Background: One Running Surface Instead of Two Rails
A conventional railway track carries wheels on two parallel rails spaced at 1435 mm gauge, supported on sleepers and ballast or a concrete slab. The fastening system holds the rail foot, transfers vertical and lateral loads to the sleeper, and resists longitudinal creep. A straddle monorail removes the second rail entirely: rubber-tired vehicles straddle a single guideway beam, usually a prestressed concrete beam 700 to 850 mm wide, and the running wheels roll on steel running plates fixed to the top surface of the beam. Guidance is provided by horizontal guide wheels running against steel guide wheel rails on the two sides of the beam. Because there is no gauge pair to maintain, the entire concept of the track fastening changes from rail-to-sleeper clamping to beam-mounted anchorage.
Load Path and the Role of the Fastening System
In a two-rail track the load path is wheel, rail, rail pad, sleeper and ballast, and the clip must clamp the rail foot with a defined toe load while allowing longitudinal expansion. In a monorail the load path is running tire, steel running plate, anchor bolt and concrete beam. The anchor bolt is embedded in the concrete or fixed in a pre-cast insert, and the running plate is drilled to accept the bolt. Guide wheel forces, which are significant in curves, are carried horizontally through the guide wheel rail into clips and bolts on the beam side face. The fastening system therefore performs three jobs: it must hold the running plate flat under repeated wheel passes, clamp the guide wheel rail securely against lateral thrust, and keep all live-metal components insulated from the return current system.
Component-Level Differences
Running Plates and Anchor Bolts
Monorail running plates are rolled steel plates, typically 10 to 16 mm thick, machined flat and bolted to the beam top. Anchor bolts are usually high-strength bolts with resin or mechanical anchors embedded in the concrete, tightened to a specified torque with lock washers or adhesive locking to prevent loosening under vibration. Two-rail fastenings, by contrast, clamp the rail foot with spring clips and transfer load through a baseplate or direct fixation.
Guide Wheel Rails
The guide wheel rail is a special steel section or a machined strip fixed to the beam side by clips and bolts. Its vertical position and straightness are set with shims, because the guide wheel clearance, typically a few millimetres, controls ride quality and lateral stability. This adjustment function resembles the gauge adjustment of conventional fastenings but is performed on a vertical face.
Electrical Insulation
Monorail traction systems use DC supply with the running plates as part of the circuit. Insulation pads, glass-fiber-reinforced epoxy bushings and insulating sleeves are used at every bolted interface to prevent stray current leakage to the concrete beam and to protect signaling and grounding. Insulation resistance is specified and tested as part of routine maintenance, similar to insulated rail joints in two-rail track.
Application Scenarios
Straddle monorail systems are built for urban transit corridors with tight curves and steep grades, because the rubber tire and single beam allow gradients of 6 percent and curve radii of 50 m or less, far below the limits of steel-wheel two-rail systems. Suspended monorails, where the vehicle hangs below the beam, use a similar but inverted arrangement of running plates and guide rails. Two-rail fastening systems remain the standard for mainline, metro, heavy-haul and tramway track, where high axle loads, long service life and standard gauge interchangeability are decisive.
Selection and Maintenance Considerations
Check the anchor bolt pattern and torque specification against the running plate design before procurement; plate thickness and bolt spacing are not interchangeable between manufacturers.
Use shims under guide wheel rails to set vertical alignment; record the shim stack in the maintenance log.
Verify insulation resistance of every bolted interface during commissioning and at defined intervals.
Retorque anchor bolts after the first month of service, then on a scheduled cycle, because concrete creep and seating settlement reduce the initial preload.
Inspect running plate surfaces for pitting, corrugation and edge deformation; grinding is possible only within a limited depth before replacement.
Common Misconceptions
Monorail fastenings are the same as crane rail or tram rail fastenings. In fact the mounting surface, load path and insulation requirements are different, and parts are not interchangeable.
A monorail does not need gauge control. The beam and guide wheels replace the gauge function, but vertical and lateral adjustment is still required and is done with shims and spacers.
Any high-strength bolt can anchor a running plate. In practice the embedded anchor, bolt grade, corrosion protection and insulation must be matched to the beam design and traction system.
Frequently Asked Questions
Q1: Do monorails use standard rail clips?
No. Straddle monorail running surfaces are steel plates on a concrete beam, not rail sections on sleepers, so standard rail clips are not used. Guide wheel rails may use clip-type fastenings, but they are mounted on the beam side and are not interchangeable with two-rail track clips.
Q2: What carries the vehicle weight in a straddle monorail?
The running wheels roll on steel running plates bolted to the top of the guideway beam. The plates spread the tire contact load into the concrete through anchor bolts and embedded plates.
Q3: How is electrical insulation achieved in monorail track?
Insulating pads, epoxy bushings and sleeves isolate bolted steel components from the beam and the return circuit, and insulation resistance is verified by testing during commissioning and maintenance.
Q4: Why does a monorail need guide wheel rails?
Guide wheels run against rails on both sides of the beam to provide lateral guidance in curves and to resist side forces, replacing the flange-rail interaction of conventional track.
Q5: Can two-rail fastening components be reused on a monorail?
No. Bolt patterns, plate geometry, insulation design and load cases differ fundamentally, so components should be sourced specifically for the monorail guideway design.
Q6: How often are monorail fastenings inspected?
Anchor bolt torque, guide rail alignment and insulation resistance are typically checked at intervals defined by the operator, often every 3 to 6 months, with running plate surface inspection on a similar cycle.