A friend and I were discussing the amount of vertical track movement we could see at a crossing and I thought it should have, essentially, none but he thought (and some online posts agreed) that the track needs to move up and down. Online, someone stated that the flex allows the force on the track to be better distributed and reduces stress on the track.
Which is right?
Track is a dynamic structure. It bends and flexes on account of the rail section and the condition of the ties/ballast/ subgrade. That flexure/stiffness is looked at by railway engineers as "track modulus' in an over simplified definition. The rail is acting as a simple beam.
Highway pavement has a lot less point loading than track does. (even with chronically overloaded taxpayer subsidized trucks) you normally won't see it bend unless you start encountering long under-designed bridge spans.
Would there be any harm to the track if there was no vertical movement?
Is that movement something that the engineers want?
If nothing else, it would seem that any movement would cause more problems, especially where water collected under the ties. Every time the tie would be forced down, a small amount of soil would splash out and after a while, the problem would become much worse.
Perry Babin Would there be any harm to the track if there was no vertical movement? Is that movement something that the engineers want? If nothing else, it would seem that any movement would cause more problems, especially where water collected under the ties. Every time the tie would be forced down, a small amount of soil would splash out and after a while, the problem would become much worse.
There is no soil directly under the ties, there is ballast - those big rocks - they drain the water away from the ties. And when those rocks move to much, a big machine picks up the track and pushes the rocks back under the ties.
No movement would be bad. Someone else will have to explain why because I have to get to bed soon.
Sheldon
Perry Babin Would there be any harm to the track if there was no vertical movement?
No.
Correct.
(Significant) vertical movement of track is a failure of design, installation, or maintenance.
If you see it, someone(s) have been incompetent.
I came back and added "significant" because I'm sure someone will pipe up and say it's impossible to get rid of it. True. But it's not your friend. You don't want it. It causes problems. As an engineer, you should be minimizing it.
IT'S NOTHING TO BE PROUD OF!
Ed
PS: In decent trackage, water does not collect under the ties. That's because ballast is under the ties, and the water drains through. "Soil" is NOT under the ties, so it cannot "splash out".
7j43k Perry Babin Would there be any harm to the track if there was no vertical movement? No. Is that movement something that the engineers want? No. If nothing else, it would seem that any movement would cause more problems, especially where water collected under the ties. Every time the tie would be forced down, a small amount of soil would splash out and after a while, the problem would become much worse. Correct. Vertical movement of track is a failure of design, installation, or maintenance. If you see it, someone(s) have been incompetent. Ed
Vertical movement of track is a failure of design, installation, or maintenance.
Then all heavy haul railroading must be incompetent.
Rail gets loaded and unloaded with passage of each truck. The track structure responds to that loading and unloading.
Never too old to have a happy childhood!
That's why I went back and added "significant".
Please don't endorse this "crap track is entirely acceptable because I've seen it somewhere" idea.
Mud squishing out from the track when a train passes is absolutely pathetic, and is not "heavy haul railroading". It's loser railroading on a loser railroad.
"Rail gets loaded and unloaded with passage of each truck."
Sure does.
"The track structure responds to that loading and unloading."
Absolutely.
What's your point?
duplicate post
Muggles ....OP needs to watch track on an approach to an open deck bridge, then somewhere nearby at a ballast deck bridge , slab track , open deck bridge and so on...
He's clearly thinking like the rubber-tired bubbas and not like the steel-wheeled set. Only experience in the real world is going to change that. Railroad civil engineers, roadmasters, trackmen and the like have developed an eye for normal track physics and what's going on, knows where the track structure can be forgiving and where it won't tolerate deviations. (This is also why so many state DOT's can't railroad - they have nobody on staff that can comprehend what's going on. .... go back and look at the old threads about rusty bridges in Covington KY, difference between ASCE and AREMA, FHWA and FRA et al)
The mudmonster won't ever go away and is a fact of life. You had better learn to deal with it. (remediate it or slow order it) Roadmasters would love to have some of the money spent on the shiny toys be spent on track and more people, but that isn't realistic. Do the best you can with what you are given and always remember mother nature hates/loathes the track and bridge departments.
