Rolling shear modulus and strength of beech wood laminations

Abstract Previous research indicated that the rolling shear properties of European beech wood (Fagus sylvatica) are considerably higher than those of softwood. The aim of the presented investigation was to substantiate previous data on rolling shear modulus and strength of European beech wood and to further evaluate its substitution of softwoods in applications where shear properties are influential, namely as cross layers in cross-laminated timber (CLT). Further, the effect of the annual ring orientation within the boards on shear modulus and strength was of major interest. The beech specimens comprised four different sawing patterns, classified unambiguously with reference to the pith location. The shear properties were determined by 50, two-plate shear tests with specimen cross-section dimensions of 33 mm × 135 mm. A mean rolling shear modulus of 370 N mm-2 was obtained, whereby no significant detrimental effect for pith boards with cracks was observed. In agreement with continuum mechanics, the semi-quarter-sawn boards revealed the highest shear moduli whereas the quarter-sawn boards showed roughly 30% lower values. The mean rolling shear strength was 5.6 N mm-2 for all specimens, whereby pith specimens resulted in generally lower values. The 5% quantile, disregarding pith specimens, was 4.5 N mm-2. In conclusion, the rolling shear strength and modulus exceed the respective characteristic values for softwoods by roughly factors of 5 and 7, indicating great potential for beech wood cross-layers in CLT.