RAILROAD WELDED RAIL TRACK EXPANSION

[Anonymous]

No one has mentioned the track items known as "rail anchors" which are used on either side of a crosstie to minimize the movement. Some railroads "box anchor" (an anchor on both sides of a tie) at least every other tie in welded rail territory.

I know of a district where welded rail had to be laid in the dead of winter. In the spring, switch points were provided every couple of miles and the rail headed off to the side so it could run at its pleasure. When it got as hot as it was going to get and the rail had expanded as far as it was going to expand, it was cut and tied into the string and welded in place.

Old Timer

[Anonymous]

If the rail is sufficiently anchored to the ties and if the ties are held in place by sufficient ballast, then there is no expansion. The rail is held in place.

[Anonymous]

QUOTE: Originally posted by jockellis

The longest continuous welded rail is probably in western Australia, some 297 miles. <snip>
Jock Ellis

If this is the section I think it is it is also the longest stretch of *straight*
track in the world. Dead straight for 297 mi. (498 km)!

So what happens to the expansion then? Is the track completely in the air somewhere? [:D]

[Overmod]

Jock, what makes you think they don't? That's one of the things that "breathing" in the literature describes...

A couple of key points (by no means the only ones*) are:

1) that the 'breathing' not cause sufficient damage or displacement to the ballast and track structure that nonlinear degradation occurs, and

2) that no stress concentrations occur that serve as triggers for rapid buckling.

If you divide your 300 feet into your 300 miles, then consider the length, radius, etc. of an average curve, you can figure out more or less exactly what the unconstrained expansion would be, and from that get an estimate of the increased anchoring, clamping, ballasting, etc. forces needed to retain necessary track geometry...


* STILL waiting for Mudchicken and others to chime in on this subject in detail, wisdom included...

[jockellis]

The longest continuous welded rail is probably in western Australia, some 297 miles. On some rail forum I posted a question concerning expansion and several smart engineers figured up what the expansion would be. Unfortunately, my computer crashed, taking everything with it and I don't remember what forum it was on. I think the rail expanded about 300 feet. I always thought curves would expand in hot weather and contract with the cold to offset the effect of the weather, but I guess not.
Jock Ellis

[Overmod]

Adjusting rail neutral temperature to a higher value is still a wise practice in many locations.

An interesting discussion available via the Web is:

www.volpe.dot.gov/sdd/docs/buckling.pdf

with a somewhat more technical discussion at

www.fra.dot.gov/downloads/Research/trk-risk.pdf

The incidence of problems begins to increase dramatically at rail temperatures above about 145 degrees F, according to the authors; see Fig. 6 in the latter paper in particular (there is a similar graph with less detail in the other paper).

I'd be interested to hear the opinions of the real-world track maintenance people on this forum, including their experience with measurement equipment, techniques, and software.

[dldance]

If one were to use a thermal resistance heater to quickly heat the top of an entire rail and if the bottom of the rail were unconstrained, then you would expect a verticle bow. The rail would act like a bi-metal strip -- expanding on the top while remaining in the contracted state at the base. Maintaining the heat for a period of time then would allow the heat to diffuse from the top to the bottom of the rail. As the bottom of the rail started to expand, the rail would flatten.

I read somewhere that in UP's early installations of CWR, they heated the rail to 105 F before fastening it in place so that the rails were in tension most of the time.

dd

[Overmod]

One other interesting point: When I was in college, we looked at some of the German studies of track mechanics, done in the 1920s (would you believe springs in the *track*?). They developed some models for experimental observation of rail expansion, and produced one very interesting result...

Their methodology involved artificially heating the rail in order to model the expansion due to warmer climate. To get that Teutonic multiple-decimal-place precision, they decided to use electric resistance heating over the entire span of the test rails (which to me seemed a reasonable simulation of 'distributed' heating due to solar radiation). What they got when they did this: the track lifted straight up in a perfect bow, something I have never seen or heard of 'in nature'. There were some attempts to explain the mechanics behind this -- but as it rather obviously didn't mirror "railroad reality" in the field, they changed their experimental model instead. My own guess is that they heated the rails too much and too fast at the same time, with 'perfect' consistency between the two so there wasn't enough 'induced inconsistency' to cause sideways shifting or buckling.

Be interesting to see whether there are accident conditions under which this effect might be observed, for example in track where the tie ends are restrained from moving laterally, or where a given 'span' of welded rail is pinned more strongly at each end (cf. on slab track) than in the middle.

[Anonymous]

Thanks Mark, Overmod and dldance for your replies. I will accept your words as gospel, especially since you pointed out that the rail cannot move freely in the longitudinal plane. It was this point that caused me problems to understanding howcome we got fewer heat kinks in the Summer or broken rail in the Winter. Thanks
Norman - engineman 1

[morseman]

engineman1 notes that 1/4 mile lengths of rail are welded together.

Would anyone out there hazard a quess where the longest such CWR would be?

[dldance]

I know that an old MOW trick for fixing cold weather related breaks in stick rail involved spraying the rail with a mixture of diesel and gasoline - which was then set on fire warming the rail. The crew would then bolt the joiners together while the rail was hot to minimize sun kink's next summer.

dd

[Overmod]

One small point to add to the explanation given so far -- a fair thing, because you'll find it mentioned it in another post on welded rail earlier ;-} --

The rail is laid and secured at a known temperature, or during a period of time when the ambient temperature is within an accepted range. My understanding is that the high (hot) end of the temperature scale is preferable, as it's easier for the track structure to accommodate tension than compression (and if a rail fails, it will often crack and thereby "announce its failure" via continuity failure in the signal circuit).

Note that Pandrol clips et al. give much better connection of rail to ties than a couple of spikes and a tieplate. Furthermore, the spring clips can 'give' to relieve expansion stress, then clamp down when the rail cools -- spikes will start working loose in this situation.

[Anonymous]

O.K., this is a question that I have wondered about for some time, but I have yet to get a REALLY GOOD explanation. Perhaps one of you fellows out there who KNOW whats going on might be able to provide the explanation. I remember, when I ran steam locomotives and early generation diesels, that we used stick track (34 foot sections of rail) and some railroads still do, and we, quite often got heat kinks on those really hot days of Summer. Then, along came welded rail and we got fewer heat kinks or problems with the rails. What I would like to know is - howcome? I know that the rails are held in place by special clamps at each tie, but what happens to the rail expansion - I think the scientific guys call it the coefficient of metal expansion - or something like that. One fellow told me that it's because these clamps, plus the fact that the rail expands in all the planes (Up, down, sideways, left and right - all around the rail) keeps the rails in place and prevents them from expanding and twisting out of shape. But I find that this is not really a good explanation - I mean, the quarter mile sections of rail are then welded together, once in place, so that, in total, this makes a pretty long piece of welded rail. When the temperatures get into the 100 degrees F. or more, how is it that the rails stay in place and don't kink?
[:)] Can anyone give me a good explantion or where I can go to get a good explanation? Thanks.
Norman - Engineman 1