MONITORING OF A LOW-ORDER EVEN RADIAL VIBRATIONAL CIRCUMFERENTIAL MODE
IN A ROUND HOLLOW CYLINDER
AbstractCylindrical 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.