The Following might be of interest?http://www.cbc.ca/news/business/cp-layoffs-derailment-risk-1.3652528Safety First.
Euclid These are my thoughts regarding the leverage model: The rail force is to tip over to the outside. When it exerts this tipping force onto the tie plate, the tie plate becomes a lever that pivots on the fulcrum point of its edge that is on the field side of the rail. If movement is possible, this tends to exert shear, bending, and upward tensile force on all four screws. Here is where it gets confusing.....
These are my thoughts regarding the leverage model: The rail force is to tip over to the outside. When it exerts this tipping force onto the tie plate, the tie plate becomes a lever that pivots on the fulcrum point of its edge that is on the field side of the rail. If movement is possible, this tends to exert shear, bending, and upward tensile force on all four screws.
Here is where it gets confusing.....
Euclid:
This is the first time that I have thought about this in any detail. It just might be much simpler than one might think at first glance.
Assume the outward radial force is 4,150 lb outward (from my post above) on the rail acting 8" from the pivot point you mentioned in your post. This produces an overturning moment of about 2,800 ft-lb. Further assume that the car weight of 65,750 lb is acting downward 4" from the same pivot point. The weight produces a moment of about 22,000 ft-lb in the opposite direction, preventing the rail from tipping over.
(Note that the moment arm values are just assumptions, but they shouldn't be too far off.)
If these calculations are anywhere near reasonable, then the weight of the car generally prevents the rail from tipping over.
AnthonyV,
I definitely see and agree with your points about the weight of the car resisting the rail tip-over.
I conclude that in the CN wreck, all four lag screws are subject to tensile, bending, and shear forces. I am not sure how the lag screws are used with the U.P. system involved in wreck at Mosier. With the BNSF system, I conclude that the four lag screws are only subject to tensile stress lengthwise with the shank.
Here is where it gets confusing. Consider the following scenarios:
1) There are two screws on the field side and none on the gage side.
2) There are two screws on the gage side and none on the field side.
In scenario #1, the tensile force is much higher on the two screws than it is in scenario #2. This is because in #2, the screws are much further from the fulcum point of the lever.
So, in the normal arrangement of two screws on each side of the rail, I conclude that as long as the two gage-side screws are tight, no upward tensile force is exerted on the two field side screws.
Therefore, the failure must begin with the two gage-side screws. Then when they break, the two field side screws will be subject to far more tensile uplift than were the two gage-side screws; and so they will fail relatively quicker than did the two gage-side screws.
Just another thought:
I always assumed that the outside rail in a curve has to be held securely in order to prevent tipping over. I often wondered how the rail doesn't tip over, even with loose spikes, spikes sticking up, missing spikes, etc. it just might be that the weight of the car does prevent the rail from tipping over and the purpose of the spikes is to prevent the lateral movement of the rail.
Clearly this depends on the curvature, car mass, and train speed.
Euclid The TSB report of the CN wreck cites the cause of broken lag screws to be a combination of shearing and bending stress. What about the tensile stress lengthwise with the screw shank? Why would that not also contribute?
The TSB report of the CN wreck cites the cause of broken lag screws to be a combination of shearing and bending stress. What about the tensile stress lengthwise with the screw shank? Why would that not also contribute?
This is what I suggested back on Page 8, although not as clear.
AnthonyV 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.
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.
However, the moment (or torque) tending to cause the rail to tip over must be balanced against the opposing moment due to the weight of the car.
For example, a 263,000 lb tank car on a 3 deg curve at 30 mph exerts an outward radial force on the outside rail (one truck only) of about 4,150 lb. The downward force produced by the weight of the car is 65,750 lb (one side of one truck).
Since we should be comparing moments (or torques), we need to factor in the point of application of each force and the moment arm for each force. I don't have that data handy, but my sense is that two forces are applied very closely to each other and the moment arms are comparable. If these assumptions and calculations are reasonable, then it appears that the car weight can prevent the rail from tipping over.
Does this seem reasonable or am I way off?