Just like the first law of thermodynamics: " You can't win, you can't break even and you can't get out of the friggin' game"
7j43kThat's why I went back and added "significant". Please don't endorse this "crap track is entirely acceptable because I've seen it somewhere" idea. Mud squishing out from the track when a train passes is absolutely pathetic, and is not "heavy haul railroading". It's loser railroading on a loser railroad. "Rail gets loaded and unloaded with passage of each truck." Sure does. "The track structure responds to that loading and unloading." Absolutely. What's your point? Ed
Track structure in railroading is the process of crushing ballast into powder over time. With time and water that powder becomes mud and form the notice to the MofW personnel that it is time for more tamping of the ballast and most likely more ballast. The passage of trains transfers the weight of the engines and cars down from the rail top to the rail bottom to the tie plate and then the ties that are resting on top of the ballast (presuming the ballast has been tamped to be under the ties) and the weight is then compressed into the ballast. The track structure is dynamic and moves to some degree whenever weight of sufficient qunatity is placed upon it.
After the track structure is disturbed - passage of a tie and surfacing gang - the first train after work is completed for the day will be restricted to 10 MPH over the extent of the work, the train will be closely observed by MofW personnel, with the successful passage of that first train the track will then be restricted to 25 MPH for the passage of a specified amount of tonnage - I have heard 100K and 200K or more tons mentioned, I don't know which is correct, mudchicken would know.
Track and ballast are the part of the track structure we can see - a lot of effort is expended upon creating the sub-grade and drainage options which the ballast and track rest.
We can't forget that contaminants get added to the ballast as well. I understand that this has been a problem with the Powder River coal lines, with coal dust fouling the ballast.
Hence, ballast cleaners, which scoop up ballast alongside the track, and some machines also reach under the track, filtering out the "fines" (dirt, coal dust, ground up ballast), discarding those fines and replacing the cleaned ballast from whence it came.
Of course, this will require said ballast to be tamped, and possibly new ballast added.
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...
I've seen some track structure in the Midwest when I was a kid that could dribble a basketball better than a lot of NBA basketball players.
BaltACD 7j43k That's why I went back and added "significant". Please don't endorse this "crap track is entirely acceptable because I've seen it somewhere" idea. Mud squishing out from the track when a train passes is absolutely pathetic, and is not "heavy haul railroading". It's loser railroading on a loser railroad. "Rail gets loaded and unloaded with passage of each truck." Sure does. "The track structure responds to that loading and unloading." Absolutely. What's your point? Ed Track structure in railroading is the process of crushing ballast into powder over time. With time and water that powder becomes mud and form the notice to the MofW personnel that it is time for more tamping of the ballast and most likely more ballast. The passage of trains transfers the weight of the engines and cars down from the rail top to the rail bottom to the tie plate and then the ties that are resting on top of the ballast (presuming the ballast has been tamped to be under the ties) and the weight is then compressed into the ballast. The track structure is dynamic and moves to some degree whenever weight of sufficient qunatity is placed upon it. After the track structure is disturbed - passage of a tie and surfacing gang - the first train after work is completed for the day will be restricted to 10 MPH over the extent of the work, the train will be closely observed by MofW personnel, with the successful passage of that first train the track will then be restricted to 25 MPH for the passage of a specified amount of tonnage - I have heard 100K and 200K or more tons mentioned, I don't know which is correct, mudchicken would know. Track and ballast are the part of the track structure we can see - a lot of effort is expended upon creating the sub-grade and drainage options which the ballast and track rest.
