Design of reinforced and unreinforced timber beams under uncertainties

Uncertainty in the strength of natural material, 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, designer usually employs high factor of safety to incorporate this material strength uncertainty in design; an approach that can lead to overdesigned structures with unpredictable performance. This paper, firstly, presents the evaluation of the performance of classical design method against nondeterministic design technique. The nondeterministic design is carried out with Monte Carlo technique in order to estimate failure rates corresponding to the adopted factors of safety utilized in the classical design. It is shown that increase in factor of safety does not necessarily yield a reliable design. Secondly, two methods of reinforcement, namely, Fibre Reinforced Polymers (FRP) and Steel Reinforced Polymers (SRP), are investigated in this study. The uncertainty in the strength of reinforced timber is also quantified and modeled. It is shown that reinforcement of timber has a two-fold effect on its strength, namely, enhanced strength and reduced uncertainties, directly leading to reduction in the overall cost of the structure.