Steel train rails are laid in 12.0-m-long segments placed end to end. The rails are laid on a winter day when?

German Thal: If you don't understand the question, ask your teacher. You'll NEVER learn anything if you just keep getting the answers for free from total strangers on the Internet.DO YOUR OWN HOMEWORK.

Moira Woodrow: I agree with JetDoc: look up the co-efficient of expansion of steel, and from this you will be able to work out how much a 12m rail will expand between -2 degrees and plus 33 degrees C. If they 'just touch' at the higher temperature, they will surely not be pressing against one another and therefore there is no stress at all.

Lue Podewils: These days rails with joints are in short supply. The Continuous Welded Rail (CWR, aka 'ribbon rail') is laid in 1320' lengths off a train created for that purpose alone. Then the welders come along and weld that together. As a result welded rails run for miles.I can't tell you the physics but I am familiar with the stuff. When welded they are heated to a certain temperature at those joints as a sort of 'standa! rd candle' concept. But that will allow for deformation in extreme temperatures.In extreme cold, as in our mountains where I have worked, winter nights are accompanied by a 'pull apart' at least 2 to 3 nights a week. The rail is so cold it breaks from extreme contraction. Stress mitigation only goes so far. MOW folks use some angle bars (fishplates) are used as a temporary fix, and then the welders come along in a day or two and weld up the joint.The flip side of the coin is in high temperature, when the rails expand to the point, they will kick the ties out of the ballast and in some cases I know lifted the rail on the outside of curvature. These are commonly referred to as 'sun kinks,' and have caused numerous derailments. The reason why is, with a pull apart the rail is broken and that will turn signals red so the train will stop before getting to the failure. If you come upon a sun kink at speed with green signals, you're in trouble, as well as anyone else in close prox! imity.In severe cases, the speed of trains is limited so that ! if a train stumbles across disturbed track the pile up will be smaller.Especially at risk are areas where some kind of roadbed maintenance has occurred, such as laying new ties (sleepers). Here train speeds are limited anyway until 'consolidation' takes place. That is an engineering term meaning that after the passage of sufficient tonnage, the ballast and the ties have all been packed into place, when the structure is much more rigid afterwards, and at designed capacity....Show more