How to improve the on-site MOE assessment of old timber beams combining NDT and visual strength grading

Abstract

For the conservation and restoration of old timber structures, the knowledge of the mechanical properties of each element is fundamental. For this reason, various nondestructive techniques were developed and investigated since the 1990s. Some of them provide very good results, but the solutions and the proposed models were applied only in few circumstances as a consequence of the on-site restrictive working conditions: no possibility to remove the elements, limitation to ends and faces accessibility and unknown density. The on-site inspection, including the visual strength grading, has been identified as the first step for the timber assessment. In this research, 13 old timber members of Silver Fir (Abies alba Mill.) were visually graded and tested with different nondestructive techniques for the density and modulus of elasticity (MOE) estimation: flexural and longitudinal vibrational tests, stress wave transmission time and Pilodyn penetration depth. The timber elements were also tested in a four-point bending test to determinate the local and global MOE. Finally, a reliable method, applicable to the limiting on-site conditions, was proposed and the results were showed.