Definition: A body is said to be rigid if relative displacement or relative displacements or relative deformations of various points of a body is negligibly small.
For a certain load body may be rigid but if we increase the intensity of load it may deform because it exceeds its allowable limit.
- No object is absolute rigid.
- During analysis we assume all structures as rigid.
- If structure is very rigid then it becomes brittle and can be collapsed.