Abstract

Cylindrical elements made of concrete or metal are found in buildings and bridges for supporting other building elements. These building elements are often exposed to environmental conditions and strength-weakening agents that may compromise their vigor and their bearing capacity. A technique or a method is therefore often desirable for controlling the health condition and integrity of these elements. Such a method is expected to be easy to implement, using light-weighted equipment, affordable and most importantly of non-destructive character. The aim of this paper is to present such a method, which is based on vibrations, and which may be used in a circular cylinder for tracking a range of vibrational modes, namely the radial ones with a prior specific emphasis on the so-called ovalling mode. This mode may be extracted from the response of the cylinder as a result of its excitation by a mechanical stress applied in the radial direction. This method uses a single concentrated source of excitation and two vibration sensors diametrically positioned and fastened onto the surface of the cylinder. The ovalling mode may then be extracted from the frequency response through adding the signals recorded by the two sensors. These two signals are in phase in the case of a test object with a circular cross-section. This study is a preliminary investigation into the feasibility and the extent of reliability of this non-destructive method when applied to the identification of corrosion or other strength-weakening agents hosted by concrete or steel pillars or columns. The degree of severity in strength loss in such elements may be assessed through an evaluation of the change in value of the resonance frequency of the ovalling mode.