How Do Railroads Deal With Thermal Expansion?
Josef11. Oktober 2019
With the advancement of modern continuous welded rail (CWR), rail networks worldwide have had to cope with thermal expansion, or rail stressing. In short, rails contract at low temperatures and experiences tensile stress, in high temperatures, the rail expands and compresses under the stress. This could lead to heat kinks, which force the track out of gauge and could cause derailments if preventive measures are not taken.
How do railroads deal with thermal expansion?
Railroads deal with thermal expansion by heating the rail prior to installation. Therefore, the rail is heated to its rail neutral temperature, being heated, then cooled as the rail is laid. Additionally, various technologies utilizing wayside devices are implemented to detect rail faults.
Background
When railroads were first constructed in the 19th century, each rail was held together by a fishplate (UK) or joint bar (US), which provided the classic clickety- clack sound when a train passed by. However, maintenance of the joints was tedious, as they had to be properly lubricated and serviced in order to prevent unwanted wear on the rail ends. This was a tedious task administered by track crews, as they had to inspect each joint to ensure that it was maintained to an acceptable standard.
Jointed rail was joined together by a joint bar on either side of the rail, with bolts holding it in place. However, a common issue was that the bolts would oftentimes crack the joint bar, especially under the strain of a heavy train. Furthermore, the joints oftentimes had to be insulated when signal circuits were present, where an epoxy type substance was installed between the rails, strengthening the joints.
The effects of train wheels constantly hitting rail joints.
Jeff Hampton
Jointed rail additionally provided for a bumpy ride for passengers, as each wheel would slam the joint as it passed over. As rail technology progressed and high speed trains began to come to fruition, an alternative to the old practice was duly needed. Although a replacement for jointed rail was on the horizon, it did evoke various benefits.
Although jointed rail was rougher on both the train and track infrastructure, it proved advantageous when the rail reacted to intense temperatures. Installed correctly, there should be a tiny lubricated gap between the rails at the joint bar to handle thermal expansion. However, an instance where the joint does not move would have similar reactions to CWR.
Beginning in the fifties, welded rail was installed on various rail networks and began to prove its worth. It encompassed a much smoother ride for passengers, and was less of a maintenance headache. Furthermore, welded rail reduces friction, and wear on both the rail infrastructure and the train’s running gear. However, due to the lack of joint bars, when the rail expanded due to excessive heat, the rails had no leeway, therefore, they expand and buckle under the pressure. However, various precautions are taken to lessen the chance of the rail being damaged due to thermal expansion.
According to
Progressive Railroading, if the force of the expanding rail is not repaired in a timely manner, the rail will have no more room to expand, thus, the rail will begin to buckle, resulting in the rail being out of gauge. If the rail was shifted far out of gauge, it will be troublesome for a train to navigate, thus, causing a derailment. This highlights the importance of preventive measures to detect faults before they become a dire issue.
Installation of Continuous Welded Rail (CWR)
In order to prevent thermal expansion, welded rail is installed at its stress free temperature (SFT), which is usually 90 to 110 degrees Fahrenheit in the U.S., and 27 degrees Celsius (81 Fahrenheit) in the United Kingdom. If the temperature of the rail exceeds these temperatures, the rail could begin to buckle under the high stress.
According to Progressive Railroading, the rail must be set at a neutral temperature, however, when the rail is laid, it is impossible to determine the rail’s neutral temperature, therefore, the temperature is set by the railroad determined by the location and its climate.
Prior to the installation of a section of continuous welded rail, the temperature of the rail must be taken to ensure it meets the stress free temperature, if the rail is below the desired temperature, the rail will be heated, causing it to expand gradually. The rail is heated either by a gas burner or a tensioner. A tensioner is widely preferred as it evenly expands the rail, as opposed to the gas burner, where the heat is unevenly distributed. However, the tensioner can only be utilized on certain areas of the rail.
Richard Dyke
To improve the strength of the rail, instead of the standard spikes, concrete sleepers utilize elastic fasteners. These fasteners have the ability to prevent vertical and lateral motions on the rails on the sleepers and prevents the rail from raising from the sleeper in the event of an expansion, thus, preventing derailments. However, railroad spikes and wooden ties are widely utilized with CWR, and are equally as effective.
Repairing Rail Stress
When thermal expansion occurs, the issue must immediately be repaired before a derailment occurs. To repair a rail that has endured thermal expansion, the rail must be cut, heated, and welded together. If a rail is found to exceed its stress level, or has experienced a kink, the rail is reheated to expand the steel. Similar to when the rail is installed, when repaired, the rail must be heated to reach the stress free level. If the rail is beyond repair, the piece of rail is completely replaced.
