Multi-step creep tests of notched beams of silver fir (Abies alba) at different initial moisture contents

Abstract

Silver fir is an important species for French timber engineering industry but its application faces drying issues. This paper presents the results of creep and ramp-loading bending tests on full-scale silver fir notched beams at different initial moisture contents. Initial moisture content showed no discernible impact on instantaneous maximum force, while dynamic compliance appeared to be proportional to this force, possibly due to the dowelling effect. Beam-theory equations are solved using finite differences with crack propagation assimilated to a height reduction, providing an estimation of the compliance and that total deflection primarily results from creep rather than crack. No correlation is observed between the maximum relative compliance and the initial moisture content. Besides this maximum value never reaches the deformation factor for serviceability design in Eurocode 5, suggesting oversizing for green wood. The discrepancy between experimental and theoretically derived crack openings highlights limitations in traditional beam theory, especially concerning fracture mechanics analysis and non-linear effects. For all tests upward crack trajectories towards compression zone are observed and physically discussed. These findings contribute to a better understanding of the mechanical behaviour of wood, particularly regarding creep and crack propagation, with implications for structural design and material characterisation.