STIFFNESS DEGRADATION OF RC BEAM BY DYNAMIC METHODS

This paper investigates the reduction of stiffness, variation of flexural rigidity and nonlinear response of RC member to detect flexural cracks. The positive cyclic pseudo static load was applied stepwise to the specimen to induce damage. Flexural rigidity characteristics were studied by conducting free vibration test on RC beam at various stages. Vibration characteristics of each damage state were successfully identified to detect the relationship between damage levels and fundamental frequencies under various failure loads. Due to flexural cracks longitudinal bars may yield resulting in reduction in effective flexural rigidity and hence frequency. This yielding of reinforcement in longitudinal bars can be detected from change in natural frequency. The non-linearity was detected by checking the changes in the fundamental frequency during various stages of loading.