On our Holidays last summer, we travelled by train from Prince Rupert to Jasper,where we came across a train full of rails. the train was quite long and the rails were stacked about 4 tiers high and I think about a dozen wide and maybe,seemed like about 1/4 mile long.The flat cars holding the rails were obviously built specially for rails.My question is how do they navigate curves and could a rail train travel the CPR through the spiral tunnels and what length are the rails.
thanks, Dale
Standard length of a CWR (continuous welded rail) stick is ~ 1,500. It’s flexible. Welded rail trains can pass through curves easily, including relatively tight curves such as the Spiral Tunnels.
RWM
I saw a trainload of rails pass through the local yard, where it had to negotiate a fairly tight curve. The rails squeeled like crazy.
Perhaps surprisingly, the vertical axis of a big, heavy, seemingly stiff piece of rail - which is the plane involved in going around curves - is significantly less strong = weaker = more flexible than the rail’s stiffness in the horizontal axis (which is what carries and distributes the weight of the wheels across the ties). That’s because the stiffness of the rail is a (complicated) function of - put simply - how much metal is farthest away from the center of the rail. For the horizontal axis, the most metal - the head and the base - is pretty far away from the middle of the rail. For the vertical axis, most of the metal in the head is pretty close in to the web, and of the base, only the comparatively thin outer edges are farthest away from the web. I’ll try to find some values for either I (“Moment of Inertia”) and/ or S (“Section Modulus”) for one of the common mainline rail sections to give you a sense of the magnitude of that difference.
The other surprising aspect is that the relative stiffness of the rail is defined by the fraction I (same I as above) / L, where L is the length of the stick of rail or string of Continuous Welded Rail (“CWR”). Clearly from this fraction, for a given rail section as the length gets longer, the stiffness gets lower. What may not be obvious is that for a typical string of CWR, that length is from 35 to 40 times longer than a conventional 39 ft. stick of rail, so it’s stiffness is only 1/35 to 1/40 as much, or only from around 3 % to 2.5 % as much. That’s why the CWR is so flexible - it can droop into a shape looking like a piece of overcooked spaghetti if it is not placed carefully on the ground. I’ll also see if I can find a good photo of that.
Our old friend Archimedes (the Greek mathematician) who famously said, “Give me a lever long enough and a place to stand, and I can move the world” would appreciate this next point: Another
They run through main-track 16 degree curves at 25 mph (track speed) just fine.
RWM
Stiffness of rails in horizontal and vertical planes:
Second Area Moments of Inertia (in inches to the 4th power)
I-yy = Vertical bending inertia for entire rail = strength for carrying weight
I-zz = Lateral bending inertia for the entire rail = resistance to curving
For the 136 RE rail section in new (unworn) condition, I-yy = 94.9 in.^^4; I-zz = 14.5 in.^^4
Source/ reference: U.S. DOT - FRA - Office of Research and Development, Volpe National Transportation Systems Center, Cambridge, Mass., “Estimation of Rail Wear Limits Based on Rail Strength Investigations”, by D. Y. Jeong, Y. H. Tang, and O. Orringer, December 1998 Final Report, DOT/FRA/ORD-98/07, DOT-VNTSC-FRA-98-13, APPENDIX A. - SECTION PROPERTIES FOR NEW OR UNWORN RAIL, pages 31 and 31 (pages 35 and 36 of 44 of the PDF version), at: http://www.fra.dot.gov/downloads/research/ord9807.pdf (Note: The value for I-yy is commonly available from various suppliers and published reference tables; it’s the value for I-zz that was hard to find.)
Ratio of I-yy to I-zz = 94.9 / 14.5 = 6.54; inverse is 0.15.
Thus, the 136 RE rail section is 6.5 times stronger against vertical bending (wheel loads) than it is against horizontal bending (curving forces). Or, said another way, it is only 15 % as strong against curve-bending as it is against wheel load-bending.
With those kinds of ratios, you can see why CWR is so flexible in curves.
“Stock Photo” of a welded rail train going around a curve, from slightly overhead, by Ernrest H. Robl, is at:
A couple of photos of welded rail installation, showing how flexible it is, at:
http://www.trainweb.org/tgvpages/jpg/construction4.jpg
http://www.trainweb.org/tgvpages/jpg/construction7.jpg
If I find any other photos in the near future that show this better, I’ll post them here as well.
Thank you all for the information,very informamative,one last question.How many rails can be transported at once.
I think you’ll find that those tiers hold ten rails, so figure forty long lengths to a train, or 30,000 feet for each of the two rails to a track. If someone has a more authoritative answer, I’ll defer to it.
The ConRail CWR train that I worked most often was 4 rows high, but only 8 rails across (maybe that’s why they were so helpful - happy to flog that one off on me, and keep the ones with more capacity for themselves ?). So if full, that would be 32 strings of CWR at a nominal 1/4 mile each = 8 miles of rail, enough for 4 track-miles (both rails). If it is 132 lb. per yard RE rail section, that load would weight about 930 tons - which is pretty light for a whole trainload, though not too bad for a train only a 1/4 mile long. I’m sure the cars were heavier than normal with the roller stands and all the other equipment, but I’ll bet the gross weight of everyhting wasn’t much over 2,000 tons.
