Strength assessment of historic timber using non-destructive methods

This paper presents the findings of a study into the relationship between the Modulus of Elasticity and Modulus ofRupture of historic oak timber for use in the prediction of the in-situ strength of existing timber beams within historic buildings.For structural oak, the current grading process is generally performed through visual grading, by identifying key features that mayinfluence the strength, such as knots, slope of grain, etc, and then comparing them against the limiting values for each strengthgrade to derive the design parameters. For this study, the Modulus of Elasticity and Modulus of Rupture of representative samplesof circa 100-year-old English Oak (Quercus Robur), with nominal dimensions of 50mm x 45mm x 875mm, were obtained through4-point bending tests. The correlation between Modulus of Elasticity and Modulus of Rupture from these tests was not consistent.Hence, a hybrid approach is proposed for further research, using visual grading parameters from CP112 Pt 2: 1971, to account fortimber defects in the derivation of Modulus of Rupture. In tandem, the Modulus of Elasticity of the samples was also derivedusing ultrasonic time-of-flight and transverse vibration, to investigate their feasibility as a Non-Destructive Method of assessingin-situ strength.