Genoa bridge collapse

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M4Simon
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Re: Genoa bridge collapse

Post by M4Simon » Tue Aug 04, 2020 12:48

BOH wrote:
Tue Aug 04, 2020 08:37
mikehindsonevans wrote:
Mon Aug 03, 2020 23:13
Certainly, one heck of an achievement to build a bridge and have it ready to open in just two years.

Hats off to our Italian neighbours.
It was built in around 1 year as construction did not start until Summer 2019. It took a year for all the investigations and demolition following the collapse of the Ponte Morandi.
Gareth wrote:
Tue Aug 04, 2020 08:33
Yeah. Here, we'd still be consulting people on whether or not we should have a consultation on building it.

Let's hope it's built properly though!
As I said above, the circumstances meant that they could avoid the many things that strangle construction projects in the UK, including consultation, as the route was already decided, the links to the road network already exist, the properties below were bought quickly to enable the remainder of the old bridge to be demolished for fear that gravity and the previous lack of maintenance would do the job for them, and there was no need to try and maintain existing traffic flows.

I can't think of a comparable example where a bridge of that scale has collapsed in the UK. Eastham Bridge near Tenbury Wells collapsed and was replaced within a couple of years, but it was a small stone arch bridge. The Cleddau Bridge collapsed while under construction, and was delayed by about 3 years, but the issue there was a look at the entire bridge design and technical approval process because of inherent problems with standards then applicable for box girder bridge design.

That said, I agree that all credit is due for rebuilding the bridge so quickly.

One of the first things we were told at university is that concrete is no good in tension but very strong in compression. Every time I look at the old bridge, I struggle with the fact that someone (or presumably several people) thought it would be a good idea to encase the main cables in concrete. Firstly, the extra dead weight the bridge would need to carry would be significant. Secondly, the dynamic loading on the bridge would cause the cables to stretch and contract a little, which would apply variable amounts of tension to the concrete. It seems inevitable that the concrete around the cables will crack and eventually break off. That concrete would be impossible to reach and repair, and it would make it very difficult to inspect the cables. When compared with the elegant cable-stayed Millau Viaduct, the Morandi Bridge looked far too heavy and clunky, and given that concrete is not suitable for use in tension, it just looked wrong.
Owain wrote:
Tue Aug 04, 2020 09:53
[...I assume that the engineers spent much of their childhoods playing with Lego.
I thought that was a given for all civil and building engineers?

Simon

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Re: Genoa bridge collapse

Post by RichardA35 » Tue Aug 04, 2020 13:45

Picking up on Simon's points, two dual carriageway viaducts I can think of that have been replaced on the HE network over recent years are the A38 Marsh Mills Viaducts and the A34 Wolvercote viaducts.
Both were picked up as in need of replacement by regular inspection and both were replaced by innovative solutions with two lanes of traffic running in either direction with only the odd weekend closure and a speed limit as the noticeable effects on the public.

As with all good things replacement works like this are carried out unobtrusively with little effect on the public and no great fanfare on completion. This is the characteristic of a good industry with good control over the condition of their assets. Far sooner this than the way exemplified by the Italian experience of collapse and reconstruction. Rather than giving plaudits for speedy reconstruction we should be asking ourselves why it was necessary in the first place and how the system failed so catastrophically and thanking ourselves that, in the UK, we have the processes in place to prevent this.

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Re: Genoa bridge collapse

Post by ChrisH » Tue Aug 04, 2020 14:52

RichardA35 wrote:
Tue Aug 04, 2020 13:45
Rather than giving plaudits for speedy reconstruction we should be asking ourselves why it was necessary in the first place and how the system failed so catastrophically and thanking ourselves that, in the UK, we have the processes in place to prevent this.
For the most part this is true, but we could equally ask how close we've got to a similar catastrophe in the UK. Hammersmith Flyover was close to collapse in 2011; and we now have significant closures on London, Vauxhall and Hammersmith bridges because of structural instability - with the Rotherhithe tunnel, Westway and Brent Cross structures not far behind. And that's just in London.

