Overmod,
You brought up some points in the tenth post from the top of the preceding page which I was going to respond to, but I am a little confused. In some of the quotes there that you respond to, you appear to be responding to me. But those quotes are what I quoted from the TSB report of the CN wreck.
I definitely understand your point about the lag screws not being able to provide clamping much force unless they were to have spring washers or some means to store energy. It was the TSB that said the plates lost some of their ability to resist lateral movement due to the loss of clamping pressure, which was the result of the screws breaking. If I am not mistaken, the plates in the CN wreck had elastomer cushion plates under them. If so, perhaps the compression of those plates would act as a force accumulator to provide active compression that would maintain the friction to resist lateral movement of the plate on the tie.
Electroliner 1935 Also, has anyone learned about the cause of the bolt failure?
Also, has anyone learned about the cause of the bolt failure?
As I understand it, the screws fail from fatique cracking, I suppose from a combination of tension and bending force. From what I see, this U.P. derailment has the same cause as the CN derailment in 2012, yet U.P. is acting like the cause of the Mosier wreck was unprecedented.
It also seems as though the cause of the CN wreck was unanticipated because they had no previous experience with breaking lag screws. I would have thought that the CN wreck would have been recognized throughout the industry for revealing this screw breaking problem and the inability to detect it. So I am puzzled that this has apparently now caught U.P. off guard.
I'm using the 'quote' function to cite references, whether in a previous post or an outside reference. If that's irritating or confusing to anyone I can go back to using inline single or double quote marks, or type in a more specific 'user+"xxx"' tag to identify each reference when it comes up.
EuclidIf I am not mistaken, the plates in the CN wreck had elastomer cushion plates under them.
I think you are mistaken, but it is important to realize where the specific "mistake" is, and why. Go back and look at a couple of descriptions of the Pandrol wood-tie system (and the UP lag-screw explanation) and see where the 'elastomer cushion plate' is located.
Early spring-clip track systems suffered from metal-to-metal contact and lack of shock attenuation -- there is no place for the reflected energy that makes the rail 'bounce' against the clips to go but into noise and vibration and so forth. So a compliant 'damping' substance is put under the base of the rail, and sometimes between the clip and the top of the base, to absorb the running shock.
It would make less than no sense to put the elastomer under the plate itself, where compression would instantly unload the screws. The idea is to have the plate held down solidly whatever the forces in the rail itself, with the relatively elastic wood of the tie being all the 'elastomer' needed under the plate, and compression of the wood by the volutes of the lag screws providing the clamping force and preload to keep the plate bases firmly on the ties so they cannot slide.
If so, perhaps the compression of those plates [he means 'elastomer plates'] would act as a force accumulator to provide active compression that would maintain the friction to resist lateral movement of the plate on the tie.
That is a good thought in principle, but not the place you want the compliance, and of course far more expensive than putting it in the right place, e.g. between the plate and the underside of the bolt heads to keep the plate clamped down on a flat datum surface (and also in a different way between the rail base and the top of the plate to damp the shock between rail and the structure that elastically holds and aligns it)
[EDIT -- I seem to be getting more and more confusing in describing things so they make no sense to 'normal people'. The bottom of the 'plates' -- rolled or cast -- needs to rest firmly on the ties, with the screws holding it down very firmly BOTH so that it can't shift laterally in any direction AND so that it can't lift or rock. It might help to think of the design as re-creating the effect of seats and anchors in concrete ties, where any relative motion is a Bad Thing but very careful damping and shock reduction needs to exist between the rail and the clips and seats that hold it in line and gauge and cant.]
From NTSB statement by Christopher O’Neil
“The NTSB recognizes the impact of this accident, or any rail accident involving hazardous materials, in environmentally sensitive areas and in proximity to residential, commercial and recreational areas, and understands the concerns of those affected…
“Upon notification of this accident we gathered information from the Federal Railroad Administration, the operator (Union Pacific) and local responders to understand the preliminary information related to the accident. Based on that information, the NTSB did not launch a full investigative team. However, because the accident involved the breaching of rail cars, including the CPC-1232 tank cars, we are actively collecting information from the FRA and the UP. Information collected will be assessed to determine whether further safety recommendations are necessary.”
