NDT on large ancient timber beams: assessment of the strength/stiffness properties combining visual and instrumental methods

Twelve ancient beams of Fir wood (Abies alba Mill.), were extracted from a XV century building under reconstruction. The large timber elements were studied in order to assess stiffness and strength properties. Visual inspection was performed both for the in situ assessment and for the correct interpretation of the subsequent non-destructive (NDT) instrumental tests. The NDT techniques used were stress waves propagation, vibration and hardness. All tests were performed in the laboratory, bearing in mind the practical constraints of in situ operations (time of realisation, easiness of use, etc.). Results show that a thorough visual inspection can provide a reliable chart of the effective residual sections of the beam. Non-destructive parameters (E-moduli or strength indexes) resulted as being closely related to stiffness and ultimate bending strength of the beams (correlation coefficients R~0,8), even though the sample’s numerosity do not authorise any generalisation. Further improvements in those relationships were achieved through the combination of non-destructive and visual methods into multi-parameter regressions.