If tracks buckle

[hooverboy]

Excellent description, how do you establish the SFT of an existing site or do you have to cut it?

more to the point, why don't the rail manufacturers temperature cycle the rails prior to delivery...as steel is not perfectly elastic, this would drastically reduce some of the problems with excessive expansion/contraction as most of it will be "worked out"

 

[edwin_m]

more to the point, why don't the rail manufacturers temperature cycle the rails prior to delivery...as steel is not perfectly elastic, this would drastically reduce some of the problems with excessive expansion/contraction as most of it will be "worked out"

I don't think it works like that - the amount of expansion doesn't change with the number of cycles. "Work hardening" can reduce the brittleness of raw iron, but even if that applied to the steels in question it would benefit in cold weather not hot weather.

 

[Bald Rick]

Excellent description, how do you establish the SFT of an existing site or do you have to cut it?

You used to have to cut the rail, but I gather there is now some clever kit that can measure rail stress in situ.

Thanks for the fascinating replies @Bald Rick and others.

So is recent works the reason why New Malden and some line section of line between Euston and Milton Keynes have speed restrictions but not other parts of the south east?

The disruption notice for Euston to Milton Keynes doesn't mention Southern, so is it south of Wilesden Junction?

I find this type of discussion fascinating.

I don’t know, but I would be very surprised if this wasn’t the case on the WCML. Weybridge is most likely to be that also, but could be due to the type of pointwork there.

Presumably on the WCML it is on the fast lines, therefore Southern wouldn’t be affected?

more to the point, why don't the rail manufacturers temperature cycle the rails prior to delivery...as steel is not perfectly elastic, this would drastically reduce some of the problems with excessive expansion/contraction as most of it will be "worked out"

Have absolute faith that the hundreds of engineers and metallurgists who have been studying this subject for the last two centuries have arrived at a process for steel production and treatment that offers the very best combination of malleability, strength, durability and expansive properties in the rail application.

 

[Macwomble]

Thanks @Bald Rick....a fascinating insight.

 

[HowardGWR]

Regarding the overnight placing of temporary speed limit boards, could variable speed posts be installed which were fed their display parameters from remote (or local) transmitters, thus avoiding the need for the 'lowest speed envisaged' restriction applying throughout the whole day?

 

[Bald Rick]

Regarding the overnight placing of temporary speed limit boards, could variable speed posts be installed which were fed their display parameters from remote (or local) transmitters, thus avoiding the need for the 'lowest speed envisaged' restriction applying throughout the whole day?

As speed restriction boards are, technically, part of the signalling system, anything that can change the meaning of the message it displays, and where that change of meaning requires drivers to take different action, it must either be proved back at the controlling signalbox*, or have sufficient warning such that a driver could stop short of it. Happily, ETCS resolves this.

* this is not just a railways thing either. You will notice that on managed motorways, every gantry that has variable speed limit signs has CCTV cameras in rear which the controllers can use to check the signs are displaying the signs they should. And for those with speed cameras on, there is a further set of HD cameras about 1-200metres in rear that will take a picture of you before you get to the speed cameras with the signs all lit up showing the speed limit you are supposed to be observing.

 

[Joseph_Locke]

You used to have to cut the rail, but I gather there is now some clever kit that can measture rail stress in situ.

It's called Verse testing, which measures variations in the force required to slightly deflect a short length of unclipped rail.

 

[AndrewE]

I don't think it works like that - the amount of expansion doesn't change with the number of cycles. "Work hardening" can reduce the brittleness of raw iron, but even if that applied to the steels in question it would benefit in cold weather not hot weather.

I agree that thermal cycling has nothing at all to do with aging.
I suspect that most people don't realise that, as long as you stay within its elastic limit, steel can be bent an infinite number of times - hence its use for springs etc. On the other hand as I understand, it aluminium alloys age and work-harden (i.e. become brittle) even when stressed (probably the wrong word) below any elastic limit, hence the limited life of airframes etc.

