Prediction of shear strength parallel to grain in clear wood of oak (Quercus robur L.) on the basis of shear plane orientation, density and anatomical traits

Oak wood is popular for use in construction and as flooring. Evaluating the mechanical strength of oak timber is difficult and time consuming. Therefore, models for predicting mechanical properties, based on easy-to-obtain variables, may be useful. The purpose of the study was to build models for predicting shear strength parallel-to-grain in oak clear wood. With this goal, the shearing resistance was tested on 198 defect-free specimens (target dimensions 50 × 50 mm in tested section) obtained from a sample of 40 oak trees felled in north-western Spain. The mean shear strength of the sampled oak wood provenance was 15 N mm−2, which was almost equal to the highest mean value reported in previous studies. Analysis of the relationships between the variables tested enabled development of a model relating shear strength parallel to grain at 12% moisture content, with air-dry wood density and angle between tangential and shear plane as predictor variables ( R adj 2 ${R}_{\text{adj}}^{2}$ = 0.61, p < 0.01, bias = −0.80%, RMSE = 13.66%, for wood with wavy grain; R adj 2 ${R}_{\text{adj}}^{2}$ = 0.36, p < 0.01, bias = −1.46%, RMSE = 17.22%, for wood without wavy grain). The independence of shear strength relative to the presence/absence of sapwood or the annual growth ring width was also demonstrated.