Hot Flash!

[Willy2]

Here's a question about hot temperatures and railroads. How does extreme heat make the rails expand and twist so much that trains derail?
Last summer in Bellevue, Nebraska a train derailed because the heat made the tracks get all twisted out of shape. Can't something be done to bolt the tracks so firmly to the ground that they can't twist out of shape?

Willy

[M636C]

Willy,

As you have said, in hot weather rails expand, and can buckle causing trains to derail. This has only been a problem since rails were "continuously welded" into very long lengths, so that the amount of expansion and the forces involved were high enough to overcome the restraint provided by the ties, the tie fasteners and the ballast. Until the 1960s, rails were generally bolted together with "fishplates" (at least that's what they call them here!), and the small gaps at the ends allowed enough expansion for the short rails.

By welding rails together, the joints, which needed to be checked (for cracks) and tightened were eliminated and this saved money. But the old spikes used to hold the track to the ties didn't hold the rails tightly enough to absorb the expansion forces, so "rail anchors" were applied next to ties, underneath the rail to share the expansion forces out among the ties.

Another method of "locking" the track to the tie was to use very strong spring clips to hold the rail to the tie. The most common one I've seen is called a "pandrol" clip (but that is used in England and Australia - I don't know how much it is used in the USA).

Another technique usually used with spring clips, is to use concrete ties, which are much heavier, and are better at restraining the track.

The ultimate answer is to lay 12" or more thick continuous concrete slabs (as are used in building Interstate Highways) under the rails, and tie the rails to it with spring clips. This has been tested on high speed lines in Germany, and is sometimes used in tunnels where other problems exist, like water leaks which could cause the track to shift.

The problem is that all these methods cost more money, and the problem has been fairly rare over all.

One answer is to weld the rail together at a temperature close to the highest expected temperature, so then the rails won't expand any further, because they were already expanded when welded. The down side to that is that then, in cold weather, the rails are in tension, and if it gets sufficiently cold, the rails will break at a weak point, like a weld, or where some slag may have been caught in the rail when it was rolled into shape (from a big slab).

So, it's not just hot days, but cold days can break the rail and cause a derailment too! The track engineers just have to do the best they can with the money available. Since world temperatures are rsing, this may become more of a problem. Putting in more joints for expansion could help, but they will have to be checked, or they could break and cause a derailment.

In Australia, rail in curves has been painted white on the sides to see if this will reduce the heating effect! It doesn't stay white long!

My favourite solution is concrete ties, but these should be laid together (replacing all the wood ties) to work properly, and this costs a lot!

But there are no easy answers, and the problem is relatively small, if you compare the incidents with the total number of trains running. It only makes the news if a passenger train derails.

I hope this helps - you'd never know I used to work for a company that made rail!

Peter

[tree68]

I read somewhere that rail sufficiently secured to the ties will actually be forced to expand across its section rather than lengthwise. I can't speak to the accuracy of said concept, but it does make a certain amount of sense.

[Rick Gates]

Peter has made a good explanation of the problem. I thought they used a chart that takes into account the ambient temperature when installing the rail, location, and so on. I don't see how any type of spike, clamp, or tie clip will keep the rail from expanding or contracting lenthwise in extremme temps and causing breaks or buckles from time to time. I'm curious as to what mudchicken would say. [bow]

[Anonymous]

Their are speed Restriction in Hot Weather

DOGGY

[jchnhtfd]

Ill be interested in mudchicken's comments, too -- I don't think I've ever read a post from him from which I didn't learn something! -- but in the meantime, while he's getting up...

It's quite true that a real effort is made to place CW rail at a reasonably high temperature, within what is regarded as the 'normal' range of temperatures for the area, so that it spends most of its time in what one might think of as 'neutral' -- neither pushing on itself nor pulling on itself. If the temperature rises, the rail tries to expand (in all directions, but the problem, obviously, is lengthwise). Properly restrained, it is quite strong enough to take the expansion forces internally and no problems result. Properly restrained can be any good tie system -- concrete with Pandrols or other clips is fine, but so are wood ties with rail anchors and good ballast. But properly restrained is the key: the rail must not be able to move either sideways or up and down. If you keep it straight (or on a gentle and continuous regular curve) and properly aligned, you are fine. If it is allowed to get out of line -- even a little; a couple of inches misalignment in 39' is plenty -- the rail can't take the 'squeeze' internally, and instead pops out to one side (called Euler buckling; don't ask, it's a complicated topic!). Poor ballast can allow it to squiggle, or vibration from heavy fast traffic, or... you can try the effect for yourself with an ordinary drinking straw: if the straw is straight, it will take a pretty amazing push -- but if you allow it to bend, even a little, boing!

That help any?

[Willy2]

Thank you everyone! Quite interesting how all of these things work! I should have known that since rails expand in hot weather they contract in cold weather.

Willy

[vsmith]

They make expansion joints for garden model railroaders to deal with heat expansion, how come the railroads dont have expansion joints for welded rails? they would only be needed every few hundred feet to allow the rail to expand or contract

[M636C]

Guys,

I have seen pictures of special expansion joints, that looked like a pair of switchblades put together on a special base plate. They were about eight tie spaces long. But they would need checking and lubricating - not much use if they rusted in place, or if they were so stiff that the rail buckled somewhere else. I expect that they would be costly, too. But if there were places that had really big temperature changes, they might be worthwhile.

Peter

[Hugh Jampton]

Expansion joints are usually installed near switches to protect them from the longitudinal forces

[jchnhtfd]

Part of the idea of CW is that the expansion and contraction forces should be taken up in the rail itself -- there should be no change in overall length, as the rail is not supposed to slide on the ties, nor the ties slide on the ballast. Expansion joints are needed in a few places (like complex trackwork)...