 

[Macwomble]

Talking of buckled rail.......just come across this on the NR web site.

https://www.networkrailmediacentre....s-track-temperatures-buckle-rail-at-carlisle#

Friday 29 Jun 2018

49 degrees Celsius track temperatures buckle rail at Carlisle
Route:
London North Western
Temperatures approaching 50 degrees Celsius are usually reserved for Death Valley in California or certain parts of the Middle East - not the north of England.

But yesterday as the air temperatures in Cumbria hit the mid to high 20s, the sun-baked tracks north of Carlisle railway station hit 49 degrees Celsius.

This caused the rails to expand and bend slightly in their settings, as shown in the photograph taken by a Network Rail engineer.

Ian Joslin, head of Network Rail’s Carlisle delivery unit, said: “We maintain our rails to withstand fluctuations in temperature so they flex as little as possible. However sustained baking by the sun can occasionally lead to steel rails buckling, like they did yesterday at Carlisle. When this happens we slow down trains to keep everyone safe.”

Services were temporarily restricted from using the affected portion of track. Network Rail engineers monitor track temperatures continually, but even more keenly during heat waves.

For more information on how tracks behave in hot weather please visit: https://www.networkrail.co.uk/runni...er-the-railway/delays-explained/buckled-rail/

 

[Joseph_Locke]

So, badly maintained jointed bullhead on wood - nuff said.

 

[AndrewE]

Interesting picture... I note the wooden sleepers (shallower and lighter than concrete) and no ballast shoulders to help keep them in line.
JL: can you see that it's badly maintained? and is Bullhead rail more vulnerable? I would have though that jointed rail should be better in the circumstances, given that the joints will allow a measure of expansion?

 

[Ploughman]

Is it still the case in standards, that Jointed track has no heaped stone at sleeper ends?

 

[Joseph_Locke]

Is it still the case in standards, that Jointed track has no heaped stone at sleeper ends?

It is, but that doesn't mean you can't.

Interesting picture... I note the wooden sleepers (shallower and lighter than concrete) and no ballast shoulders to help keep them in line.
JL: can you see that it's badly maintained? and is Bullhead rail more vulnerable? I would have though that jointed rail should be better in the circumstances, given that the joints will allow a measure of expansion?

Jointed track is called so because it has joints in it, nominally every 18.288 metres. These are made specifically so that the rails can expand and contract. If they can't, the track will buckle, particularly if the track structure (bull head rail, which is weak in lateral bending plus lightweight wood sleepers, dodgy chairscrew grip, no ballast shoulder, seized steel keys, etc.) isn't up to resisting it. They can fail because the gap isn't maintained (closed at this kind of temperature, but 6mm open at (IIRC) zero degrees), the plates have seized to lack of oiling, the bolts are too tight or someone's gone berserk with the rail anchors*. It's buckled, so it's badly maintained.

* or the rails are too long ...

 

[bishdunster]

Funny this new fangled stuff, never heard of rail in 19.288 metre lengths, standard lengths were 30ft, 39ft American WWII imports, 45ft and 60ft lengths !

 

[AndrewE]

Jointed track is called so because it has joints in it, nominally every 19.288 metres. These are made specifically so that the rails can expand and contract.

I thought it was because of maximum steel billet size and handling issues (so it's no coincidence that old freight wagons are roughly 60 feet long.) Which is why rails were lengthened to 120 ft when steel, rolling and production/handling technology allowed. I remember a visit to Castleton rail welding depot for a totally different reason when I was told about the modifications they had made as a consequence of Workington producing 120-ft lengths. Maybe it was in RailNews or somewhere, they had to find a way of the opposite of telescoping the production line because the welds were arriving at downstream workstations too hot to work, (because they moved 120 feet per weld rather than 60.) I believe that the BR metallurgists or others people developed a spray-cooling system that did the job but wasn't so severe that it interfered with other characteristics, like unwanted hardness and embrittlement.

 

[Joseph_Locke]

Funny this new fangled stuff, never heard of rail in 19.288 metre lengths, standard lengths were 30ft, 39ft American WWII imports, 45ft and 60ft lengths !

Curses - typo - 18.288m (corrected).