Preventive Maintenance
According to progressive railroading, there are various mechanisms available to combat thermal expansion and rail stressing. One device called the Railstress Montior, will report the stress level and temperature of the rail. The device is attached to the rail and utilizes various technologies in its analysis, and provides a detailed report of its finding, which is then sent to a wayside device. The device then sends alerts via an alarm if it indicates an issue with the rail’s integrity. In addition to the Railstress Monitor, various devices with similar technology exist.
Nicolas Taveneaux/Public Domain
Expansion Joints on the French TGV.
In addition to this technologically advanced equipment, the
Federal Railroad Administration (FRA) has issued various guidelines, mandating that railroads with CWR have an ample training program in place for the track crews and engineers. These programs pinpoint the issue of rail stress, and familiarize railroad personnel with the anatomy of thermal expansion, how to repair track that has expanded or kinked, and the preventive maintenance implemented to prevent these issues.
Furthermore, expansion joints are placed in between lengthy sections of CWR to allow the track to expand, and are oftentimes present near certain pieces of infrastructure such as bridges, as these areas have a tendency to expand differently than the rest of the continuous welded rail. Unlike jointed rail, these joints are tapered diagonally. These expansion joints are one of the many preventive techniques against rail kinks. With CWR the standard for many country’s rail networks, rail companies will continue to be reliant on these technologies and the companies that develop and provide them. Because of these technologies and the education and training being invested to maintain CWR, this type of rail will continue to be standard practice worldwide.
How do railroads deal with thermal expansion? Railroads deal with thermal expansion by heating the rail prior to installation. Therefore, the rail
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What Do High Speed Trains Run On?
Josef5. Dezember 2019
There is an exponential amount of engineering work that must be taken into account before operating high speed trains, as the track infrastructure, such as rails, ties, and ballast must be properly engineered to accept speeds over 150 mph.
So, what do high speed trains run on?
Conventional rail. The rail is reinforced, equipped with special sleepers and fasteners. Furthermore, copious amounts of ballast is utilized to keep track in place.
There are many infrastructural elements that must work together seamlessly in order for a high speed rail network to operate properly, including other technologies that could be utilized to power high speed trains in the future.
Track Infrastructure
Super-elevated Curves
Track infrastructure for high speed networks must be properly prepared, as there are various forces that come into play at such high speeds. One of the most common forces is the centrifugal force, which by definition, is an outward acting force, directing away from the axis of the force. This force comes into play in the context of high speed trains when rounding a curve. When a train makes a left turn, passengers would sway to the right, if a train makes a right turn, passengers would sway to the left.
In order to negate some of the effects of centrifugal forces, high speed rail networks are built with banked turns, where the track is either elevated or super-elevated. The tighter the radius of the curve, the higher centrifugal forces present inside the train. This elevation is made possible through copious amounts of ballast underneath the track, thereby, elevating the outer edge of the rail.
A BR Class 390 “Pendolino” rounds a super-elevated curve as it enters the Crawford Viaduct on a Euston-Glasgow service. Note the tilting mechanism of the Pendolino as it leans into the turn.
Richard Dyke Photo
Super-elevated curves are designed to lessen the movement of passengers within the train, as the train’s suspension balances much of the forces encountered within the curve. The most pertinent feature of a banked curve is to balance both the centrifugal forces, pulling the train outward, and the force of gravity, pulling the inner part of the train down, therefore, keeping the train on the track.
Although super-elevated curves offset some of the centrifugal forces at play, choosing the proper radius is perhaps the most important aspect of curves on a high speed rail network. Typically, a high speed railway has a larger curve radius compared to a traditional rail line to further negate the effects of centrifugal forces.
Rail
The manner in which rail is laid on a high-speed line is imperative as well. Since the dawn of rail travel, jointed rail was commonplace, however, beginning in the fifties, welded rail was found to deliver improved ride quality, ease of maintenance, and was more apt to handle high speeds. Continuous welded rail had become particularly advantageous in the sixties, when the world’s first high speed rail line opened in 1964, the Japanese Shinkansen.
High-speed railways have continuous welded rail, which prevents excessive friction, provides a smoother ride for passengers, and is less maintenance heavy. Although welded rail is less maintenance heavy, its installation is increasingly more expensive that its jointed rail counterpart, and various precautions must be taken to prevent inconsistencies in the rail.
