This paper examines the application of equations used to define the effect of section depth on the ultimate bending stress of timber to characteristic stress values obtained from tests carried out at Princes Risborough Laboratory and in Canada. It deals specifically with the determination of the most suitable general equation for adjusting test results to a standard depth. From a comparison of root mean square differences between depth factors obtained from the test results, and those predicted by the equations, it is concluded that, for visually stress-graded softwood timber, the depth effect is best defined by the equation K = (200/h)0-4
A.R. Fewell and W.T. Curry