I know rails buckle during heat waves, but I do not understand why. Steel does not even start to get soft until he temperature is over 2000 degrees. Mainline rail these days is at least 136 lbs or more per yard so it is pretty heavy.
It’s not that the rail is getting soft, it’s that the rail is expanding. Metals like to expand when the temperatures go up and get contract when the temps go down.
It is not about soft! It is about expansion.
Never too old to have a happy childhood!
Consider for a moment how rails can be laid around curves ... or. more dramatically perhaps, how rail trains can possibly travel.
Then consider that most metals expand when heated, and that if a long thin strip held at the ends from expanding mechanically is heated enough, it will buckle either laterally or vertically. These two things are what cause the 'sun kink'.
In the old days of 39' sectional rail that will fit in a gondola for transport, the expansion could be compensated by laying with a known 'gap' corresponding to temperature, and kink thereafter staved off by periodically loosening the bolts at the fishplates and letting the gaps close. With the advent of continuous welded rail, accommodating the thermal expansion became progressively more difficult, with the use of rail anchors becoming essential not just for 'creep'. Then along come flexible Pandrol-style rail holding systems that use spring tension to hold the rail in alignment but do little to restrain it longitudinally.
The usual buckling occurs when the rail is in compression and there is a spot failure of lateral support of some of the ties. The compression relieves preferentially as the rails and ties physically shift to one side, usually not humping up because the structure is strongly 'constrained' by gravity in the vertical direction.
The opposite of this occurs in cold weather when the rail rather than 'stringlining' the track structure tends to cold-fracture and the ends pull apart, sometimes to a considerable distance. Usually to fix this the rails are heated, either electrically or via a 'flaming rope', until they expand enough to bring the dressed ends together, at which point they are either temporarily bolted or field-welded.
When the Germans were researching track mechanics in the 1920s, they got the bright idea to 'accelerate' sun-kink testing by resistance heating the rails electrically at a fairly rapid rate, equally. This had the startling effect of bowing the sample track off the ground, not at all what is observed in nature.
Meanwhile, as an amusing aside: in the 1970s there was a contest in engineering colleges for the best use of asphalt in track structure. Now as you might imagine there are precious few areas where the stuff has much use, but one of them is as a 'barrier layer' in the subgrade to keep drainage through the ballast from soaking through, and this has advantages when doing high-speed reconstruction or improvement of main lines ... provided you don't have so much heat soak that it reaches the asphalt and softens it, enough to facilitate the beginning of almost lubricated lateral excursion... Once that happens, it can be amazing the extent of the carnage before it stops.
So, what's the answer to the problem?
Go back to 39' bolted rail? Paint the rails white like the Italians do? Or just live with it? Is there even an answer?
Not trying to be funny, mind you.
caldreamer I know rails buckle during heat waves, but I do not understand why. Steel does not even start to get soft until he temperature is over 2000 degrees. Mainline rail these days is at least 136 lbs or more per yard so it is pretty heavy.
The previous responders mean well, but they're quite wrong. The truth is that all matter has something called 'phlogiston' in it. It's sort of like the element we know as fire. When rails heat up, the phlogiston is released and the opposite element, water, moves into the interstices between the molecules. As you know, it's akin to dry and hard noodles in hot water; they eventually soften, and this makes the rails do all sorts of goofy things.
You're welcome.
Metals are also elastic. If rails are heated up, they get longer, but if they are constrained as they are heated up, the growing length can be absorbed in the resulting compression of the rail to some extent. This would be like compressing a coil spring. This is how welded rail deals with an expasion force that wants to make it longer.
If you physically block that increase of length and also block the tendency for the rail to buckle due to its constrained expansion; the rail will simply absorb its growing length internally like compressing a spring.
I've read that rails in compression will actually expand in the cross section, at least until they can't. Then they expand longitudinally, resulting in "sun kinks."
I think someone mentioned that the roadbed helps keep the kink problem in check, until it can't.
When CWR is laid, they try to do it at a "neutral" temperature. When the ambient temperatures get too far off that mark, there will be problems with breaks and pull-aparts (cold), and kinks (heat).
