Why Railroads Don't Need Expansion Joints
TLDRThe video script delves into the evolution of railway engineering, focusing on the transition from jointed rails to continuous welded rail (CWR). It explains how the famous 'clickety-clack' sound of trains was a result of the joints in the tracks, which also led to increased wear and maintenance costs. Modern railways use CWR to reduce noise and maintenance, addressing thermal expansion and contraction through restrained movement and stress management. The script also highlights the importance of safety regulations and innovative solutions, such as neutral temperature and expansion joints, to prevent rail buckling and ensure a smooth, quiet, and efficient railway system.
Takeaways
- 🚂 The iconic clickety-clack sound of trains is becoming less common due to advancements in rail technology.
- 🔧 The rhythmic clicks and clacks were caused by joints in the tracks, which were initially implemented to solve transportation and thermal problems.
- 🌡️ Modern railways often use continuous welded rail (CWR) that eliminates most joints, reducing noise and maintenance costs.
- 🔥 Rails expand and contract with temperature changes, and the traditional jointed rail design accounted for this thermal expansion.
- 💼 The shift to CWR involves understanding and managing the stresses that come with thermal expansion and contraction.
- 🔩 CWR segments are welded together using various welding techniques, resulting in a stiffer and smoother rail system.
- 🌤️ Continuous welded rails overcome thermal expansion by restraining the rails and allowing them to build up stress as their temperature changes.
- 🏗️ Safety regulations in the US require detailed procedures for the installation and maintenance of CWR to prevent issues like buckling.
- 🔄 The neutral temperature concept is crucial for CWR, where rails are installed or stressed at specific temperatures to avoid compression and buckling.
- 🔧 Expansion joints and breathers are still necessary at certain points, such as bridges or breaks in CWR sections, to accommodate thermal movement.
- 🛠️ Despite challenges, the use of CWR significantly improves the longevity of rails and the overall quality of the train ride.
Q & A
Why have the characteristic 'clickety-clack' sounds of trains become less common?
-The 'clickety-clack' sound was caused by the joints in the tracks. Modern railways often use continuous welded rail (CWR) which eliminates most joints, leading to a quieter ride.
What problem did the joints in the tracks solve?
-The joints addressed two main issues: one was the transportation problem of moving long lengths of rail, making it easier to handle short segments; the other was the thermal problem, allowing for expansion and contraction due to temperature changes.
What are the disadvantages of jointed rail?
-Jointed rail creates noise and impacts the steel each time a wheel passes over a joint, leading to wear and tear. It also causes additional load on the ballast and can result in freight cars rocking side-to-side, increasing maintenance costs.
How does continuous welded rail (CWR) address the issue of thermal expansion?
-CWR segments are welded together, creating a higher stiffness and smooth surface without joints. Rails are connected to ties to restrict movement, allowing for stress to build up as the temperature changes, which counteracts the thermal expansion.
What is the significance of the neutral temperature in continuous welded rail?
-The neutral temperature is the temperature at which the rail experiences no stress. Rail is installed at or above this temperature to ensure that it almost never undergoes compressive stress, which can lead to buckling.
How do railroads prevent rails from buckling due to thermal stress?
-Railroads manage buckling by controlling the spacing of ties, using ballast to hold ties in place, and ensuring a high neutral temperature to avoid compression. They also use expansion joints with diagonal tapers at bridges or older jointed rail sections to allow for thermal movement.
What is the role of the crushed rock or ballast in railway engineering?
-Ballast holds the ties in place and prevents them from sliding horizontally, which helps to prevent the rail from buckling under thermal stress. It plays a crucial role in maintaining the structural integrity of the track.
Why do railroads install rail at high temperatures?
-Installing rail at high temperatures ensures that the neutral temperature is also high, which means the rail is less likely to undergo compressive stress and buckle. This is a safety measure to prevent derailments caused by sun kinks.
What are expansion joints or breathers used for in rail tracks?
-Expansion joints or breathers are used to allow smooth transitions for train wheels between sections of rail while accommodating thermal movement. They also serve to break up electrical circuits for grade crossings and signals.
How does the use of continuous welded rail (CWR) affect the lifespan of rails and wheels?
-CWR reduces wear and tear from joints, leading to an extension of the life of both rails and wheels. It also results in a smoother and quieter ride for trains.
What is the role of mathematics in engineering, as illustrated by the script?
-Mathematics forms the foundation of engineering, allowing engineers to predict and calculate changes in materials due to temperature and stress. It helps in designing and maintaining structures like railways to ensure safety and efficiency.