Lateral pressure from the train against the outside curve rail tries to tip the rail over. This rail tipping force would tip the tie plate with the rail since the plate is fixed to the rail base. Tipping the tie plate would exert uplift of the four lag screws holding it to the tie. The leverage of this action would have the potential of applying the greatest upward tension on the screws on the field side of the rail outside of the curve. This is except for the fact that the two gage-side screws have the greatest leverage advantage of holding the rail against tipping the plate. So if the two gage-side screws succeed in doing that, it prevents the field-side screws from failing due to their relative leverage disadvantage.
So generally, I conclude that the two gage-side screws would be the first to break from fatigue caused by the dynamic tensile stress cycles of passing trains. And when one or both of those gage-side screws break, it opens the door to more easily breaking the field-side screws due to their relative leverage disadvantage. I wonder if it would be a better design to have just one screw on the field side and three screws on the gage side. Perhaps moving the three gage-side screws further from the rail by lengthening the tie plate would also help.
In the BNSF presentation, the tie plate lateral shear force is absorbed by shoulders in the concrete tie. All the lag screws do is hold the rail base down. However, the uplift force on the screws caused by the tipping force on the rail is likely greater than it would be in the in the case of the CN system. This is because the BNSF screws are nearer the centerline of the rail, and thus subject to greater leverage advantage of the tipping rail to pull the screws. I assume that these lag screws as shown on page 89, failed only because of the tensile stress lengthwise with the shank.
NDGYour Diagnosis IS OCD, Sir. There can never be too much info regarding Safety esp when so much Placarded material is moving by rail, and others who are responsible for Track Maintenance might well take pointers from any of the information presented in these threads regardless of track, ties or fasteners. Wide Gauge can have many causes, some right under one's nose, IF he knows where to look beforehand.
There can never be too much info regarding Safety esp when so much Placarded material is moving by rail, and others who are responsible for Track Maintenance might well take pointers from any of the information presented in these threads regardless of track, ties or fasteners. Wide Gauge can have many causes, some right under one's nose, IF he knows where to look beforehand.
This is true, and indeed Safety should be First, but the thread topic is specifically LAG SCREW FIXATION with respect to wide gauge or other derailments. I repeat: what is the relevance of the report you posted with respect to that topic? (I am serious; you've partly answered it already above. Be as OCD as you want; even if nobody else may care about that stuff but me, I'll still read it with interest.
The old saying was 'Sun Kink'
How is that supposed to be different from the current saying, "sun kink"?
There can also be too much information presented, seemingly in an obsessive fashion? regarding locomotives scrapped half a century or more ago. ( Groan! ) I like steam, but, there is overkill. Younger folk will wonder about forum folk and may well get turned off by steam overkill? if they had any interest to begin with?
I like steam, but, there is overkill.
Younger folk will wonder about forum folk and may well get turned off by steam overkill? if they had any interest to begin with?
You are starting to get dangerously personal with these remarks, which is strange coming from someone who certainly goes on at length with stream-of-consciousness recollections of Canadian minutiae from bygone days that may be of equal, if not greater, deterrent effect on casual Forum readers. (Not that I want you to stop posting them -- I find them fascinating both in the subject matter and in the telling!)
Some people have had a life, some have not?
And some still do. I certainly have one outside the Forum, but I enjoy passing along some thoughts to perhaps-interested parties here.
There is a world of difference in changing and spiking ties in real life, than reading about it in an obscure manual.
There is also a world of difference between understanding the engineering of track fixation systems, and the refinement of automated reporting systems for effective track safety, and recounting riding obsolete locomotives over sun-kinked track.
I, on the other hand, have been trying not to make fun of non-engineers who post on technical topics disparagingly. (Having done that myself too often in the past, and repenting of it)
(I do, however, ask how your supposed experience with changing and spiking ties might relate to automated track inspection and maintenance... particularly with respect to track fixation systems that do not show physical signs of damage as they fail)
Some have no other reason to contribute that to overlord others with their knowledge, much of which may not be of interest to others.