7j43k That's why I went back and added "significant". Please don't endorse this "crap track is entirely acceptable because I've seen it somewhere" idea. Mud squishing out from the track when a train passes is absolutely pathetic, and is not "heavy haul railroading". It's loser railroading on a loser railroad. "Rail gets loaded and unloaded with passage of each truck." Sure does. "The track structure responds to that loading and unloading." Absolutely. What's your point? Ed
The OP was asking about track design: is it meant to be as rigid as possible, or is it meant to flex as a train passes?
That it DOES flex I won't argue.
That a rigid design DOES degrade I won't argue.
What I disagree on is that the intent of the track designers and installers is that it is DESIRABLE and INTENDED to do so. It is not. That "quality" is minimized as much as possible.
My answer to this starts with the quote from Herbert Spencer on the wall of the University Cottage Club -- to play a good game of billiards is the mark of a well-rounded education. But to play too good a game of billiards is the mark of a misspent youth".
Good track will depress slightly and 'controlledly' under HAL and then come up as the load comes off. This shows reasonable compression and shock absorption, which is part of what good track does (that reduces noise). Concrete ties don't 'give' -- they largely depend on the elastomer pad and spring clips to provide shock cushioning.
But more than a slight depression -- and different depression at different close points along the track -- is a Bad Thing. This is not just limited to mud spots pumping themselves ever deeper into a hole; where there is a difference in track stiffness (MC will give you the technical terms if you want them) the smooth vibration up and down can suffer an abrupt reflection, leading to increased wear and other problems at places like crossings or unballasted bridges. In the old days you 'tuned' the track across such transitions, sometimes by varying rail size or tie spacing. Amtrak did a study a few years ago that purported to find that bridge tuning turned out to be largely unnecessary, which I doubted at the time and find I still doubt; this may be another finding like the one that flat wheels don't cause covert roller-bearing damage.
What you ESPECIALLY don't want is track that is so bad that wheels in adjacent bad spots don't actually bend the rail ABOVE rest level. I had forgotten this was technically possible until someone showed a video of it.
As an aside: Paul Kiefer at NYC conducted augment tests on one of the Hudsons, spinning it up on a greased section of test track to the equivalent of 161 to 163mph. On properly stiff lined and surfaced track, this rotational speed produced no wheel-lifting in augment (something that couldn't be said for C&NW E4b at a far slower rotational speed!) BUT on what Kiefer called 'softer' track, that level of augment was observed.
7j43k... The OP was asking about track design: is it meant to be as rigid as possible, or is it meant to flex as a train passes? That it DOES flex I won't argue. That a rigid design DOES degrade I won't argue. What I disagree on is that the intent of the track designers and installers is that it is DESIRABLE and INTENDED to do so. It is not. That "quality" is minimized as much as possible. Ed
Things are designed in reality - not in absolutes.
Ever been stopped on a substansial bridge in your lane of traffic and feel the effects of moving traffic that continues to move on another lane? You can feel motions that are generated by that moving traffic.
Engineering structures do move when subjected to the forces they are designed to handle. Trouble happens when that movement EXCEEDS the designed allowance. Everything in Engineering has design allowances.
Even more to the point, most engineering structures are DESIGNED to move. They don't move enough to reach the yield point of their materials.
A truly stiff track structure -- like the old slab track with direct fixation -- was a reflected-shock nightmare. Both in terms of noise and poor riding. Some of the development of 'corrugations' over time in light rail systems is the interaction of very stiff primary and soft secondary suspension and track vibration.
Conversely, the Germans had the clever idea shortly after WWI that actually putting spring action in the track would reduce running shock and augment problems. What they neglected was damping. On test, oscillations rapidly built up to bounce greater than flange height. Now you will recall from the US Army demolition film that trains can be tolerant of all sorts of vertical interruption... as long as they're going straight and, as before East Palestine, with all the cars in draft. Bounce on a curve and...
I have nothing to add, other than this is a very informative discussion.
Thanks to all.
