Oil Trains & Lag Screws

[Euclid]

Both the U.P. and the FRA seem to be in the hot seat over the fact that the lag screw mass failure at Mosier was not seen as it developed over many years.  U.P. said they did the inspections required by the FRA, and the FRA says the inspections they require are only the minimum.  I would say that inspecting the lag screws should have been a part of that “minimum.”

The TSB of Canada clearly defined the lag screw problem after investigating the CN Fabyan Bridge derailment in 2012.  That should have been a red alert wakeup call to the FRA.  But I guess the FRA was not required to consider it.   

http://www.opb.org/news/series/oil-trains/how-inspectors-missed-broken-bolts-mosier/

 

[tree68]

Barring some other technique (assuming such screws actually still get used after all this), I would suggest that perhaps the only inspection that will work will be the removal of some percentage of the lag bolts for an actual physical inspection.

As I recall, it's already been established that current inspection methods (I presume a visual in-place look at them) are not enough.

Should such bolts be considered for future use, I'd think that the screws pulled from Mosier would be carefully scrutinized for how they failed, and even when.  Some of the bolts in the picture look to have been broken off for quite some time, and others in the image seem to show a wide variety of modes of failure.

[Euclid]

tdmidget

[Euclid in blue text] "What this does is allow the screw shank to bend over some distance of the unthreaded shank, so the bending stress does not concentrate at the start of the threads and reduced shank"

"But bear in mind, that there will also be less bending with the use of the bushing because it spreads out the lateral force to a much larger area of wood surface."

Trying to have it both ways ,Bucky?

" The entire bolt would be encased in the threaded insert, so it cannot bend"

How can a bolt, or any other fastener, hold anything if it is entirely encased in something? A threaded fastener works by being in tension between the head of the fastener and what it is screwed in to, be it a nut or threaded object.

"So its ultimate failure would be shearing or breaking off right under the shoulder or flush with the top of the tie"

No, the weakest part of any threaded fastener is the minor diameter, which is usually the gullet of the threads. You can't change the laws of physics. The weakest point is where the least material is.

Curious, Buckey, What do you do for a living? Apparently nothing to do with machines or materials or you would know better.

Have it both ways?  You’ve got to be kidding.  I thought you of all people would readily understand it.  It is indeed a matter of having it both ways if you stop to think about it. 

The application of rail securement is full of constraints that prevent it from being one bit more reliable than what it takes to get by.  I don’t expect my suggestions to be adopted.  Any proposal that even requires an added part will be rejected out of hand.  At the very most, a slight change in screw metallurgy might be considered.  So there can be no ideal design solution.  That calls for compromise, or as you call it: “Having it both ways.”

As you must know, the lateral force on the screw causes it to crush the wood of the tie that surrounds the screw.   To do that, the screw must bend. 

So, the overall resistance to the lateral shifting of the tie plate is from two factors:

1. The screw’s resistance to bending.

2. The surrounding wood’s resistance to crushing. 

The wood’s resistance to crushing depends on the surface contact area between the screw and the wood.  The bushing adds to the screw diameter, thereby increasing the contact area.

Thus, the greater resistance to the crushing of the wood also adds to the screw’s resistance to bending. 

There is also a third element that contributes to the resistance of the lateral shifting of the tie plate.  That is that the bushing also directly stiffens the screw shank by effectively increasing its diameter.  That is what I mean by the screw being “encased” in the bushing.  Obviously, by “encased” I do not mean that the screw and bushing are bonded together as one; as you have seized upon as a point of criticism.  Obviously, it is a sliding fit between the screw and the bushing.   

HOWEVER: There will still be crushing of the wood and bending of the screw, even though they are greatly reduced by the application of the bushing.  The bending and crushing can never be zero.  And since ultimate failure always culminates over time with repeated load cycles, even a greatly reduced amount of bending and crushing will inevitably lead to failure if given enough time of use. 

The effect of the solid bushing around the unthreaded portion of the screw will nearly prevent bending there because for the screw to bend, the bushing would also have to bend.  But as you point out, the crushing of the wood will allow the bushing to tip; and that will allow bending of the screw shank; and that bending will simply be shifted to the part of the screw shank that is not surrounded by the bushing. And that part of the screw will be at the bottom of the bushing where the screw threads begin, which is the weakest point of the screw in terms of resisting bending, as you mention.  So, in that regard, while the bushing solves one problem, it creates another problem.