Let's charitably hope you are not referring to me with this sentence. Most people on this (and other) forums do understand the point of the delete key, and are aware that no one (in or out of 'the Government') is twisting their arm to have to read or follow something that's posted. If you are not interested in steam technology ... don't read about it. No one is likely to care whether you do or not, although some might be concerned about the associated arrogance in dictating what is and isn't interesting to younger readers.
One is not likely to experience a superheater element failure on the road in Oregon? Nor shed a tire by too much Independent on the engine.
And this is relevant ... how? Because most readers won't be doing this firsthand?
I'll happily grant you that readers over in the Classic Trains forum are more likely to be interested in arcane steam-era details of that kind. My own experience with "shedding tires at high speed" didn't involve too much brake on a steam engine, and occurred much later than typical steam experience -- and I suspect you'd probably think my discussing it would be both OCD and 'overlording' with special knowledge -- but some people might find it interesting, or amusing. Is there a reason discussing something like that ought to be verboten because some folks are turned off by it?
When the Post Count reaches 5550, will there be a party?
I tried to figure this out, but couldn't. It might have been funnier to ask 'when the post count reaches 5550, will everyone participating receive a patch in the mail', but you probably couldn't figure that one out any more that I could figure out yours.
Fortunately we can now return to actual subjects ... some, you may be dismayed to know, probably containing more actual technical discussions of technical material with (horrors!) dry technical analyses.
Get out the popcorn...
Whatever for? Show's over.
Your Diagnosis IS OCD, Sir.
The old saying was 'Sun Kink' and I have 'chased a few' down the track on a Unit, often a H-16-44 in hot weather after sledding for ballasting, 50 years ago.
Safety First.
There can also be too much information presented, seemingly in an obessive fashion? regarding locomotives scrapped half a century or more ago. ( Groan! )
There is a world of difference in changing and spiking ties in real life, than reading about it in an obsure manual.
As just mentioned. Forums are a place for old guys to voice their opinion, no matter what it is.
Safety is No. 1, regardless of the source.
Thank You.
I'm going to empty my catheter bottle, shamble to the kitchen, take my Meds and go back to bed and try to dream of Steam, and Youth, esp the latter.
God Bless Lawrence Welk and Depends.
Get out the popcorn.
NDGThe following might be of interest? http://www.tsb.gc.ca/eng/rapports-reports/rail/2014/r14w0137/r14w0137.asp
Not sure I see the relevance to the thread topic here -- please be more specific. Are you referring to a parallel between this incident and Mosier (or Fabyan Bridge) in the frequent claims of inspection and 'remediation activities' like surfacing in the effective absence of recognition of or attention to critical faults in the track?
The track fixation in the report's area is spiked construction (albeit with more than 4 spikes per plate in some places) and the proximate cause is sun kink. (A rather obvious and predictable sun kink, in my not-so-humble opinion, on the hottest day of the year with the stress in one rail recently relieved, and many places where tie bearing was not sufficient. Perhaps there is intentionally-understated terminology in the report, perhaps I am reading too much into the semantics.)
Something of concern, reading between the lines: It would appear that telemetry with a certain amount of what looks to me like good data fusion was in use ... in raw data fed to TC, but not evidently used effectively by the railroad. We see what I consider clear (and knowing the details of recent 'maintenance', alarming) indication of a developing kink, clearly identified by video and lateral accelerometer ... and not reported by the crew as out of the ordinary, or apparently flagged for attention at the time by any sort of program reviewing data. Unless of course there were so many similar combinations of data in this section of track that this one was filtered out with 'others'. I cannot imagine that sun kink would be depreciated in importance vs., say, vertical accelerations indicating poor areas of tie bearing that might lead to increased rail breakage, but after reading this report ... I find I don't know. Likewise, I imagine that TC could run some sort of analysis for trends on the data it evidently receives, and issue some sort of notice when it 'sees' a developing critical situation exacerbated by known maintenance factors ... but for all I know there were hundreds of competing problem areas in this section of line, and it would be like the security situation in the week prior to the Pan Am Lockerbie bombing.
