Bridge collapse in Genoa

[Steve81]

One theory a friend shot out (an actual engineer who designs bridges) was that the rain could have contributed by softening up and shifting the soil around the foundation. Combined with the high load on the bridge, maintenance issues, etc...

 

[Swerd]

One theory a friend shot out (an actual engineer who designs bridges) was that the rain could have contributed by softening up and shifting the soil around the foundation. Combined with the high load on the bridge, maintenance issues, etc...

I would hope that the support towers were deep enough to reach bedrock, or at least be deep enough to never shift.

But I'm old enough to know there can be a difference between what "we would hope" and what "we find out was really done".

Italy is the home of Roman concrete bridges that have lasted 2000 years. It's also the home of the Leaning Tower of Pisa.

 

[2channel lover]

It will be something I want to watch for. Tragically, I'm an engineer and always interested in knowing what went wrong and why. Not that I haven't had a design flaw shown on ESPN or anything... But my screw ups didn't kill people.

One problem with structures built with new and designs that really reach for new boundaries is they tend to have something overlooked. Look at the bridge failure in Minneapolis. Look at the World Trade Center, look at many infrastructure failures. They all usually have one or more design flaws that trigger or compound an event the structure should survive into one that it cannot.

I feel for the people and families impacted. That is a horrible way to go...falling that distance.

Our company builds bridge abutment supports...not as an exclusive trade, but enough to where we get calls to bid on them half dozen times a year. So we get engineering plans on bridges in here from time to time...that has made me curious how it failed as well. The one abutment just gave way entirely from what I can see.

 

[KEW]

One theory a friend shot out (an actual engineer who designs bridges) was that the rain could have contributed by softening up and shifting the soil around the foundation. Combined with the high load on the bridge, maintenance issues, etc...

That makes some sense to me!
I cannot reconcile the way the support structure just got (comparatively) leveled the way it did. If the supports are free to flop over (like a house of cards can) that makes it easier to understand. Massive girders like this should not just disappear after a failure!

 

[mtrycrafts]

I would have thought the tower footing and all the others would go to bedrock depth. Maybe the next round?

 

[slipperybidness]

Anyone ever seen the TV show Seconds From Disaster?
https://en.wikipedia.org/wiki/Seconds_From_Disaster

I love this show!

But, when you start to learn about man-made disasters, you start to notice a pattern. Every single disaster has some unexpected event that starts off the chain reaction. But, along the way, there are always other seemingly minute details or flaws that contribute to the disaster. Any one of these small details could have prevented the final disaster, but for one reason or another these become another escape point that contribute to the disaster rather than prevent it. Very fascinating!

 

[Midwesthonky]

Me too. I'm not an engineer, but I've always had a fascination for bridges. I tend to like bridges that don't collapse. But those that have collapsed are remembered better – with morbid fascination.

Possible reasons for the bridge failure that I've read so far (at various news sites, including BBC, CBS, CNN, Washington Post):

• Steel reinforced concrete is known to deteriorate after about 50 years. The steel buried inside the concrete rusts enough to weaken the structure. It can be addressed with major reconstruction efforts. This bridge was built in 1967. At the time of the collapse, the bridge was undergoing some major reinforcement this summer.
  
  
• This bridge was said to be built using new (for the time) steel/concrete techniques that have not been used since. I'm not sure why, but I assume the technique was less expensive, but led to weaker than intended structures.
  
  
• One Italian bridge engineer was quoted as saying this bridge was designed to carry much lighter loads than it has been routinely exposed to for decades. It was a failure waiting to happen.
  
  
• Not nearly enough maintenance (as mentioned above by others).
  
  
• The torrential rain storm. Heavy rain and high winds? Would this alone be enough to cause failure? Probably not, but it cannot be ignored.

Stay tuned. As usual, there are news stories of Italian leaders who are calling for criminal investigations. Why look for someone to blame (the bridge designer died in 1989) when the bridge clearly needed major repair or replacement. I do not understand the Italian legal system.

It certainly is looking like typical issues we see in the US. Built during the big infrastructure boom in 60's using new (at the time) techniques. Bridge lasted longer than design life and has been carrying higher load than it was designed for for decades.

Sadly, I suspect they will find the concrete wasn't as strong as it should be. Combine that with the excessive loads and deterioration and it's a disaster that occurred. It's only a matter of time when it will happen in the US. We've had several already yet still have very deficient bridges in service.

Heck in Milwaukee, a few years back a major bridge (Hoan) along the harbor had a big failure that was discovered when a guy went over a section and landed 3 feet down on the next section. He called it in and a city plow truck went and investigated. Thankfully they caught it in time. Section had failed and dropped 3 feet. It was super early in the morning with little traffic so no one injured. But it's going to happen in the US. Sadly...

 

[Midwesthonky]

I would have thought the tower footing and all the others would go to bedrock depth. Maybe the next round?

Would, should, could? Like the Millenium Tower in San Fran? Yeah, let's build a massive concrete building in earthquake country and not go to bedrock.

Don't forget Italy is a seismically active country too.