You are right that there is no cushion between the plate and the tie. I gather that your comment on the lack of any spring loading to maintain friction of that joint was directed to the TSB. They had said this:
“If the screws are tight on the rolled plates, the clamping force produces friction between the plate and the tie, providing lateral resistance to gauge-widening forces in the curve. If the screws are loose, they act as pins, providing the sole lateral resistance. When this happens, the flat bottom rolled plates move under load and can break (Photo 8). Failure of the screws is usually due to a combination of shear and bending, as all screws do not receive even loading.”
It sounds like they are saying that clamping force is maintained just by keeping the screws tight, notwithstanding your point that the slightest loosening of the screws would eliminate 100% of the clamping force because there is very little storage of that force.
Regarding the quotes you used in your earlier post that I mentioned, I have no problem with multiple quotes. Here is what I was referring to: You began with a quote that I said, and attributed it to me. Then you followed with several other quotes with no attribution identified. Some of those were said by me and some were said by the TSB of Canada. In the case of one or more of those that were said by the TSB, you responded as though I had said it. Here is an example:
Statement by the TSB that you quoted:
“Even with broken lag screws, there was little indication that the curve was under stress, as track gauge was maintained by the lag screws that did not break. The remaining intact lag screws experienced much higher lateral curving forces.”
Your response to the quote from the TSB:
“These are important points to remember, together. It is not exactly a contradiction to what you said above, because what you meant was that there was little VISIBLE sign of the curve being under stress, a plurality of screws (whether still clamping or loose but acting as pins) holding the plates in rough gauge no matter how far they were deflected or bending. Naturally, the fewer the fasteners taking up the particular vectors of load, the more failures were induced, leading to some acceleration of deterioration which -- unsurprisingly -- proceeded to the point of failure.”
********************************************
There are things about the quote function of the forum that I do not understand. With my computer, it leaves a lot of wasted space in the quoted material between multiple quotes from a stack of people when all extracted as one quote. I find that if I try to close up some of that wasted space by editing it out, the quote structure loses its natural attribution labeling of who actually said the quote. And of course, once the message is posted, there is no way to edit the quote in a way to re-insert that natural attribution because you cannot re-take quotes during an edit.
EuclidIt sounds like they [the TSB] are saying that clamping force is maintained just by keeping the screws tight, notwithstanding your point that the slightest loosening of the screws would eliminate 100% of the clamping force because there is very little storage of that force
Yes, and further, I think the TSB establishes (although they do not make the point directly in context) that if one screw loosens, it throws additional force on the others, including in directions the screws and their 'interaction zone' with the holes in the tie are not designed to withstand directly.
I remember a discussion of similar forces in conjunction with the wrought-iron rivets used in Titanic's construction. While I do not want to encourage any comparison of modern lag-screw fabrication or 'quality' with wrought-iron riveting technology and its demonstrable shortcomings, I do see a number of applicable parallels in the assumptions of the "fabricating systems", and personally I experience a similar level of alarm looking at that situation.
Regarding the quotes you used in your earlier post that I mentioned, I have no problem with multiple quotes. Here is what I was referring to: You began with a quote that I said, and attributed it to me. Then you followed with several other quotes with no attribution identified.
