I have subscribed to Model Railroader off and on for twenty years (and have read issues in the library when not a subscriber) and have always wondered about a very simple subject but have felt too dumb to ask, but after triple bypass surgery, time is running out! My question concerns the way railroad ties are secured on prototype roads. It’s difficult for my simple brain to imagine that simply driving even long spikes into the earth could hold ties and rails in place against the tremendous forces generated by the massive tonnage and momentum of trains moving at speed, especially on curves, Someone please help this old geezer understand what I’m obviously overlooking!
Many thanks.
jglawson
The ties/sleepers on prototype track aren’t secured by long spikes driven into the earth. The ballast and the weight of the rail is all that holds ties in position. The rail in turn is spiked or clipped to the ties - the spikes are only long enough to secure the rail to the tie. As you note, the forces acting on the track are considerable, which is why prototype track needs regular tamping and alignment to maintain its proper geometry. Cheers, Mark.
What Mark said. In addition, keep in mind that the downward force of a loco’s/car’s mass on curves, coupled with the spikes mentioned above and superelevation of track and roadbed, provides tremendous friction to inhibit rails and ties from shifting on curves.
Mark: Thanks for the answer re: Con Cor Airslide part. It indeed looks like a compressor.
I’ve seen film of gandy dancers using long bars under the rail to lever the track back into alignment, maybe twenty men sliding the track sideways in rythmn with each other. As was said above, essentially the track is spiked to the ties creating one unit which is held in place by the ballast and the weight of the rail. The weight of the train going on the track contributes downward pressure to hold the track down as it goes by…except on curves, which is one reason why superelevation is so important. It helps spread the weight more evenly onto both rails, not just the outside one in the curve.
I must pause and think about this one… okay… when you drive an aouto or semi rig what keeps the surface together under the tyres? Clearly if it’s concrete or asphalt it’s sort of stuck together… how about a dirt track?
there’s a madness in the method of my approach…
A road vehicle tyre “squashes” to get traction. The old solid rubber tyres and things before modern pneumatic tyres could get all sorts of trouble.
Now… a rail wheel is a hard steel wheel on a hard steel rail… and the point of contact is not only minute but constantly changing.
In fact one element of what happens between rail wheels and rail is that the track distorts a fraction tipping down at the leading end in the direction of travel so that the wheel is not trying to turn on a constant horizontal and rigid surface but is slightly dropping into a depression and pushing against a tiny angle… this combination constantly moves allong the rail. This is similar to what happens when you walk… when walking you are constantly leaning forward until you start to fall forward but then you reflexively (if all is well0 move a leg through and catch yourself on it… only to repeat the action until you either straighten up and stop or fall over.
This flexibility is why track is laid in a balllast base rather than in a rigid/solid concret plinth. Vast experiments have gone into all of this. Part of what the ballast does is provide flexibility.
If you go into the physics a basic that applies to all modern rail vehicles except maglevs is the following…
If you take four equal sized cones and glue two pairs thick end together and then mount them by the points in bearings in a rigid frame you will get a vehicle which will travel in a straight line if you put it on two parralel rails and tilt the rails from one end to the other.
The trouble with this fact is that the vehicle will always want to go straight.