Why are rails jointed between sleepers?

n97 mini

and not on them?

Losty Dublin

If you mean why are sleepers placed across and not under the rails, it's down to two reasons. The criss-cross way we see nowadays holds the rails in place far more firmly and securely; this means that the gauge of the rails will stay in place and is very unlikely to slip out of place. Also, the weight of the trains traveling on the rail is spread move evenly so erosion, vibrations and drainage are more spread out and less damaging in the long run. Several ways of laying track were used in the early days of building lines including length way sleepers but trial and error saw to it that the current system was more favored as a rule.

if you mean why a rail isn't placed directly onto a sleeper, using a chair or plate for the rail to sit on is again far more reliable and firm than pegging a track onto a sleeper, especially if it's carrying heavier trains. Some narrow gauge lines did make do without them but this was due to they carrying lighter and less frequent trains and plain old cost cutting.

In both cases there are other reasons in play here which I know others will add to; they are what spring to mind here.

n97 mini

Thanks for answering, but I mean like in this picture.

I was noticing in Connolly that the ends of the rails flex downwards quite a lot when a train goes over the joint. If the joint was on a sleeper it wouldn't happen.

Louche Lad

If it was on a sleeper, it might break the sleeper, I suppose is an answer. But I'm not sure that's a useful answer because I suppose rails ought not to flex so much. But I'm not an engineer.

I noticed when I used to wait for trains at Clapham Junction in London some years ago that some joints would flex quite alarmingly — maybe 10 cm at the ends.

Davy

n97 mini wrote: »

Thanks for answering, but I mean like in this picture.

I was noticing in Connolly that the ends of the rails flex downwards quite a lot when a train goes over the joint. If the joint was on a sleeper it wouldn't happen.

No room to tie the sleeper to the track due to joint plate to hold the two lengths of track

steamengine

Seems like a good idea to me, but from an engineering point of view it is obviously not considered essential. The fishplates should form a snug fit on either side of the rail and counteract this movement.

Here's an example of another type of expansion joint, used with continuous welded rail that is supported by sleeper chairs.

link

noelfirl

In the case of continuous welded rail, would there be a risk that the flash welding would crack concrete sleepers if done on top of them or in the case of wooden sleepers, set them on fire?

Judgement Day

Is that the Cavan & Leitrim Railway in the photo?

I have seen the joint on sleepers - in sidings - but I should imagine it's down to expansion. It's odd, despite having laid plenty of track I did it in the time honoured fashion without question. The annual unbolting and greasing of all the fishplates on the C&L used to be one of our favourite tasks. I doubt they bother doing it these days.

Losty Dublin

N97, the join between tracks needs to be between sleepers in order to allow a little latitude in bending and better maintainance. Jointed track has a little overhand for this reason. Were it attached to a sleeper then the plate would loosen from the sleeper over time and ultimately wear down the sleeper, the rail end and the ballast underneath it; a well fitted will have little to no wear in time as Steamengine says.

Noelfitz, there is zero risk in any damage to sleepers by welding or cutting on site. Wood sleepers treated with tar or creosote have a very high resistance to heat so you'd nearly need melt the welding torch before the wood

Steamengine, the flat rails used today expand a little less than bull heads as the bed diffuses a bit more heat so expansion joints are less common; points also help lessen the need of them but they do turn up here and there.

JD, that's not a C+L joint. You know well they use wet turf and seat foam on their track

steamengine

Losty Dublin wrote: »

............
Steamengine, the flat rails used today expand a little less than bull heads as the bed diffuses a bit more heat so expansion joints are less common; points also help lessen the need of them but they do turn up here and there...............

Maybe so to an extent, but on one of those baking hot summer days the whole 'caboodle' will heat up. The thermal coefficient of expansion of steel doesn't distinguish between different rail profiles and while the frequency of expansion joints on CWR is way less, the allowed expansion is 'inches' rather than just a 'fraction of an inch' as can be seen from the photos above. Those angled sliding joints eliminate the old familiar 'clickety click' noise, however they still exist at regular intervals.

Losty Dublin

steamengine wrote: »

Maybe so to an extent, but on one of those baking hot summer days the whole 'caboodle' will heat up. The thermal coefficient of expansion of steel doesn't distinguish between different rail profiles and while the frequency of expansion joints on CWR is way less, the allowed expansion is 'inches' rather than just a 'fraction of an inch' as can be seen from the photos above. Those angled sliding joints eliminate the old familiar 'clickety click' noise, however they still exist at regular intervals.

That is true; there is always some expansion but the rail diffuses the heat a lot better from the flat bottom of rail so it's less of an issue than it used to be. Also, todays heavier rails absorb the heat better via a higher density so there is less expansion to deal from that end.

So my track laying friends tell me at least

steamengine

Losty Dublin wrote: »

That is true; there is always some expansion but the rail diffuses the heat a lot better from the flat bottom of rail so it's less of an issue than it used to be. Also, todays heavier rails absorb the heat better via a higher density so there is less expansion to deal from that end.

So my track laying friends tell me at least

Apparently CWR is continuous to all intents and purposes, the track is stretched either by heat or mechanically when it's being laid. This leaves it in a natural state of tension apparently, but even if it does heat up and start to expand it is restrained by the clips, heavy sleepers and extra ballast.

I'd be interested in finding out more so I'll go by your track laying friends - they're the guys that know !!!

Victor

Having the joint between two sections of a rail on a sleeper would mean that the rail would be somewhat compromised by having all the bolt holes at more or less the same point - a bit like 'tear along the dotted' line on a form. The risk would be more broken rails.

In laying track panels, it is easier to have the joints between panels - no messing about in trying to attach a rail from one panel to a sleeper on the adjacent panel.