That is just laziness or sloppy application of "proper" attribution semantics. In particular, with respect to:
[quote] ... Here is an example: Statement by the TSB that you quoted: “Even with broken lag screws, there was little indication that the curve was under stress, as track gauge was maintained by the lag screws that did not break. The remaining intact lag screws experienced much higher lateral curving forces.” Your response to the quote from the TSB: “These are important points to remember, together. It is not exactly a contradiction to what you said above, because what you meant was that there was little VISIBLE sign of the curve being under stress, a plurality of screws (whether still clamping or loose but acting as pins) holding the plates in rough gauge no matter how far they were deflected or bending. Naturally, the fewer the fasteners taking up the particular vectors of load, the more failures were induced, leading to some acceleration of deterioration which -- unsurprisingly -- proceeded to the point of failure.”]
the only excuse I can provide is that I was commenting on your having provided the TSB comment in your post, rather than your expressing the idea(s) in the TSB comment as your own ... it's a poor excuse. Made even more so by the work I have to do on quotes inserted by the forum software ...
I have to do a relatively enormous amount of editing, especially with nested quotes, to get them to register properly and not contain excessive 'white space'. I note, for example, that the 'close quote' tag is autospaced by a couple of carriage returns down from the end of the material that was quoted -- hard to explain this as anything but sloppy coding or poor choice of usability -- but with some care I can use delete and backspace to edge out most of the vertical space ... occasionally using the edit-undo feature if I go too far and screw up the weird default paragraph spacing my system renders. (I also have to go through and re-insert all the little emoticon smileys that aren't properly rendered in quoted text, another telling little coding failure on tech's part, and I usually just delete them if I'm short on time or patience...)
Something that has relatively recently shown up in the circus programming is the use of some kind of tabs-and-backspace-set-quote-level thing when I quote something that already contains nested quotes. Here even one delete or backspace 'too far' completely deranges how the quotes display, and of course there is no help or guidance for how that formatting works or was intended to work. So I have to go through manually and insert all the quote and /quote tags properly, checking each time by "posting early" that the actual result renders correctly, and this takes time and -- occasionally, as in a post I made a couple of days ago -- the tags even though seemingly correctly formatted fail to produce actual quotes; they just sit there in undifferentiated text unrecognized.
Now, I will say this: on the system I am using (Firefox 47 on a Lenovo X220 running Windows 10) I get all the quotes in editable form when I respond to a post, so I can go in and clean up all the previous quote syntax if I want (and I try to do that, including correcting spelling errors or trimming some of the actual material -- some people, Juniatha for one, don't think that is ethical.) So you will have to tell me what system you're using and what the problems with quote editing actually manifest as -- do you have screen captures that show what you're seeing?
I am evidently not smart enough, or gamer enough, to figure out the mystery-meat syntax for easy 'default' formatting of quotes without excess white space but with proper quote level preserved. I also often find it tedious to insert the "user="" " tags into quotes to get the attributes properly attributized... although of course that's a nifty way to comment on sources, not just identify who originally said a particular thing.
Maybe tech will improve this ... but I think it is a relatively small priority for them, and in any case I would much rather have them concentrate on fixing the issues with improperly-crafted scripting or hangs in the ad-serving mechanisms for forum pages, or hunting down and disciplining advertisers using certain kinds of full-motion ads that are annoying...
