Toward a quantitative evaluation of timber strength through on-site tests

Aiming at the structural health evaluation of building materials in historical constructions, it is necessary to identify investigation techniques that gather the desired mechanical data. If old timber roofs are the concern, the characterization of strength and stiffness requires a mix of non-destructive tests (NDT) and visual inspection. In this paper, ultrasonic wave propagation (US) and Helifix fastener extraction (HF) are discussed with reference to two softwood species (spruce and pine) and three hardwood species (lime, beech, oak). Young's modulus and bending tensile strength derived by NDT investigations are then compared with values provided by four point bending tests (4PBT). For the selected woods, the behavior of the modulus of rupture (MOR), and the modulus of elasticity in bending (MOE), are related to the specific density of timber directly measured. Since a good match is found among the NDT derived mechanical parameters and those directly measured, the proposed procedures can help in estimating the reference grade for existing timber structures.