The following might be of interest?http://www.tsb.gc.ca/eng/rapports-reports/rail/2014/r14w0137/r14w0137.aspThank You.
Overmod Again, of course, we are treated to just how irritating it is when a PowerPoint slide presentation lacks its actual presentation audio track...
Again, of course, we are treated to just how irritating it is when a PowerPoint slide presentation lacks its actual presentation audio track...
I share your frustration. In my earlier days working for a large engineering consulting firm, we always included key points on the slide (we called them topical sentences) rather than using the slide as a prop for the audio. This avoided the frustration you mention above, in which no one can remember the purpose of the slide once the presentation is complete.
Such a slide might read:
Broken Lag Screws and Lubrication
Reports from the field indicate that about 5 percent of lag screws fail during retightening, possibly due to high friction torque between the tie and bolt.
(show picture of broken screws)
Testing of a teflon-based lubricant intended to reduce the friction between the tie and lag screw during retightening is underway. Preliminary results indicate that use of the lubricant reduced the frequency of broken screws to less than 0.1 percent.
Of course the above info is total fiction, but it illustrates how adding a few sentences to a slide can help retain its meaning long after the presentation is given.
rdamonOne also has to wonder if the move to copper based preservatives has aided in premature corrosion.
Here is a useful reference to get you started.
Note in particular the moisture range at which the effect occurs, the steepness at which small increments of additional moisture produce increased corrosion, and consider the likelihood of rainwater or other moisture intrusion along the shank of one of these lags if lateral deflection of the fastener (e.g. by a shifting tie plate) enlarges part of the bore in a tie.
I got laughed at a couple of years ago for mentioning copper preservatives instead of creosote/borate for ties. Here is the current RailroadTie Association FAQ entry for preservative information:
What types of wood preservatives are used to pressure treat wood crossties?Most hardwood crossties produced in North America today are pressure treated with creosote or creosote solutions. The US Environmental Protection Agency (EPA) has approved and registered creosote for this industrial application. Other approved standardized preservatives include Ammoniacal Copper Zinc Arsenate (ACZA) Copper Naphthenate (CuN) and Pentachlorophenol although Penta has not been used by railroads in decades. Some producers also use a dual treatment system where ties are treated with borate compounds prior to a second treatment with creosote. The borates diffuse throughout the hard-to-treat heartwood of many species and provide additional protection for wood used in high decay areas. In January 2010, the AWPA approved the use of ACZA as an accepted wood preservative for ties. For example, Douglas fir is a strong, plentiful species, well-suited for use as ties, but not readily treatable with standard preservatives. Tests of ACZA-treated Douglas fir ties have shown low corrosivity and excellent spike-holding characteristics. ACZA enables wood to resist termite damage and fungal decay and has been found to reduce flame spread in wood timbers.How far does creosote penetrate?Some species treat nearly 100% while in others only the sapwood treats easily. In refractory (hard to treat) species, many railroads use borates in a dual treatment process to provide protection to the heartwood.What are the other approved treatments for hardwood ties?98% of all wood crossties produced in the US and Canada are treated with creosote or creosote and oil blends. In addition to creosote, Pentachlorophenol and Copper Naphthenate (CuN) are approved preservatives for hardwood ties by the American Wood Protection Association (AWPA). ACZA is now also approved for Douglas fir and hardwood ties. CCA (copper chrome arsenate) is not recommended for hardwoods but may be sometimes used for certain Southern Yellow Pine timbers and ties. Generally, CuN is applied with lighter oil carriers than creosote that may not provide the same extent of weather-proofing properties as the heavier creosotes. CuN is applied with oils that have lower flash points than creosote, some typical processing steps used when treating with creosote alone (sterilizing the ties under high heat to condition the wood and eliminate decay fungi that may have begun to grow while the wood is air-drying prior to processing) cannot be done. It is expected that CuN would be most effective in hardwood ties when used in high decay hazard areas if the ties were dual-treated