In recent years, from the viewpoint of structure maintenance, the demand for Non-Destructive Evaluation (NDE) increases. The primary objective of this evaluation is to determine whether a structure performs as expected or it has an abnormality in its behavior as compared to the normal condition. Vibration based assessment is an NDE method which monitors a structure using its natural frequency. It has been recognized that changes in natural frequencies are considered as a diagnostic parameter in a structure assessment procedure. The approach is based on the fact that shifts in natural frequencies can indicate a damage in the structure. In this paper, A primary nondestructive evaluation method is used to test a sound plain concrete beam and a defected one. The decrement in the natural frequency of defected one confirms damage in the structure. For the assurance of evaluation, theoretical analysis is performed and, both theoretical and experimental results are presented