↵Rail Fishplate Fastening System
This report provides a concise technical examination of Railway Fishplate (joint bar) systems, focusing on their mechanical splice function, distinct subclassifications, and failure progression mechanics. The analysis deliberately avoids overlap with prior discussions regarding elastic clips, screw spikes, concrete sleepers, or standard rail section dimensions. The focus here is practical and distinct: insulated block joints, compromise bars, glued assemblies, and fatigue-driven replacement logic.
Technical Specifications:
| Fishplate Type | Rail Section Compatibility | Bolt Configuration | Distinct Visual Feature | Standard / Specification | Common Mis-Selection |
|---|---|---|---|---|---|
| UIC Standard Fishplate | UIC54, UIC60 (matching profile) | 4-hole or 6-hole | Symmetrical profile; curved top edge matching rail head transition | UIC 864-3 / EN 16704 | Used with AREMA rail-web thickness mismatch |
| AREMA Joint Bar | 115RE, 136RE | 4-hole or 6-hole | Angled head contact; shorter height than UIC | AREMA Chapter 4, ASTM A759 | Used with UIC rail-bolt spacing differs (5.5" vs 140 mm) |
| Insulated Fishplate | All UIC/AREMA sections | 4-hole or 6-hole | Visible fiberglass/epoxy layer between bar and rail; colored end posts | EN 13146-5 / AREMA Ch. 33 | Standard bar installed-signal circuit shorted |
| Compromise Fishplate | UIC54 ↔ UIC60, UIC60 ↔ 136RE | 4-hole or 6-hole | Asymmetrical profile-different rail seats left vs right | Manufacturer drawing; no universal standard | Ordered by rail type only (missing transition direction) |
| Slotted / Expansion Fishplate | UIC54, UIC60 | Elongated holes (4) | Oval bolt holes; longer bar length | Bridge engineer specification | Standard bar installed-thermal movement restrained |
Performance Range:
Insulated Block Joints (Signal Section Isolation):
Mandatory for track circuit demarcation. Fishplates with epoxy-bonded fiberglass/PA66 insulation layers electrically isolate rail sections while maintaining mechanical continuity. Non-insulated joints would short-circuit signalling, causing false occupancy and collision risk .
Compromise Joints (Transition Between Rail Sections):
Required where different rail profiles meet-UIC54 to UIC60, UIC60 to AREMA 136RE, or new to worn rail. Compromise fishplates have asymmetrical bolt hole spacing and profiled rail seats to match dissimilar web thicknesses and head heights. No other joining method accommodates mixed sections .
Maintenance & Operational Perspective
- Corrosion Wastage (Coastal & Immersion Zones):
Plain fishplates (uncoated) exhibit 0.10-0.20 mm/year uniform corrosion. Pitting rate: 0.25-0.40 mm/year. Replacement triggered when section loss >20% at bolt hole (measured by ultrasonic thickness gauge). Visual rust coverage is not the condemnation metric-internal hidden corrosion dictates 60% of replacements .
- Bolt Tension Relaxation (Weekly Re-Torquing):
Fishplate bolts (M22–M24, grade 8.8/10.9) lose 10-15% clamp force per week under traffic. Re-torquing interval: every 7-14 days on >20 MGT lines. Torque specification: 450-550 Nm (UIC 864-7). Impact wrenches prohibited-risk of thread galling. Progressive relaxation >30% triggers bolt replacement .
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