Either situation will often result in slow orders. Visitors to one of the rail cams today were wondering why everything seemed to be running slow - that was likely one reason.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Flintlock76So, what's the answer to the problem?
MC and others will have more careful details. But, basically:
1) Determine the 'average' temperature (weighted with respect to severity; most track can handle much more 'compression' than tension, and rail metallurgy can get strange with age in very cold weather). Call this the 'neutral temperature' and make all your rail lengths and joints relative to this temperature.
2) Be sure your structure is as 'restrained' as your budget for track allows. Rail anchors, good ballast shoulders, ballast dressed right up to top-of-tie height, keep the ballast clean and well-drained, etc.
3) Overall adjustment is made with certain points 'variable' at different times of the year; you make adjustment here (I believe more by cutting out and welding in sections than providing variable-length precision bolted sections, but I defer to professionals) and the accommodation handles the intermediate expansion in the 'rest' of the sections of the track structure.
4) Have people ready to respond quickly and knowledgeably when problems are detected, or expected, and give them the knowledge, the tools, and the support to act wisely and well to make adjustments when things look like getting 'extreme'.
The science of LWR has been developing at least since D&H started the first practical use of 1440' (I think it was) sections, if memory serves me in the 1930s. It's an interesting field, and I have had the privilege of knowing a number of experienced experts over the years.
BTW, you might think that some form of slab track with very robust longitudinal constraint of rail movement would be a 'better' answer than a bunch of ties restrained by tamped ballast. In some respects it can be. But it is a much more expensive initial solution, and an even more expensive one to make fine-tuning modifications on should those be necessary.
tree68I've read that rails in compression will actually expand in the cross section, at least until they can't. Then they expand longitudinally, resulting in "sun kinks." I think someone mentioned that the roadbed helps keep the kink problem in check, until it can't. When CWR is laid, they try to do it at a "neutral" temperature. When the ambient temperatures get too far off that mark, there will be problems with breaks and pull-aparts (cold), and kinks (heat). Either situation will often result in slow orders. Visitors to one of the rail cams today were wondering why everything seemed to be running slow - that was likely one reason.
CSX Heat Orders, when issued are in effect from 1300 to 1900 - ie. the hottest part of the day.
Rails buckle because if they didn't their pants would fall down.
Oh wait... No... Um...
Rails buckle because if the cops stop them they will get a ticket for not buckling.
Assume you have 1000 feet of rail that is perfectly fastened down at each end such that the ends cannot move. Further assume the rail is perfectly constrained on the sides such that it cannot move sideways.
Then assume the rail has been cut exactly in half and a hinge installed between the two halves.
If the rail expands, the only thing that can happen is for it to compress or hinge in the middle and raise up off the ground ("Tenting").
Assumming the rail halves do not bend in the vertical direction (sag) but each half remains perfectly straight, how high will the center raise up from the ground if the rail expands by 1 inch?
Semper Vaporo
Pkgs.
Heated rail can expand, and if contrained end to end, up and down, and side to side; and it can thus expand without getting any longer, wider, or taller.
Or look at it this way. You can contrain a rail side to side and up and down; and then apply opposing force to each and make the rail get shorter.
The weak point will be found!
Remember - the passage of a train will act like a vibrator on the entire track structure - rail, fastenings, ties, ballast, sub-grade.
Phlogiston!
Holy smoke, I haven't thought about phlogiston in years! Probably when I used my last batch of it! Thanks for reminding me Selector! I'll have to run out to Diazinon Alley and get some more!
I DO have a Philosopher's Stone laying around somewhere...
I put Diazinon and Malathion right up there with creosote. Three things essential for the outdoorsy man who wants to keep his timbers longer and his plants the same.
Flintlock76I'll have to run out to Diazinon Alley and get some more!
That's pretty funny, although Ms. Rowling might not approve.
Can we fix the Title to 'Buckle' .. we look like a bunch of illiterates.
Flintlock76I DO have a Philosopher's Stone laying around somewhere...
I bet the philosopher screamed when the passed it!