So this is where it calls for compromise, or “having it both ways” as you say.  The compromise is to open up the bushing bore for some distance above the start of the screw threads so the bending can spread out and not be concentrated at the weakest point of the screw shank.  Although the bore is opened up to clear the screw shank, the full length of the bushing O.D. is still tightly fitted to the corresponding bore in the wood tie.  That is the design compromise; the “having it both ways” with just the right amount of each way to achieve the “sweet spot.”  It is not perfect, but will nevertheless vastly improve the resistance to failure over the present system without bushings. 

[Euclid]

U.P. routinely inspected the track at Mosier every few days, but completely failed to detect the lag screw failure that had been in progress for many years.  Detecting the lag screw problem requires walking the track and pulling up on the heads of the screws.  The broken ones will lift right out of the hole, thus revealing the fact that they are broken.  In addition, every so many screws, one is actually unscrewed, removed, and visually inspected for corrosion, cracks, and damage.  Of particular importance is to check the condition of the screw shank right under the head because this damage precedes the actual breaking failure further down on the screw shank. 

In addition, the walking inspection includes looking for damage to the tie plate.  This link has a photo of the track at Mosier, and shows what can be found without actually lifting or unscrewing lag screws:

http://www.portlandmercury.com/blogtown/2016/06/16/18240394/state-defect-that-caused-mosier-oil-train-crash-wasnt-detectable

Even without the presence of broken and dislodged screws (as shown in the photo), there is critical visual evidence that the tie plate experiences cyclical sliding on the tie.  There is bluish, polished wood, stained with the carbon in the tie plate steel that exposed next to the outer edge of the plate.  This shows that the plate is worked back and forth with the passage of trains.  That visual indication alone is clear evidence of the defective screw connection.  But it will be missed by inspectors riding in hi-rail vehicles. 

These walking inspections need not be done every few days.  I suspect that every several months would be sufficient.  Another way to inspect in less detail, but sufficient find evidence of lag screw failure is by the use of a gage restraint vehicle.

Broken lag screws lead to gage widening, but simply checking the gage is not enough. This is because, as the problem develops, the gage on track with no passing train can be normal.  But when a train passes, the rails spread as the trucks pass, but spring back to normal gage after the trucks pass. 

So, to check if they will spread under a passing train, the gage restraint vehicle places lateral pressure on the rails as would happen with a passing train. It measures the track’s ability to hold the gage under the lateral force of a passing train:

https://www.fra.dot.gov/Page/P0291 

[Overmod]

Euclid

... there is critical visual evidence that the tie plate experiences cyclical sliding on the tie. There is bluish, polished wood, stained with the carbon in the tie plate steel that exposed next to the outer edge of the plate. This shows that the plate is worked back and forth with the passage of trains. That visual indication alone is clear evidence of the defective screw connection.

But note that the extent of this 'visual evidence' is likely very slight, in any case other than colossal deferred maintenance, for most of the early 'tension failure' effects -- it is only when all four lags are broken that horizontal excursion much more than shank clearance plus deflection will occur, and even then unlikely that one plate will deflect measurably more than its neighbors.  Much more likely in the latter case will be preferential 'shedding' of the deflection load into the perhaps-already-compromised lags in those neighbors, accelerating their own tendency to loosen, then deflect, then fail.  But note that the actual deflection needed to drop a wheel into the gauge, as presently claimed to be proximate cause at Mosier, is not much more than an inch.

This calls for much better machine vision systems for inspection and reporting, including proper three-axis positioning systems that will stand up to anticipated "inspection" running, storage, and maintenance conditions.  The hardware and at least some of the required control logic and software versions of such systems are, I think, already available from a number of industry suppliers: they just have to be adapted and reprogrammed for this use.

But it will be missed by inspectors riding in hi-rail vehicles.

Not if those vehicles have the machine-vision systems installed on them.  It might require some careful editing of existing rules to permit realtime monitoring screens to be used in rail-guided hi-rail vehicles (or permit their use by a second inspector riding in the vehicle) but high-speed data acquisition and automated pattern recognition can easily flag potential defects for near-instant review.

I also see little reason why some of the gage-restraint functions cannot be installed on a comparatively light vehicle (as they involve some mutual lateral outward displacement of paired wheels while the machine-vision system observes the effect).  Here the light weight of the vehicle may actually enhance the integrity of the measurements as there will be little tendency for the spring clips to deflect or the plates to friction-lock under the load of a typical geometry train or Sperry car.  (Note that it may be necessary to distinguish rail movement in the Pandrol spring clips from lateral movement of the plate due to loose or broken fasteners, but this should pose little technical difficulty for a properly-designed system.)