with a borate pre-treatment. Mississippi State University has conducted studies on dual treatment with CuN which you can find here . Nisus Corporation has assumed the EPA registration for CuN and built a new manufacturing facility in Knoxville, TN, which will fuel more widespread use of CuN. At least five treating companies now offer ties or timbers treated with CuN for railroad use. Borate compounds are now used in dual treatment processes for roughly 7 to 7.5 million of the 24+ million or so ties produced per year. Over the years of testing (50+ documented years now for creosote - see the 1958 cooperative study) creosote has proven to be the most efficacious and cost effective wood preservative for hardwood ties. It has significant weatherproofing properties and is an excellent preservative for hardwood species. However, some wood species are refractory (hard-to-treat) and the heartwoods of those species are almost impenetrable by any wood preservative with the exception of borate compounds which diffuse through the wood over time. Thus, for these refractory species destined for high decay areas, it has now become relatively common practice to use borates as a pre-treatment to protect the wood prior to processing with creosote. Borate dual-treatment protects the entire cross-section of the wood tie providing excellent service life even in high biological-hazard service conditions. Each preservative system has its place in the wide variety of railroad applications and climactic conditions in North America. RTA is continually researching and testing other systems, but not one is in use other than those mentioned here. What is RTA doing to research alternate preservatives?RTA is working in conjunction with AAR to determine the relative effectiveness of alternative tie treatments with the ongoing Alternative Wood Protection Research Project (AWPRP) at Mississippi State University. The objectives of the project include determining the relative biological durability to decay fungi and subterranean termites of crossties commercially treated with existing and alternative preservatives exposed side-by-side in a replicated test on a site in AWPA Hazard zones 4 and 5, to determine the effectiveness of treatments against Formosan termites, to determine the corrosivity of alternative preservatives, and to determine the tie dimension stability effects of alternative treatments.
In January 2010, the AWPA approved the use of ACZA as an accepted wood preservative for ties. For example, Douglas fir is a strong, plentiful species, well-suited for use as ties, but not readily treatable with standard preservatives. Tests of ACZA-treated Douglas fir ties have shown low corrosivity and excellent spike-holding characteristics. ACZA enables wood to resist termite damage and fungal decay and has been found to reduce flame spread in wood timbers.How far does creosote penetrate?Some species treat nearly 100% while in others only the sapwood treats easily. In refractory (hard to treat) species, many railroads use borates in a dual treatment process to provide protection to the heartwood.What are the other approved treatments for hardwood ties?98% of all wood crossties produced in the US and Canada are treated with creosote or creosote and oil blends. In addition to creosote, Pentachlorophenol and Copper Naphthenate (CuN) are approved preservatives for hardwood ties by the American Wood Protection Association (AWPA). ACZA is now also approved for Douglas fir and hardwood ties. CCA (copper chrome arsenate) is not recommended for hardwoods but may be sometimes used for certain Southern Yellow Pine timbers and ties.
Generally, CuN is applied with lighter oil carriers than creosote that may not provide the same extent of weather-proofing properties as the heavier creosotes. CuN is applied with oils that have lower flash points than creosote, some typical processing steps used when treating with creosote alone (sterilizing the ties under high heat to condition the wood and eliminate decay fungi that may have begun to grow while the wood is air-drying prior to processing) cannot be done. It is expected that CuN would be most effective in hardwood ties when used in high decay hazard areas if the ties were dual-treated with a borate pre-treatment. Mississippi State University has conducted studies on dual treatment with CuN which you can find here .
Nisus Corporation has assumed the EPA registration for CuN and built a new manufacturing facility in Knoxville, TN, which will fuel more widespread use of CuN. At least five treating companies now offer ties or timbers treated with CuN for railroad use.
Borate compounds are now used in dual treatment processes for roughly 7 to 7.5 million of the 24+ million or so ties produced per year.
