Proper railroad design is foundational to the safety, efficiency, and longevity of any track system. A critical aspect of this design process involves selecting the appropriate rail sections and fastening systems, including essential components like rail clips. The interaction between the rail, ties, and fastenings dictates how the track structure responds to the immense vertical and dynamic loads imposed by passing trains. Therefore, a thorough understanding of rail specifications is not just a matter of compliance but a core element of robust engineering.
Rail Specifications in Railroad Design
The selection of a rail section is a primary step in railroad design. Different rail profiles, designated by weight per yard (e.g., 115 RE, 136 RE), offer varying levels of strength, stiffness, and durability. The choice depends on factors like expected traffic volume (tonnage), maximum train speed, and axle loads. Heavier rail sections generally provide greater flexural rigidity, which helps distribute the wheel load over a larger number of ties, reducing stress on the ballast and subgrade.
Key properties considered during selection include the moment of inertia, section modulus, and the dimensions of the head, web, and base. The moment of inertia (I) is a measure of the rail’s resistance to bending, while the section modulus (Z) relates to its bending strength. A higher value for these properties indicates a stronger rail capable of handling heavier loads and higher speeds. The following table provides specifications for typical rail sections used in modern railroad construction.
|
Section |
Weight per Yard (lb) |
Moment of Inertia (in⁴) |
Section Modulus (Base) (in³) |
Height (in) |
Base Width (in) |
Head Width (in) |
|
141 RE |
140.6 |
97.0 |
29.0 |
7 1/8 |
6 |
3 |
|
136 RE |
136.2 |
94.9 |
28.3 |
7 1/8 |
6 |
2 15/16 |
|
132 RE |
132.1 |
88.2 |
27.6 |
7 1/8 |
6 |
3 |
|
115 RE |
114.7 |
65.6 |
22.0 |
6 5/8 |
5 1/2 |
3 |
|
100 RE |
101.5 |
49.0 |
17.8 |
6 |
5 1/2 |
2 11/16 |
|
90 RA-A |
90.0 |
38.7 |
15.2 |
5 5/8 |
5 1/8 |
2 9/16 |
Rail Clips in Track Integrity
Rail clips are a vital component of the track fastening system, responsible for securing the rail to the tie or supporting structure. Their primary function is to restrain the rail against vertical, lateral, and longitudinal movement, ensuring that track gauge is maintained and that the rail remains stable under thermal expansion and contraction. Unlike traditional cut spikes, modern elastic rail clips exert a constant clamping force, or toe load, on the rail base.
This elasticity is crucial for several reasons. It allows for controlled rail movement due to temperature changes without losing its grip, which is essential for the integrity of continuously welded rail (CWR). It also helps absorb shocks and vibrations from passing trains, reducing wear on other track components and providing a smoother ride. There are numerous designs, including boltable, weldable, and adjustable clips, each suited for different applications, from standard tee rail tracks to heavy-duty crane rail systems.
Rail Clips Specifications
The selection of rail clips is based on the rail section, the type of tie (wood, concrete, or steel), and the performance requirements of the track. Important specifications include the material, toe load, and physical dimensions. The toe load must be sufficient to prevent rail slippage but not so high as to overly constrain the rail. The material, typically spring steel, is chosen for its durability and ability to maintain its clamping force over millions of load cycles.
Below is a table outlining specifications for some common types of rail clips.
|
Clip Type/Model |
Application |
Fastening Method |
Key Features |
|
E-Clip |
Tee Rail, Concrete Ties |
Inserted into tie shoulder |
Elastic, high clamping force, widely used in mainline and transit. |
|
Safefok/Pandrol FASTCLIP |
Tee Rail, Concrete/Steel Ties |
Pre-installed on tie, simple installation |
Rapid installation, captive system, high creep resistance. |
|
Weldable Clips (e.g., 100 Series) |
Crane Rail, Tee Rail on Steel |
Welded directly to steel base |
Provides a rigid, fixed fastening for industrial and port applications. |
|
Boltable Clips (e.g., 60 Series) |
Crane Rail, Tee Rail on Concrete/Steel |
Bolted to foundation or steel plate |
Adjustable, allows for precise rail alignment, suitable for high side thrust. |
|
Adjustable Clips |
Crane Rail, Special Trackwork |
Bolted with adjustment mechanism |
Offers lateral adjustability to compensate for wear and ensure alignment. |
Frequently Asked Questions about Rail Specifications
What is the most common type of rail used?
The most common rails for mainline freight tracks in North America are heavier sections like 136 RE and 141 RE. These are chosen for their ability to support heavy axle loads and high-density traffic, which is a key consideration in modern railroad design.
What does “RE” signify in a rail section?
“RE” stands for “American Railway Engineering” and Maintenance-of-Way Association (AREMA). It indicates that the rail profile conforms to the standards set by this organization, ensuring consistency and interoperability across the network.
How does rail weight affect track performance?
Heavier rail distributes load more effectively, reduces deflection, and wears more slowly than lighter rail. This leads to a more stable track structure, lower maintenance requirements, and a longer service life, making it more economical for high-traffic lines.
Frequently Asked Questions about Rail Clips
What is the main advantage of elastic rail clips over spikes?
Elastic rail clips provide a continuous clamping force that holds the rail more securely than spikes. This prevents longitudinal rail creep, maintains gauge more effectively, and improves the overall stability and safety of the track, especially under heavy loads and high speeds.
Are rail clips interchangeable between different rail sizes?
Generally, no. Rail clips are designed to fit the specific profile of a rail base. Using a clip designed for a different rail section can result in improper clamping force, leading to potential rail movement and compromising the safety of the track structure.
How often do rail clips need to be replaced?
Rail clips are designed for a long service life, but they can be damaged by derailments or lose their elasticity over time due to fatigue. They should be inspected regularly for signs of wear, corrosion, or damage and replaced as needed to maintain the integrity of the railroad design.
