Types of supports and their reactions

Supports connect a structure to the ground and give the reactions needed for equilibrium. For a plane structure the common types are:

1. Roller support

Allows horizontal movement and rotation but prevents movement perpendicular to the supporting surface.

• Reaction: one force, perpendicular to the surface (normally vertical).

   ────────
     ○
  ▔▔▔▔▔▔▔▔   R_y

2. Hinged (pin) support

Prevents translation in any direction, but allows rotation.

• Reactions: two components, $H$ (horizontal) and $V$ (vertical), or one resultant of unknown magnitude and direction.

    ────────
      ▲   H, V
   ▔▔▔▔▔▔▔

3. Fixed (built-in) support

Prevents translation and rotation.

• Reactions: three: horizontal force $H$, vertical force $V$ and a moment $M$.

  ▒│─────────
  ▒│  H, V, M

4. Link or tie support (cable, wire or short strut)

A member pinned at both ends restrains movement along its own axis.

• Reaction: one force along the axis of the link.

5. Other: spring support and guided (sliding) support

• A guided or sliding support (roller that cannot rotate) gives one force perpendicular to the guide and a moment (two reactions).
• A spring support gives a force proportional to the displacement of the spring.