The Amtrak rail train looks to be - I had to check an old photo, and it was hard to see - 12 rails across, again 4 tiers high. So that would be 50 % more capacity = 48 strings at 1/4 mile = 12 rail-miles, 6 track-miles’ worth; about 1,400 tons of 132 RE - maybe 2,500 tons of train.
A lot of people worry about rails on a train bending to go around curves. Take a step back and consider for a moment. Shouldn’t it be able to bend just as much as the track it is riding on?
The key is how the bending is controlled. In track, the bending is controlled (forced if you will) by the anchorage to the ties. On a rail train, the rails are only contstrained longitudentally at the center. Imagine picking up a 10’ piece of rebar in the middle. It will droop.
When a rail train is in travel mode, it will have an empty hopper car (typically) on either end of the strings of rail racks. The rails are tied down on a special rack in the middle of the train and allowed to float free on the ends. The racks provide constraint sideways and vertically. As a train goes around a curve the rails to the inside bend more than those on the outside and their ends move relative to each other. Grab a hand full of raw spaghetti and gently bend it, paying attention to the ends.
The buffer cars are there just in case the center tie down comes loose and a rail starts to move. It will hit that car before an engine or a revenue car. When ready to unload rail, the center tie downs are removed and the threader car pulls rails off the racks to start and then each rail is hooked to the next one as it goes out to permit essentially continuous unloading. There is a lot more to it than that, but that is the basic idea.
As to length of strings, since the rail manufactures are now using continuous casting methods, the most common rail length being produced is 80’. Rail trains are now most often built to handle 1600’ strings (20-80’ pieces welded together at the plant and shoved driectly onto the rail train). Train capacity varies, but the newer trains can carry 50 strings, or 80,000’ of rail.
[tup] And there’s the rest of the story ! Thanks, Steve.
Although: The last time I picked up a 10 ft. long piece of rebar a few months ago (#6 = 3/4 inch diam.), it didn’t droop too much - maybe a foot at most. But a 20 ft. long piece - I had to hold it on my shoulder to keep the ends from dragging in the dirt. Which is not to be “nit-picky” here, but to better illustrate the dramatic effect that a longer length has on the flexibility and amount of bending that a rebar - or a rail - will display.
Rail Train Oops!
.
[:O] Oh, wow ! Makes my day, though, in comparison. [:D] Thanks for sharing that.
Looks like it is 6 tiers high - can’t tell how many rails across, though.
Now think about this a minute - the caption says it was a break-in-two. Steve above aptly explained how the tie-down system works. So the CWR rails are restrained only in and at the middle of the train, which is the point up to which the cars and the couplers will feel most of the “draft” (pulling force) for the rails; after that, the rails are just sitting on rollers on the trailing cars.
So when the coupler broke and this pull-apart occurred, it probably happened where the pulling forces were the greatest, right ? Which would be in the front half of the train, between the locos and the tie-down car, right ? So what happened next ? Well, I suspect that the locos and the front portion of the train - probably less than 1/2 of 1/4 mile, so only 700 or 800 ft. long at most, and maybe not even that, perhaps only the 1st “roller car”, because some of the rails are displaying bolt holes, so this might have happened right at the front of the rail train - pulled ahead quickly as they will do. Meanwhile the trailing rest of the train went into emergency braking as it should from the loss of train line air pressure. So the front car(s) were pulled out from underneath the rail strings - kind of like the showbiz trick where the magician pulls the tablecloth out from underneath a fully set table without disturbing anything - which left the rail strings suspended in mid-air for a fraction of a second. Then the rails dropped down onto the track structure while still moving and started plowing through the ballast, ties, dirt on the side, and anything else around. Since the rear portion of the train was essentially “pushing on a rope” becasue the rails are so flexible, they sprung and coiled
These remind me of what I saw in 1964 when the IC was installing CWR on a curve south of Jackson, Miss. I remember noticing how the rail drooped and turned as the thimble on the crane moved it into place. I took some pictures of the operation, and one or two of the men worried that I would show them leaning on their tools.
Johnny
Wow! What a mess.
Tele-photo of a loaded NS CWR train going through an S-curve at the McKees Rocks Bridge ¶ on June 12, 2008, at:
http://www.railpictures.net/viewphoto.php?id=244205
Any quesiotns ? [:D]
PDN: Have a question: Do the side forces on the rail train car’s wheel flanges limit the number of rails that can be carried on a specific train?. Are these some of the factors that might need to be considered?/.
Size of rail 141#, 136# 112# etc each which would have a different stifness
Curvature of route rail train runs on?
Types of turnouts #6, #8, #20 etc that train will pass through? All rail trains meets I’ve observed the rail train stays on the main?
Closer tolerances required on wheel flanges?
Turnouts with or without guard rails?
Cross ties condition of route or sidings?
Do RRs issue special instructions especially on an older branchline or does engineering department specify number of rails on a train?
Is condition of removed or relay treated differently?
Are wheel profiles on rail trains different?