Genoa bridge collapse

[Halmyre]

I came over the Erskine bridge on Friday, which seems to be single cable cable-stayed.

I imagine someone might have ordered up a sudden inspection of the stays in the last few days.

The bridge was strengthened during its build when a similar box-girder design collapsed in Australia. It also survived when someone clouted it a few years back while floating an oil-rig out to sea. I don't know if it's still nowhere near carrying the amount of traffic it was designed for.

[B9127]

Interesting that Autostrade the bridge operator is a company called Atlantia which in turn is controlled by the holding company for the Benetton clothing family.

[KeithW]

That may be so, but if the design cases used for analysis didn't expect these loads to be present then there would be no reinforcement to resist them and none of us know whether there should have been more reinforcement there than there was.
The knowledge and standards of the time were fairly primitive compared to today's knowledge and I would expect the investigators to be looking far further back up the design chain and examining the standards to which the structure was designed and constructed, the load cases used in analysis, how the bridge has been maintained or strengthened over the years with e.g. higher axle weights and what features would have been present in the bridge built to today's standards that were missing in the design.

A couple of questions come to my mind,
How was the integrity of each of the single cables or anchorages to be guaranteed?
What would be the outcome if a cable or anchorage failed?

I would suggest they will examine closely the arrangements surrounding what appears to be a bridge with several possible single points of failure at the cable anchorages and how the owning authority managed the inspection, maintenance and renewal to ensure that any one of these failures was not triggered.

It is interesting to see how generally the cable stayed designs have evolved away from these large single cables to multi anchorage cables (e.g. Millau Bridge, Dartford Crossing) where the loss of anchorage on one cable is unlikely to lead to complete collapse of the structure but (merely) a degradation in serviceability.

The anchorages and towers on the bridge had the barriers that protect them from vehicle impact replaced some years ago and the cables were provided with a permanent gantry to allow inspection and repainting to be done as required. You are quite correct that modern practice is to use multiple stays but the structural analysis required to to get the design right was in the past excessive. There is some experience with impact loads since in 1996 the bridge survived being struck by an oil rig being towed down the Clyde !

http://hbsscotland.co.uk/wp-content/upl ... -STUDY.pdf
http://www.heraldscotland.com/news/1211 ... re_damage/

One of the big concerns with the Morandi Bridge was that encasing the cable stays in concrete meant that inspecting their condition was difficult if not impossible.

As for the rebar issue I would note that this is a seismically active region and being somewhat familiar with how much rebar is used in construction in the San Francisco Bay area I would expect to see more of it. Buildings in Genoa have to meet requirements for resistance to earthquakes but this bridge predated that. In California they replaced the eastern section of the Bay Bridge as result of concerns about such matters. Poorly reinforced concrete has low resistance to lateral forces and this was a tall slab sided structure. I would guess that one active line of enquiry would be to look at wind forces during the bad weather at the time of the collapse.

[roadtester]

This German newspaper report is saying that inspections have shown that the rest of the viaduct is in danger of falling down as well:

https://www.zeit.de/gesellschaft/zeitge ... mpaign=ref

[KeithW]

This German newspaper report is saying that inspections have shown that the rest of the viaduct is in danger of falling down as well:

https://www.zeit.de/gesellschaft/zeitge ... mpaign=ref

There was a piece in the New Civil Engineer that indicated that investigators were focusing on the stays. Apparently when they inspected the collapsed bridge they found the cables and steel fittings inside the concrete sheath to be very corroded. It was also reported that CCTV showed the concrete breaking off the sheathing immediately before the collapse indicating a failure of the cables. Of course by sheathing the cables in concrete they became virtually impossible to inspect. On the 2 towers that survive external steel plates have already been fitted to reinforce the stay structure but not on the section that failed. They also seem to have found extensive chloride corrosion of reinforcing bars elsewhere in the structure. Genoa is a very high risk area for such structures as chlorine ions are freely available both from the sea and industrial pollution. At least one of the other piers has moved since the collapse and is now actually touching an apartment building built underneath it.
https://www.thelocal.it/20180823/commit ... demolition

The same problems affected a number of M1 and M6 concrete viaducts and the A14 Huntingdon viaduct. The difference is that these were fitted with monitoring systems, repairs were made to expansion joints (the Thelwall Viaduct for example) to minimise chloride penetration and corrosion control measures implemented.
https://flexcrete.com/reinstatement-of- ... ay-bridge/

The Huntingdon Viaduct was of strengthened, an acoustic monitoring system fitted to detect tendon breaks and it will be demolished when the new A4 opens.

[Steve in Cumbria]

Around 10 buildings are going to be demolished to allow the rest of the bridge to be brought down (not sure if this means just the 2 remaining towers to the east or the whole thing).