More to the point:  It should be cost-effective to adapt OTS machine-vision systems to multiple hi-rail vehicles, and then use them for streaming data acquisition and near-realtime analysis (to reduce the data-storage and transmission requirements) continuously, whenever a hi-rail vehicle runs over a given stretch of track.  What is then required is more prompt attention to the remediation of 'loose' lag screws ... at a minimum, gang-tightening them (at which time, of course, any broken lags or 'spindled' or internally-compromised ones will be discovered for remediation as well ... than existing track-geometry deviation calls for.  That was an expensive lesson for railroads to learn, but I think a far less expensive one than replacing miles of sprung track with dubious alternative technology...

[Norm48327]

If, as the article in the Portland Mercury News says, those bolts were installed in 2013 it kinda confirms my suspicion they were made from "junk steel" and not of a satisfactory grade for the task.

[Buslist]

Overmod

 

 

Euclid

... there is critical visual evidence that the tie plate experiences cyclical sliding on the tie. There is bluish, polished wood, stained with the carbon in the tie plate steel that exposed next to the outer edge of the plate. This shows that the plate is worked back and forth with the passage of trains. That visual indication alone is clear evidence of the defective screw connection.

 

 

But note that the extent of this 'visual evidence' is likely very slight, in any case other than colossal deferred maintenance, for most of the early 'tension failure' effects -- it is only when all four lags are broken that horizontal excursion much more than shank clearance plus deflection will occur, and even then unlikely that one plate will deflect measurably more than its neighbors.  Much more likely in the latter case will be preferential 'shedding' of the deflection load into the perhaps-already-compromised lags in those neighbors, accelerating their own tendency to loosen, then deflect, then fail.  But note that the actual deflection needed to drop a wheel into the gauge, as presently claimed to be proximate cause at Mosier, is not much more than an inch.

This calls for much better machine vision systems for inspection and reporting, including proper three-axis positioning systems that will stand up to anticipated "inspection" running, storage, and maintenance conditions.  The hardware and at least some of the required control logic and software versions of such systems are, I think, already available from a number of industry suppliers: they just have to be adapted and reprogrammed for this use.

 

 

But it will be missed by inspectors riding in hi-rail vehicles.

 

 

Not if those vehicles have the machine-vision systems installed on them.  It might require some careful editing of existing rules to permit realtime monitoring screens to be used in rail-guided hi-rail vehicles (or permit their use by a second inspector riding in the vehicle) but high-speed data acquisition and automated pattern recognition can easily flag potential defects for near-instant review.

I also see little reason why some of the gage-restraint functions cannot be installed on a comparatively light vehicle (as they involve some mutual lateral outward displacement of paired wheels while the machine-vision system observes the effect).  Here the light weight of the vehicle may actually enhance the integrity of the measurements as there will be little tendency for the spring clips to deflect or the plates to friction-lock under the load of a typical geometry train or Sperry car.  (Note that it may be necessary to distinguish rail movement in the Pandrol spring clips from lateral movement of the plate due to loose or broken fasteners, but this should pose little technical difficulty for a properly-designed system.)

More to the point:  It should be cost-effective to adapt OTS machine-vision systems to multiple hi-rail vehicles, and then use them for streaming data acquisition and near-realtime analysis (to reduce the data-storage and transmission requirements) continuously, whenever a hi-rail vehicle runs over a given stretch of track.  What is then required is more prompt attention to the remediation of 'loose' lag screws ... at a minimum, gang-tightening them (at which time, of course, any broken lags or 'spindled' or internally-compromised ones will be discovered for remediation as well ... than existing track-geometry deviation calls for.  That was an expensive lesson for railroads to learn, but I think a far less expensive one than replacing miles of sprung track with dubious alternative technology...

 

 

The problem with your machine vision approach is it only detects gage widening if the plates are translating, there is at least one other cause, rail rotation As it only measures delta gage. The beauty of the GRMS system is that it will detect both and any other causes Of wide gage under load. In fact a GRMS development vehicle detected a rash of broken hair pin spikes on Pandrol rolled plates around North America in the 90s. Peed off Pandrol as the industry heard about it first (as it was an FRA funded test)rather than Pandrol. I believe this lead to the use of the coach screw (as it was then called) rather than the hair pin as standard kit in the rolled plate system. Several Engineering Dept. officials assure me that a GRMS inspection would have caught this if conducted more frequently than UP's 18 month interval.

