Hot
OK—-that’s it. I’m officially fed up of the hot weather. It would be fine if I could just laze around with a cool drink in my hand, but working, commuting and clearing out dusty shelves and cupboards is decidedly not fun in these kinds of temperatures.
All this week, my commute has been disrupted by bending or broken rails. Leaving aside the question of why Network Rail seems to use a metal with a melting point of 30 deg Celsius (perhaps Cadbury makes the rails for them at Bournville?), cramming a lot of hot, sticky and—-above all—-late commuters on to trains and platforms does not make for happy customers.
On Thursday, I abandoned the train at New Street Station because it was clear I wasn’t going to get much further very quickly, and tried to head out of the station to catch a bus. I left the platform by the escalators, and there were so many people on the concourse at the top, that there was a cartoon pile-up. People stepping off the escalator had nowhere to go but to crash into the backs of those in front of them. Ah, what fun!
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Precisely why if I can't walk there or go by car, I don't go - well, except by yacht (Not mine I hasten to add, I just cadge a ride occasionally)
by Jonathan Briggs @ 21/07/2006 6:08 pm • Permalink •
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The rail issue is heat expansion. Heated rail is longer. The coefficient of expansion is about 0.001% per degree F. So for a km of track and 20 degrees above normal, you've got 20-cm of steel expansion looking for a place to go. The rail to sleeper attachments just hold on hard and squeeze that rail to keep it in place.
Trains run slower both to avoid over-stressing the rail and triggering a failure, and to be able to see a failure up the track and stop before getting there. Failures are not big dramatic rail explosions. The tracks just kink or spread out laterally or vertically. That will derail a train.
by rjh @ 22/07/2006 8:07 pm • Permalink •
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I think Ms Bsag already knew that...........
by Jonathan Briggs @ 23/07/2006 7:07 am • Permalink •
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I have been working on a few occasions this year in Tokyo where the train service is something else. All of the "Metro" lines run to a timetable and on time which is extremely refreshing and takes some getting used to. However, with an (alleged) 27m people in the city on a daily when it goes wrong it's true chaos. rjh - the science is understood, so why not more expansion joints in the track or a new engineering solution as we enjoy a warmer climate? Creative thinking on the railways...?
by Julian @ 24/07/2006 7:07 am • Permalink •
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Creative thinking on the railways�
Now there's an oxymoron if ever I've heard one!
by Jonathan Briggs @ 24/07/2006 5:08 pm • Permalink •
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rjh: Yes, I was making a bit of a bitter joke. But I do have a serious point: the laws of physics are the same the world over, and yet countries like Japan (as Julian mentioned), that suffer more extreme conditions in parts than we do in the UK, manage to cope with the problem without major disruption. So it must be possible.
Jonathan Briggs: Quite.
by bsag @ 24/07/2006 5:08 pm • Permalink •
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First, expansion joints introduce even worse problems. You want the smooth effect of welded rail for high speed.
Second, most railroads have a nominal maximum design temperature. When laying the rail you heat it up (usually by the simple technique of lighting a fire along it). You get it up to the design temperature over its whole length, then weld it in place. It's much easier to deal with steel in tension (it stretches) than steel in compression (where it really wants to buckle).
The railroad picks a nominal maximum based on climate. Too high and you get tension failures in cold weather. Also, too high and it's hard to keep true. As the rail is used and wears it tends to stretch, so from time to time a repair is needed to reset the tension. Running trains over the rail converts some of the tension into permanent stretch for each train that passes.
The worst area for this kind of behavior is the central US and Russia. The summer/winter swings are huge and they sometimes just give up on welded rail and accept the much slower top speed limit introduced by expansion joints. Also, go slow orders due to high temperature are fairly common in the US in the summer.
The Japanese have track crews adjusting the high speed rails every night. There are variety of techniques for adjusting rails, including the extreme step of cutting out a chunk and re-welding the rail to be shorter.
My guess is that in Britain you have a combination of insufficient frequency of rail adjustment with a too low design temperature.
by rjh @ 24/07/2006 6:07 pm • Permalink •
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For a report with some nice pictures of buckling, see: http://www.volpe.dot.gov/sdd/docs/buckling.pdf
Googling for "welded rail destressing" will give you lots more.
by rjh @ 24/07/2006 7:07 pm • Permalink •
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Foxy
by Jonathan Briggs @ 24/07/2006 8:08 pm • Permalink •
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Hmmmm, the Japanese high speedtrains managed 300kph ok but I haven't seen much "high speed" on the local UK train networks! .
by Julian @ 25/07/2006 10:08 am • Permalink •
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