Asymmetric Flexural Behavior of Glulam Beams Based on Bamboo-inspired Functionally Graded Structure for High Bending Load Applications

Natural materials are being further processed into functionally engineered products to reduce their natural variability and enhance their performance for use in construction, given their noteworthy recyclability, availability and sustainability traits. To date, the mechanical strengths of natural and engineered wood products are limited by their inherent micromechanical characteristics which are outclassed by homogeneous materials like steel and concrete. This study proposes a less process-intensive technique to improve the strength of engineered wood products by considering glulam based on a bio-inspired functionally graded structure. The finite element method was considered to investigate the effects of the functionally graded arrangement on the asymmetric flexural deformation and on the underlying fracture mechanisms in glulam beams. The numerical results showed that the functionally graded arrangements across the cross-section led to an improvement in the bending strength and consequently enhanced the resistance to transverse crack propagation. In the functionally graded glulam beam, the stiffer layers at the bottom were found to promote the onset for longitudinal crack initiation. Moreover, transverse cracks tended to propagate sideways in an orthogonal direction in the beam layers with a high longitudinal to transverse stiffness ratio whereby the tangential normal stress was a maximum. The improvement in performance, which resulted from a shift of the neutral axis and redistribution of stress within the glulam beams, was attributed to the degree of graded arrangement across their cross-section besides the orthotropic characteristics of their individual layers. Key findings of this study could be useful to further develop high-strength engineered wood products based on bio-inspired solutions to replace conventional materials in the construction industry for improved sustainability.