[Overmod]

Buslist

... a GRMS development vehicle detected a rash of broken hair pin spikes on Pandrol rolled plates around North America in the 90s.  Peed off Pandrol as the industry heard about it first (as it was an FRA funded test)rather than Pandrol.  I believe this led to the use of the coach screw (as it was then called) rather than the hair pin as standard kit in the rolled plate system.

I feel reasonably certain that we are to see reintroduction of one sort or other of hairpin spike in this plate fixation system, as I think while we may chuckle a bit at Moishe's name, he's conducted a reasonable analysis of some of the requirements. I am not sure how the 'hairpin' top of these spikes can be reshaped to give positive clamping pressure (and lateral 'centering' with elastic restoring force) through the shape of the 'eye' and the shape of the seats adjacent to the spike holes in the plates.  Relatively small refinements here may make for increased clamping and 'nonlifting' performance, even when comparatively great deferred maintenance occurs.

[Euclid]

I surmise that before a screw breaks, it does a lot of bending cycles.  It might bend several million times before it finally breaks from fatigue.  In order to bend, the screw shank has to crush the wood on the side of the screw hole opposing the bend movement.  So I conclude that the presence of exposed polished tie surface indicating the tie plate moving back and forth does not necessarily mean that any or all of the screws have broken.  All it indicates is that the tie plate frequently moves in and out laterally in relation to the tie. As screw holes enlarge from the bending force crushing the wood, and the loss of anchoring of the screw, the tie plate is free to shift latterly.

So the tie hole is progressively ovaled due to the bending of the screw.  Each bend is progressively larger, and makes the oval slightly deeper.  At the same time, the bending and plate shifting exert an upward pull on the screw which begins stripping the threads out of the wood.  This loss of threads then combines with the ovaling of the hole; and further reduces the resistance to tie plate shifting.  Thus the tie plate shifts further with each bend cycle, and becomes capable of considerable lateral movement without breaking the screw.  Finally, as the oval widens; the screw bends further; the number of completed bend cycles grows larger; fatique cracking develops, and the screw finally breaks. 

This evidence of tie plate shifting would be easy to spot while walking, and it seems to me that the degree of shifting evident in the published photo would be more than adequate to raise the alarm of a serious securement problem.  In observing the evidence of tie plate lateral movement, one would have to conclude that the gage is not being properly constrained. 

I doubt that one would find such plate movement evidence as shown in the photo with just one isolated tie.  Several adjoining ties would be most likely to exhibit the same condition.  The tie plate moves because the rail moves.  So how could the rail move that far and carry just one tie plate?

In the Fabyan Bridge wreck, investigators found plenty of evidence indicating an imminent failure by just looking closely at the track.  Such evidence included broken tie plates and broken screws that had been dislodged from their holes and were lying there in plain sight. 

Apparently, however, assuming track inspectors had noticed these problems, they did not perceive it as evidence of imminent failure. Instead, they must have regarded the problem as random and limited individual breakages. 

[Overmod]

Euclid

I surmise that before a screw breaks, it does a lot of bending cycles.  It might bend several million times before it finally breaks from fatigue.

You might want to backcheck and see how many trains it would take to deflect a screw severely 'several million times'.  The number deflects attention from your valid point, that there is a 'common mode' failure in these screws for which an explanatory mechanism is needed stat.

 

In order to bend, the screw shank has to crush the wood on the side of the screw hole opposing the bend movement.  So I conclude that the presence of exposed polished tie surface indicating the tie plate moving back and forth does not necessarily mean that any or all of the screws have broken.

Look a little more carefully at the physics.  The hole in the plate is not reamed precisely to a fit with the shank.  So as soon as the effective clamping force is limited, the plate can slide relative to the shank, and does.  Even slight motion with the associated lateral force will produce high acceleration and, probably, high contact force between the edge of the hole and the screw shank.  This may be augmented by effects of the spring clip that holds the rail in the seat on the plate.  I'm looking forward to seeing some instrumented data on this.

[quote ... As screw holes enlarge from the bending force crushing the wood, and the loss of anchoring of the screw, the tie plate is free to shift laterally (note sp.) ... the tie hole is progressively ovaled due to the bending of the screw.  Each bend is progressively larger, and makes the oval slightly deeper.[/quote]

I suspect lateral motion may not be the only kind experienced by the bolts.  Rail anchors may not preclude longitudinal motion to an extent that causes displacement of the shank, perhaps in a 'resultant' direction.  But this, too, awaits more specific analysis.

At the same time, the bending and plate shifting exert an upward pull on the screw which begins stripping the threads out of the wood.