Miningman Can we fix the Title to 'Buckle' .. we look like a bunch of illiterates.
That's on the OP.
Overmod Flintlock76 I'll have to run out to Diazinon Alley and get some more! That's pretty funny, although Ms. Rowling might not approve.
Flintlock76 I'll have to run out to Diazinon Alley and get some more!
Can't imagine why she'd get "bugged" about it, she's rich enough!
PS: You gents NEVER disappoint me! I was hoping the "diazinon" joke wouldn't go over anyone's heads!
Flintlock76I was hoping the "diazinon" joke wouldn't go over anyone's heads!
It did take a moment. Coulda have been spell check ... then I remembered you need to be a Hogwarts graduate to use it here.
It is an indication of how far Harvard has declined that we don't have a 'companion volume' to "Bored of the Rings" for at least some of the Potter saga. Organophosphorus compounds and ISAN names would loom large in such a work, I think.
Organophosphorus compounds. The first things I think of when I see the term are "Tabun," "Sarin," and "Soman." Scary stuff indeed!
Although I do know they had their origins in insecticide research.
Anyone remember chlordane? Dad used it around the house to kill bugs and swore by the stuff. Dad ALWAYS followed the directions for its use and never had a problem with it. Too bad a lot of people didn't, it was a good product.
OvermodThe usual buckling occurs when the rail is in compression and there is a spot failure of lateral support of some of the ties. The compression relieves preferentially as the rails and ties physically shift to one side, usually not humping up because the structure is strongly 'constrained' by gravity in the vertical direction.
And are you sure it is gravity holding the track down? The amount of pull from gravity over such a short distance on such a small mass would seems to be practically irrelevant.
selectorThe truth is that all matter has something called 'phlogiston' in it.
zardoz selector The truth is that all matter has something called 'phlogiston' in it. I understood that this hypothetical element's existence was mostly disproved by sometime in the 18th century.
selector The truth is that all matter has something called 'phlogiston' in it.
I understood that this hypothetical element's existence was mostly disproved by sometime in the 18th century.
It was.
Phlogiston was an old alchemist's theory, no more real than the "Philosopher's Stone" that was supposed to turn lead into gold.
Selector had his tongue firmly planted in his cheek, just as I did when I mentioned "Diazinon Alley."
zardozCompression, not expansion?
Yes. The expansion is a thermodynamic effect, caused by the increased atomic vibration from the heating. This causes the component atoms in the alloy to move on average slightly farther apart, making the outside dimensions 'grow' proportionally. That in and of itself will not and cannot make a rail bend.
Meanwhile, the physical dimensions measured from 'end to end' of the heated rail section can be treated as fixed -- if, in fact, not actually pressed against by expansion in the neighboring parts of rail, so the longitudinal component of the thermal expansion is resisted. (This is the reason for the observation that the cross-section preferentially 'grows' in this situation; the width and to an only slightly lesser extent the height can expand unrestrained, so the proportions change in the stressed case... but not by enough to matter much; the very long resultant of longitudinal stress can still express itself as considerable force without causing extensive lateral distortion (let alone plastic change past the yield point) in the rail section. It is the longitudinal constraint, which can be thought of as causing 'compression' in the heated rail section, that produces the force that expresses as bending.
Gravity may not be 'all that' strong but it is very consistently acting. Since there is comparatively little if any lateral restoring force in the track structure once the usual causes providing that have been deranged in some way, even if the track might tend to lift at a given point enough to weaken the lateral resistance, it is much more likely that all the expansion will go into the lateral -- into progressively buckling the rails into lateral curves -- rather than hold the rails elevated against constant restoring force. There is certainly enough aggregate weight to transfer most vertical deflection, should it develop, into additional lateral excursion relieving the gravitational potential energy increase from elevation. The timescale here, from whatever physical events produced the buckle or 'kink' to its being observed by a human being, is so dramatically long that we can expect any transient effects to have 'relaxed' to equilibrium long before a human observes it; I believe most cases of observed sun-kink propagation have been, as expected, lateral.
