Shear Strength of Douglas Fir Timber Bridge Ties

Tests on 480 240- × 290-mm (nominal 10- × 12-in.) bridge ties, both old and new, indicate that the characteristic strengths for shear given in most North American codes of practice seem to be unduly conservative. As a result of this test program, it is suggested that design requirements for shear in timber codes of practice be revised to reflect more correctly the structural behavior of the material, using concepts such as the weakest link principle and fracture mechanics considerations. The test program also clearly demonstrates that in many cases the allowable shear capacity can be doubled by using an overhang equal to the beam depth. The research indicates a savings on paper of over Can$200 million for the Canadian National Railway Company if the recommendations presented in this research are followed instead of those in the current Canadian Standards Association design code (086.1, 1994), the American Railway Engineering and Maintenance of Way Association’s manual of recommended practice, or other typical North American codes of practice.