Has this actually been observed in the bolts that are breaking?  I had thought the problem was that the threading was effectively overconstraining the bottom of the bolt, keeping any ovaling or lifting at all from reaching most of the threaded portion (unless the tie were suffering 'killing' from water and foreign-matter incursion along the enlarged portion of the bore).  That is a far more serious effect than if the whole bolt were 'working'.

 

... the tie plate shifts further with each bend cycle, and becomes capable of considerable lateral movement without breaking the screw.  Finally, as the oval widens; the screw bends further; the number of completed bend cycles grows larger; fatique cracking develops, and the screw finally breaks.

I asm not convinced this is as extended or cumulative a process as that.  Most of the lateral bending effects will commence with some severity as soon as the effective clamping preload is lost.  What I'd start looking at instead would be some of the mechanisms by which relaxation of lateral resistance in some bolts puts additional load on intact screw fixation clamping, in a direction the loading system is not designed to resist.

 

This evidence of tie plate shifting would be easy to spot while walking, and it seems to me that the degree of shifting evident in the published photo would be more than adequate to raise the alarm of a serious securement problem.

I think this is one of those situations where 'it's easy to spot now that we know what to look for'.  Where the problem appears to be arising is what to do when the problem is observed -- it appears that just periodic redriving of the bolts, as one would do with cut spikes, is not an acceptable answer whether or not you remediate broken bolts when you come across them during the redriving process.

Part of the problem appears to me to be that the 'cause' of adjacent plates moving may not be 'the same' as the movement from an initial lateral clamping failure, so there may not be the distinctive signature for a trackwalker to note.  It is true that you'd need several adjacent plates loose to cause a 'critical' widening of gauge; on the other hand, once the gauge widens enough in any spot to start dropping a wheel, catastrophic progression of lateral shift and gauge widening, even if the rail doesn't roll in the clips, is likely to follow. 

 

In the Fabyan Bridge wreck, investigators found plenty of evidence indicating an imminent failure by just looking closely at the track.  Such evidence included broken tie plates and broken screws that had been dislodged from their holes and were lying there in plain sight. Apparently, however, assuming track inspectors had noticed these problems, they did not perceive it as evidence of imminent failure. Instead, they must have regarded the problem as random and limited individual breakages.

You seem to have forgotten that in the TSB report it is clearly and repeatedly stated that the track was 'borderline' critical, but hadn't "quite" reached the trigger point using standards appropriate to spiked track.  Track inspectors probably quite rightly 'regarded the problem' as a widespread inability to hold gauge, with evidence of bad ties, loose hardware, and other associated problems.  The real issue I saw was that the result of such failures was, and is, far more critical with screw fixation than with spikes, in part I think because of a tacit assumption that using four big screws per plate instead of two scrawnier hammered spikes just had to mean far more securement.

I suspect there is relatively little 'shared lesson' between the maintenance procedures used at Fabyan Bridge and at Mosier.  That may change if the NTSB investigation shows any kind of not-quite-critical maintenance alert for the whole stretch of track, but from what I've been given to understand UP was reasonably diligent in performing both routine and preventative maintenance on a 'reasonable' basis.  The emergent issue is that, for this track-fixation system, the reasonable basis does not seem to be adequate.

[Norm48327]

Euclid

I surmise that before a screw breaks, it does a lot of bending cycles.  It might bend several million times before it finally breaks from fatigue.  In order to bend, the screw shank has to crush the wood on the side of the screw hole opposing the bend movement.  So I conclude that the presence of exposed polished tie surface indicating the tie plate moving back and forth does not necessarily mean that any or all of the screws have broken.  All it indicates is that the tie plate frequently moves in and out laterally in relation to the tie. As screw holes enlarge from the bending force crushing the wood, and the loss of anchoring of the screw, the tie plate is free to shift latterly.

So the tie hole is progressively ovaled due to the bending of the screw.  Each bend is progressively larger, and makes the oval slightly deeper.  At the same time, the bending and plate shifting exert an upward pull on the screw which begins stripping the threads out of the wood.  This loss of threads then combines with the ovaling of the hole; and further reduces the resistance to tie plate shifting.  Thus the tie plate shifts further with each bend cycle, and becomes capable of considerable lateral movement without breaking the screw.  Finally, as the oval widens; the screw bends further; the number of completed bend cycles grows larger; fatique cracking develops, and the screw finally breaks. 