We might also add that many examples, including the one Balt illustrated, show a further effect: once some part of the track starts to move, shock propagates through the track and allows effects like sinusoidal modes to appear in the lateral deflection. Hence you can get, instead of one big bump like the Australian example on YouTube, these complicated multiple esses by the time everything comes to rest at the elevated temperature. (Would that it would be less nondeterministic and 'go back where it started' when things cool down!)
Flintlock76Phlogiston was an old alchemist's theory, no more real than the "Philosopher's Stone" that was supposed to turn lead into gold.
It was considerably more than that; in fact, it was an early demonstration of how organized bullying can distort good scientific practice to the point of destroying careers in the service of promoting a dubious theory. Kind of like a free-world version of the business with Lysenko, or the current anthropogenic-climate-change scam (as opposed to legitimate theories or concerns with AGW, which I repeat I support).
Very dangerous precedent for actual science, and while ridiculed now, there was a time not too distant where 'phlogiston deniers' had a hard time of it.
Some things NEVER change bro, hence the veracity of the old saying...
"My mind's made up, don't confuse me with the facts!"
And some of us hear the story of "The Emperor's New Clothes" and get the moral right away. Some never do.
Semper Vaporo {Snip} Assume you have 1000 feet of rail that is perfectly fastened down at each end such that the ends cannot move. Further assume the rail is perfectly constrained on the sides such that it cannot move sideways. Then assume the rail has been cut exactly in half and a hinge installed between the two halves. If the rail expands, the only thing that can happen is for it to compress or hinge in the middle and raise up off the ground ("Tenting"). Assumming the rail halves do not bend in the vertical direction (sag) but each half remains perfectly straight, how high will the center raise up from the ground if the rail expands by 1 inch?
{Snip}
I guess nobody knows how (or maybe nobody cares). Since I have an experience with track doing what I just described in the story problem, I'll relate it first and then GIVE you the answer.
I have an Aster Mikado Live Steam 1:32 scale steam locomotive and the only track I could afford after purchasing the kit to build the loco, was cheap 2nd hand plastic track (like that comes with the toy trains you find at Christmas time to have a battery operated train go around the Christmas tree). I had enough straight sections to lay on four 10-ft long 1x8 boards on the ground, end to end. The plastic track was 2nd hand and had been outside a few years and the molded in clips on the ends that held the sections together were quite brittle. Thus I was concerned that a wind storm might blow the track around and break it at the joints. So I nailed down the end pieces with just one nail each. I ran my train many times using a Radio Control for the Throttle and Reverser lever. Worked great and was lots of fun going as fast as I could for most of the 40-ft of track yet bring it to a stop before it ran out of track.
I put the track down in about mid Spring and it served me well for a couple of months... then one day, I came home from work and that day had been a scorcher. As I drove up the driveway I could see my track off to the side and noted that it was in the shape of a bell curve, the center being about THREE FEET above the boards.
Like a fool, I went over and BARELY touched the middle of that humungus arch and it fell over, breaking nearly every molded-in joint.
Now, the story problem: 1000-ft. of track cut in half in the middle, the whole track expands by 1 inch, how far does the middle raise from the ground?
Old man Pathagorius comes into play here... (remember him?)
A^2 + B^2 = C^2
We know that A = 500 (1/2 of the 1000 ft.)
and C is the hypotenuese of what will be a right triangle when the rail expands and lifts in the middle, so it will be 500ft + 0.5 inches.
Solving for B gives us, sqrt (C^2 - A^2) = B
Convert it all to inches:
A=500*12 = 6000 inches.
C=500*12) + 0.5 = 6000.5 inches.
Squaring both gives:
A=36,000,000
C=36,006,000.25
Solving for B^2 thus becomes 36,006,000.25 - 36,000,000 = 6,000.25
And the square root of 6,000.25 = 77.46 inches.
The track would 'tent' about 6 and a half feet from the ground in the middle.
This is assumming that the rail does not sag on the ends to form more of a bell curve instead of a straight sided triangle. If it sagged, then the height would be much more since the sag along the length would effectively shorten the space where the rail would lift, but the total expansion would remain the same.
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