Outlines
🚂 Evolution of Railway Sounds and Tracks
This paragraph discusses the common misconception about the sound of trains, explaining that modern trains are much quieter than their predecessors due to advancements in rail technology. It delves into the historical use of jointed tracks and the issues they presented, such as noise and wear. The introduction of continuous welded rail (CWR) is highlighted as a solution to these problems, offering a smoother and quieter ride while reducing maintenance costs. The paragraph also touches on the thermal expansion and contraction challenges that railways face and sets the stage for further exploration in the video series.
🔧 Understanding Thermal Expansion in Rails
This section delves deeper into the concept of thermal expansion and its effects on railway structures. It explains how continuous welded rail (CWR) overcomes the need for expansion joints by using restrained thermal expansion, a principle that allows the rail to experience stress in response to temperature changes without changing its length. The concept is illustrated with a demonstration involving an aluminum rod subjected to heat and tension. The paragraph also discusses the phenomenon of buckling, a risk associated with compressive stress in rails, and how it can lead to serious issues like rail failure and train derailments.
🏗️ Management Strategies for Continuous Welded Rail
This paragraph focuses on the strategies employed by railroads to manage the challenges of continuous welded rail (CWR), particularly the risks of buckling under compressive stress. It explains how safety regulations in the US mandate detailed procedures for the installation, adjustment, inspection, and maintenance of CWR. The use of restraints, such as closely spaced ties and ballast, is highlighted as a way to prevent buckling. Additionally, the concept of a 'neutral temperature' is introduced, which is the temperature at which the rail experiences no stress. The methods used by railroads to ensure that the neutral temperature is kept high to avoid compressive stress are discussed, as well as the use of expansion joints and insulated joints to accommodate thermal movement and maintain electrical circuit integrity.
📚 The Role of Mathematics in Railway Engineering
In this final paragraph, the presenter reflects on the importance of mathematics in understanding and designing modern railway systems. It acknowledges the mathematical content of the video and emphasizes that even basic math and algebra form the foundation of engineering. The presenter encourages viewers not to be intimidated by the formulas and equations, as they are crucial for a deeper understanding of the topics covered. The paragraph concludes with a sponsorship message for Brilliant.org, a platform that offers interactive lessons in math and other subjects, highlighting the value of learning through doing and the continuous addition of new lessons.
Mindmap
Keywords
💡Continuous Welded Rail (CWR)
💡Thermal Expansion
💡Elastic Deformation
💡Buckling
💡Ballast
💡Neutral Temperature
💡Expansion Joints
💡Track Circuits
💡Railroad Maintenance
💡Thermal Coefficient
Highlights
Most trains no longer make the traditional clickety-clack sound due to advancements in rail technology.
The rhythmic clicks and clacks were a result of joints in the tracks, which were initially a solution to transportation and thermal problems.
Modern railways often use continuous welded rail (CWR) that eliminates most joints, leading to a quieter and smoother ride.
CWR is achieved through electric flash butt welding, arc welding, or thermite welding, which creates a stiffer and smoother connection than old joints.
Despite the use of CWR, rails still experience thermal contraction and expansion, similar to other materials.
The famous clickety-clack sound was not only noisy but also caused wear and tear on the rails and ballast, increasing maintenance costs.
Elastic deformation, like thermal expansion, can be predicted and managed to prevent rail failure due to stress.
Restrained thermal expansion is a key concept in CWR, where the rails are fixed to ties, allowing them to build up stress and restrict movement with temperature changes.
The stress from restrained thermal expansion in CWR is well below the tensile or compressive strength of modern steel, ensuring the rail's durability.
Safety regulations in the US require detailed procedures for the installation and maintenance of CWR to prevent issues like buckling.
The spacing of railroad ties is crucial in managing buckling and ensuring the stability of the rails under thermal stress.
Neutral temperature is a concept used in rail installation, where the rail is fixed at a temperature that prevents it from undergoing compressive stress.
Expansion joints on rails, also known as breathers, allow for smooth transitions for train wheels while accommodating thermal movement.
Continuous welded rail significantly extends the life of rails and wheels, enhancing the overall performance and longevity of the railway system.
Despite the challenges, the use of CWR demonstrates the continuous innovation in railway engineering for improved efficiency and safety.
The video also emphasizes the importance of understanding basic math and algebra for a deeper comprehension of engineering concepts.
Transcripts
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