This evidence of tie plate shifting would be easy to spot while walking, and it seems to me that the degree of shifting evident in the published photo would be more than adequate to raise the alarm of a serious securement problem.  In observing the evidence of tie plate lateral movement, one would have to conclude that the gage is not being properly constrained. 

I doubt that one would find such plate movement evidence as shown in the photo with just one isolated tie.  Several adjoining ties would be most likely to exhibit the same condition.  The tie plate moves because the rail moves.  So how could the rail move that far and carry just one tie plate?

In the Fabyan Bridge wreck, investigators found plenty of evidence indicating an imminent failure by just looking closely at the track.  Such evidence included broken tie plates and broken screws that had been dislodged from their holes and were lying there in plain sight. 

Apparently, however, assuming track inspectors had noticed these problems, they did not perceive it as evidence of imminent failure. Instead, they must have regarded the problem as random and limited individual breakages. 

 

Have you not already taken this subject far beyond what any reasonable person would? The beating of the dead horse continues. Let go of it.

[Overmod]

Norm48327

Have you not already taken this subject far beyond what any reasonable person would? The beating of the dead horse continues. Let go of it.

Let the poor fellow think out loud if he wants to -- and help his thought process constructively, if you can.

No one is twisting your arm to read the horse-beating.

[schlimm]

Overmod

 

 

Norm48327

Have you not already taken this subject far beyond what any reasonable person would? The beating of the dead horse continues. Let go of it.

 

 

Let the poor fellow think out loud if he wants to -- and help his thought process constructively, if you can.

No one is twisting your arm to read the horse-beating.

 

In the spirit of these Scholasticist lines one could ask whether it is helping "his thought process constructively" or merely enabling the dysfunctionality?

[Norm48327]

schlimm

In the spirit of these Scholasticist lines one could ask whether it is helping "his thought process constructively" or merely enabling the dysfunctionality?

Thank you.

[Overmod]

schlimm

In the spirit of these Scholasticist lines one could ask whether it is helping "his thought process constructively" or merely enabling the dysfunctionality?

I do ask myself that.  Sometimes repeatedly.

But perhaps one of the dead horses may learn to sing.

[Euclid]

Overmod

 

Euclid

I surmise that before a screw breaks, it does a lot of bending cycles.  It might bend several million times before it finally breaks from fatigue.

 

You might want to backcheck and see how many trains it would take to deflect a screw severely 'several million times'.  The number deflects attention from your valid point,...

Overmod,

Depending on how you factor the number of wheels into the number of cycles:  Ten trains per day at 100 cars each = 1000 cycles.  That is 365,000 cycles per year.  In ten years, that is 3,650,000 cycles.  That is what I mean by “several million.” 

If you count each wheel as a load cycle, it is 14,600,000 cycles in ten years.  So you might say it is 3-14 million.  I thought “several million” was a fair way to capture the general idea. 

What number would you use so as not to distract from attention from my valid point?

And how do you spell laterally? 

[Overmod]

Euclid

What number would you use so as not to distract from attention from my valid point?

I'm not certain every wheel passing represents a full lateral load excursion; I'm waiting for some more defined physics and geometry testing to get some idea of how, and when, the lateral excursions in the loosened fixation system behave.  I was concerned that some readers would see 'several million' and start to overreact.  Perhaps 'up to several million' captures the possibilities without invoking too much undue "wrath."

You spell laterally the way I corrected it, not the way you had it in your original prose.

[Buslist]

Overmod

 

 

 

I'm not certain every wheel passing represents a full lateral load excursion; I'm waiting for some more defined physics and geometry testing to get some idea of how, and when, the lateral excursions in the loosened fixation system behave. 

 

generally only the lead axle of a truck would exercise a fastener unless the truck is misbehaving.

There are curving detectors out there to identify "bad actors"

[Euclid]

Overmod

 

Euclid

What number would you use so as not to distract from attention from my valid point?

 

 

I'm not certain every wheel passing represents a full lateral load excursion; I'm waiting for some more defined physics and geometry testing to get some idea of how, and when, the lateral excursions in the loosened fixation system behave.  I was concerned that some readers would see 'several million' and start to overreact.  Perhaps 'up to several million' captures the possibilities without invoking too much undue "wrath."

Well, I did not get into the fine point of how to count the wheels in the affect, so I counted all four wheels in the two adjacent trucks as one rail-pushing cycle.  But even that gets into several million cycles.  Believe me, I gave deep thought to the use of the number because I just knew that several readers would take it as an overreaction or exaggeration.  So I was ready. 

