An acoustic impact imaging method was developed to map damage in concrete bridge deck slabs and was evaluated by conducting a survey on a damaged full-scale bridge deck model. The imaging system consisted of a mechanical hammer source, two acoustic sensors and a digital waveform recorder. Imaging surveys were conducted along transverse lines that resulted in acoustic measurements on a 30-x-30-cm grid covering the entire upper surface of the slab. Acoustic measurements were processed to determine relative attenuation and then displayed using spatial imaging software. The resulting images showed increased levels of attenuation around punch-out failure zones and coinciding with many of the cracks mapped on the upper deck surface. Overall, the imaging technology showed good potential as a means of rapidly and nondestructively mapping damage in concrete bridge deck slabs.

The investigation focuses on the evaluation of a novel acoustic transmission technique (ATT) for tracking the fatigue-induced damage in a steel-free bridge deck slab under laboratory conditions. The technique comprises the identification of changes in acoustic waveform attenuation through concrete by comparing integrated waveform amplitudes recorded at two or more acoustic sensors. This methodology is based on the experimental observation that cracking in concrete leads to increases in attenuation of the acoustic signals. The mapping of cracks and other means of detecting damage induced by cracks were used to independently verify the conclusions from the ATT Each of the four deck slab panels was subjected to approximately 1700 cycles of a heavy wheel load; the damage induced by this loading was tracked reliably by the ATT. The procedure of evaluating dimensionless integrated amplitude ratios rather than absolute signal magnitudes proved to be a highly robust and stable means of measuring attenuation, hence damage in the slab.

Grout laminated wood decks (GLWDs), representing the third generation of stressed wood decks, comprise either laminates or logs trimmed to obtain two parallel faces. The logs or laminates, running along the span, are held together by means of transverse internal grout cylinders that may be in either compression or tension. Two full-scale models of GLWD were constructed at Dalhousie University, Halifax, one with grout cylinders in compression and the other with the cylinders in tension. Service load tests conducted in Halifax showed that the former deck had better load distribution characteristics. Two years after the tests in Halifax, the models were shipped to The University of Manitoba in Winnipeg, where they were tested to failure under a central patch load. Because of miscommunication with the supplier, the logs of the GLWD with grout cylinders in compression were also trimmed to the third face that was kept at the bottom of the deck. The failure tests showed that despite its superior load distribution characteristics, the deck with grout cylinders in compression failed at a significantly lower load than the GLWD with cylinders in tension. It is argued that a planar surface in the logs at the flexural tension face not only reduces their flexural stiffness but also brings the defects of wood to the surface with maximum stress. The deck with the flat bottom surface underwent tension failure of the most heavily loaded logs, whereas the deck with the intact round surface of the logs at both top and bottom failed by horizontal splitting of all the logs.Key words: articulated plate, bridge deck, grout laminated deck, orthotropic plate, timber.