Predicting the mechanical properties of timber from existing structures by the longitudinal vibration method, visual grading and definition of the nominal cross-section

The modulus of elasticity (MOE), bending strength (MOR) and density of 45 150 x 200 x 5400 mm(3) Salzmann pine timber pieces from an existing eighteenth century structure were obtained by testing and also estimated by non-destructive testing. Density was estimated by means of the drilling technique and the MOE and MOR by recording the longitudinal natural frequency of vibration. Four methods for defining the dimensions of the nominal cross-section were applied to establish which was most adequate to address the high variability in the cross-sections along the length. MOE and MOR linear regression results showed r(2) = 59-68% using dynamic MOE, relative edge knot diameter and slope of grain as independent variables. The nominal cross-section defined as the mean cross-section area along the length proved to be the most effective for estimating mechanical properties, followed by the nominal cross-section defined as the average measurements of the piece taken at the middle part or central third along its length. The longitudinal vibration method enables the acquisition of superior predictive models compared to time-of-flight measurement-based methods.