BeginnerTopic 10 of 106Engineering Mechanics
Supports and reactions
Pins, rollers and fixed supports restrict motion and generate specific reaction forces.
In depth
A roller gives one reaction perpendicular to the surface, a pin gives two components, a fixed support gives two forces plus a moment, and a link gives one force along its axis. Each constraint removes a degree of freedom.
Key points
- Reaction counts determine determinacy
- Rollers allow thermal expansion
- Fixed supports resist rotation
ExampleA bridge usually has a pin at one end and a roller at the other.
Supports define how a structure is held, and they decide which reactions exist, so they must be identified correctly before any equations are written.
What is Supports and reactions?
Pins, rollers and fixed supports restrict motion and generate specific reaction forces.
Why is it important to understand supports and reactions?
Supports define how a structure is held, and they decide which reactions exist, so they must be identified correctly before any equations are written.
What is the difference between a pin and a roller?
A pin resists movement in both directions and gives two reaction components. A roller resists movement in one direction only and gives one reaction perpendicular to the surface.
What does a fixed support provide?
Force in two directions and a moment, so it resists both translation and rotation.
How is Supports and reactions used in practice?
Typical applications include choosing a pin for a bridge end and a roller for thermal expansion, modelling a cantilever sign post clamped to a footing and checking the reactions on a shelf bracket fixed to a wall.
What should I learn before Supports and reactions?
Study "Equilibrium of rigid bodies" first (topic 9 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Supports and reactions?
Reaction counts determine determinacy. Rollers allow thermal expansion. Fixed supports resist rotation.
Can you give an example of Supports and reactions?
A bridge usually has a pin at one end and a roller at the other.
What comes after Supports and reactions?
The next topic is "Friction", which builds directly on this one.
How difficult is Supports and reactions?
It is classed as Beginner in Engineering Mechanics (topic 10 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.