[schlimm]

Overmod

 

 

schlimm

In the spirit of these Scholasticist lines one could ask whether it is helping "his thought process constructively" or merely enabling the dysfunctionality?

 

 

I do ask myself that.  Sometimes repeatedly.

But perhaps one of the dead horses may learn to sing.

 

Nah!  At the risk of sounding sexist, we need the moment when "the fat lady sings" i.e., the end is nigh!

[Overmod]

schlimm

Nah! At the risk of sounding sexist, we need the moment when "the fat lady sings" i.e., the end is nigh!

We already have this -- but the lady involved is far from fat!

[Euclid]

Overmod

 

Euclid

I surmise that before a screw breaks, it does a lot of bending cycles.  It might bend several million times before it finally breaks from fatigue.

 

 

 

 

 

In order to bend, the screw shank has to crush the wood on the side of the screw hole opposing the bend movement.  So I conclude that the presence of exposed polished tie surface indicating the tie plate moving back and forth does not necessarily mean that any or all of the screws have broken.

 

 

Look a little more carefully at the physics.  The hole in the plate is not reamed precisely to a fit with the shank. 

 

At the same time, the bending and plate shifting exert an upward pull on the screw which begins stripping the threads out of the wood.

 

 

Has this actually been observed in the bolts that are breaking? 

 

 

 

 

 

 

 

Overmod,

Yes I do realize that the screw hole in the plate is not reamed for a tight fit to the screw shank.  It would be nice if it was, but the plate holes and tie holes are in a pattern and the patterns must match.  It would be interesting to know what the fit of the plate hole to the screw shank is.  I would guess the hole is at least about .040 over in the diameter.  But the lateral movement of the plate that shows up in the photos must be at least a half inch. I would not be surprised if it can move that far without breaking any screws.  I agree that the visual appearance of the plate movement gives no indication of what is happening below, but I would be very curious, and would open one up to find out.  

As to your question about whether lifting has been observed, I don’t know if it has.  I only conclude that it exists and contributes the bending fatigue that ultimately causes the breaking.  Here is why I conclude that lifting exists:

When you bend the screw with the corresponding shift of the tie plate, the elevation of its head must drop vertically.  But it cannot drop because it is being upheld by the tie plate.  If the lower part of the screw threads is still holding, the screw cannot rise from the tie to accommodate the reduction in vertical distance due to bending of the shank.  So the reaction to bending the screw causes a lifting force against the bottom of the head that is resisted by the threads still fully engaged in the lower part of the screw.  It is the bending force that lifts the screw.  I am not convinced that even the maximum clamping pressure on a new installation is sufficient to prevent the onset of tie plate lateral shifting.  But even if it is, I think that sufficient clamping force is quickly lost just by the plate compressing the wood due to the vertical compression.

So, overall, I see these forces and their affects culminating in the final breaking of the screw:

1. Lateral force of the tie plate upsets and abrades the screw shank under the head, and around the hole in the tie plate.

2. Lateral force of the tie plate bends the screw shank in a range extending downward from the head.

3. Bending of the screw shank causes crushing and ovaling of the tie hole, and damages thread engagement.

4. Bending of the screw shank causes fatigue cracking in the screw shank near the weak point where the top of the threads begin.

5. Bending of the screw shank causes upward lift of the screw which contributes to the fatigue cracking induced by bending. 

 

[Overmod]

Technically at least it would be possible to gang-drill the tie directly through the plate so that a reamed bolt would 'line up' reasonably well (or would reasonably self-align as the head came down to clamping range).  The problem is that you'd have zero gauge adjustment other than shimming the clipped seats thereafter, and any deformation of the tie seat relative to the plate would throw additional bending stress down into precisely the area of the bolts where we're now apparently seeing the accelerated failures.

A potential concern with 'hard' bushings in the ties is that they'd have to align very precisely with the plate holes to be any good.  I would note by analogy that this is similar to the concern between lug-centric and hub-centric wheel fits on motor vehicles, and I'd repeat that some mechanical means of restraining the lateral (probably with a pin-and-bushed-hole arrangement completely independent of the screw fixation) is going to be the 'best' overall kind of answer -- might even be done with cut or hairpin spikes...

Once you have eliminated the plate laterally striking the shank of the screw, or tending to deflect it, you have solved most of the 'bending' or 'bowing' issues for the screws, and can concentrate much more on maintaining effective clamping force, without having to machine careful fits or overconstrain part of the track geometry.

