Made of steel, railway track (railroad track in AE) will expand when the temperature rises and contract when it’s cold. When the railway track is exposed to extreme heat, it may buckle. When the ground temperature reaches 37℃, the rail surface temperature can reach about 50℃. Due to the principle of thermal expansion and contraction of metals, steel rails will deform, which will affect the safety of train operation. If the tracks buckle, serious consequences such as derailment may happen. How to deal with railway track expansion?
How do jointed rails deal with the expansion?
A traditional way of overcoming railway track expansion is to leave gaps between sections of rails. That solves the track thermal expansion for the railroad tracks joined end to end by rail joints (joint bars or fishplate). However, it brings out a series of problems. The most unneglectable one is the “clickety-clack” noise which approximates to 100 decibels. At the same time, when the train wheel passed over the gaps, passengers feel the train bumps up and down. That is quite a discomfort. What’s more, it is calculated that more than 60% of rail damage happens at the weak point, the gap. Then you can imagine the costs of maintenance and fixing hit the top.
The good news is the continuous welded rail is invented and widely applied. Continuous welded rail eliminates most of the gaps. Only a few gaps are left between very long lengths of rail (i.e. every 1.5km). High-speed rails use CWR to provide high smoothness, high stability, and low maintenance. Here comes the question people always wonder, “how do the High-speed rails deal with railway track expansion if there are no gaps between rails?”
How do continuous welded rails overcome the expansion?
The internal temperature stress of a long rail is only related to the change in rail temperature and has nothing to do with the length of the rail. Therefore, in theory, the CWR can be welded to any length. The key to controlling thermal stress is to reasonably control the amplitude of the rail temperature change. It is necessary to get a neutral temperature for the long rail, and use fasteners one by one. The point locking method strengthens the control of the thermal expansion and contraction of the “no-gap” rail. In general, the choice of the neutral temperature should ensure that the rails do not buckle under the maximum temperature rise in summer, and not break under the maximum temperature drop in winter. Under special circumstances, it should also be ensured that the fracture value of the rail after the rail is broken does not exceed the allowable value of the rail fracture. When laying and welding long rails, the stress-free temperature should be strictly controlled within the designed range. In daily maintenance, the relevant regulations on the rail temperature of the maintenance and repair work should be strictly followed to ensure the rail stress caused by the thermal expansion and contraction is within a safe range. To be more specific, five ways of dealing with railway track expansion is advised by railroad maintenance personnel.
- The long rail section itself bears all the temperature stress. For example, in some areas in southern China, the long rail is locked on the sleeper so that it does not expand or contract due to temperature changes. This method is suitable for areas where the temperature varies little throughout the year.
- The second is optimizing the fasteners using on the railway road, that is, to replace the shrapnel fasteners with single reed fasteners (also called spring fasteners). Fasten the rails tightly to the sleepers to forcibly digest the energy generated by thermal expansion and contraction.
- In some areas with large temperature differences, another strategy should be adopted. When the energy generated by heat and cold shrinkage is greater than the adhesion of the sleeper within a unit distance, the rail is easy to buckle. To solve this problem, the railway department would make several holes in the rail web within a certain distance to release the energy. Also, rail joints are kept within a certain distance (about 1500m) to assist in releasing heat.
- When constructing track laying, try to choose the time when the season has the least impact on the thermal expansion and contraction of the rail.
- An observation unit is set up between the unit rails of some high-speed railway stations, and observation piles are buried on the shoulders of each unit rail. The unit rails should be measured for creeping regularly. When the creeping amount is abnormal (that is, the internal stress is abnormal) ), stress relief construction is required to eliminate the abnormal stress caused by the heat pulse and cold shrinkage of the rail. Finally, there are generally telescopic adjusters on long-span steel girder bridges to adjust the expansion and contraction of steel rails.