Acoustic wave velocity in long pieces of Salzmann pine for in-situ structural assessment

In-situ assessment of timber members by acoustic measurement usually requires specific procedures (indirect and semidirect measurement) compared with those used in the laboratory (direct) and over longer distances. This research aims to determine which procedure is the most suitable. Acoustic Non-Destructive Testing measurements were taken in 21 150 × 200 mm2 nominal cross-section Salzmann pine structural timber pieces from 9.5 to 11.0 m long from a 1768 structure. Wave velocity was obtained from ToF measured with different sensor arrangements (direct, indirect and semidirect) in different lengths using stress wave and ultrasound. The direct velocity value was very close to non-direct measurements (0.4% higher), while previous research works with shorter pieces (3–4 m) showed larger differences (3.3–5.4%). There were no significant differences between indirect and semidirect measurements when using the same device or between devices, although a steady ratio was observed in the last case. The most predictive velocity procedure was determined by the correlation between static and dynamic modulus of elasticity. The most reliable stiffness prediction was obtained with the global velocity method, taking ToF measurements at distances from 1 to 10 m. A second method was proposed, consisting of taking only 2 measurements, and it achieved practically the same predictive capacity.