Forth Replacement Crossing

[A303Chris]

Good BBC article earlier today about ways of stopping Ice falling off bridges.

However when you see the damage to the windscreen of the driver hit by ice, you can wee why they closed it on terms of safety

[KeithW]

Good BBC article earlier today about ways of stopping Ice falling off bridges.

However when you see the damage to the windscreen of the driver hit by ice, you can wee why they closed it on terms of safety

I would be wary of drawing too many conclusions from the Vancouver example as it has a moderate oceanic climate with an average low temp in Feb of 2.7 C and its at 49 deg latitude - about the same as Jersey

[KeithW]

I suppose you could fit another main cable without removing the existing one and move over one at a time but it would be completely impractical for most bridges (not being able to anchor in the same place would introduce uneven loading whilst the work is going on and there'll probably be no way the towers could hold two cables in place, even temporarily). You could of course close the bridge completely, remove the deck, and replace the cables but that's a large chunk of just building a new bridge.

The big problem with a conventional suspension bridge is that the lateral load keeping the cables taut is carried by the huge concrete anchorages at both ends of the bridge so not only would you have to remove the deck and cables but also attach the new cable to the concrete anchorages which are 160 feet long, 132 feet high and weigh 90,000 tons each.

The Humber Bridge has anchorages with separate attachment points for the cables like this so it would be feasible but the question then becomes do you trust 50 year old uninspectable anchorages for your new bridge ?

[nowster]

Wasn’t this a similar reason that the original Emley Moor tv mast collapsed??

Some info on the Emley Moor TV mast collapse:

http://tx.mb21.co.uk/emley/index.php
http://tx.mb21.co.uk/emley/emley.php
http://tx.mb21.co.uk/emley/eyewitness/index.shtml
http://tx.mb21.co.uk/emley/emley-memories.php
http://tx.mb21.co.uk/gallery/gallerypag ... &pageid=68

[Nwallace]

Are the angled 'stays' on a cable stay bridge more prone to icing that the vertical hangers and (mostly) horizontal suspension cable on the old bridge?

Well there was an incident where falling ice damaged a number of cars on the Severn Crossings in 2009. It also seems there have been problems from time to time in the USA, mainly in the mid west where icing conditions are more frequent.
https://www.newcivilengineer.com/archiv ... 0-08-2016/
http://www.engineeringnewworld.com/?p=440

ISTR they had to close the Newport Bridge across the Tees a couple of years ago for the same reason. In general it happens when the surface temperature is very low and it rains so the rain freezes onto any surface. The problems come when it thaws and large lumps of ice start coming down from on high.

That NCE article has a great quote in it:

“People turn up to the US Cold Regions Lab and expect that they’re going to get a solution. And it’s like the Kubler-Ross model for five stages of mourning: first there’s denial… But you have to manoeuvre to admitting that there is no solution, and it then becomes a question of how to manage it in the best way,” says Nims.

That from a man who at that point had been focused on the problem for roughly 10 years.


What stands out to me is that the bridges that suffer from it; every single one of them has slightly different circumstances.

[cb a1]

That NCE article has a great quote in it:

“People turn up to the US Cold Regions Lab and expect that they’re going to get a solution. And it’s like the Kubler-Ross model for five stages of mourning: first there’s denial… But you have to manoeuvre to admitting that there is no solution, and it then becomes a question of how to manage it in the best way,” says Nims.

That from a man who at that point had been focused on the problem for roughly 10 years.

What stands out to me is that the bridges that suffer from it; every single one of them has slightly different circumstances.

Nah, there's this bloke who sells some thermal spray of some sort. He got in contact with Radio Scotland this afternoon 'cause he didn't know who to get in contact with at the Queensferry Crossing.

Bit of that on the cables and it'll be right, I'm sure

[Glen]

The leader of the opposition thinks the First Minister should be climbing the cables and pulling the ice off with her bare hands.

https://twitter.com/Jackson_Carlaw/stat ... 26434?s=19

Although, two years ago he was proud to have chaired the committee responsible for the design.
https://twitter.com/Jackson_Carlaw/stat ... 38240?s=19

[roadtester]

The articles suggest the ice isn't a structural issue but I wonder about something else mentioned in the articles Nwallace and KeithW link to, where various possible methods for combating the ice-build up are mentioned - heating elements, blowing warm air and so on.

My engineering credentials are zero, but just thinking about this as a lay person, mightn't those measures complicate the question of corrosion protection for the cable stays, which is an issue for e.g. the old bridge on the Forth?

