Essai de flexion 4 points: relation entre MOE local-MOE global pour la caractérisation normative des bois de structure
Abstract
This communication presents a study concerning the characterization of maritime pine according to standards EN408 and EN 384 necessary for timber engineering. A comparison of the standard test configuration is performed with a new 4-point bending protocol avoiding the effects of the shear force in the deflection measurement zone. The study highlights difficulties for the estimation of the elasticity model of wood with EN408, which are probably due to inaccuracies in the measurements of low curvatures and due to the complex configuration of loading (coexistence of bending moment and shear force). The standard (EN384) anticipates these difficulties by introducing a fitting function, which is not adequate for the characterization of maritime pine and probably other species. A population of 173 beams sawn timber was tested to estimate their rigidities. An original 4-point bending test with a zone of pure bending covering 75% of the length of the beams is proposed. This configuration clearly exhibits the convergence of measurements, in contrast to EN 408, revealing the reliability of the approach. The deformations generated by this new loading protocol allow a better evaluation of the bending modulus E0. We obtained an increase of elasticity modulus close to 18%, which represents a significant gain for design and strength grading of maritime pine.