Upon its installation, continuous welded rail is installed utilizing a process known as “flash butt welding”, where ends of the rail are heated up to a certain temperature, then pushed together, therefore, welding the two ends of the rails together.
Nicolas Taveneaux/Public Domain
Expansion Joints on a piece of continuous welded rail on the French TGV network. These types of expansion joints are imperative in order to prevent kinks in the rail as a result of expanding or contracting. These are especially important for the safety of high speed running.
A continuous welded rail line could stretch several miles long, and allow for much higher speeds than traditional jointed rail. However, due to the phenomena known as
thermal expansion, joint bars or spacers must be placed every few miles to negate rails becoming kinked due to expansion and contraction as a result of changing temperatures.
Furthermore, it is important to ensure the rail is properly restrained in the event of an expansion or contraction. On a high speed line, such as the TGV or Shinkansen, it would be commonplace for specialized clips to be attached to the sleepers or cross ties in order to prevent the track from becoming misaligned.
In addition to restraints such as Pandrol clips, the ballast underneath the track must be properly supporting the track infrastructure. In order to keep sleepers in place, it is ideal that ballast is placed underneath, beside, and in the between the sleepers to ensure the infrastructure is properly in place, and the track bed is secure.
Sleepers or Cross Ties
Sleepers support the rails, and are positioned perpendicular to the rail. When a train passes, the function of the ties is to transfer the load and weight of the train through to the ballast and sub grade on the infrastructure. Furthermore, sleepers assist in maintaining the proper gauge of the rail line, and prevents the rails from falling sideways, or becoming misaligned.
Interestingly, concrete ties are both cheaper and more plentiful than concrete. In addition to being able to handle high speed operation, concrete sleepers are also apt to handle heavier trains than traditional wooden ties. Proper installation of concrete ties is critical to their performance, as they require the ballast to have ample draining capabilities, which is achieved through properly preparing the railway’s sub-grade.
Although concrete sleepers are advantageous on many fronts, one major downfall of utilizing concrete sleepers as opposed to conventional wooden ties is higher pitched sounds when trains pass. Concrete ties amplify the wheels and other sounds of the train, thus, wooden ties are oftentimes utilized in populous areas.
On Amtrak’s high-speed Northeast Corridor, two Acela trains pass each other near Crum Lynne, Pennsylvania. Note the elevated curve, concrete ties, and tie clips.
Jonathan Lee Photo
Grade Separated Right-of-Way
The interesting aspect of high speed networks is that oftentimes they are completely separated from conventional railways. Grade separated right-of-way is defined as having different modes of transit separated at a different height from one another. This allows trains to operate at much higher speeds, as slower trains are not present on the same rail line.
This has been extremely advantageous for high speed trains such as the TGV and Shinkansen, as they are able to stay on schedule, and operate at increased intervals. In fact, due to grade separation, when trains such as the Shinkansen are late, it is by only mere seconds, as opposed to other services, which must operate slower due to other trains utilizing the same track.
Maglev Technology
Although most high speed trains operate on conventional tracks, new technology such as Maglev trains have come to fruition in recent years. Maglev trains lack rails, sleepers, and ballast, and instead utilize a guide-way in which the train levitates due to the strength of opposing magnetic forces.
Maglev technology allows passengers a nearly completely smooth ride, as no contact is made with the guide-way, or a rail, such as a conventional train. Maglev trains can utilize either a single or double guide-way, however, they are both elevated above the guideway in a similar manner.
An example of a single guide-way system is the German “Transrapid”, and the Shanghai Maglev, which transports passengers from the city’s airport to the city center. The Shanghai Maglev is the only example in revenue operation, as its German counterpart is not longer operable.
An example of a double guide-way Maglev is JR Central’s experimental SC Maglev MLX01, which holds a speed record of 370 mph (590 kp/h). The Miyazaki test track, the MLX01’s guide-way, resembles a trench, and operates via superconducting magnets placed inside the bogie, guided by two sets of metal coils on each side of the guide-way. The SCMaglev remains in testing phases, however, the train has garnered much interest internationally, in countries such as the United States and Australia.
Related Questions?
What are the fast trains called?
Fast trains are oftentimes called “Bullet Trains”. The term bullet train originated in Japan, with the introduction of the Shinkansen in 1964. The name was given due to the train’s speed of 130 mph, and the pointed shape of its nose.
So, what do high speed trains run on? Conventional rail. The rail is reinforced, equipped with special sleepers and fasteners. Furthermore, copious amounts
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