Vibration monitoring of slotted beams using an analytical model

This paper reports part of a research program aimed at developing the scientific basis for vibration monitoring in rapid and automatic global inspection of structures for faults. Slotted steel beams in various conditions were used as experimental samples. A mathematical model of the slotted beam's vibration was solved using a perturbation method. Relationships between the defect parameters and the vibration signature showed a strong dependence of the modal frequency on the slot characteristics, including location and size. The method is computationally efficient, robust and could be used for on-line signal processing. The experimental modal parameters were determined from the mobility function calculated from the excitation and response signals. The modal frequencies and their shifts were then used to quantify the slot. A test of 11 beams with various conditions demonstrated that the slot can be characterized inversely. Frequency shift contours which were numerically calculated from the analytical model were used to do this, The slot locations were assessed with great accuracy, although the slot depths were estimated to be larger than the actual values, due to the limitation of the perturbation method. (C) 1997 Acoustical Society of America.