Monitoring of a Low-Order Even Radial Vibrational Circumferential Mode in a Round Hollow Cylinder

This paper presents a nondestructive testing method for assessing the structural integrity of cylindrical elements by monitoring a range of radial vibrational modes, with a specific emphasis on the so-called ovalling mode. The method involves exciting the cylinder with a single vibration source in the radial direction and measuring the response using two vibration sensors positioned diametrically on the cylinder's surface. The ovalling mode was extracted from the frequency response by adding the in-phase signals recorded by the sensors. Experiments conducted on a PVC pipe showed good agreement between the measured resonance frequency of the ovalling mode and its predicted value, calculated using the theory for thin cylindrical shells and Finite Element Method simulations. This research is an investigation into the potential and reliability of this nondestructive technique for detecting corrosion and strength-weakening defects in concrete building elements, steel pillars, and columns. The extent of the strength reduction can be determined by analyzing the change in the resonance frequency of the ovalling mode.