Variability analysis of timber bridge responses

Abstract

Large variations in timber moduli of elasticity cause large variations in the loads accepted by various girders (stringers) of a timber bridge. These variations cannot be accounted for by deterministic analyses based on the assumption of constant material properties. In this paper the problem of variation of loads accepted by timber stringer is studied through Monte Carlo simulations. Two separate mathematical models are used for representing timber bridges; one model assumes that transverse load distribution is due only to the transverse shear stiffness of the bridge, and the other that it is due to the transverse bending stiffness. Each model, however, is a special case of the more general and accurate bridge model, known as the semicontinuum model. It has been shown that both models yield similar conclusions regarding the variability of load acceptance by the girders. It is found that the coefficient of variation of loads accepted by those girders which resist appreciable amounts of the applied loads is always less than the coefficient of variation of the timber modulus of elasticity, and that the amount of variation depends upon the transverse position of the loads and the load distribution characteristics of the bridge. A simple expression is given by which the upper bound value of a distribution coefficient, corresponding to a desired confidence limit, can be estimated.