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Re: Genoa bridge collapse

Post by ForestChav » Tue Aug 04, 2020 15:06

ChrisH wrote:
Tue Aug 04, 2020 14:52
RichardA35 wrote:
Tue Aug 04, 2020 13:45
Rather than giving plaudits for speedy reconstruction we should be asking ourselves why it was necessary in the first place and how the system failed so catastrophically and thanking ourselves that, in the UK, we have the processes in place to prevent this.
For the most part this is true, but we could equally ask how close we've got to a similar catastrophe in the UK. Hammersmith Flyover was close to collapse in 2011; and we now have significant closures on London, Vauxhall and Hammersmith bridges because of structural instability - with the Rotherhithe tunnel, Westway and Brent Cross structures not far behind. And that's just in London.
A52 as well, admittedly not in London, but still
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Re: Genoa bridge collapse

Post by Owain » Tue Aug 04, 2020 20:58

M4Simon wrote:
Tue Aug 04, 2020 12:48
Owain wrote:
Tue Aug 04, 2020 09:53
[...I assume that the engineers spent much of their childhoods playing with Lego.
I thought that was a given for all civil and building engineers?
Maybe ... during my last year at primary school I built a genuine model suspension bridge out of wood (structure), paper (road deck), and wool (cables). The hardest bit was painting straight lines on the carriageway, which - crazily enough - was an S3!!!

I say "genuine", because my classmates kept asking me why I didn't just glue the road deck to the towers. Answer: "because it wouldn't be a suspension bridge". :roll:
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Re: Genoa bridge collapse

Post by Big L » Tue Aug 04, 2020 21:05

Owain wrote:
Tue Aug 04, 2020 20:58
M4Simon wrote:
Tue Aug 04, 2020 12:48
Owain wrote:
Tue Aug 04, 2020 09:53
[...I assume that the engineers spent much of their childhoods playing with Lego.
I thought that was a given for all civil and building engineers?
Maybe ... during my last year at primary school I built a genuine model suspension bridge out of wood (structure), paper (road deck), and wool (cables). The hardest bit was painting straight lines on the carriageway, which - crazily enough - was an S3!!!

I say "genuine", because my classmates kept asking me why I didn't just glue the road deck to the towers. Answer: "because it wouldn't be a suspension bridge". :roll:
Reminds me of an old Mythbusters program where they covered suspension bridges being damaged by armies marching in time.

They made something that looked like a suspension bridge from metal and solidly soldered all of the joints; they announced it a myth because the bridge didn't wobble at all. Surprisingly.
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Re: Genoa bridge collapse

Post by Bryn666 » Tue Aug 04, 2020 21:50

Big L wrote:
Tue Aug 04, 2020 21:05
Owain wrote:
Tue Aug 04, 2020 20:58
M4Simon wrote:
Tue Aug 04, 2020 12:48

I thought that was a given for all civil and building engineers?
Maybe ... during my last year at primary school I built a genuine model suspension bridge out of wood (structure), paper (road deck), and wool (cables). The hardest bit was painting straight lines on the carriageway, which - crazily enough - was an S3!!!

I say "genuine", because my classmates kept asking me why I didn't just glue the road deck to the towers. Answer: "because it wouldn't be a suspension bridge". :roll:
Reminds me of an old Mythbusters program where they covered suspension bridges being damaged by armies marching in time.

