Thermo-hygro-mechanical behaviour of notched beams of European species under creep loadings in outdoor conditions
Résumé
-The main objective of this study is to know, the coupled impact of climatic variations (moisture content, temperature, wind and snow), wood defects (crack initiations and propagations), wood proprieties or characteristics (nodes, orientation of annual rings) and the creep effects on the behavior of the beams of European species: white fir (Abies Alba Mil, WF) and Douglas fir (Pseudotsuga Menziesii, DF). After machining, the beams were stored at about room temperature (Relative humidity 22% and Temperature of 12%). Then, these beams have been notched at the ends, to favor the initiations and propagations of cracks, and loaded in 4-point bending test. The evolutions of initial cracks, and the climatic parameters, were monitored manually, each hour, during 10 days. The experimental device is compound of a comparator, to follow the crack opening and a graduated line, to follow the crack length. The evolution of the beam deflection is monitored by a LVDT sensor, placed at the mid span of the beams. The moisture content (and temperature) has been recorded by a moisture meter placed in the same environment of the experiments. The results show that, the climatic variations have a significant impact on the rise of the beam deflection. The impact are manifested themselves during the moisture process (moisture content adsorption) and during the drying process (increase of temperature). Indeed, the moisture process favor the softening of wood and the increase of deflection of the beam during the creep test. However, during the drying phase, the increase of creep is favor by the initiations and the propagations of the cracks witch can induce the total collapse of the beams.