Stressing Bullhead Rail on the London Underground

[_Henry_]

Hello everyone,

I know there is lots of bullhead track on the London Underground - because I often see it when I take the tube and look down at the track. As I see so much of it on the London Underground I guess that it must be stressed because surely the London Underground wouldn't want to maintain all the fish plated joints they would need if they kept their bull-headed track jointed.

I then wondered - how do they stressed bullhead rail? Is it not in a key and a chair - will this allow stressing?

I also thought - they often have wooden sleepers on the London Underground - are they allowed to stress rails in wooden sleepers?

Finally I thought, where their bullhead track is in a tunnel - perhaps they don't need to stress the rail and can just weld it altogether into long welded rail lengths? My logic was that the temperature in the tunnel won't change very much so maybe there is not requirement to stress rail at all?

Lastly, if the London Underground does allow its bullhead rail to be stressed - do they have a standard for doing this? (I think, but I might be wrong, that NR does not allow its bullhead rail to be stressed and it is always jointed on the National Network).

 

[Dstock7080]

It was stressed/de-stressed about twice a year by a gang of workers removing about 5 in every 6 keys, over a long section with hand signalling reducing the train speed.

I have not seen this practice for many years and suggest the introduction of sliding expansion joints has eliminated this.

 

[furnessvale]

Hello everyone,

I know there is lots of bullhead track on the London Underground - because I often see it when I take the tube and look down at the track. As I see so much of it on the London Underground I guess that it must be stressed because surely the London Underground wouldn't want to maintain all the fish plated joints they would need if they kept their bull-headed track jointed.

I then wondered - how do they stressed bullhead rail? Is it not in a key and a chair - will this allow stressing?

I also thought - they often have wooden sleepers on the London Underground - are they allowed to stress rails in wooden sleepers?

Finally I thought, where their bullhead track is in a tunnel - perhaps they don't need to stress the rail and can just weld it altogether into long welded rail lengths? My logic was that the temperature in the tunnel won't change very much so maybe there is not requirement to stress rail at all?

Lastly, if the London Underground does allow its bullhead rail to be stressed - do they have a standard for doing this? (I think, but I might be wrong, that NR does not allow its bullhead rail to be stressed and it is always jointed on the National Network).

I doubt there is any need to destress CWR inside a long tunnel section like the underground. Leave the rails where they are to be installed and they will naturally take up the ambient temperature.

Having said that, removal of fishplated joints gets rid of a maintenance requirement irrespective of temperature.

A second consideration is that, over time, rails tend to roll out to longer than original length like being in a rolling mill. Even with jointed track we used to lose fished joints gaps and eventually had to regain them by cutting one bolt hole off the rails and pulling back the rails to regain the joint gaps. How many rail lengths you had to pull back until you had lost the large gap you created was sometimes in the lap of the gods.

 

[godfreycomplex]

I doubt there is any need to destress CWR inside a long tunnel section like the underground. Leave the rails where they are to be installed and they will naturally take up the ambient temperature.

Having said that, removal of fishplated joints gets rid of a maintenance requirement irrespective of temperature.

A second consideration is that, over time, rails tend to roll out to longer than original length like being in a rolling mill. Even with jointed track we used to lose fished joints gaps and eventually had to regain them by cutting one bolt hole off the rails and pulling back the rails to regain the joint gaps. How many rail lengths you had to pull back until you had lost the large gap you created was sometimes in the lap of the gods.

Learn something new every day!

 

[Ploughman]

The big problem when stressing BH rail is the wear or Gall in the underside of the rail at the chair locking it together.
You can try jacking and dropping the rail but you must check the tell tales and gauge readings and that you get the expected readings. You may need to respace sleepers especially on longer pulls.
Stressing in Tunnels is not normally carried but if new rail it should be left to acclimatise before installation.
In longer tunnels you only stress into the tunnel a distance of 40m.