Euclid Overmod, You are right that there is no cushion between the plate and the tie. I gather that your comment on the lack of any spring loading to maintain friction of that joint was directed to the TSB. They had said this: “If the screws are tight on the rolled plates, the clamping force produces friction between the plate and the tie, providing lateral resistance to gauge-widening forces in the curve. If the screws are loose, they act as pins, providing the sole lateral resistance. When this happens, the flat bottom rolled plates move under load and can break (Photo 8). Failure of the screws is usually due to a combination of shear and bending, as all screws do not receive even loading.” It sounds like they are saying that clamping force is maintained just by keeping the screws tight, notwithstanding your point that the slightest loosening of the screws would eliminate 100% of the clamping force because there is very little storage of that force. Regarding the quotes you used in your earlier post that I mentioned, I have no problem with multiple quotes. Here is what I was referring to: You began with a quote that I said, and attributed it to me. Then you followed with several other quotes with no attribution identified. Some of those were said by me and some were said by the TSB of Canada. In the case of one or more of those that were said by the TSB, you responded as though I had said it. Here is an example: Statement by the TSB that you quoted: “Even with broken lag screws, there was little indication that the curve was under stress, as track gauge was maintained by the lag screws that did not break. The remaining intact lag screws experienced much higher lateral curving forces.” Your response to the quote from the TSB: “These are important points to remember, together. It is not exactly a contradiction to what you said above, because what you meant was that there was little VISIBLE sign of the curve being under stress, a plurality of screws (whether still clamping or loose but acting as pins) holding the plates in rough gauge no matter how far they were deflected or bending. Naturally, the fewer the fasteners taking up the particular vectors of load, the more failures were induced, leading to some acceleration of deterioration which -- unsurprisingly -- proceeded to the point of failure.” ******************************************** There are things about the quote function of the forum that I do not understand. With my computer, it leaves a lot of wasted space in the quoted material between multiple quotes from a stack of people when all extracted as one quote. I find that if I try to close up some of that wasted space by editing it out, the quote structure loses its natural attribution labeling of who actually said the quote. And of course, once the message is posted, there is no way to edit the quote in a way to re-insert that natural attribution because you cannot re-take quotes during an edit.
Just a few thoughts:
If friction between the plate and tie as a result fo the clamping force provides significant resistance to movement, would not the weight of the car provide a similar clamping force, enhancing the friction?
Once the lags get loose and act like pins, how does that differ from a spike? Do plates fail with spikes as well?
Question: Is there any indication which side of the rail the lag failures occur? Gauge side or field side? I would think that the screws on the inside would be subjected to shear, bending, and tensile forces where the screws on the ouside would be subjected just shear and bending.
AnthonyV Just a few thoughts: If friction between the plate and tie as a result fo the clamping force provides significant resistance to movement, would not the weight of the car provide a similar clamping force, enhancing the friction? Once the lags get loose and act like pins, how does that differ from a spike? Do plates fail with spikes as well? Question: Is there any indication which side of the rail the lag failures occur? Gauge side or field side? I would think that the screws on the inside would be subjected to shear, bending, and tensile forces where the screws on the ouside would be subjected just shear and bending.
I think the weight of the car weight would add a lot to the clamping force, although it would be of a pulsing nature as each wheel loads and unloads its weight on the plate. Whereas, the lateral force of a curve that the clamping force is hoped to offset may be more constant, if it happens to be more spread out through the rail compared to the compression of the weight of the wheels.
Broken lags acting as loose pins differ from spikes in that the loose upper part of the broken lag is not as deep and tight as a spike. But spikes can loosen and cause the same effect as the loose part of the broken lag, so the lag screws are intended to be an improvement over that shortcoming of spikes. As I understand it, the U.P. Mosier line only uses the lag screws on curves.
I assume that lag screws typically break on the outside rail of curves. I don't know if they tend to break more on one side of the rail versus the other sides. I can see your point that screws on the outside of the rail would not provide much, if any, tensile force on the screws.
These are reasonable thoughts.
AnthonyVIf friction between the plate and tie as a result fo the clamping force provides significant resistance to movement, would not the weight of the car provide a similar clamping force, enhancing the friction?
Yes, and it is possible to calculate the length of rail near or over the plate where this clamping force becomes substantial.
Part of the problem is that you should remember that the spring clips always provide a 'perfect' elastic connetion in tension between the plate and the rail base, just as they do when concrete ties are used. But only the inertia of the plate itself -- which is not very much -- actually resists any forces other than compression that the rail exerts on the tie.
And there are vertical accelerations in tension, both due to force transmitted from the train's motion to the rail as a beam, and to the acceleration of the rail as the train's weight comes off the increased loading. If you watch even well-maintained CWR track it's not unusual to see the whole structure move up and down repeatedly as the weight comes on and off. There is an upward acceleration on the lags each time the rail rises back up and the springs carry the plate along... although, of course, the load on the rail never comes anywhere near zero (which would be an open invitation to a different sort of catastrophe altogether!)