I thought it was because of maximum steel billet size and handling issues (so it's no coincidence that old freight wagons are roughly 60 feet long.) Which is why rails were lengthened to 120 ft when steel, rolling and production/handling technology allowed. I remember a visit to Castleton rail welding depot for a totally different reason when I was told about the modifications they had made as a consequence of Workington producing 120-ft lengths. Maybe it was in RailNews or somewhere, they had to find a way of the opposite of telescoping the production line because the welds were arriving at downstream workstations too hot to work, (because they moved 120 feet per weld rather than 60.) I believe that the BR metallurgists or others people developed a spray-cooling system that did the job but wasn't so severe that it interfered with other characteristics, like unwanted hardness and embrittlement.

Sixty feet is big for a wagon - that's salmons and things.

Despite what BR might have thought, if you want to keep the rail gap within a sensible range, then there is an upper limit on rail length. A 18.288m long rail will use up a 6mm rail gap in a 30 degree range of temperature - the UK rail temperature for design goes from -9 to +52-ish, so it's clear that long jointed rails will suffer massive cyclic tension and or compression.

 

[AndrewE]

Curses - typo - 18.288m (corrected).
Sixty feet is big for a wagon - that's salmons and things.

Isn't this what they were built for then (rails and track panels?) Agreed, apart from Bogie bolsters for exceptional loads most old mineral wagons and vans were short-wheelbase, but surely these engineers wagons have almost always been this big?

 

[suzanneparis]

Bald Rick, many thanks again for such a thorough and very interesting post. You really are a credit to the forum.

Best wishes

 

[HowardGWR]

As speed restriction boards are, technically, part of the signalling system, anything that can change the meaning of the message it displays, and where that change of meaning requires drivers to take different action, it must either be proved back at the controlling signalbox*, or have sufficient warning such that a driver could stop short of it. Happily, ETCS resolves this.

* this is not just a railways thing either. You will notice that on managed motorways, every gantry that has variable speed limit signs has CCTV cameras in rear which the controllers can use to check the signs are displaying the signs they should. And for those with speed cameras on, there is a further set of HD cameras about 1-200metres in rear that will take a picture of you before you get to the speed cameras with the signs all lit up showing the speed limit you are supposed to be observing.

Indeed. What I was thinking, and I am sure you good people have, is that such devices under ETCS could reduce delay penalty payments by NR to TOCs considerably, by not having such lower speeds enforced before the sun 'rises above the yard arm' so to speak. The BCR for implementing these would seem to be favourable.

 

[suzanneparis]

Thinking of the World Cup, how on earth do they cope with these temperature swings in Russia. Even in Moscow the records are roughly -42C to +38. In Ulan Ude it's approx -66C and +40 (I once met a woman who lived in Ulan Ude and she told me that they sometimes have huge temperature swings in one day. So much so that people may set off to work in the morning in shorts and T shirts but need thick warm parkas and hats with ear flaps in the evening coming home from work). 106 degrees swing would be a lot to cope with. Presumably, impossible. Even the average high to low is +26C to -27C in Ulan Ude. (would they be shade temperatures).

https://en.wikipedia.org/wiki/Ulan-Ude#Climate

 

[Bald Rick]

Indeed. What I was thinking, and I am sure you good people have, is that such devices under ETCS could reduce delay penalty payments by NR to TOCs considerably, by not having such lower speeds enforced before the sun 'rises above the yard arm' so to speak. The BCR for implementing these would seem to be favourable.

No need for a ‘device’ as such; once the details of the restriction are known, it is programmed into the ETCS system and it just goes straight to the in cab display. Indeed there is a way of doing something similar with SSI signalling today by restricting the aspects, although this can’t guarantee the speed trains are driven at.

Thinking of the World Cup, how on earth do they cope with these temperature swings in Russia. Even in Moscow the records are roughly -42C to +38. In Ulan Ude it's approx -66C and +40 (I once met a woman who lived in Ulan Ude and she told me that they sometimes have huge temperature swings in one day. So much so that people may set off to work in the morning in shorts and T shirts but need thick warm parkas and hats with ear flaps in the evening coming home from work). 106 degrees swing would be a lot to cope with. Presumably, impossible. Even the average high to low is +26C to -27C in Ulan Ude. (would they be shade temperatures).

https://en.wikipedia.org/wiki/Ulan-Ude#Climate

Given that climate, they may well be out restressing the rail twice a year in Spring / Autumn with different SFTs; probably around 27C for May-September, and somewhere not too far above 0C for the rest of the year.

