Ensuring the structural integrity of a railway track system relies heavily on the precise engineering of its connection points. The rail joint bar, often referred to as a fishplate or splice bar, acts as the critical link connecting two rail ends. While it may seem like a simple steel component, the rail joint bar dimensions must adhere to strict engineering standards to withstand the immense vertical and lateral forces exerted by passing trains.
This guide provides a comprehensive technical overview of rail joint bar dimensions, including AREMA specifications, material properties, and detailed tables for various rail sections. Whether for heavy-haul freight lines or industrial crane tracks, understanding these specifications is essential for safe and efficient track maintenance.
Rail Joint Bar Dimensions
The geometry of a rail joint bar is far from arbitrary. Every curve, hole placement, and thickness is calculated to match the specific rail section it supports. When engineers discuss rail joint bar dimensions, they are primarily concerned with ensuring that the bar fits snugly into the “fishing chamber”—the space between the rail head and the rail base—to provide maximum support.
Key Dimensional Parameters
To fully grasp the specifications, one must understand the primary measurements that define a joint bar:
- Length: Standard bars typically come in 24-inch (4-hole) or 36-inch (6-hole) lengths. The length determines how much support is distributed across the rail ends.
- Hole Spacing: This is critical for alignment. The distance between bolt holes must match the drilling pattern of the rail web exactly to allow for proper bolt insertion and thermal expansion.
- Height: The bar must fit precisely between the head and base fillets of the rail. If the bar is too high, it interferes with the wheel flange; if too low, it fails to support the rail head.
- Web Thickness: This dimension dictates the shear strength of the bar. A thicker web offers greater resistance to bending under heavy loads.
AREMA Standard Rail Joint Bar Specifications
For North American railways, the American Railway Engineering and Maintenance-of-Way Association (AREMA) sets the gold standard for track components. AREMA specifications ensure interoperability and safety across different rail networks.
Below are the detailed specifications for common AREMA rail sections, specifically the 115RE and 132RE profiles, which are industry workhorses.
115RE Rail Joint Bar Dimensions
The 115RE rail section is widely used in mainline and industrial applications. The joint bars designed for this rail typically feature a “head-free” design, meaning they support the rail head at the fillet rather than under the head itself, reducing stress concentrations.
|
Parameter |
Specification |
Tolerance |
|
Rail Section |
115RE |
N/A |
|
Bar Type |
Head-Free, Toeless |
N/A |
|
Number of Holes |
6 |
N/A |
|
Total Length |
36 inches |
± 1/8″ |
|
Height of Bar |
4-11/16 inches |
± 1/32″ |
|
Web Thickness |
5/8 inch |
± 1/32″ |
|
Bolt Hole Diameter |
1-1/16″ x 1-13/32″ (Oval) |
± 1/32″ |
|
Hole Spacing |
6″ x 6″ x 7-1/8″ x 6″ x 6″ |
± 1/16″ |
|
Weight per Pair |
Approx. 70-74 lbs |
N/A |
132RE and 136RE Rail Joint Bar Dimensions
Heavier rail sections like the 132RE and 136RE are utilized for heavy-haul freight lines carrying coal, grain, and aggregates. The joint bars for these sections are more robust to handle increased axle loads.
|
Parameter |
Specification |
Tolerance |
|
Rail Section |
132RE / 136RE |
N/A |
|
Bar Type |
Head-Free, Toeless |
N/A |
|
Number of Holes |
6 |
N/A |
|
Total Length |
36 inches |
± 1/8″ |
|
Height of Bar |
5-1/16 inches |
± 1/32″ |
|
Web Thickness |
5/8 inch |
± 1/32″ |
|
Bolt Hole Diameter |
1-1/16″ x 1-13/32″ (Oval) |
± 1/32″ |
|
Hole Spacing |
6″ x 6″ x 7-1/8″ x 6″ x 6″ |
± 1/16″ |
|
Bolt Elevation |
2-1/2 inches |
± 1/32″ |
Bolt Hole Patterns and Spacing
The “Hole Spacing” dimension mentioned above (e.g., 6″ x 6″ x 7-1/8″ x 6″ x 6″) refers to the distance between the centers of adjacent holes.
- 7-1/8 inch center spacing: This is the distance between the two middle holes where the rail ends meet. This gap is crucial for accommodating the rail expansion gap.
- 6 inch spacing: This is the standard distance between the remaining holes moving outward toward the end of the bar.
Toeless vs. Flanged Joint Bar Dimensions
When sourcing components, you will often encounter terms like “toeless” or “flanged” (also known as full-toe). These designations refer to the shape of the base of the joint bar, which significantly impacts rail joint bar dimensions and compatibility with tie plates.
Toeless Joint Bars
Modern rail systems predominantly use toeless joint bars.
- Profile: These bars sit entirely within the fishing chamber and do not extend over the rail base flange.
- Dimensional Advantage: Because they lack a “toe” extending outward, they do not interfere with the tie plates or spikes. This makes them universally compatible with various tie plate designs, provided the hole pattern matches.
- Usage: Standard for almost all new AREMA 115RE, 132RE, and 136RE installations.
Flanged (Full-Toe) Joint Bars
Flanged bars have a toe that extends horizontally over the rail base.