Perhaps a better way to make the point I think you're intending is that it is precisely at the times of highest increased wheel load that you'd be getting lateral flange force trying to displace the plate sideways against friction, bending lag shanks, etc. So yes, I'd expect this to help against a 'shift under the train'
AnthonyV Question: Is there any indication which side of the rail the lag failures occur? Gauge side or field side?
Once the lags get loose and act like pins, how does that differ from a spike? Do plates fail with spikes as well?[/quote]
I don't think anyone has implemented sprung-clipped track with spikes, at least not successfully -- for reasons you can easily imagine if four substantial lag screws are specified for necessary plate retainment! You'd want to go back and look at the history of systems that used lag-screw type primary retention (I think France being an example of a country that used that method of fixation) to see what the maintenance intervals, failure modes, etc. were as compared to driven spikes.
That noted, part of the issue is how little a 'lifted' spike still deflects laterally, compared to a bolt with a circular shank and perhaps sharp edges on its threaded 'retaining' surfaces, and the degree to which the rail itself would move in spiked track (relative to the hard contact of its seat in the tieplate) rather than lever the whole tieplate itself with a longer lever arm.
Some of this was covered in the TSB report Euclid linked, but I do not think that by the time the accident occurred and the TSB actually investigated the conditions it was possible to determine where the 'action' initially started. Once a lag is loose, gauge or field side, it is likely to aid in loosening others - it certainly won't help relieve any forces that would tend to cause a derailment, as far as I can see...
I would think that the screws on the inside would be subjected to shear, bending, and tensile forces where the screws on the ouside would be subjected just shear and bending.
Assuming we are talking about the 'loaded' outside rail in a curve, I would tend to agree, except there may be some (relatively slight) tension on the field side if the actual rotation of the plate takes place around its outer edge, rather than the 'fulcrum' of a pinned connection due to lateral contact with the plate shifting outward. Remember that some of the force involved may be the result of energy 'stored' in the spring action of the clips, or transmitted via shock for a railhead impact that accelerates through spring compliance and then transfers momentum when the clip action 'bottoms' more or less abruptly.
AnthonyVOnce the lags get loose and act like pins, how does that differ from a spike?
A lag bolt without a head would have near zero holding power on the track structure.
A loose spike may not be able to prevent a rail from rolling over, but would likely still help hold the track in gauge.
If the lags are failing due to corrosion, the damage to the metal may reach into the tie. If that is the case, a broken lag may have no presence above the top of the tie. And, as there is apparently no current method for inspecting the lags, a section of track may well be almost literally hanging on by a thread so that when a few bolts give way and begin the process of allowing the rail to move, other bolts may follow in rapid succession.
Then there comes the maintenance angle. If a spike is coming out, I can drive it back in, or pull it out, drive in a plug, then redrive a spike into the tie. Problem solved.
I would opine that dealing with broken lags may well require complete replacement of the tie, unless the tie place can be moved over to where new lags can be driven.
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...
Based on the experience of the 2012 CN derailment, here is what the TSB says to do in order to inspect for this problem:
When conducting inspections of curves, turnouts, and bridge decks with screw spikes, please be governed by the following:
tree68I would opine that dealing with broken lags may well require complete replacement of the tie, unless the tie place can be moved over to where new lags can be driven.
The solution I developed involves special tools that are applied to one or more spindles of a machine that drills holes to plug ties in the field.
If necessary, a tool is inserted to gauge any deflection or binding of the broken lag stem in the hole, and straighten it as vertical as possible.
A tool that is basically a tube saw with relief for 'saw chips' is then inserted into the hole, and cuts out an annular recess with the broken stem in the center, self-aligning over the metal piece as it goes. Air can be blown in to clear if desired. When drilled to appropriate depth, the stem piece is cross-fractured and lifted out of the hole (probably with a magnet rather than a gripping tool).
