Structural damage assessment using vibration modal analysis

Vibration techniques have been employed for detecting the presence and monitoring the progression of damage in structures. Pinpointing the location of damage is a more complicated and elaborate task. This paper presents modal analysis techniques for locating damage in a wooden wall structure by evaluating damage-sensitive parameters such as resonant pole shifts and mode shapes, residue and stiffness changes. Artificial damage (simulating termite degradation) was created in one of the walls of a specially constructed room. The wall was excited using an impact hammer and its frequency response measured using a laser vibrometer. Resonant poles (plotted in the s-plane) were used for identifying modes that are sensitive to damage, since not all modes are equally affected by the presence of damage. The damaged region was identified by visual comparison of the deformation mode shapes before and after damage. The modal residue and stiffness changes were also quantified for a better representation of the damage location.