Verhältnis von Zug- zu Biegefestigkeit bei Vollholz

Acc. to EN 338 the characteristic tensile strength is determined to be 60 percent of the characteristic bending strength for all strength classes. The present investigation involving timber from Central Europe (mainly spruce, Picea abies) shows that the relationship of tensile to bending strength is affected by wood quality. Through a modification of the classic brittle fracture theory this relationship can be expressed in terms of bending strength and hence the influence of wood quality can be shown. Together with available results from literature a total amount of 2642 tension and 1,739 bending tests divided into 28 and 27 subsamples respectively, were evaluated. A relation of f_t,k/f_m,k = 0,24 · f_m,k^0.28 or f_t,k = 0,24 · f_m,k^1.28 is suggested for the characteristic strength values. A comparison with the characteristic strength values acc. to EN 338 indicates that for safety and economy reasons the consideration of the influence of wood quality would be desirable.