- Profile: The dimension of the base is significantly wider than a toeless bar.
- Dimensional Constraint: The extended toe must contain slots or notches to allow spikes to pass through into the sleeper (tie).
- Usage: These are older designs, often found on lighter rail sections (e.g., 85 lb or 90 lb rail) or legacy track. Replacing them requires careful measurement of the spike notch spacing to ensure alignment with existing tie plates.
Material Standards and Mechanical Properties
The physical dimensions of a joint bar are useless if the steel composition does not meet the required strength standards. AREMA Chapter 4 outlines specific metallurgical requirements for Quenched Carbon Steel Joint Bars. High-quality joint bars must undergo heat treatment to achieve the necessary balance of hardness and ductility.
Chemical Composition
The steel used for manufacturing joint bars must adhere to specific chemical limits to ensure weldability and strength.
|
Element |
Symbol |
Composition Percentage (%) |
|
Carbon |
C |
0.35 – 0.60 |
|
Manganese |
Mn |
0.60 – 1.20 |
|
Phosphorus |
P |
Max 0.04 |
|
Sulfur |
S |
Max 0.05 |
|
Silicon |
Si |
0.15 – 0.35 |
Mechanical Property Requirements
After forging and punching, the bars are quenched (rapidly cooled) and tempered. The final product must meet the following mechanical specifications:
|
Property |
Requirement |
|
Tensile Strength |
Minimum 100,000 psi (690 MPa) |
|
Yield Point |
Minimum 70,000 psi (483 MPa) |
|
Elongation in 2 inches |
Minimum 12% |
|
Reduction of Area |
Minimum 25% |
|
Cold Bend Test |
90 degrees without cracking |
These mechanical properties ensure that the joint bar can flex slightly under the weight of a train without snapping, while still maintaining rigid alignment of the rail ends.
Compromise and Insulated Rail Joint Bar Dimensions
Standard joint bars connect two rails of the same weight and section. However, track networks often require connecting dissimilar rails or electrically isolating sections of track.
Compromise Joint Bars
Also known as offset bars, these connect rails of different sections (e.g., connecting a 132RE mainline rail to a 115RE siding rail).
- Complex Dimensions: The dimensions of a compromise bar are unique. One half of the bar is forged to fit the fishing chamber of the heavier rail, while the other half is forged to fit the lighter rail.
- Center Alignment: The critical dimension here is the “gauge line” and “top of rail” alignment. The bar is dimensioned to hold the heads of both rails at the same level and gauge, regardless of the difference in rail height or base width.
- Ordering Specs: When ordering, one must specify “Left” or “Right” hand layout, as the dimension offsets are not symmetrical.
Insulated Joint Bars (IJ)
Used in signaling territory to stop electric current from flowing between rail sections.
- Dimensional Padding: These bars have standard steel cores but are coated or lined with non-conductive materials (fiberglass, epoxy, or polyurethane).
- Increased Width: Due to the insulation layer, the overall width dimension of an IJ assembly is slightly larger than a standard bar.
- Bolt Dimensions: They require specialized “encapsulated” bolts or bushings, which changes the effective hole diameter requirements.
Rail Joint Bar Dimensions and Bolt Compatibility
The relationship between the joint bar hole dimensions and the track bolt is a tight tolerance fit.
- Oval vs. Round Holes: Most standard joint bars feature alternating oval and round holes.
- Oval Holes: These match the oval neck of the track bolt, preventing the bolt from spinning while the nut is tightened. The dimension of the oval hole is typically 1/16″ larger than the bolt diameter.
- Round Holes: These accept the threaded end of the bolt.
- Standard Bolt Sizes:
- 115RE: Uses 1-inch diameter bolts.
- 132RE/136RE: Uses 1-1/8 inch or 1-inch diameter bolts depending on the specific drilling pattern.
Failure to match the bolt diameter to the joint bar hole dimension can result in “slop” in the joint, leading to rapid wear, battered rail ends, and potential derailment risks.
Frequently Asked Questions (FAQs)
What is the standard length for AREMA rail joint bars?
AREMA standard rail joint bars are typically 36 inches long with six bolt holes for heavy rail (like 115RE and 132RE). Lighter or older rail sections may use 24-inch bars with four bolt holes.
What is the difference between oval and round holes in joint bars?
Oval holes are designed to fit the oval neck of a track bolt, preventing the bolt from rotating during tightening. Round holes are positioned on the opposite side of the rail web to accept the bolt shaft and nut.
Why are there different hole spacings for rail joint bars?
Hole spacing varies to accommodate thermal expansion and specific rail drilling patterns. The standard center spacing for the middle two holes is often 7-1/8 inches to bridge the gap between rail ends, while outer holes typically use 6-inch spacing.
Do toeless joint bars fit all tie plates?
Generally, yes. Toeless joint bars are designed to sit within the rail web area without extending over the rail base. This dimensional profile prevents interference with spikes and tie plates, making them universally compatible with most track fastening systems.
What steel grade is used for rail joint bars?
Rail joint bars are manufactured from quenched carbon steel. They must meet AREMA specifications for mechanical properties, including a minimum tensile strength of 100,000 psi (690 MPa) and a yield point of 70,000 psi (483 MPa) to withstand heavy dynamic loads.
