New 4-point bending test protocol for the strength grading of timber: relationship between local and global Modulus of Elasticity (MOE) of maritime pine

This study focuses on the characterization of maritime pine (pinus pinaster) according to standards EN408 and EN384 required for timber grading. A comparison of the EN408 bending test setup is performed with a new 4-point bending protocol, reducing as much as possible, the effects of the shear force in the span where the deflection is measured. The study highlights difficulties to estimate accurately, the elasticity modulus of wood by using EN408 bending test setup, since two approach can be used. This is probably due to inaccuracies in the measurements of small curvatures and due to the local heterogeneities of wood. The EN384 standard anticipates these difficulties by introducing a fitting function, which is not well fitted for maritime pine and probably other species used in timber engineering. An original 4-point bending test is proposed with 75% of the span of the wood beams in pure bending. This configuration clearly exhibits the convergence of measurements, in comparison to EN 408 setup. The deformations generated by this new loading protocol, allow a better evaluation of the bending modulus E 0 . Moreover, the study reveals that the proposed setup, supplies an increase of elasticity modulus close to 20%. In addition, dynamic tests are also performed in order to characterise the Young's modulus. The experimental results reveal a better agreement between static test, using the new four-point bending configuration and dynamic method, than considering EN408 as a reference.