What is a roller bearing support?
A roller bearing support is a support on which a structural member rests on rollers: it is carried perpendicular to the rolling surface but is free to translate parallel to it and to rotate. Think of it as a pinned support on a trolley. It can therefore provide only one reaction force, normal to the rolling surface — no horizontal force and no fixing moment.
Why that freedom is wanted
Every structure changes length. Steel and concrete expand and contract with temperature; with concrete, shrinkage and creep add to it. On a bridge of a few tens of metres that adds up to centimetres. If both ends are held, the material cannot accommodate the movement and enormous restraint forces build up in the bearings and the piers.
The classic answer is therefore: fixed at one end, free at the other. One support is fixed or pinned and takes the horizontal actions — wind, braking and traction forces. The other is a roller bearing that lets the length change happen. The structure is then statically determinate, and temperature movement produces no stresses.
| Fixed or pinned support | Takes the horizontal actions: wind, braking and traction forces. |
|---|---|
| Roller bearing | Lets the length change happen; provides only one reaction force, normal to the rolling surface, with no horizontal force and no fixing moment. |
Where you meet them
- Bridges and viaducts — the classic application; the deck can move within defined limits, with an expansion joint in the carriageway.
- Large halls and canopies — on long steel trusses, often realised as a slotted hole in the base plate.
- Crane runways and plant frames.
In buildings, true roller bearings are little used: because they provide no horizontal restraint, stability has to be resolved elsewhere, through shear walls or bracing. In modern practice the rollers have also largely given way to sliding bearings with a low-friction layer (such as PTFE on stainless steel) and to elastomeric bearings of rubber laminated with steel plates: lower maintenance, and vibration-absorbing as well.
On the drawing
In a structural scheme a roller support is drawn as a triangle on rollers, or as a triangle with a line beneath it. Watch the orientation of the rolling surface: the reaction acts normal to the rolling surface, not normal to the beam. If the rolling surface is inclined, the reaction therefore has both a horizontal and a vertical component — a classic trap when working a scheme through.
Related terms
- Sliding bearings
- Bridge abutment
- Span
- Truss
- Load bearing
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