3 ms·
They do (sometimes) preheat continuous welded rail during installation to prevent buckling. The temperature used will vary based on the local environment (Minne
by chiph 3y ago
They do (sometimes) preheat continuous welded rail during installation to prevent buckling. The temperature used will vary based on the local environment (Minnesota will use a lower destressing temperature than Florida). Shorter sections of track (like in a switching yard) may not be destressed at all because there isn't enough length to cause a buckle.
> Compressive forces result from stresses induced in a constrained rail by temperature above its "stress free" state, and from mechanical sources such as braking, rolling friction and wheel flanging on curves. The temperature of the rail at the "stress-free" state is known as the rail neutral temperature (i.e. the temperature at which the rail experiences zero longitudinal force). Initially, the rail's installation temperature or "anchoring temperature" is the rail's neutral temperature. Hence, at rail temperatures above the neutral, compressive forces are generated, and at temperatures below the neutral, tensile forces are developed. Track maintenance practices address the high thermal load problem by anchoring the rail at (neutral) temperature of 95 -110 F. This high neutral temperature range prevents the generation of excessively high buckling forces even when the rail temperatures reach 130 -150 F.
https://www.volpe.dot.gov/infrastructure-systems-and-technology/structures-and-dynamics/track-buckling-research https://www.volpe.dot.gov/infrastructure-systems-and-technol...
Some railroads that experience wide summer vs. winter temperature differences may choose to install expansion joints. Like most things, there are trade-offs, like increased maintenance costs and increased chance of derailment at the joint.
- Animats 3y agoWelded rail buckling in hot weather has become a real issue with global warming and wider temperature swings.[1][2] Australia has especially bad problems, due to wide temperature swings and very long runs of straight track. [1] https://toolkit.climate.gov/topics/transportation-and-supply-chain/land-based-transportation https://toolkit.climate.gov/topics/transportation-and-supply... [2] https://thelincolnite.co.uk/2015/07/kink-in-track-freight-train-derailment-investigation-continues/ https://thelincolnite.co.uk/2015/07/kink-in-track-freight-tr...
- moooo99 3y agoThere was a lot of reporting regarding the same issue in the UK last year https://www.itv.com/news/anglia/2022-07-19/why-cant-uk-roads-and-rail-cope-with-the-heat https://www.itv.com/news/anglia/2022-07-19/why-cant-uk-roads...
- chiph 3y agoWhen I was in London in the early 2000's, the Central Line was closed because of the heat damaging the tracks (they never used the word buckle in their announcement, but that was probably what happened). If they have a track problem that far under ground, it's a serious heat wave.
- moooo99 3y ago> If they have a track problem that far under ground, it's a serious heat wave. Unintuitively, parts of the London underground are notorious for being extremely hot. Especially the central line is super hot due to the material the tunnels are dug into being an extremely good insulator/heat store. https://www.forbes.com/sites/lauriewinkless/2017/06/22/sweating-on-the-underground-why-are-tube-tunnels-so-hot/ https://www.forbes.com/sites/lauriewinkless/2017/06/22/sweat...
- namibj 3y agoIt's also that they don't cool the tunnels like they really really ought to (just feed frozen water into the tunnels and drag the meltwater back out if it won't drain by itself, say by fitting some cars with slush sprayers like how manure is sprayed from the back of a tanker on agricultural fields, or dropping ice cubes spread-about). Use ice-based AC for the passengers, not heat pumps dumping into the tunnels. Change the breaking resistors to not be on the train, but the rectifier stations, and make them vent outside. Or change them to dump heat into what's a big insulated kettle that gets filled with ice or at least disposes the resulting hot water outside, not hot air into the tunnels.