So those blocks of flats you can see on Google Streetview with the eaves notched out to accommodate the deck supports are going. It means that 550-odd people will be displaced and rehoused temporarily until permanent accommodation is found. Due to fears about the condition of tower 10, they are no longer able to access their flats to retrieve belongings.

Motorway operator ASPI has to submit plans for the bridge demolition within a matter of days.

-------------------

Some clever person has analysed the CCTV footage of the bridge collapse- based on the reflections cast onto the wet flat roof of an industrial building immediately to the south of tower 9.

LINK

[Viator]

There was a piece in the New Civil Engineer that indicated that investigators were focusing on the stays. Apparently when they inspected the collapsed bridge they found the cables and steel fittings inside the concrete sheath to be very corroded. It was also reported that CCTV showed the concrete breaking off the sheathing immediately before the collapse indicating a failure of the cables. Of course by sheathing the cables in concrete they became virtually impossible to inspect.

Can anyone who knows about such things explain why it was ever thought to be a good idea in the first place to sheathe the cables in concrete?

[KeithW]

There was a piece in the New Civil Engineer that indicated that investigators were focusing on the stays. Apparently when they inspected the collapsed bridge they found the cables and steel fittings inside the concrete sheath to be very corroded. It was also reported that CCTV showed the concrete breaking off the sheathing immediately before the collapse indicating a failure of the cables. Of course by sheathing the cables in concrete they became virtually impossible to inspect.

Can anyone who knows about such things explain why it was ever thought to be a good idea in the first place to sheathe the cables in concrete?

Puts Italian Hat on

"Hey It looks sleek and modern right !"

There again we used prestressed tendons embedded in concrete for the A14 Huntingdon Viaduct and will have to full it down. Concrete was the hip material at the time, it was only later we discovered the problems. The sad thing of course is the Romans worked it out 2 millenia ago. There are bridges built with concrete cores by the Romans all over their Empire which are still as strong as when they were built. The Ponte di Tiberio in Rimini was built in 20 AD and is still carrying vehicular traffic , in WW2 the Germans tried and failed to demolish it with high explosives. Most are faced with stone or marble but the core is Roman concrete. Only in the last 30 years have we begun to make concrete that is as good as theirs.

[Chris5156]

There was a piece in the New Civil Engineer that indicated that investigators were focusing on the stays. Apparently when they inspected the collapsed bridge they found the cables and steel fittings inside the concrete sheath to be very corroded. It was also reported that CCTV showed the concrete breaking off the sheathing immediately before the collapse indicating a failure of the cables. Of course by sheathing the cables in concrete they became virtually impossible to inspect.

Can anyone who knows about such things explain why it was ever thought to be a good idea in the first place to sheathe the cables in concrete?

One piece I've read about the bridge collapse referred to this as an attempt to protect the cables from the sea air and thus reduce the chances of corrosion.

[KeithW]

There was a piece in the New Civil Engineer that indicated that investigators were focusing on the stays. Apparently when they inspected the collapsed bridge they found the cables and steel fittings inside the concrete sheath to be very corroded. It was also reported that CCTV showed the concrete breaking off the sheathing immediately before the collapse indicating a failure of the cables. Of course by sheathing the cables in concrete they became virtually impossible to inspect.

Can anyone who knows about such things explain why it was ever thought to be a good idea in the first place to sheathe the cables in concrete?

One piece I've read about the bridge collapse referred to this as an attempt to protect the cables from the sea air and thus reduce the chances of corrosion.

Its possible I suppose but if so it didn't work. The Wadi El Kuf bridge in Libya was closed for safety reasons last year
https://africatimes.com/2018/08/15/liby ... ety-fears/

The Venezuela bridge is also in a marine environment but it uses exposed steel cables which can at least be inspected.
http://www.globalconstructionreview.com ... enezuelan/

One thing we have relearned is that inspection is a key factor when it comes to safety.

[Chris5156]

Can anyone who knows about such things explain why it was ever thought to be a good idea in the first place to sheathe the cables in concrete?

One piece I've read about the bridge collapse referred to this as an attempt to protect the cables from the sea air and thus reduce the chances of corrosion.

Its possible I suppose but if so it didn't work. The Wadi El Kuf bridge in Libya was closed for safety reasons last year
https://africatimes.com/2018/08/15/liby ... ety-fears/

No, quite right - if it was the intention it was a grave miscalculation because it prevented any attempt to inspect them.

[Steve in Cumbria]

I may be mistaken, but on Google Streetview it looks like a grey-ish paint was applied to the stays- perhaps an earlier attempt at reducing water ingress?

Though there was still spalling of the concrete and rust stains on the stays suggesting ongoing corrosion of the internal cables.

