse) economic damage of closure than the risk of blame for another thing like this.

 

[anorlunda]

bridge maybe having near forty years of on site experience with concrete and structural building might give me some experience

However that is not a good reason in my opinion to not have reasonable and reasoned conjectures from qualified engineers here

You are both misunderstanding what this public forum is.

We have no way to check the credentials or background of PF members. You should know that from when you first joined PF, and no background investigation was needed.

We have many qualified engineers and scientists here on PF. We're proud of that. But by no stretch can we say that all PF members have such qualifications. We have PF members as young as 11 years old.

In addition, anyone on the whole Internet can read what is posted here without joining PF. So by no means can this be considered a conversation private to qualified engineers.

Also, there is a big difference between saying that I think there is not enough rebar, to saying that a particular person or persons or companies are negligent. Accusations might be legally defamatory if untrue, and PF is not in a position to judge the truth of such posts. Also, as I just said we can't verify credentials, and we certainly don't want to open the floor to the entire public for making potentially defamatory statements here. So, opinions are fine, accusations are not, and I don't think I need to explain more the difference.

In the case of the Boston Marathon bomb, members on a different online forum did "expert" analysis of news photos and began publishing online the names and addresses of people they believed were the terrorists. They were wrong. Some of the falsely accused had their lives ruined. Other forums allow that, we don't.

If you're really interested in a rational discussion among qualified individuals, then go to the closed forums of the engineering societies. Or if you want to discuss or accuse on a public forum with few or no rules, then there are other places on the Internet that welcome that.

And yes, this entire thread is inherently speculative. We are bending PF rules a bit to allow the thread at all. If we were strict, no thread would be allowed until the final report on the incident is published sometime in the distant future.

 

[jrmichler]

I want to know how we can make bridges that fail gradually by plastic deformation, rather than by a catastrophic collapse?

Can a redundant structure allow a significant deflection, one that clearly indicates an approach to failure, but which somehow strengthens the structure as deflection increases.

Normal procedure for designing reinforced concrete is to design for ductile failure. A concrete beam without reinforcing steel (rebar) supported on simple supports at the ends and loaded in the middle will fail catastrophically when it fractures on the tension side. Adding a little (as in not enough) rebar on the tension side, and the beam will still fail catastrophically because the insufficient rebar will not be able to carry the entire load when the concrete cracks in tension. Adding more rebar (the right amount) to the tension side will transfer the load to the steel when the concrete cracks. The steel will yield without breaking. Adding too much steel to the tension side keep the tension steel from yielding until the compression side fails in brittle compression. Suddenly and catastrophically.

Reinforced concrete design is a complex specialty of its own. I designed a simple concrete slab once, and convinced myself to let real civil engineers do similar jobs in the future. Some good Google search terms: seismic design concrete.

 

[Baluncore]

Reinforced concrete design is a complex specialty of its own. I designed a simple concrete slab once, and convinced myself to let real civil engineers do similar jobs in the future.

Last week I was designing RC for use in the ground, under hydrostatic compression. Yesterday I was trying to counter that design with a plastic cellular box formation, the problem then becomes fire …

Yes, I know civil engineers like to use RC because it is cheap and acceptable, but even ignoring the carbon cost it has long passed the time when we should consider alternatives. I certainly do not advocate reinforced concrete for the design of slender bridge members.

To escape the RC paradigm of the last century, I want to consider other materials and other structures. I am thinking of hierarchical closed cell foam structures inside tensile tubes, think tapered members a bit like a bird's bones.

 

[nsaspook]

Another info point.
https://www.nytimes.com/interactive/2018/09/06/world/europe/genoa-italy-bridge.html

 

[anorlunda]

Another info point.
https://www.nytimes.com/interactive/2018/09/06/world/europe/genoa-italy-bridge.html

Very interesting. Thanks for sharing. But I do note that NYT is no longer a trusted source of news in my opinion. Also, that the article claims many anonymous sources, and that the named sources may have motivations to point the finger elsewhere.

 

[cjl]

Why do you not think the NYT is a trusted source? I have usually found them to be fairly reliable.

 

[Baluncore]

Why do you not think the NYT is a trusted source? I have usually found them to be fairly reliable.

I have never gone to the NYT for engineering information or advice. Your experience may be different.

When it comes to the rational engineering analysis of bridge structures, there can be nothing more corrosive and damaging than reports that include the emotional response of the unfortunate victims.

All engineering evidence reported in the NYT article will now need to be re-examined and decontaminated before it can be used to support any hypothesis. Indeed, the inclusion of that article in this thread has done more to undermine rational engineering analysis than it has to understand the reasons behind the structural failure.

Printing something in a newspaper does not make it true. The author of that NYT article is clearly interested in selling entertainment. We do not yet know what political barrow they are pushing, or who they will point their uneducated finger of blame at next.

 

[jim hardy]

Somebody seems to have been worried over the years about the stay attachments.

https://www.eng-tips.com/viewthread.cfm?qid=443075

 

[nsaspook]

This link was in Jim's post above.
https://files.engineering.com/getfi...sc=212727627.1.1536693115435&__hsfp=494127832

the full project explained in details by the designer himself, Mr Morandi

 

[CWatters]

Somebody seems to have been worried over the years about the stay attachments.
View attachment 230548

https://www.eng-tips.com/viewthread.cfm?qid=443075

Indeed. Soon after the accident there was an article in the UK press that said that some of the stays had been reinforced but not those on the tower that collapsed.