Figure P12 shows an L-shaped beam with eight different support arrangements, labelled A–H.

Each case uses a combination of supports that may or may not adequately restrain the structure. The supports are either guided rollers (providing a reaction force normal to the surface, in either direction) or pins.

Which of the following cases are unstable? 

In your assessment, consider whether the structure is sufficiently restrained against both translation and rotation.

Assume all supports are ideal and that the beam behaves as a rigid body in a 2D plane.

Select all that apply.

Figure P12. Different L-shaped beam systems.