A second tool can be inserted to provide 'undercuts' or waves in the wall of the hole, so that the material of the subsequent plug will expand and key into the tie wood more positively.
The plug itself is made out of stronger 'engineered wood' than an ordinary spike plug, and can of course be made as a tube with preboring of appropriate size to expand it into the above-mentioned keying when a new lag screw is inserted. It will probably be driven a bit more than flush with the seating surface so as not to produce a false clamping surface, but I welcome informed opinion that would prescribe otherwise. I expect the normal sort of preservative and then adhesive, fiber-swelling material (cf. 'Chair-Loc'), "wood hardener", etc. that is used with plugging to be applicable here. Grain and binder is such that the 'joint' between the bore and the inserted lag is reasonably watertight even upon some lateral deflection of the bolt shank with age.
Of course ordinary treated-wood plugs of the appropriate 'oversize' could be driven in, and then drilled in the usual fashion for installing the plate fixation system in the first place,
Overmod The solution I developed involves special tools that are applied to one or more spindles of a machine that drills holes to plug ties in the field.
That sounds very interesting. Did you invent that and develop it as a product that is being sold to the industry? It sounds well thought out and useful.
Excerpt from The Dalles Chronicle, Jun. 14
Jason Rea, chief engineer for the western region of Union Pacific Railroad, described at a community meeting Friday in Mosier what had caused the June 3 derailment of 16 oil cars.
The so-called lag screws, which are threaded, are used on curves instead of a straight track spike. And while the lag screws had been severed about two and a half inches below the head of the screw, the top of the screw did not dislodge. Had they dislodged, it would have been detected by a visible inspection, Rea said.
Rather, the sheared screw or screws remained in place.
“I don’t know of any that it has ever happened to,” Rea told the Chronicle after the meeting. “I’ve never experienced this kind of derailment.” He said he’s seen multiple derailments in his many years with the railroad.
The lag screws were implemented in 1999, he said.
Each rail tie has eight spikes or screws in it. The spikes or screws – four on each end — hold in plates that secure the rail to the tie.
The railroad doesn’t know how many were sheared before the derailment, but some were sheared after a wheel was derailed.
The wheel derailed about 3/10 of a mile east of where the crash actually occurred. Technically, the derailment is where the wheel leaves the rail, and the crash site is called the point of rest.
When the derailment site was inspected, Rea said some of the lags didn’t pop off, but some did.
So; a question for Mud Chicken.
Why the lag screws. I have photos of a class one near me doing a curve rail I believe is six degrees or more and they used rolled tie plates and Pandrol clips. That was in '06 and they just redid it this year. What is the (supposed) advantage of the lag screws?
Norm
tree68 AnthonyV Once the lags get loose and act like pins, how does that differ from a spike? It's been my impression here that the problem is not loose lags - it's broken lags. A lag bolt without a head would have near zero holding power on the track structure. A loose spike may not be able to prevent a rail from rolling over, but would likely still help hold the track in gauge. If the lags are failing due to corrosion, the damage to the metal may reach into the tie. If that is the case, a broken lag may have no presence above the top of the tie. And, as there is apparently no current method for inspecting the lags, a section of track may well be almost literally hanging on by a thread so that when a few bolts give way and begin the process of allowing the rail to move, other bolts may follow in rapid succession. Then there comes the maintenance angle. If a spike is coming out, I can drive it back in, or pull it out, drive in a plug, then redrive a spike into the tie. Problem solved. I would opine that dealing with broken lags may well require complete replacement of the tie, unless the tie place can be moved over to where new lags can be driven.
AnthonyV Once the lags get loose and act like pins, how does that differ from a spike?
It's been my impression here that the problem is not loose lags - it's broken lags.