Something else to consider about your proposed mechanism is that I have yet to see a reported 'catastrophic' failure of these lags in a gauge accident that involves the heads popping off -- and if I recall, the Fabyan Bridge report makes specific mention of this and why it is curious.  Any sort of rotation of the plate (as for example that which presumably occurs as the seat in the tie begins to 'cut' or crush downward) will put tremendous spot pressure on the edge of the head immediately adjacent to the almost-square 'corner' between the clamping face of the head and the adjacent shank.  Any microcracking here will tend to repetitively open, fill with water or debris, and start 'jacking itself open' as well as providing a very likely environment for SCC.  Preferential head failures are noted in other environments, so there is no 'magic' for the lag fixation here.  And you would see this, I think, long before you observed 'macro' pulling of all those threads out of the tie wood (which has yet to be established, and I think in fact we won't see it much).

Of course rotating the plate relative to the head is going to reduce the clamping pressure on a considerable portion of the expected clamping area, which will likely facilitate some sliding and selective wear of the underside of the heads.  If we do not see this, it's an indication that the resultant of stretch and bending is being communicated to the 'critical' breaking zone, a couple of threads below the initial transition area, and augmentation there might be the most 'logical' place to start with a redesign analysis.

[Norm48327]

schlimm

Nah! At the risk of sounding sexist, we need the moment when "the fat lady sings" i.e., the end is nigh!

I know one who is not fat, just pleasingly plump, but has a great soprano voice. When can I bring her on stage?

[Norm48327]

Euclid

Yes I do realize that the screw hole in the plate is not reamed for a tight fit to the screw shank. It would be nice if it was, but the plate holes and tie holes are in a pattern and the patterns must match. It would be interesting to know what the fit of the plate hole to the screw shank is. I would guess the hole is at least about .040 over in the diameter. But the lateral movement of the plate that shows up in the photos must be at least a half inch. I would not be surprised if it can move that far without breaking any screws. I agree that the visual appearance of the plate movement gives no indication of what is happening below, but I would be very curious, and would open one up to find out. As to your question about whether lifting has been observed, I don’t know if it has. I only conclude that it exists and contributes the bending fatigue that ultimately causes the breaking. Here is why I conclude that lifting exists: When you bend the screw with the corresponding shift of the tie plate, the elevation of its head must drop vertically. But it cannot drop because it is being upheld by the tie plate. If the lower part of the screw threads is still holding, the screw cannot rise from the tie to accommodate the reduction in vertical distance due to bending of the shank. So the reaction to bending the screw causes a lifting force against the bottom of the head that is resisted by the threads still fully engaged in the lower part of the screw. It is the bending force that lifts the screw. I am not convinced that even the maximum clamping pressure on a new installation is sufficient to prevent the onset of tie plate lateral shifting. But even if it is, I think that sufficient clamping force is quickly lost just by the plate compressing the wood due to the vertical compression. So, overall, I see these forces and their affects culminating in the final breaking of the screw: Lateral force of the tie plate upsets and abrades the screw shank under the head, and around the hole in the tie plate. Lateral force of the tie plate bends the screw shank in a range extending downward from the head. Bending of the screw shank causes crushing and ovaling of the tie hole, and damages thread engagement. Bending of the screw shank causes fatigue cracking in the screw shank near the weak point where the top of the threads begin. Bending of the screw shank causes upward lift of the screw which contributes to the fatigue cracking induced by bending.

Sheesh Bucky. I bet it takes you two hours to eat breakfast because you analyze each and every flake of oatmeal in your bowl.

Time to give us a break.

[Euclid]

Norm,

I am amazed that I can inflict such pain on you just by getting into a little detail here.  How do you cope with real problems? 

[Norm48327]

Euclid

Norm,

I am amazed that I can inflict such pain on you just by getting into a little detail here.  How do you cope with real problems? 

 

My uncle Guido takes care of them for me.

[Overmod]

My uncle Guido takes care of them for me.

[Euclid]

 

Overmod,

 

Earlier you questioned my mention of the uplifting force on the screw causing its threads to strip out of the tie.  You are right in your conclusion.  In thinking about it, this uplifting force is not stripping the threads out of the wood.  This is evidenced by the fact that the break leaves most of the threaded portion intact in the tie.  The wallowing out of the hole by the cyclic bending probably compromises the first few threads at the top, but is probably not instrumental in actually stripping the lower portion of the bolt’s proper fitting threads out of the wood.  However, the lifting force pulses on the lag bolt may be capable of unscrewing the screw from the wood. 

 

[Norm48327]

There are simple solutions for complex problems and most of them are wrong.