As it happens if the air is dried it could be used to inhibit corrosion as was done on the Severn Bridge.
https://www.munters.com/en/munters/cases/severn-bridge/

Another approach could be to apply electrical heat tracing to stays was is sometimes done on pipelines, you can also purchase off the shelf wireless sensors to activate the heat tracing when needed. Having a pipeline full of solidified oil is less than ideal The Alaska

https://www.heat-trace.com/admin/news/1 ... imised.pdf
https://www.chromalox.com/en/catalog/he ... heat-trace
https://www.chromalox.com/en/catalog/he ... -solutions


One of the advantages of a cable stayed bridge is that in theory an individual cable could be replaced which is not possible with a suspension bridge main cable so in theory while you cannot replace the main suspension cable on the old Forth Bridge a corroded cable on the new crossing could be replaced.

I suspect that the frequency of serious icing is rare enough that what will happen is that sensors will be fitted to detect ice build up and if necessary close the bridge in severe conditions. This is what seems to happen with many of the US examples

Thanks - interesting.

[A9NWIL]

I suppose you could fit another main cable without removing the existing one and move over one at a time but it would be completely impractical for most bridges (not being able to anchor in the same place would introduce uneven loading whilst the work is going on and there'll probably be no way the towers could hold two cables in place, even temporarily). You could of course close the bridge completely, remove the deck, and replace the cables but that's a large chunk of just building a new bridge.

IIRC, you're right, the towers on the FRB were not strong enough to support an extra main cable as they are.

Options were a 5 year full closure, a 10 year half closure, or a replacement crossing.

Perhaps in the future if the towers and anchors are sound then replacing the cables and the decking would be a good idea.

[hat]

Drove across the old A9000 forth bridge today without realising that it’s supposedly restricted. The road markings on the slip are contradictory, can anyone confirm if the restrictions are in law and if there are fines in place? I didn’t see any obvious cameras

[Nwallace]

Yes there's a big red circle with iirc nothing in the middle and a massive plate below it with "except for"

The except for is everything not allowed no the motorway except for pedestrians, cycles and tractors, the former have lanes for them the later has to go round by Kincardine...

Sent from my BKL-L09 using Tapatalk

[Bryn666]

Yes there's a big red circle with iirc nothing in the middle and a massive plate below it with "except for"

The except for is everything not allowed no the motorway except for pedestrians, cycles and tractors, the former have lanes for them the later has to go round by Kincardine...

Sent from my BKL-L09 using Tapatalk

Unless it's changed recently there are the following signs: https://goo.gl/maps/iHpDxRnZZ3UUKpA99 and https://goo.gl/maps/2Y6Cux1ePQbPzSWP6

The latter off-slip could have been opened to all traffic to remove the pointless 800 yard gap in the M90. It's still a complete mess, up there with the A90 at Aberdeen. Transport Scotland dropped two very large balls with these jobs.

[smidget]

Yes there's a big red circle with iirc nothing in the middle and a massive plate below it with "except for"

The except for is everything not allowed no the motorway except for pedestrians, cycles and tractors, the former have lanes for them the later has to go round by Kincardine...

Sent from my BKL-L09 using Tapatalk

Unless it's changed recently there are the following signs: https://goo.gl/maps/iHpDxRnZZ3UUKpA99 and https://goo.gl/maps/2Y6Cux1ePQbPzSWP6

The latter off-slip could have been opened to all traffic to remove the pointless 800 yard gap in the M90. It's still a complete mess, up there with the A90 at Aberdeen. Transport Scotland dropped two very large balls with these jobs.

Still the same. They could do the same with the onslip and allow non motorway traffic to join at the Echline junction and onto the A90 after the A90/M90 diverge point. Part of me wonders if the short section of A90 is purely to cater for the event where all traffic is diverted across the FRB and you'd end up with non motorway traffic running onto the M90.

[haggishunter]

Part of me wonders if the short section of A90 is purely to cater for the event where all traffic is diverted across the FRB and you'd end up with non motorway traffic running onto the M90.

There was a several hour diversion via the Kincardine and Clackmannanshire bridges in January to test that out:

Traffic will initially be diverted via Kincardine Bridge from 22:00 on Friday 29 January while emergency crossovers connecting the Forth Road Bridge to the motorways on either side of the bridge are opened up.

The diversion via Forth Road Bridge is expected to be fully operational by 06:00 on Saturday morning at the latest.

All traffic will then use the Forth Road Bridge until 22:00 on Saturday night, when traffic will again be diverted via Kincardine Bridge while the motorway over the Queensferry Crossing is reopened.

[Gav]

The bridge diversion is being looked at as it takes time to get it operational - they were looking at ways to step the transition in such a way that it can be done quick without much interruption.

old bridge link to the A90 south of the bridge opened

South bound traffic take off and through the rosyth junction to allow them to pull the barrier over just south of the junction to take traffic off of the M90 to the old bridge without live traffic.

Traffic runs away from the M90 and then they move that barrier. southbound traffic is then returned to flowing along the M90 and off the temporary diversion to the old bridge. North bound traffic can then be swung over to the temporary diversion and over the old bridge and then back onto the M90 north of the bridge.

All about quick alignment and doing it with minimal disruption and safely.