Stress distribution in a tapered beam is an important issue in timber engineering, because splitting failure is possibly initiated at the taper edge. The conventional formula for the stress distribution after Maki and Kuenzi, which is adopted in current manuals of timber construction, is based on elementary mechanics assuming the Bernoulli-Euler hypothesis. However, it is not a correct solution for tapered beams, because it does not satisfy the strain compatibility as well as the boundary condition. In fact, many test data show that splitting occurs at a position apart from the maximum stress point given by the elementary solution. In this paper, exact stresses in tapered beams were derived by using stress functions in mathematical theory of elasticity. The solution was compared with those of elementary mechanics and FEM for some typical cases. It was found that the elementary solution has an unacceptable level of errors when the taper slope is greater than 0.2 or when the entire beam depth is less than three times the depth at the support.
