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This study aimed to compare the mechanical performance of two truss typologies, the modified Fan and Howe trusses, using five different wood species: Cambará-rosa, Cupiúba, Angelim-pedra, Garapa, and Jatobá. The spans considered were 6, 9, 12, and 15 m, and the optimization algorithm used was a swarm intelligence algorithm to minimize the structure weight. The study found that wood is a sustainable and viable option for truss constructions, with different wood species having distinct mechanical properties that must be considered when designing the structure. The Howe truss typology presented lower results for the objective function in comparison with the modified Fan truss. The distribution of normal forces in the truss correlated with the characteristic strength in compression and tensile of the species. The Howe truss typology presented a larger amplitude in relation to the modified Fan truss typology in most of the conditions adopted for the Ultimate Limit State constraints. Constraints associated with deflection in the immediate condition were observed to limit the optimization process. The study used the matrix analysis method to evaluate internal efforts and nodal displacements in the trusses. In summary, this study demonstrates the importance of considering all constraints when dimensioning timber structures and the benefits of using different wood species for sustainable construction.

Abstract This work investigates the effect of eco-friendly chemical treatments on the mechanical and physical properties of composite laminates based on sisal fibres. A 2231 full-factorial design is conducted to test the influence of chemical solution types, fibre treatment time, and polymer matrix type on the mechanical and morphological characterisation of the composites. Chemical treatments remove impurities from fibre surfaces, and enhance fibre-matrix adhesion. The treatments, especially with sodium carbonate (Na2CO3), also progressively reduce the hemicellulose fibre content. Polyester composites made with sisal fibres treated with Na2CO3 for 96h achieve enhanced strength and stiffness under tensile, compressive and impact loads. The results evidence the feasibility and efficiency of the proposed eco-friendly treatments for natural fibres and the application of renewable fibre laminates in secondary structural applications.

Abstract This work investigates the mechanical behaviour of a sustainable sandwich panel, consisting of bamboo rings core, treated aluminium skins and epoxy adhesive. A Design of Experiment (DoE) is used to identify the effects of bamboo diameters (30 and 45 mm) and aluminium skin treatments (alkaline degreasing and application of primer) on the mechanical and physical properties of sandwich panels. The aluminium skins treated with the wash primer significantly increase adhesion to the polymer, resulting in greater maximum load, flexural strength, maximum skin stress and maximum core shear stress; while the skins treated with NaOH resulted in a greater flexural and core shear modulus. Relatively more rigid and resistant structures are obtained with Ø30 mm rings, due to the increased surface contact area and the number of constraints on the core. The samples fail due to the skin fracture, implying an efficient face-core bond that is attributed to the proper absorption of the polymer by bamboo and the treatment of the aluminium surface. The proposed panels present good mechanical performance, proving to be a feasible and promising alternative for secondary structural applications.

This work focuses on the fabrication and characterisation of epoxy composites reinforced with natural fibre layers extracted from the inner bast (phloem) of the papaya plant (Carica papaya) under tensile and three-point bending loading. The papaya phloem is composed of fibrous laminas that wrap and reinforce the stem of the plant. A set of quasi-periodically arranged holes disrupt the continuity of these layers, through which the branches emerge. The fibres in each layer constitute an anisotropic honeycomb-like structure, whose elongated cells align along a single preferential direction. Papaya-reinforced epoxy composites are fabricated by hand lay-up and evaluated using two full-factorial designs based on the fibre-to-load direction in longitudinal (0°) and transverse (90°) conditions, for configurations without holes and alternating holes. Composites made with randomly-oriented short fibres are also evaluated along with the first experiment. The tensile and flexural properties obtained are compared to other materials in the literature to assess its potential as a structural material. The results show that the papaya bast fibre layers can be a promising reinforcement for polymeric composites.