The structural use of timber coming from fast growing and low-grade species such as poplar is one of the current challenges in the wood value chains, through the development of engineering products. In this work, a qualitative comparison of the behavior of mixed glued laminated timber made of pine in their outer layers and of poplar in their inner layers is shown and discussed. Single-species poplar and pine laminated timber have been used as control layouts. The investigation includes destructive four-point bending tests and three non-destructive methodologies: finite elements numerical model; semi-analytical model based on the Parallel Axes theorem and acoustic resonance testing. An excellent agreement between experimental and numerical results is obtained. Although few number of samples have been tested, the results indicate that the use of poplar as a low-grade species in the inner layers of the laminated timber can be a promising technology to decrease the weight of the timber maintaining the good mechanical properties of pine. Likewise, the need for the use of the shear modulus in both experimental measurements and numerical analysis is suggested, as well as the need to reformulate the vibration methodology for non-destructive grading in the case of mixed timber.

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Due to the strong demand for wood, and the need to reduce the carbon footprint in construction, fast-growing low-graded planted species like poplar are promising wood for the supply chain in the context of engineered wood products, EWPs. Finger joints constitute a key technology for the manufacture of long structural elements of EWPs. Thus, evaluation of the mechanical properties of finger joints is important when designing these structural members. This paper shows the results of mechanical behaviour in tension of poplar timber of the I-214 cultivar, for specimens with and without finger joints, using experiments monitored by DIC (Digital Image Correlation) and simulated by the Finite Element Method. For moderate and intermediate loads, the samples with finger joints showed behaviour similar to those without joints. However, the presence of the fingers decreased the mechanical properties of the modulus of elasticity in the longitudinal direction anywhere from 7.7 to 23.7%; and there was a decrease of around 27.5% in tensile strength. An agreeable correlation between the DIC results and FEM simulations is obtained for the longitudinal, transversal, and shear strain fields, thus demonstrating the high potential of both methodologies.

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