Correct option is C
Castigliano's theorem is primarily used in the force method of structural analysis.
It is based on the principle of strain energy and helps in determining displacements in a structure by differentiating the total strain energy with respect to applied forces.
Why It Falls Under Force Method:
The force method involves determining the unknown forces in indeterminate structures.
Castigliano's theorem uses strain energy to compute deflections and forces, making it a part of the force-based approach.