Euclid If the screws are tight on the rolled plates, the clamping force produces friction between the plate and the tie, providing lateral resistance to gauge-widening forces in the curve. If the screws are loose, they act as pins, providing the sole lateral resistance. When this happens, the flat bottom rolled plates move under load and can break (Photo 8). Failure of the screws is usually due to a combination of shear and bending, as all screws do not receive even loading.” It sounds like they are saying that clamping force is maintained just by keeping the screws tight, notwithstanding your point that the slightest loosening of the screws would eliminate 100% of the clamping force because there is very little storage of that force.
If the screws are tight on the rolled plates, the clamping force produces friction between the plate and the tie, providing lateral resistance to gauge-widening forces in the curve. If the screws are loose, they act as pins, providing the sole lateral resistance. When this happens, the flat bottom rolled plates move under load and can break (Photo 8). Failure of the screws is usually due to a combination of shear and bending, as all screws do not receive even loading.”
My question was in reference to the comment noted above.
Norm48327 What is the (supposed) advantage of the lag screws?
What is the (supposed) advantage of the lag screws?
https://en.wikipedia.org/wiki/Rail_fastening_system
“The screw spike has a higher cost to manufacture than the rail spike, but has the advantage of greater fixing power - approximately twice that of a rail spike.”
AnthonyVMy question was in reference to the comment noted above.
Have you gotten a good enough answer yet?
Overmod AnthonyV My question was in reference to the comment noted above. Have you gotten a good enough answer yet?
AnthonyV My question was in reference to the comment noted above.
What are you talking about? I was responding to Tree68's comment that we were not talking about loose lag screws, when in fact there was discussion of this.
Euclid Norm48327 What is the (supposed) advantage of the lag screws? https://en.wikipedia.org/wiki/Rail_fastening_system “The screw spike has a higher cost to manufacture than the rail spike, but has the advantage of greater fixing power - approximately twice that of a rail spike.”
MC posting under two screen names now?
wanswheel[Jason Rea, chief engineer for the western region of Union Pacific Railroad said] The railroad doesn’t know how many were sheared before the derailment, but some were sheared after a wheel was derailed.
I would say that some broke over a long period of time leading up to the derailment. Then one or more broke as the final triggering event for the cause of the derailment. And finally one or more broke after the derailment began.
As I mentioned earlier, dragging the derailed car or cars for 3/10 of a mile between the initial point of derailment and the final resting place could have broken several screws on each tie.
It's not terribly difficult to differentiate between a recent break in a bolt and one that's been there for a while.
The question would be whether enough "forensic" information was preserved in the effort to re-open the line.
Inspection of the bolts beyond the reaches of the damage from the wreck will provide a lot of information as well - or maybe it already has.
Overmod I don't think anyone has implemented sprung-clipped track with spikes, at least not successfully
I don't think anyone has implemented sprung-clipped track with spikes, at least not successfully
In the process of searching for rail clip deflection data, I found this Pandrol document that discusses various projects, including a CSX project that uses clips and spikes (Page 22).
I found it interesting that the rail is held in place with both clips and spikes.
http://www.pandrol.com/wp-content/uploads/Track_Report_11.pdf
AnthonyV Overmod I don't think anyone has implemented sprung-clipped track with spikes, at least not successfully www.pandrol.com/wp-content/uploads/Track_Report_11.pdf
www.pandrol.com/wp-content/uploads/Track_Report_11.pdf
I appear to be wrong, repeatedly. Note the discussion of how the plates are fabricated from standard AREMA.
I noted also that some of the plates in R12E0008 have rectangular holes in them, which I understood to be used for a purpose like temporary spiking to position while the lags were driven. It might be interesting to find a discussion of why those holes are provided where they are.
I am wondering if this breaking lag screw problem is just a matter of growing pains in an evolution from cut spikes to screw spikes. Or is the problem perhaps now a thing of the past due to better fastening systems making the lag screw obsolete?
