Design of reinforced and unreinforced timber beams subject to uncertainties

Uncertainty in the strength of natural materials, such as timber, is considerably higher than man-made construction materials which are produced through controlled and precise manufacturing processes. Adopting a classical deterministic design approach, the designer usually employs high factors of safety to incorporate this material strength uncertainty in the design; an approach that can lead to overdesigned structures with unpredictable performance. This paper, first presents the evaluation of the performance of a classical design method against a nondeterministic design technique. The nondeterministic design is carried out with the Monte Carlo technique in order to estimate failure rates corresponding to the adopted factors of safety utilised in the classical design. It is shown that an increase in factor of safety does not necessarily yield a reliable design. Second, two methods of reinforcement, namely, fibre reinforced polymers and steel reinforced polymers, are investigated in this study. The uncertainty in the strength of reinforced timber is also quantified and modelled. It is shown that reinforcement of timber has a two-fold effect on its strength, namely, enhanced strength and reduced uncertainties, directly leading to a reduction in the overall cost of the structure.