Anyone know how the Austrailian railroad with the nearly 300-mile straight track deals with heat expansion or cold contraction whichever the case may be?
when I find a guy’s forum name I’ll be back.
Jock,
That track is laid with 60kg/m (120lb/yd) rail on concrete ties with spring clip fastenings. I don’t think they have any special expansion joints. While it is a desert, and is hot in summer (maybe 40 degrees celcius, 105 Fahrenheit), temperatures would not get much below 0 degrees celcius (32 degrees Fahrenheit) even at night in winter.
I’ve travelled across twice, and the weather was overcast at Cook, the station stop on the long straight. There are maybe four active stations on the straight, which would have insulated joints for signals, which might take up some expansion.
If they have carried out the welding at an appropriate neutral temperature, it should all work. But you don’t want a major derailment 150 miles from the nearest town, either!
Peter
…Never thought of that issue before it was raised by the above post…[Jock], and that is a real interesting situation. First off, I thought the temps. extremes would be much more than Peter noted. That’s surprising to me, as I thought the desert temp would be much higher in sunlight and summer. Our desert areas sure can be.
Just for the thought of it…What would be the normal expansion it could experience if the numbers were added up for the total 300 miles…? We all know by observing a length of 39’ rail between summer and winter the gap is noticeably different…say at least 1/2"…so how much would all this [by theory], add up to in length if this expansion was totaled on out for the 300 miles…Anyone care to do the math…Must be yards and yards and then some…! It really is interesting when one gives this situation some thought how it really is kept under control.
You’re going to make me dust off my engineering text books!
This is going to be a ridiculously over-simplified analysis, so please bear with me and feel free to make additions or corrections.
The governing theory here is the linear thermal expansion of a material. Note that by “linear expansion” we’re already simplifying the problem to one dimension, when in fact the real world exists in three dimensions. The three dimensional problem is highly complex and well beyond my capacities, so fortunately the one dimensional problem yields a reasonable approximation. Here’s the governing equation:
(alpha) = (change in length) divided by (original length) times (change in temperature)
We’re curious about the (change in length), so we’ll solve the equation for it:
(change in length) = (alpha) times (original length) times (change in temperature)
Now we insert our three known quantities. Original length is easy, that’s 300 miles. Change in temperature can be determined from M636C’s information. He gives us a range of 0 to 40 C. We’ll assume the rail was welded (or installed) at a neutral temperatue of 20 C. Thus, the maximum change in temperature is 20 C in either direction (warming from 20 to 40 or cooling from 20 to 0).
Alpha is the linear thermal expansion coefficient for the material. For steel, we’ll use 12 x 10^-6 (that’s 0.000012). The units here are inverse degrees C. This is only an approximation, as the exact number would depend on the specific type of steel.
Plugging these numbers into our equation gives:
(change in length) = 0.000012 x 300 miles x 20 C
(change in length) = 0.072 miles = 380 feet
So, if we have a solid, continuous piece of uniform steel that’s 300 miles long, it would grow by 380 feet in the heat of a 40 C day or shrink by 380 feet on a cold 0 C night.
Again, please bear in mind this is a grossly over-simplified approximation. A more precise answer w
They’ll have expansion joints near Switches or every few miles or so on plain line.
Plus the average track temperature is higher than the average air temperature because rails are usually dark in colour on the sides from rust and or oil.
In the UK the average track temperature is 27 Centegrade (80F) and it hardly ever gets that hot here.
The rail won’t expand or contract if you keep it from doing so. The track structure and rail anchors hold the rail in compression or tension instead of letting it expand or contract. Imagine it this way. You take a length of rail and let it expand 1/2 throug heating. Now, you apply a large enough longitudinal force to squeeze the raila 1/2" back to it’s original length. Then you apply rail anchors to hold it there, in compression.
In the hot weather, if the compressive forces get too high, the track will “sun kink” as the whole track displaces sideways to relieve the strain. In cold weather, if the tension forces get too high, the rail will break.
Hope that helps.
…Thanks Scott for bringing out the book and doing a bunch of figuring for us…Your analyses was great and interesting. I just don’t see how rail anchors contain a rail from expanding when the sun is beating down on it…One would think forces such as when a train travels over it and causes movement the rail would stretch [expand] through it’s anchors…But I know for the most part, it does work some how because it is a reality every day in the hot summer sun and only sometimes does the system get into trouble. And of course it does have the opportunity to expand in width and height.
Digging even deeper here. . . .
From oltmannd’s good comments, it might be useful to find out just how much force the average tie clip must withstand. We’ll start by determining how much force it would take to squeeze our heated rail that’s expanded by 380 feet back to its original length of 300 miles even. The equation to use here is as follows (again, over simplified):
d = PL / EA
d is the change in length, 380 feet or .072 miles
P is the force, what we want to know
L is the original length, 300 miles
E is the modulus of elasticity, 30 million pounds per square inch (psi) for steel
A is the cross sectional area of the rail, 11.75 square inches for 120 lb/yd rail
Solving for P:
P = dEA / L = .072 * 30000000 * 11.75 / 300
P = 84,600 pounds
So it takes a force of 84,600 lbs to keep 300 miles of rail from expanding over a temperature change of 20 C. Assuming ties spaced 22 inches on center, there are about 864,000 ties in 300 miles of track. Thus, at each tie plate there only has to be 0.1 pounds of horizontal force applied to the rail to keep it in place (84,600 divided by 864,000).
