Effect of depth of a sawn slit parallel to the fiber direction on shear modulus of commercial size square timbers

Effects of sawn slits on static and dynamic shear moduli of square timbers were studied experimentally using torsion tests. Shear moduli decreased greatly with increasing slit depth, the reduction am ounting to about 40% when the slit extended to one half of the timber thick ness. The relationship between shear modulus and slit depth followed a cubi c equation, with a high correlation coefficient of R=0.982. Dynamic and static torsion test results showed a high degree of correlation of R=0.976. The dynamic torsion test is therefore recommended as a practic al test method which can be used as a nondestructive proof test for structu ral timbers with a large slit.