Structural performance and analytical modelling of hybrid pine-poplar glulam beams through efficient use of resources

Abstract

This paper presents an experimental and analytical study on the structural performance and resource efficiency of hybrid glulam beams manufactured from pine (Pinus nigra) and poplar (Populus × euramericana, clone MC). In hybrid glulam beams, the modulus of elasticity is inherently non-uniform, varying both longitudinally and transversely because individual boards exhibit spatial stiffness variability along their length and across the cross-section. The main objective is to quantify the mechanical benefits of pine-poplar hybridization and to develop a predictive formulation for the beam modulus of elasticity accounting for these longitudinal and transverse stiffness distributions. Single-species and hybrid glulam beams were manufactured from pine and poplar boards and characterized by non-destructive testing and four-point bending tests according to UNE-EN 408. A new analytical formulation was developed to predict the beam modulus of elasticity from the spatial distribution of board elastic moduli, explicitly considering the strategic placement of the highest-stiffness boards in the outer lamellas, where bending stresses are maximum. The results show that this selection and placement increases the modulus of elasticity of hybrid glulam beams by 21 %, reaching values comparable to single-species pine beams, while also increasing flexural strength by 18 % and reducing beam density by 22 %. These findings are relevant for both researchers and the structural timber industry, enabling efficient, lightweight, and competitive hybrid glulam solutions for structural applications.