Abstract: It is required that structures must work safely during its service life. But damages initiate a breakdown period on the structures. Damage in the form of cracks may be dangerous due to static or dynamic loadings on the structure and so crack detection plays an important role for Structural Health Monitoring applications. The presence of cracks causes changes in the physical properties of a structure which in turn alter its dynamic response characteristics. The change in the physical properties is characterized by changes in the Eigen parameters, i.e. natural frequency, damping values and the mode shapes associated with each natural frequency. Due to presence of crack the local flexibility due strain energy concentrates at the crack location. So it is important to detect the damages in a beam at the initial stage of the crack. For detection of damages, free vibrations are applied on a simply supported steel beam in undamaged and damaged condition, the instrumentation for which is carried out using strain gauge and accelerometer on wireless data acquisition system. The results of strains and natural frequency which were obtained from experiment are then compared with modal analysis by preparing a finite element model in ABAQUS and checking its significance with theoretical calculations. It is verified from both experimental and simulation analysis that presence of cracks decreases natural frequency of structure. It is observed that as the crack size and number of cracks increase, the natural frequency of the structure decreases. The significance of this study is to detect the damage in vibrating structure by observing the change in natural frequency, which may prove helpful for structural health monitoring of the various structures.

Keywords: Beams, Vibration, Damage