Delaware Bridge Leaning
Don't forget this one from 2015 where the big dump pile of dirt caused the soil to shift and move the bridge abutments. Could be something that in Italy with the buildup around the bridge. Looks like the river was right there too.

 

[highfigh]

You can play only if you are an unqualified Monday-morning bridge engineer.

As far as I know, that before photo was taken before any collapse occurred. The photo is on a sunny day. The collapse occurred suddenly during a heavy thunder storm (see the video I cited above). It is possible that structural repairs were underway when the before photo was taken.

Sorry for the late response- I was on vacation.

I studied Architecture at an engineering skool- does that mean I qualify?

 

[Swerd]

I studied Architecture at an engineering skool- does that mean I qualify?

It depends on what grade you got. A or B, forget it. C or lower, now we're talking.

 

[highfigh]

It depends on what grade you got. A or B, forget it. C or lower, now we're talking.

It wasn't just one class, it was a whole curriculum, part of which was structural engineering, statics & strengths of materials and other fun stuff like that. Basically, it was a lot of Physics & Math with other topics thrown in.

 

[Swerd]

It wasn't just one class, it was a whole curriculum, part of which was structural engineering, statics & strengths of materials and other fun stuff like that. Basically, it was a lot of Physics & Math with other topics thrown in.

Curious minds want to know all the answers, right now. Where's that bridge failure analysis?

 

[highfigh]

Curious minds want to know all the answers, right now. Where's that bridge failure analysis?

My finding is: gravity 1, bridge 0.

 

[highfigh]

One theory a friend shot out (an actual engineer who designs bridges) was that the rain could have contributed by softening up and shifting the soil around the foundation. Combined with the high load on the bridge, maintenance issues, etc...

If that actually happens, the engineers should be prosecuted for fraud. There's no way the soil around a bridge should be carrying the load- that's the job of the footings. Any soil under the footings should be very deep and it's likely that a bridge of that type may be resting on bedrock, if it's available. If not, piers would be installed so the foundation couldn't push it deeper into the ground. I think the center support had some kind of flaw.

 

[Swerd]

The bridge looks like it was made with three main concrete towers. I've not seen anything like it in the USA. Each tower had diagonal stays that appear to work like cable stays (concrete clad steel cable?) that support road bed on each side of each tower. They resemble cantilevered steel bridge towers. The concrete towers are under compression and the cable stays are under tension. Between the far end of each cable stay is a suspended section of road. The cantilevered tower sections should stand alone, even without the suspended road section. One of these towers, the closest one in the photo, came down.

Watch the video:
https://www.cnn.com/videos/world/2018/08/14/genoa-italy-bridge-collapse-sje-lon-orig.cnn

It shows one concrete tower falling at 24 seconds (repeated again at 27 seconds). At 31 seconds a construction crane tower falls. The crane was apparently used in the major repairs going on at the time. One theory I read suggested the construction crane fell onto the bridge during the storm, causing catastrophic damage. But the video shows the concrete tower fell first. I would think that rules out the crane as the cause or the trigger of the bridge failure.

That leaves inadequate design/construction, age, and corrosion causing the cantilevered steel-reinforced concrete tower to collapse. The heavy wind and rain was only the trigger, not the cause. I guess the answer will come after a lengthy analysis of bridge debris.

 

[Swerd]

Wikipedia already has a page for this bridge and it's collapse https://en.wikipedia.org/wiki/Ponte_Morandi. The bridge was named Ponte Morandi, after its designer Ricardo Morandi.

"Morandi's cable-stayed bridges are characterized by a prestressed concrete structure for the piers, pylons and deck, very few stays, as few as two per span, and a hybrid system for the stays constructed from steel cables with prestressed concrete shells poured on. The concrete was only prestressed to 10 MPa, resulting in it being prone to cracks and water intrusion, which caused corrosion."​

​

There is a lengthy section, Maintenance and strengthening, which discusses the severe problems and restoration efforts of this bridge. It sounds bad as I read it.

​

"An early 2018 meeting report indicated resistance and reflectometry measurements had been performed indicating an (average?) reduction of the cross section of 10 to 20% of the tendons. A crack in the road had appeared at least fourteen days before the collapse near one of the stays of the now collapsed pillar 9. The crack may have indicated that the stay had stretched. At no point has there been a suggestion to reduce the load on the bridge. It has been reported that one of the stays gave way explosively due to corrosion and damage. With only four stays, if one of the stays had given way, the structure could have lost stability. There is speculation that lightning may have struck the stays, or a landslide could have destabilized the base."​

Read the rest as it's too much to quote.

 

[Midwesthonky]

Wikipedia already has a page for this bridge and it's collapse https://en.wikipedia.org/wiki/Ponte_Morandi. The bridge was named Ponte Morandi, after its designer Ricardo Morandi.

"Morandi's cable-stayed bridges are characterized by a prestressed concrete structure for the piers, pylons and deck, very few stays, as few as two per span, and a hybrid system for the stays constructed from steel cables with prestressed concrete shells poured on. The concrete was only prestressed to 10 MPa, resulting in it being prone to cracks and water intrusion, which caused corrosion."​

​

There is a lengthy section, Maintenance and strengthening, which discusses the severe problems and restoration efforts of this bridge. It sounds bad as I read it.