They made something that looked like a suspension bridge from metal and solidly soldered all of the joints; they announced it a myth because the bridge didn't wobble at all. Surprisingly.
Iron suspension chains would have potentially been affected by the vertical movement that marching could cause. It was a valid fear at the time, and let us not forget that we had several high profile bridge failures involving cast iron - the Tay Bridge springs to mind.
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Re: Genoa bridge collapse

Post by RichardA626 » Tue Aug 04, 2020 22:05

Tacoma Narrows suspension bridge collapsed because of vibrations when the wind blew too hard.
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Re: Genoa bridge collapse

Post by ForestChav » Tue Aug 04, 2020 22:28

RichardA626 wrote:
Tue Aug 04, 2020 22:05
Tacoma Narrows suspension bridge collapsed because of vibrations when the wind blew too hard.
Should have steered clear of Taco Bell then...
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Re: Genoa bridge collapse

Post by M4Simon » Tue Aug 04, 2020 23:22

RichardA626 wrote:
Tue Aug 04, 2020 22:05
Tacoma Narrows suspension bridge collapsed because of vibrations when the wind blew too hard.
The Millennium Bridge in London was notoriously wobbly when first opened because its resonant frequency was that of typical walking pace. Dampers were installed soon after to deal with the problem, and it is now just a pleasant walk over the Thames.

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Re: Genoa bridge collapse

Post by Owain » Thu Aug 06, 2020 12:39

The traffic monitor in my Google Maps app is now showing traffic flowing across the new bridge, so it's open to traffic.

The lines showing the traffic flow are slightly out of line with the road on the map.
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Re: Genoa bridge collapse

Post by doebag » Thu Aug 06, 2020 17:19

Satellite vies shows a ghostly traffic flow over the demolition site.

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Re: Genoa bridge collapse

Post by Chris5156 » Sat Aug 08, 2020 09:37

Delighted to hear the new bridge is open - and fascinating to see Renzo Piano talking about it in the BBC video posted upthread. (Doesn't he look well for 82? That's a Mediterranean diet for you.)

The new bridge isn't at all showy, but it does look like exactly the thing that is required - a simple structure based on known and well-used technology, that could be put together quickly and can be maintained easily. It's nicely designed and has some clever touches (solar panels along the sides, the number of lighting columns, etc), but they're really just accessories - fundamentally it's a series of very solid columns supporting simple horizontal spans, and repeats none of the mistakes of the original. Well done, Italy.

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Re: Genoa bridge collapse

Post by KeithW » Sat Aug 08, 2020 10:33

ChrisH wrote:
Tue Aug 04, 2020 14:52

For the most part this is true, but we could equally ask how close we've got to a similar catastrophe in the UK. Hammersmith Flyover was close to collapse in 2011; and we now have significant closures on London, Vauxhall and Hammersmith bridges because of structural instability - with the Rotherhithe tunnel, Westway and Brent Cross structures not far behind. And that's just in London.

There were also the Huntingdon and Thelwall viaducts and the original Forth and Severn Road bridges. I think the difference here is that there is a nationwide bridge inspection requirement and a published manual indicating what must be inspected and how often. In Italy it seems to have been left to the company that was also running the toll roads. In the cases you mentioned all were picked up in the process of such inspections. One result was the equipping of compromised structures with sensors that use accoustic methods to monitor the deterioration of internal tendons that cannot be visually inspected. The bottom line is that older bridges were simply not designed with inspection in mind and that was the main problem in Genoa, there was simply no way of knowing there was a problem unless concrete started spalling off. The section that collapsed was considered safe and not reinforced as there were no visible signs of the scale of the problem.

Another change is much better quality control of concrete cast in situ, now each load is tested on site and will be rejected if it does not pass. If the concrete is too viscous it will not flow properly and leave voids in which the steel tensions can corrode unseen which happened with the Huntingdon Viaduct. If it has too much water it will be weak and may crack. This is why there was a rash of failures in buildings in the 80's and 90's that meant even iconic buildings such as the Wembley Conference centre had to be demolished. The irony in the case of Italy of course is that their ancestors, the Romans, built astonishing concrete structures such as the Pantheon and Castel St Angelo (Hadrians Tomb) that are still standing nearly 2000 years later.