 

[Bald Rick]

It's called Verse testing, which measures variations in the force required to slightly deflect a short length of unclipped rail.

Thank you, and I remember it now (it’s been a while!)

 

[edwin_m]

No need for a ‘device’ as such; once the details of the restriction are known, it is programmed into the ETCS system and it just goes straight to the in cab display. Indeed there is a way of doing something similar with SSI signalling today by restricting the aspects, although this can’t guarantee the speed trains are driven at.

I think the aspect restriction in SSI can only be done by the technician, although it would be possible to add more data so the signaller could operate a control that restricted all signals in a particular area to no better than single yellow for example.

It would also be possible to add switchable speed "boards", probably similar to theatre route indicators or the speed indications in German signalling which I think are clear enough to be visible to approaching trains at any speed. These could even, in theory, be enforceable by extra TPWS loops. However it would need a change to the rule book and would obviously be quite a lot of safety-critical alteration especially if the nearby trackside modules don't have spare connections.

 

[infobleep]

I don’t know, but I would be very surprised if this wasn’t the case on the WCML. Weybridge is most likely to be that also, but could be due to the type of pointwork there.

Presumably on the WCML it is on the fast lines, therefore Southern wouldn’t be affected?

When I first read about the disruption my initial thought was is there disruption affecting Govia Thameslink Railway but they just have reported it. Rather than actually thinking this issue isn't occurring on any lines affecting those services.

Obviously the latter did cross my mind too but the former was first. I guess that's due to my cynicism of GTR. I immediately think what haven't they done rather than it's great for them for them that they are not affected by this.

 

[suzanneparis]

No need for a ‘device’ as such; once the details of the restriction are known, it is programmed into the ETCS system and it just goes straight to the in cab display. Indeed there is a way of doing something similar with SSI signalling today by restricting the aspects, although this can’t guarantee the speed trains are driven at.



Given that climate, they may well be out restressing the rail twice a year in Spring / Autumn with different SFTs; probably around 27C for May-September, and somewhere not too far above 0C for the rest of the year.

Many thanks Bald Rick, that's interesting. Especially considering the extent of their network. All the best

 

[Mag_seven]

So, badly maintained jointed bullhead on wood - nuff said.

What's more at a key station on the WCML - needs urgent renewal I would suggest!

 

[181]

Given that climate, they may well be out restressing the rail twice a year in Spring / Autumn with different SFTs; probably around 27C for May-September, and somewhere not too far above 0C for the rest of the year.

My recollection from a Trans-Siberian journey in 2007 is that much of the route was still equipped with jointed rail. This though raises the question of how that copes with the temperature range without having very large gaps at the rail joints in winter. How well do fishplated joints cope with being under tension? (John Snell's history of the Romney, Hythe and Dymchurch says that when the track there was in a poor state in the 1960s and 70s, it was common for joints to pull apart on cold nights when the bolts broke, but I would hope that well-maintained joints would be stronger).

 

[HSTEd]

Do slab track systems suffer from buckling?
I have to imagine that they hold the rail far more securely than a traditional ballasted system - but if they were to buckle I can see it causing substantially more damage.

 

[30907]

What's more at a key station on the WCML - needs urgent renewal I would suggest!

Looks to be on the up Goods just south of Kingmoor - Edit: but isn't, sorry.

 

[Joseph_Locke]

Do slab track systems suffer from buckling?
I have to imagine that they hold the rail far more securely than a traditional ballasted system - but if they were to buckle I can see it causing substantially more damage.

Whilst certain recent installations (Not on NR lines) have left a little be desired, provided the slab is rigid laterally and the bolts holding the rail down are strong enough there'd be no mechanism for slab track to buckle. It's notable that, leaving aside the "heel-kick" in 113A vertical layouts with stress transfer blocks, buckles are pretty much unheard of where there are three or more rails on a bearer, even in wood layouts on ballast.