Evaluation of cross-sectional variation of timber bending modulus of elasticity by stress waves

Serviceability limit states (related to deformation) rather than ultimate limit states (related to collapse) are often the reason for the need to assess existing timber structures. Prediction of timber members' stiffness is often accomplished using stress wave testing methods. However, these methods only provide information about the quality of the outer layers of the timber members. For a more reliable prediction assessment, one should acknowledge the spatial variability of timber's mechanical properties, especially considering the gross cross-section of old timber members. Here, it was studied the capacity of an indirect sonic stress wave method to predict the modulus of elasticity of a timber member, taking into consideration its cross-sectional spatial variability. The results show that this procedure provides a medium-high correlation (r2 = 0.91-0.94) and an average-low prediction error (∼7%). The prediction of density showed reliable results when done using wood cores where as a poorest prediction was obtained by the drilling resistance method used in this work.