The mantra has always been that you only need 3 things for good track.
Drainage, more drainage, more and better drainage
tree68 We can't forget that contaminants get added to the ballast as well. I understand that this has been a problem with the Powder River coal lines, with coal dust fouling the ballast.
Dirt and road salt at level crossings is also a big problem (concrete ties aren't used at crossings because of corrosion). Around here they seem to dig up and replace crossing panels every few years, but it only takes a few months before they start feeling rough and looking muddy again.
Bridges flex slightly under the weight of a train. So does the track, even good track, and in some areas where it has been laid over muskeg the whole subgrade will move slightly as a train passes over it.
"Just make it more rigid" isn't always the best solution.
Greetings from Alberta
-an Articulate Malcontent
In the same vein, do the heavier cars of today produce more damage than those of 50-60 years ago?
Who can forget movies of the decrepit tracks of Penn Central, with cars bouncing like a kid on a trampoline? Or was that good design?
charlie hebdoIn the same vein, do the heavier cars of today produce more damage than those of 50-60 years ago? Who can forget movies of the decrepit tracks of Penn Central, with cars bouncing like a kid on a trampoline? Or was that good design?
In as much as Penn Central documented having stopped trains derailing in place - Penn Central track was not the bastion of good design and up to date maintenance.
charlie hebdo... do the heavier cars of today produce more damage than those of 50-60 years ago?
Except... at a point not much if indeed any heavier than 315K car weight, and normal freight wheelset size, the contact patch can get so heavily stressed that the work-hardened martensite layer actually cracks and the railhead under it can deform with cracks developing. To an extent, head-hardened rail staves this off, but the effects of even small wheeltread damage are greatly magnified above a certain weight.
OvermodOddly enough, not so much to the track and subgrade, and much of that damage can be remediated with modern track-maintenance equipment and regular periodic rail dressing. This is not a railroad equivalent of heavy trucks pounding Interstate highways into tilted-slab torture. Except... at a point not much if indeed any heavier than 315K car weight, and normal freight wheelset size, the contact patch can get so heavily stressed that the work-hardened martensite layer actually cracks and the railhead under it can deform with cracks developing. To an extent, head-hardened rail staves this off, but the effects of even small wheel tread damage are greatly magnified above a certain weight.
Such frequent maintenance costs moolah and the railroads don't seem to be very generous in that regard. Add to that the large number of partially flattened wheel treads (the definition of what is a flat wheel may be designed to obfuscate the problem that anyone with decent hearing can detect) and you have hammer blow.
So many other nations that run many trains seem to manage to electrify, at least on main trunks. I suppose that won't happen here.
charlie hebdo Overmod Oddly enough, not so much to the track and subgrade, and much of that damage can be remediated with modern track-maintenance equipment and regular periodic rail dressing. This is not a railroad equivalent of heavy trucks pounding Interstate highways into tilted-slab torture. Except... at a point not much if indeed any heavier than 315K car weight, and normal freight wheelset size, the contact patch can get so heavily stressed that the work-hardened martensite layer actually cracks and the railhead under it can deform with cracks developing. To an extent, head-hardened rail staves this off, but the effects of even small wheel tread damage are greatly magnified above a certain weight. Such frequent maintenance costs moolah and the railroads don't seem to be very generous in that regard. Add to that the large number of partially flattened wheel treads (the definition of what is a flat wheel may be designed to obfuscate the problem that anyone with decent hearing can detect) and you have hammer blow. So many other nations that run many trains seem to manage to electrify, at least on main trunks. I suppose that won't happen here.
Overmod Oddly enough, not so much to the track and subgrade, and much of that damage can be remediated with modern track-maintenance equipment and regular periodic rail dressing. This is not a railroad equivalent of heavy trucks pounding Interstate highways into tilted-slab torture. Except... at a point not much if indeed any heavier than 315K car weight, and normal freight wheelset size, the contact patch can get so heavily stressed that the work-hardened martensite layer actually cracks and the railhead under it can deform with cracks developing. To an extent, head-hardened rail staves this off, but the effects of even small wheel tread damage are greatly magnified above a certain weight.