​

"An early 2018 meeting report indicated resistance and reflectometry measurements had been performed indicating an (average?) reduction of the cross section of 10 to 20% of the tendons. A crack in the road had appeared at least fourteen days before the collapse near one of the stays of the now collapsed pillar 9. The crack may have indicated that the stay had stretched. At no point has there been a suggestion to reduce the load on the bridge. It has been reported that one of the stays gave way explosively due to corrosion and damage. With only four stays, if one of the stays had given way, the structure could have lost stability. There is speculation that lightning may have struck the stays, or a landslide could have destabilized the base."​

Read the rest as it's too much to quote.

If one of the stays failed, it's only a matter of time before the bridge went. Also looking at reduction of 10-20% in the tendons would be bad. Since that was an average, you just need a spot that is higher to concentrate the stress and you have a failure point. I'm not a civil engineer but I wouldn't attempt to clad steel cables with concrete as that won't hold up long term. Wait...it didn't.

 

[highfigh]

Heck in Milwaukee, a few years back a major bridge (Hoan) along the harbor had a big failure that was discovered when a guy went over a section and landed 3 feet down on the next section. He called it in and a city plow truck went and investigated. Thankfully they caught it in time. Section had failed and dropped 3 feet. It was super early in the morning with little traffic so no one injured. But it's going to happen in the US. Sadly...

It wasn't that early- I was there about ten minutes later.

Weird and unsettling to see something like that in an adjacent lane. IIRC, it was a failure of the fasteners, not a structural member. I pass under the Hoan regularly and from that view, it looks to be in good condition, but MKE has a lot of other bridges that aren't in good condition. One is a railroad bridge over 1st St, North of Lincoln Ave and not only is it old and decrepit, trucks have hit it so often they installed steel tubing in front of the lower edge where the impacts occur.

Remember when the Locust St bridge was rebuilt (Nancy Laffee, from Channel 12 drove onto it one night, during the time when the surface was still being removed)? I was still/back in school at the time and in one of our classes, we discussed some of the problems of the roadways- that bridge had major structural members that had lost 70% of their cross-section in some areas.

I drove past County Stadium after Big Blue fell, too. Earlier in the day, I was thinking that it would be crazy to lift but sure enough, someone with a higher pay grade thought otherwise. I worked in Pewaukee at the time and the wind was blowing hard all day.

 

[Swerd]

I needed a few definitions. I figured if I didn't know them, others also might not. First, the various sections of a cantilever bridge, copied from https://en.wikipedia.org/wiki/Cantilever_bridge. The illustration shows a cantilevered truss bridge, but the cable-stayed Ponte Morandi has similar features:

What is a tendon in pre-stressed concrete? Concrete has great strength when compressed, but is weaker than steel when under tension, stretched. Steel reinforcement tendons (see the red line below) make concrete beams stronger if they are stressed (stretched) before pouring the concrete. After the concrete hardens, the tension is released as shown below. When assembled in a bridge or building, these pre-stressed concrete beams support much more weight without sagging. See https://en.wikipedia.org/wiki/Prestressed_concrete

 

[Swerd]

I also found a web page with good photos of the Ponte Morandi. Some close up photos show the cable stays in greater detail. I've copied some written text and several photos. See the web page for full details http://www.retrofutur.org/retrofutur/app/main?DOCID=1000111180&albumMode=1000111180.

(The images below (800x600px) may be freely used in any way, as long as the author "Kristian Hasenjäger" is mentioned and the inscription "www.retrofutur.org" remains visible.)

Peculiarities of the Polcevera bridge, a quick overview:

• The peculiarity of this bridge (opened in 1967) may be seen in the configuration of the three 90m high A-type pylons, one of which collapsed on August 14, 2018.
• Each of the three A-type pylons supports a statically fixed bridge table section through four cable stays
• A set of steel cable stays is channeled inside the (visible) concrete beams. The cables were pre-stressed at construction time, so that the concrete beam around it remains always under a certain compression. This may be less prone to oscillations than a steel-only cable stay configuration, and reduce stress on the cables. However, because of its weight, extension and slim cross section, the beams behave more like flexible catenaries than rigid beams.
• Since the 1980s the bridge has been continuously and thoroughly monitored.
• Preliminary checks had brought to light a worrisome situation, manifested by the presence of cavities and degradations in the concrete, especially at the fixation point of the pre-stressed cable stays.
• Especially the section which passes over highly urbanized area has been strengthened 1993 and onwards (see dedicated photos below).

A-type pylon #11 of Ponte Morandi and its access ramps. The thick cable sheathing was added after 1993 in an attempt to strengthen the system. Pylons #9 (which collapsed) and #10 did not receive this safety upgrade.

The four cable stays of the eastern pylon (#11) have been visibly reinforced in the past decades, after 1993. A set of external cables form a sheathing to strengthen the original cable stay


Pylon #10, the middle of the three 90m high pylons, was also reinforced, but with a different appearance than #11. The visible steel sheathing was added in 1993 and afterwards. Pylon 9 did not receive this reinforcement.

@Midwesthonky and @highfigh – Please continue your discussion.