[Owain]

This German newspaper report is saying that inspections have shown that the rest of the viaduct is in danger of falling down as well:

https://www.zeit.de/gesellschaft/zeitge ... mpaign=ref

So that's referring to the bit on stilts to the west of the collapsed section (the 'viaduct'), as opposed to the remaining cable-stayed section to the east?

[Bryn666]

It sounds as if the viaduct is causing concern as well, yes.

That's just made the whole thing a lot more tricky to fix. Years of disruption instead of months; not good if you work in Genoa and rely on the transport links.

[Owain]

It sounds as if the viaduct is causing concern as well, yes.

That's just made the whole thing a lot more tricky to fix. Years of disruption instead of months; not good if you work in Genoa and rely on the transport links.

It's not only bad news for people who live and work there; if you are travelling from the A26 to the A12, Genoa can be bypassed via the A7, but the A7 through the Ligurian hills is an unbelievably twisty D2M with an 80km/h limit that is in some places barely achievable due to the nature of the curves and the number of trucks negotiating them. And anybody travelling from the A10 has no way to bypass the collapsed section without leaving the autostrada.

Genoa is also the main port connecting Corsica, Sardinia and Sicily to northern Italy. The place must be in chaos.

[Fenlander]

Looking on google maps traffic there's a lot of road closed as expected but surprisingly little red traffic, its mostly green.

From the satellite shots it looks like the railways there are not what they used to be so presumably there's a bit more room on the ground to use for intermediate supports or an entirely different design?

[Owain]

Looking on google maps traffic there's a lot of road closed as expected but surprisingly little red traffic, its mostly green.

Thinking about it a bit more, all of the autostrade around Genoa are toll roads. You can start a journey on the A10, the A26 or the A7 (or even the A21, the A4 or the A5) and drive to the A12 without passing through a toll plaza and leaving the tolled section.

Perhaps, because they are tolled, they are used less than un-tolled motorways, and the loss of one is therefore less catastrophic to traffic flow than we might expect if it happened here?

[murphaph]

I also think the original design was constrained by the railway to a much greater extent than would be the case today. I suspect a standard box girder bridge will replace the entire structure.

[Reading]

Can anyone who knows about such things explain why it was ever thought to be a good idea in the first place to sheathe the cables in concrete?

One piece I've read about the bridge collapse referred to this as an attempt to protect the cables from the sea air and thus reduce the chances of corrosion.

Its possible I suppose but if so it didn't work. The Wadi El Kuf bridge in Libya was closed for safety reasons last year
https://africatimes.com/2018/08/15/liby ... ety-fears/

The Venezuela bridge is also in a marine environment but it uses exposed steel cables which can at least be inspected.
http://www.globalconstructionreview.com ... enezuelan/

One thing we have relearned is that inspection is a key factor when it comes to safety.

My wife did an engineering degree and her supervisor was also an independent consultant to the north sea oil industry - therefore she was steered towards her final year project being "non destructive testing of steel wire ropes - a study" - at the time all steel wire rope used in the north sea was replaced on a fixed time basis which was deemed safe, if they could develop a way to test the ropes in situ it would hopefully allow more accurate assessment of when they needed changing and therefore huge money savings . She investigated a number of different options including spending 2 mths in Stuttgart at the uni there but basically at the end of it concluded that as they are made up of so many differing lengths of strands it was a near impossible task with the computer processing power at the time . I believe the methods looked at included, measuring conductivity, ultrasound, magnetic flux and variation in diameter over time. I believe they now use and also the magnetic flux method but it is >25 yrs since she was at uni

[KeithW]

My wife did an engineering degree and her supervisor was also an independent consultant to the north sea oil industry - therefore she was steered towards her final year project being "non destructive testing of steel wire ropes - a study" - at the time all steel wire rope used in the north sea was replaced on a fixed time basis which was deemed safe, if they could develop a way to test the ropes in situ it would hopefully allow more accurate assessment of when they needed changing and therefore huge money savings . She investigated a number of different options including spending 2 mths in Stuttgart at the uni there but basically at the end of it concluded that as they are made up of so many differing lengths of strands it was a near impossible task with the computer processing power at the time . I believe the methods looked at included, measuring conductivity, ultrasound, magnetic flux and variation in diameter over time. I believe they now use and also the magnetic flux method but it is >25 yrs since she was at uni

When it comes to cables for suspension and stayed bridges as well as pre-stressed tendons in concrete structures one technique now used is acoustic, basically microphones listen for the distinctive sounds of strands within the cable snapping. Such a system was installed on the A14 Huntingdon Viaduct. It was also used on the tendons in concrete pressure shells for Advanced Gas Cooled reactors although there they were more concerned with degradation by fast neutrons than corrosion. Last I heard no problems had been detected. The tendons on the AGR's at Dungeness B terminated on the outside of the shell/radiation shield so could be replaced if necessary.