Detection and assessment of wood decay in glulam beams using a modified impulse-echo approach

A glulam beam retired from the field and without visible indications of wood decay was used. Towards detection and assessing wood decay, X-ray computer tomography and ultrasonic measurements were carried out. It was observed that decrease in mass density with increasing levels of wood decay affects x-rays attenuation and allows radioscopy to detect and assess wood decay. To detect and assess decay when only one lateral side of the beam is available, a modified impulse-echo was developed. The modified impulse-echo approach is based on observing the dynamic response of the glulam beams to the drop of a steel sphere onto a steel plate coupled to the glulam beam lamina. It was observed that monitoring certain frequency bands allows detection and assessment of wood decay. The selection of these frequency bands requires knowledge of the nominal beam transverse dimensions. Because of the high ultrasonic material attenuation values of decayed wood as compared with those of sound wood, the area under the power spectral density in these frequency bands is smaller in regions of decayed wood. Results show that results from both X-ray computer tomography and impulse-echo measurements are consistent with each other and can be used to detect and assess wood decay in structural lumber.