Engineering Structures Volume 251, Part A, 15 January 2022, 113501. Access >>
L.E. Moreira; M. Seixas
Abstract: Ultralight bamboo structures with flexible joints comprise a novel construction system that can meet the global demand for sustainable buildings, such as multi-use pavilions and temporary structures for disaster relief and humanitarian purposes. In this work, modular self-supporting space frames were designed, fabricated, and experimentally analyzed using bamboo culms, textile ropes, and biocomposite rings. Numerical models and a 1:3 scale prototype were used to investigate the structural response under sustained loadings. The mean values of 5.4 GPa for Young's modulus (E), a specific gravity (G) of 8 kN/m³ , and a Poisson's coefficient (ν) of 0.3 were adopted for the bamboo members. The prototype, constructed with two modular space frames, was tested under both symmetric and asymmetric loading conditions during 43-day static tests. A pronounced nonlinear behavior was observed for the symmetric loading of 4.8 kN and the asymmetric loading of 3.5 kN, whereas failure occurred at a total load of 6.5 kN for the asymmetric configuration, 7.5 times the prototype's self-weight. The observed failure of bamboo members was governed by crushing under bending, followed by local buckling of the upper rafters below the load application points. The experimental results were compared with numerical models to determine an effective modeling strategy for reproducing the actual structural behavior. A comparison revealed that the eccentricity of members at the joints must be considered for a reliable prediction and that creep can be accounted for through appropriate reductions in the modulus of elasticity. The observed differences are attributed to the sliding of members at joints under higher loads and due to local second-order effects. This paper investigates the bending stiffness of bamboo culms with and without the presence of a full longitudinal crack of the culm wall. The study aims to quantify experimentally the loss of resistance of cracked bamboo tubes in bending, in compliance with numerical modeling using the finite element method (FEM) and the classic equations of Vlasov. Experimental tests were conducted with six specimens of Phyllostachys edulis bamboo (Moso), subjected to three-point bending tests. Firstly, the samples were mechanically tested in its full-culm state without the presence of cracks and, then, with a longitudinal crack along the total lenght of the culm. The cracks were positioned in the worst-case situation, i.e., perpendicular to the bending plane. The compliance between experimental and numerical displacements measured at the center span of the samples and in FE models showed with accuracy the loss of the bending stiffness of cracked bamboo culms. The study showed that isotropic numerical models can attain the flexural properties of bamboo tubes in perfect conditions, without the presence of cracks. Although, to assess the flexural properties of bamboo tubes with the presence of a full longitudinal crack it was necessary to model the bamboo tube considering orthotropy. The numerical analysis and the Vlasov equations described with good precision the stress field in the analyzed tubes. Each sample presented a different loss of resistance, depending if the crack cut or not the diaphragms beyond the culm wall, showing a maximum loss of stiffness of 63% for cracked specimens. Thus, the results presented a significant loss of bending stiffness of cracked bamboo culms, if the culm wall cracks from one end to another, which can be considered as a damaged tube.