And thus Wheel Impact Load Detectors have been installed by the carriers at strategic locations on their properties to detect flat wheels and set in place procedures to see that the bad wheelsets are changed out.
When the PRR electrified their section of the NEC the Federal Government was involved in financing it, in part, as a public works project to alleviate the effects of the Great Depression.
I haven't heard either to current or previous administrations propose any specific corporate welfare for the railroads to electrify.
charlie hebdoAdd to that the large number of partially flattened wheel treads (the definition of what is a flat wheel may be designed to obfuscate the problem that anyone with decent hearing can detect) and you have hammer blow.
A rule of thumb that I've heard is that if you can hear the flat wheel from seven cars away, it needs attention.
NORAC 11 has a rather specific set of guidelines for evaluating a flat wheel:
71. Flat Spots If a flat spot on a wheel of a car or engine develops enroute, a member of the crew must inspect it. Upon completion of inspection, the train will be governed as follows: A. Proceed at Normal Speed: The train may continue at Normal Speed if no other defects affecting movement are observed, AND if: 1. The flat spot is less than 2½ inches in length. OR 2. If there are 2 adjoining spots, each is less than 2 inches in length. B. Proceed at 10 MPH: If a flat spot is found in excess of either of the above dimensions, but less than 4 inches, and no other defect is observed, two actions must be taken: 1. Speed must not exceed 10 MPH. 2. A report must be made promptly to the Dispatcher. C. Remain Stopped: If a flat spot of 4 inches or greater is found, the train must remain stopped until a report is made to the Dispatcher. When determined safe for movement, the Dispatcher will order the car or engine to be set out at the first available siding or terminal.
71. Flat Spots
If a flat spot on a wheel of a car or engine develops enroute, a member of the crew must inspect it. Upon completion of inspection, the train will be governed as follows:
A. Proceed at Normal Speed: The train may continue at Normal Speed if no other defects affecting movement are observed, AND if:
1. The flat spot is less than 2½ inches in length. OR
2. If there are 2 adjoining spots, each is less than 2 inches in length.
B. Proceed at 10 MPH: If a flat spot is found in excess of either of the above dimensions, but less than 4 inches, and no other defect is observed, two actions must be taken:
1. Speed must not exceed 10 MPH.
2. A report must be made promptly to the Dispatcher.
C. Remain Stopped: If a flat spot of 4 inches or greater is found, the train must remain stopped until a report is made to the Dispatcher. When determined safe for movement, the Dispatcher will order the car or engine to be set out at the first available siding or terminal.
I would imagine that other railroad rulebooks have similar parameters.
And just how could the operating crew be aware of a flat spot on a car 2000' back?
charlie hebdo And just how could the operating crew be aware of a flat spot on a car 2000' back?
WILD detectors (wheel impact), and roll-bys. By rule, every employee is required to inspect any train that passes them. This is where that seven car rule of thumb can come into play.
nevermind
An "expensive model collector"
Equipment engineers look at the track as the primary suspension with a spring constant of about 1,000,000 lbs/in. If track could be built perfectly ridged, this would result in loads infinitely high, something that no engineer would want to see. A previous employer had a lot of elevated track on precast concrete bridge structures. They resenoated at about 1.5 cycles / second. With some experience one could separate the car suspension perbations from the bridge structure motion, which was quite noticeable.
1M pounds/inch? That's not much flex. The calculations must be pretty precise if that's even included.
From what I've read here and elsewhere, infinitely rigid would be bad but having the trackbed well tamped and just the give/cushion given by the wooden ties is enough/desirable. The amount of flex I've seen is 1/2 to the full depth of the wooden ties and, from what I've read, that much movement is bad.
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