Over the years of testing (50+ documented years now for creosote - see the 1958 cooperative study) creosote has proven to be the most efficacious and cost effective wood preservative for hardwood ties. It has significant weatherproofing properties and is an excellent preservative for hardwood species. However, some wood species are refractory (hard-to-treat) and the heartwoods of those species are almost impenetrable by any wood preservative with the exception of borate compounds which diffuse through the wood over time. Thus, for these refractory species destined for high decay areas, it has now become relatively common practice to use borates as a pre-treatment to protect the wood prior to processing with creosote. Borate dual-treatment protects the entire cross-section of the wood tie providing excellent service life even in high biological-hazard service conditions.
Each preservative system has its place in the wide variety of railroad applications and climactic conditions in North America. RTA is continually researching and testing other systems, but not one is in use other than those mentioned here.
What is RTA doing to research alternate preservatives?RTA is working in conjunction with AAR to determine the relative effectiveness of alternative tie treatments with the ongoing Alternative Wood Protection Research Project (AWPRP) at Mississippi State University. The objectives of the project include determining the relative biological durability to decay fungi and subterranean termites of crossties commercially treated with existing and alternative preservatives exposed side-by-side in a replicated test on a site in AWPA Hazard zones 4 and 5, to determine the effectiveness of treatments against Formosan termites, to determine the corrosivity of alternative preservatives, and to determine the tie dimension stability effects of alternative treatments.
The links are live in the original FAQ page.
AnthonyV The slide title that shows the broken lags is "Broken Lags - Cajon Pass, Testing Lubricant is 2016." Is it possible that the focus of slide is lags breaking during installation and the lubricant reduces the friction torque and the chance of shearing the lag screw?
(Damn this shabby Web interface, the clowns who persist in leaving it poorly programmed, and the "architects" who make UI and IxD secondary. /rant)
I note that several of the illustrated lags exhibit signs of corrosion, which leads me to wonder if this is not entirely about new installation - it might involve redriving of removed lags, or maintenance tightening of those that have loosened or lifted to 'spec' tension or clamping, however that is determined. The lubricant might also be in part an attempt to make driving force better correlated to achieved clamping force, since in the current design of lag it doesn't seem possible to gauge the amount of actual clamping by any form of cost-effective direct measurement otherwise.
Again, of course, we are treated to just how irritating it is when a PowerPoint slide presentation lacks its actual presentation audio track... is there someone like MC who has seen this presentation or is familiar with the subject of lubricating these screws, new or used?
One original reason I thought the lag picture was notable is that there's a pretty consistent breakage (a couple of threads down from the supposed 'weakest point' where the shank necks down at the start of the threads) and unless I am mistaken there are other exhibits that show similar screws breaking in that range. So yes, I think it is at least possible that there is damage from driving, redriving, and perhaps tightening these screws in a dry bore (predrilled or perhaps "prethreaded", which lubrication is intended to address.
I confess that I am waiting for a detailed metallurgical analysis of the various failure modes observed in lag screws that fail in the particular Pandrol system under discussion (not the two-lag system with chairs in concrete ties, etc.) That would include analysis of whether driving damage may be contributing to the reported multiple points of corrosion stress raising that R12E0008 was describing.
Overmod Before further backing and filling on this, it might be useful to consider this recent PDF presentation detailing BNSF practice. There are several highly interesting points, including what appears to be a clear indication of where at least one type of lag screw is breaking.
Before further backing and filling on this, it might be useful to consider this recent PDF presentation detailing BNSF practice. There are several highly interesting points, including what appears to be a clear indication of where at least one type of lag screw is breaking.
There is no discussion about the circumstances surrounding the broken lags on Page 19 in the BNSF presentation. The slide title that shows the broken lags is "Broken Lags - Cajon Pass, Testing Lubricant is 2016." Is it possible that the focus of slide is lags breaking during installation and the lubricant reduces the friction torque and the chance of shearing the lag screw?
What might the relevance of the lubricant to broken lags be?
