Question

A rigid-jointed plane frame is stable and statically determinate if -
1. (m + r) = 3j
2. (3m + r) = 3j
3. (m + 3r) = 3j
4. (m + r) = 2j

Answer 1

Correct Answer - Option 2 : (3m + r) = 3j

Static indeterminacy:

Number of additional reactions required to analyse a structure is called static indeterminacy.

D_s = D_se + D_si

Type of structure	Degree of indeterminacy Ds
2D (plane) frames	(3m+r)-3j
3D frames	(6m+r)-6j
2D (plane) pin jointed truss	(m+r)-2j
3D truss	(m+r)-3j