I know the Brent Cross Flyover had to have its expansion joints repaired which is a common issue. HE have been using the lighter traffic during the Pandemic to accelerate replacement of these on the Tees Viaduct but the structure itself is in good condition. I would be interested if you could point me to other reports on the Brent Cross Flyover as I havent come across this as being a problem. As for Hammersmith Bridge that is what you get with a 140 year old bridge designed to carry horses and carts on a wooden deck upon which even the patches have been patched.

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Re: Genoa bridge collapse

Post by KeithW » Sat Aug 08, 2020 10:52

RichardA626 wrote:
Tue Aug 04, 2020 22:05
Tacoma Narrows suspension bridge collapsed because of vibrations when the wind blew too hard.
The cause was eddies causing the bridge to sway with a frequency about the same frequency as the vortex breakaway. This like pushing a swing each time it passes you, the amplitude just keeps increasing until something fails. This was found with steel chimneys which is why they have spiral vortex breakers.

Image

It was exacerbated with the Tacoma Narrows bridge as it a simple rectangular cross section, a deck and two side like a conventional bridge that also caused flutter. This resulted in the left and right side of the bridge alternately rising and falling. modern bridges have an aerofoil shape the keep them stable in wind. Some are now actively controlled to respond appropriately for each scenario. It was the combination of flutter and sway that caused the sinusoidal motion the tore it apart.

Going to to the swing analogy its as if not only was the swing being pushed each time but also being twisted. Today we test models in wind tunnels, back then they didnt exist.

https://ora.ox.ac.uk/objects/uuid:1a57f ... al+article

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Re: Genoa bridge collapse

Post by KeithW » Sat Aug 08, 2020 11:33

M4Simon wrote:
Tue Aug 04, 2020 12:48
One of the first things we were told at university is that concrete is no good in tension but very strong in compression. Every time I look at the old bridge, I struggle with the fact that someone (or presumably several people) thought it would be a good idea to encase the main cables in concrete. Firstly, the extra dead weight the bridge would need to carry would be significant. Secondly, the dynamic loading on the bridge would cause the cables to stretch and contract a little, which would apply variable amounts of tension to the concrete. It seems inevitable that the concrete around the cables will crack and eventually break off. That concrete would be impossible to reach and repair, and it would make it very difficult to inspect the cables. When compared with the elegant cable-stayed Millau Viaduct, the Morandi Bridge looked far too heavy and clunky, and given that concrete is not suitable for use in tension, it just looked wrong.
Every bridge beam has one side in tension and the other in compression with the web in between being subject to shear. Lets be honest we effectively did the same thing here. Look at almost any highway overpass and you will see a composite steel and concrete structure. The steel is in the form of rebar with the concrete cast around it.
Image

The Huntingdon Viaduct is a pre stressed concrete design where the tension is carried by steel tendons embedded in the bridge and then filled with concrete, that made it almost impossible to inspect. With other concrete structures failing an inspection was carried out to ensure it had an adequate life for the first A14 upgrade scheme.It turned out that the grouting was not done well the leaking expansion joints were permitting rainwater and road salt to penetrate the half joints and tendon sheaths causing both to deteriorate. This is a major reason the old scheme was scrapped and the Huntingdon Viaduct is being dismantled. The same is the case on the Hammersmith and other flyovers of that period. While the new section was being planned and built an active warning system was installed and monitored which listens for tendond failing, had the number of failures reached a critical point the bridge would have to be closed.

There is nothing inherently wrong with concrete or using steel tendons to carry the tensile load, that was done on the AGR Reactors in the British Nuclear power stations which use a thick (18 ft !) pressure concrete vessel strengthened by tendons. The difference is there each tendon has its attachment outside the vessel and may be removed for inspection and replaced. The other thing was that when the reactor vessel was being cast in situ each batch of concrete was tested on site before being poured, get the mix or timing wrong and the concrete can be seriously under strength. I doubt anyone was doing that on the Hammersmith Flyover or at Huntingdon but it WAS done on the new A14 bypass and critical bridges such as that at Bar Hill were prefabricated and rolled into position.

