In structural analysis, static indeterminacy of a pin-jointed plane truss is calculated using the relation:

Explanation

For a 2D pin-jointed plane truss, each joint provides 2 equilibrium equations (Sum Fx = 0, Sum Fy = 0). Total degrees of static indeterminacy Ds = Internal indeterminacy + External indeterminacy = (m – 2j + 3) + (r – 3) = m + r – 2j.