But that’s horizontal force – the tie clips hold the rail to the ties using a vertical force. Translating that vertical force into a horizontal force introduces friction (isn’t this stuff fun???). Clean steel (big simplification/assumption here) has a coefficient of friction of 0.8. That means 80% of the vertical force becomes horizontal force. However, if the steel gets lubricated (like from grease or oil on a passing train) the coefficient of friction drops all the way to 0.16. If we’re going to play it safe, we can only assume that 16% of our vertical force translates to horizontal force.
Thus, the vertical force at each tie plate needs to be 0.1 pound / 0.16 = 0.625 pound.
Again, this analysis is incredibly over-simplified, but I hope it was still useful. I found some good information on weld
Guys,
I’d guess at the tie spacing being about 18". This is based on trying to walk along the track, and the ties are too close to step on each comfortably but too far apart to walk on alternate ties comfortably. I think the spacing is greater than common in the USA.
Hugh is right about the rail being dark and heating. Some rails locally are painted white on the side as an experiment. They also have put Armco guard rails into the ballast in one curve (on the outside) to give better support for the ties (but this is a long way from the long straight).
I haven’t seen any special expansion joints on the Trans Australian (but I might have missed them!)
Peter
…Great stuff guys…!!! Really interesting. I’d say the Aussie engineers had the book out a good long time to really get it right…and I suppose they did as it’s been around for some time. Very good and interesting forum stuff.
The new railway line from Alice Springs to Darwin (opened Jan 04) is about 1000 miles with no expansion joints. There were a number of letters in the local paper about this subject as the line was being built. The engineers assured it wasn’t a proplem.
Found the following about Darwin Alice Railway construction
Answers to Frequently Asked Questions on Continuous Rail Welding - print from pdf print from word
What are the welding processes used on this project?
There are two welding processes used;
Flash Butt Welding - this method is used to weld 13 shortwelded rail sections (27.5 metres) together into longwelded rail sections (LWR) of 357.5 metres, which are then used in the tracklaying process; and
Aluminothermic (Thermit) Welding - this method is used on site to weld LWR sections together.
What is flash butt welding?
Flash Butt Welding aligns the rail, charges rails electrically and hydraulically forges the ends together. The welderhead automatically shears upset metal to within 1/8" of the rail profile. A base grinder removes the 1/8" flashing material from the rail, which leaves a smooth base and greatly reduces the likelihood of stress risers, which shorten the life of the rail. The sides and head of the rail are also ground to the profile of the parent rail. As a final step in the welding process, a mag particle test is performed. These quality checks, plus two separate checks with a straight-edge and taper gauge, contribute to the complete job that makes a quality weld.
(Source: www.cn.ca/safetyenvironment/safety/technology/en_SEFlashButtWelding.shtml)
What is aluminothermic (Thermit) welding?
Thermit welding is a welding process, which produces coalescence of metals by heating them with superheated liquid metal from a chemical reaction between metal oxide and aluminium with or without the application of pressure.
Filler metal is obtained from an exothermic reaction between iron oxide and aluminium. The temperature resulting from this reaction is approximately 2500° C. The superheated steel is contained in a crucible located immediately above the weld joint. The superheated steel runs into a mould which is built around the parts to be welded. Sin
The last summer here in Germany was hot.
The mainline here in Limburg was complete overhauled. New ballast, new ties, new rails.
They wanted to lay the new rails at one very hot weekend and the problem was the temperature outside.
They couldn´t weld the rails together when the temperature was above I think 27 degrees Celsius.
Darwin Bob…Excellent report. Lots of technology obviously goes into modern railroad construction.
Many thanks for the excellent report, Darwin Bob! I found it very informative. The really scary thing is that it agrees with the back-of-a-napkin calculations from my first post:
For one degree C of temp change,
change in length = 0.000012 * 1420km * 1 = 0.017 km = 17 meters
And for the full range of 74 degrees C,
change in length = 0.000012 * 1420km * 74 = 1.26 km
Now THAT’s scary! I was even more interested in “Each clip exerts a load of about 2 tonnes onto the foot of the rail.” That’s WAY more than I calculated. Either my figures are way off (highly likely) or a very large factor of safety is employed (also highly likely). It would stand to reason that a much greater than average force should be used, as this type of situation could easily introduce stress concentrations.
Interesting stuff,
Scott Lothes
Cleveland, Ohio
The main job of the clip is to prevent the rail from overturning when the train pass, so the clip force needs to withstand this most
Well, yes – a classic example of not seeing the forest for the trees. That happens to us engineer-folk quite a bit.
…But isn’t the spike the item specifically installed to retain the rail in place and from overturning as the train weight and forces are applied and the clip a later application to do that plus retain the rail in place laterally from forces such as expansion, etc…
Very slow spped prorably
DOGGY