If you want to see a really old concrete construction, take a look at the Pantheon in Rome which was built 1900 years ago and is still the largest self supporting concrete dome ever built.

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Re: Genoa bridge collapse

Post by RichardA626 » Sat Aug 08, 2020 14:05

KeithW wrote:
Sat Aug 08, 2020 10:52
RichardA626 wrote:
Tue Aug 04, 2020 22:05
Tacoma Narrows suspension bridge collapsed because of vibrations when the wind blew too hard.
The cause was eddies causing the bridge to sway with a frequency about the same frequency as the vortex breakaway. This like pushing a swing each time it passes you, the amplitude just keeps increasing until something fails. This was found with steel chimneys which is why they have spiral vortex breakers.

Image

It was exacerbated with the Tacoma Narrows bridge as it a simple rectangular cross section, a deck and two side like a conventional bridge that also caused flutter. This resulted in the left and right side of the bridge alternately rising and falling. modern bridges have an aerofoil shape the keep them stable in wind. Some are now actively controlled to respond appropriately for each scenario. It was the combination of flutter and sway that caused the sinusoidal motion the tore it apart.

Going to to the swing analogy its as if not only was the swing being pushed each time but also being twisted. Today we test models in wind tunnels, back then they didnt exist.

https://ora.ox.ac.uk/objects/uuid:1a57f ... al+article
Thanks, I knew the collapse was caused by something like that, but I wasn't sure of the terminology.
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Re: Genoa bridge collapse

Post by Stevie D » Sat Aug 08, 2020 15:32

M4Simon wrote:
Tue Aug 04, 2020 12:48
I can't think of a comparable example where a bridge of that scale has collapsed in the UK. Eastham Bridge near Tenbury Wells collapsed and was replaced within a couple of years, but it was a small stone arch bridge. The Cleddau Bridge collapsed while under construction, and was delayed by about 3 years, but the issue there was a look at the entire bridge design and technical approval process because of inherent problems with standards then applicable for box girder bridge design.

That said, I agree that all credit is due for rebuilding the bridge so quickly.
Workington Bridge opened to traffic in February 2011, 14½ months after floods destroyed the old bridge in November 2009. Remember that this was such a key crossing that Network Rail built a temporary station in 1 week to enable people to cross the river. Although after a temporary footbridge was opened, the station was no longer really needed, and was removed a few months before the road reopened. Although that said, Workington Bridge was probably an easier construction project than crossing Genoa.

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Re: Genoa bridge collapse

Post by ChrisH » Mon Aug 10, 2020 13:17

KeithW wrote:
Sat Aug 08, 2020 10:33
ChrisH wrote:
Tue Aug 04, 2020 14:52

For the most part this is true, but we could equally ask how close we've got to a similar catastrophe in the UK. Hammersmith Flyover was close to collapse in 2011; and we now have significant closures on London, Vauxhall and Hammersmith bridges because of structural instability - with the Rotherhithe tunnel, Westway and Brent Cross structures not far behind. And that's just in London.
I know the Brent Cross Flyover had to have its expansion joints repaired which is a common issue. HE have been using the lighter traffic during the Pandemic to accelerate replacement of these on the Tees Viaduct but the structure itself is in good condition. I would be interested if you could point me to other reports on the Brent Cross Flyover as I havent come across this as being a problem. As for Hammersmith Bridge that is what you get with a 140 year old bridge designed to carry horses and carts on a wooden deck upon which even the patches have been patched.
There are a few relevant documents about TfL's asset management, such as this from 2017 - predating the Brent Cross structures work. TfL's bid to the Major Road Network included asking for funding to fix these structures (NB this is the A406/A41 junction complex).

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Re: Genoa bridge collapse

Post by Halmyre » Mon Aug 10, 2020 15:48

Are the cables in the Ganter Bridge embedded in concrete in the same fashion as the Ponte Morandi? Can't find a definitive answer.

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