I do not know the answer to that. But whatever the answer, I am surprised that the problem was able to sneak up on the CN in 2012 and cause the disaster at Fabyan Trestle. Then after being thoroughly revealed to the industry in the subsequent TSB instigation, this lag screw problem still managed to sneak up on the U.P. in the Mosier wreck. Finally, after all this warning, the U.P. is checking all their lag screws.
The fundamental advantage of screws is that they hold better than nails. In construction, most of the loading is static, but rail fastenings are subject to dynamic loading under the passing trains. Apparently this dynamic loading and the resultant fatigue cracking has been underestimated as a colossal engineering error, only to be revealed by train wrecks. It would be interesting to learn how that miscalculation happened.
We have now learned that the holding power of the screw in a tie exceeds the screw’s ability to resist the dynamic loading over time. Can this deficiency be eliminated simply by making the screw stronger? Could the problem be solved by making the screw larger, such as 1.25” major diameter?
What about the threads themselves. The deep “V” threads of lag screws and their transition to the unthreaded shank create stress risers that that spawns the birth of fatigue cracks that grow over time and use. Could the geometry of the threads and shank be made more streamlined to reduce stress risers sufficiently?
Perhaps a better approach would be to use a rounded and shallower thread like a bottle thread, and use more of them at a finer pitch. That way, it leaves more material for a stronger shank in the threaded area. What if the hole in the tie were tapped with the proper threads to achieve a more precise relationship between the internal threads of the tie and external threads of the screw?
The goal should be to never have a screw break under any circumstance.
A sufficiently improved track screw will cost more, and some might say it will not be cost effective, but how cost effective are conventional screws that cause train wrecks?
In order to remove the burden of train wrecks from conventional screws, it requires costly regular inspection. Maybe that money should be spent on better screws.
Technology only moves forward with disasters attributed to the current technology. Creeping technology.
One failure is a fluke. Two failures indicates that the 1st wasn't a fluke and it is time to hit the design boards again. This is the path that humankind has taken to get to today and it is the path that will be followed into the future.
Improved technology always finds the weakest link in existing technology and then that gets improved and we find the next weakest link.
Never too old to have a happy childhood!
How often are lag screws replaced? UP rep said Mosier track was lag-screwed in 1999. If the one or more that broke was/were original, maximum life is 17 years?
I have not seen any information that indicates that breakage of lag screws was ever anticipated. It was known that they would unscrew. In the TSB report of the CN wreck at Fabyan Bridge, it said that partially unscrewed lag screws were easy to see because their heads were standing higher than normal. So inspectors turned those screws back down tight. But the broken lag screws gave no visual indication, so nothing was done about them during the tightening of loose screws.
The lag screws at the Fabyan Bridge site were installed in 1997 and the wreck happened 1/21/2012. So that is probably around 14 years of service. The report mentions that fatigue cracks began “many years” prior to the wreck.
wanswheelHow often are lag screws replaced? UP rep said Mosier track was lag-screwed in 1999. If the one or more that broke was/were original, maximum life is 17 years?
I think the premise 'at the time' was that the lags would outlast head-hardened rail ground at something like the 'magic wear rate', and be pulled (and cleaned and probably replaced without individual NDT inspection) en masse when the rail was turned or replaced. While I might not bet large sums of money that this assumption was not revisited when bainitic rail steels, etc. were being examined for adoption, I would not at all be surprised to find that it had not been.
The issue in any case is not that the lags would not screw out or pull 'proud' in service; it's that once they are not clamping, they experience stresses I don't think were modeled or analyzed correctly. Fabyan Bridge is sort of an extreme case in that many, many lags were known to be simultaneously loose, and the overall track geometry determined by a significant measure was verging on a need for critical intervention. So it's not surprising that what turned out to be a grossly unsafe condition progressed to catastrophe without obvious further warning -- what's new at Mosier was that similar catastrophic progression could result with good-faith inspection twice a week and conscientious attention to geometry and metallurgical rail integrity. It is only 'icing on the cake' that much of the "good faith inspection" as conducted would not detect precisely the most critical type of lag failure...
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