Journal of the International Association for Shell and Spatial Structure Vol. 62 No. 3, 2021. Access >>
M. Seixas; L.E. Moreira; P. Stoffel; J. Bina
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 presents the form finding and structural analysis of an active bending-pantographic bamboo space structure that integrates self-stressed active bending arches, tensile pantographic grids and supporting bipods. The structure was designed to roof an open-aired amphitheater in the tropical climate. The structure has a self-supporting behavior and a mobile assembly procedure, applying the hinged flexible connection (HFC) mechanism. The structure was developed initially through small-scale physical models, then, on computer models and full-scale prototypes. Empirical models were used to determine the minimum bending radius of the arches and served to embed data for the computer models. The active bending arch (ABA) applied Phyllostachys aurea bamboo rods subjected to axial loads up to the elastic limit of strain on the beams. Steel cables and diagonal rods were connected to the curved beams, avoiding buckling in the plane of the arches. Modular pantographic grids were deployed over the ABA, generating double curved space frames with free- form geometries. The coupling of active bending arches and pantographic grids resulted in a hybrid structure, with mutual operation of bending-active and form-active structural modules. The developed structure used bio-based materials for a sustainable engineering design, with lightweight techniques and low-carbon footprint.
