Question

Choose the correct option for the structure shown below.

• A. Stable
• B. Statically Unstable
• C. Geometrically Unstable
• D. Internally Unstable

Hint:

A truss without triangular frames is internally unstable. Always ensure there are enough non-collinear members forming rigid triangles.

Answer 1

The Correct Option is D

Step 1: Analyze the type of structure.
The structure shown is a truss supported at two ends and connected by three horizontal members. The support conditions appear externally stable.
Step 2: Check internal stability.
To determine internal stability of a truss:
Use the equation \( m = 2j - 3 \), where:
\( m \) = number of members
\( j \) = number of joints
If this condition is satisfied, then the truss might be internally stable, but it still depends on the arrangement.
Step 3: Check for internal instability due to collinear members.
The three joints are collinear and all lie on a straight horizontal bar. This means the structure has no triangular support frames, and such a configuration causes internal instability. The structure can collapse even if the external support conditions are satisfied.