Detection and assessment of wood decay in glulam beams using a decay rate approach

A feasibility study to evaluate the use of a modified impulse-echo approach to detect and assess the level of wood decay in glulam beams is presented using a beam retired from the field and without visible indications of decay. The modified impulse-echo approach is based on observing the dynamic response of each of the glulam beam laminae to the drop of a steel sphere onto a steel plate coupled to the glulam beam lamina, and upon a decay rate analysis of the corresponding time domain signal in a frequency band of interest. X-ray computer tomography was used to evaluate the level of deterioration, ie mass loss, caused by decay in each of the laminae of the beam and to validate the results obtained using the modified impulse-echo. It was observed that the impulse-echo decay rate approach leads to an overall rate of false calls of 7.2. Considering the variability that exists in wood, including the presence of splits, orientation and thickness of growth rings, and humidity, this relative low rate of false calls makes this approach very attractive.