What is a pinned support?
A pinned support, also called a hinged support (Dutch: scharnieroplegging), is a type of support in structural mechanics where a beam cannot move but is free to rotate. It therefore provides two reaction forces:
- a vertical reaction (V);
- a horizontal reaction (H).
A pinned support does not resist a bending moment: the beam can rotate at the support. In structural diagrams it is usually drawn as a small triangle with hatching underneath.
Comparison with other supports
| Support | Vertical force | Horizontal force | Moment |
|---|---|---|---|
| Roller support | yes | no | no |
| Pinned support | yes | yes | no |
| Fixed support | yes | yes | yes |
A beam on one pinned support and one roller support is statically determinate: the three unknown reactions can be found from the three equilibrium equations. The roller at the other end lets the beam expand and contract without building up restraint forces.
A hinge can also connect two structural members. By action and reaction, both members then exert equal and opposite forces on each other.
Application
A perfect pin is rare in practice; many connections are simply modelled as pinned. Examples include a steel beam bolted to a column via an end plate or fin plate, a timber joist in a joist hanger, or a bridge girder on a bearing with a dowel.
For DIYers the key point is that the structural engineer designs for a specific support condition. If you change a support, for example by fixing a beam more rigidly or loosening it, you can change how the structure carries load. Always have that checked by a structural engineer.
Related Terms
- Roller support
- Fixed support
- Bending moment
- Load-bearing
- Structural engineer
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