Well, at least Norm gets it. The BNSF link does show a depression for the rail to prevent lateral movement. We don't have any indication so far of what that screw engages but even if it not capable of producing the proper tension on the screw it is at least as good as a cut spike and probably better since the tie is doing the lateral location. In a wood tie, not so good. Distributed power could increase the lateral forces on the rail, making a bad situation worse.
Electroliner 1935 I note that the report blames the track but gives no specifics about the cause of that failure. Nor does it discuss the bolt failures. The BNSF presentation does allude to the bolt tension and talks about : Lag screw does not bear sideload I would like more info on why it doesn't. Does the concrete tie have a depression where the plate fits? Lag screw and insert can be replaced Derailment-damaged clips and lags can be replaced Clips can not be over driven And it further has a slide on RSD (Rail Seat Distortion) and how it can be optically detected. Does any one know what derailments BNSF has had that were blamed on track deficencies? Looks like the UP & Pandrol need to get this resolved. The preliminary report is woefully deficient in its attention to detail and root cause.
I note that the report blames the track but gives no specifics about the cause of that failure. Nor does it discuss the bolt failures. The BNSF presentation does allude to the bolt tension and talks about :
Lag screw does not bear sideload I would like more info on why it doesn't. Does the concrete tie have a depression where the plate fits?
Lag screw and insert can be replaced
Derailment-damaged clips and lags can be replaced
Clips can not be over driven
And it further has a slide on RSD (Rail Seat Distortion) and how it can be optically detected. Does any one know what derailments BNSF has had that were blamed on track deficencies?
Looks like the UP & Pandrol need to get this resolved. The preliminary report is woefully deficient in its attention to detail and root cause.
And if these are used on wood ties what prevents side loads?
Norm
FRA preliminary findings report, Jun. 23
http://www.fra.dot.gov/eLib/details/L17964#p1_z5_gD
"FRA’s investigation found that multiple lag bolts in this section of Union Pacific track were broken and sheared, leading to tie plates loosening from ties. The loosened tie plates allowed for the rails to be pushed outwards as trains moved across them, eventually resulting in an area of wide gauge, leading to the derailment."
Wish there was more info there. They show them in concrete ties so there must be some kind of anchor for the screw to engage. The screws in the picture, both broken and intact, for the most part seem to have very little thread engagement or else they were backing out.
tdmidgetI have a feeling that I'm beating my head against a wall here. IF the screw could achieve even middle of it's elastic range and the tie plate was embossed , there would be no lateral movement of consequence. Since it cannot achieve the elastic stage and the plate has no resistance to lateral movement, the screw sustains repeated impacts and fails at that point.
So I take it that you conclude that the screws in the UP wreck and the CN wreck were not tight enough to reach far enough into their elastic range for sufficient loading on the tie plates to prevent lateral shifting.
In your post last night, you said this:
“Do not try to obfuscate this with tension on the screw. Any idiot can see that a steel screw will pull the threads from a wood tie long before the steel, any crap alloy, would fail. So it is obviously not a question of tension, but lateral movement that is a problem. A steel screw into wood cannot tension the screw to any significant degree.”
So I conclude that when you say, “IF the screw could achieve even middle of it's elastic range and the tie plate was embossed, there would be no lateral movement of consequence”, you mean that tightening the screw to that extent is simply not possible; rather than being a matter of not having been done by the UP and CN in the two wrecks.
And since such unachievable tightening would be necessary to make the lag screw systems work, the systems are defective in their design. Is that a fair interpretation of your point?
Or maybe it is more accurate to say that the design is okay, but the UP and CN failed to replace their lag screw systems before their working life had ended.
I have a feeling that I'm beating my head against a wall here. IF the screw could achieve even middle of it's elastic range and the tie plate was embossed , there would be no lateral movement of consequence. Since it cannot achieve the elastic stage and the plate has no resistance to lateral movement, the screw sustains repeated impacts and fails at that point.
Waiting on the "yes, but".
tdmidget Bucky, spiking rail directly to ties is not new either, but it is not acceptable in this day and age. Pandrol claims that their smooth tieplates have more surface area which is not true. A igh school geometry student could instantly see that the embossed plate has more surfface area AND the resistance to lateral moverment. Do not try to obfuscate this with tension on the screw. Any idiot can see that a steel screw will pull the threads from a wood tie long before the steel, any crap alloy , would fail. So it is obviously not a question of tension, but lateral movement that is a problem. A steel screw into wood cannot tension the screw to any significant degree. As a millwright I tension fasteners by torque, hydraulicly , and electromechanically for a living.You cannot come anywhere near the strength of that fastener in wood, probably not achieving the elastic state at all.
Bucky, spiking rail directly to ties is not new either, but it is not acceptable in this day and age. Pandrol claims that their smooth tieplates have more surface area which is not true. A igh school geometry student could instantly see that the embossed plate has more surfface area AND the resistance to lateral moverment. Do not try to obfuscate this with tension on the screw. Any idiot can see that a steel screw will pull the threads from a wood tie long before the steel, any crap alloy , would fail. So it is obviously not a question of tension, but lateral movement that is a problem. A steel screw into wood cannot tension the screw to any significant degree. As a millwright I tension fasteners by torque, hydraulicly , and electromechanically for a living.You cannot come anywhere near the strength of that fastener in wood, probably not achieving the elastic state at all.
Did I say that a steel screw would not pull the threads from a tie from a wood tie long before the steel would fail? No sir, I certainly did not. Did I say that tension is breaking screws? No I never said that either. I also never said that smooth bottom tie plates are better than embossed bottom plates. I just attempted to illustrate that there must not have been a universal consensus that embossed bottoms were better than smooth bottoms in all cases.
You say that the steel screw is so strong that tightening it in a wood tie cannot generate tensile force in the screw shank of any consequence. Yet a steel screw will bend and break or shear before the displacing the wood of the tie that is resisting that lateral movement that causes the shear. And all it has to do to not break the screw is split the wood with the grain, yet it breaks the screw first. If the tensile strength of the screw in the wood is of so little consequence, why doesn’t the lateral force just tilt the screw by crushing the wood, and draw the screw out by stripping the threads?
mudchickenBucky - You surmised wrong (again) on the bottom of the plates, especially with the older stuff. There are all kinds of variations.
I did not surmise that there were not all kinds of variations.
I was responding to the comment by TD Midget where he seemed to believe that smooth bottom plates are something relatively new and not the emobossed plates that he is familar with.
tdmidget Thanks for the reply MC. Now I have to ask, "what would you rather have in this situation, adverse tie abrasion or lateral movement?".
Thanks for the reply MC. Now I have to ask, "what would you rather have in this situation, adverse tie abrasion or lateral movement?".
Regardless of who made the screws (Lewis, Camcar, The Chinese, the Russians, etc.), all are watching to see what's going on and is there a random/ systematic/ materials/ application/manufacturing issue at play(?). Knowing the Lewis folks from my La Junta experience, I'm sure that they are watching this and seeing if there is anything that might better the type of screws or changing the Rail Foundation System somewhere else. (it could be something goofy in the system and the damaged or failed screws are a symptom of a larger issue nobody was even aware of... like the tie plate holes (round, hopefully not square) needing to be machined and finished differently...)
Bucky - You surmised wrong (again) on the bottom of the plates, especially with the older stuff. There are all kinds of variations.
The lag screw stress is lateral shear combined with bending. Over-tightening the screws without stripping the threads would add a preload stress of axial tension in the screw shank, increasing toward the head.
That preload stress would add to the dynamic stress of a passing train. However, I don’t see any mention of that being a factor in the CN Fabyan Bridge wreck. Nor is there any mention of lag screws pulling up by stripping the threads out of the ties.
If I am not mistaken, tie plates with smooth bottoms have been widely used in the past going back to at least mid-1900s.
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