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: The creep behavior of bamboo culms under long-term loadings was investigated in the present work. Phyllostachys aurea bamboo samples were subjected to four-point flexural creep tests at loads corresponding to 30%, 50%, and 80% of the bamboo's short-term bending strength. Creep and recovery behavior were evaluated for each loading level at room temperature over 398 days, allowing the attainment of primary, secondary, and tertiary creep stages. The failure of one creep test sample occurred at 73 MPa, and the failure mode due to creep was described. Creep mechanisms assessed included node flexibility, cylindrical bending, and shear. Node flexibility contributed 50–74% of total deflection, cylindrical bending contributed 24–48%, while shear contributed less than 2%. A four-element Burgers mechanical model was proposed, matching the experimental results for all loading levels. A viscous coefficient parameter of 4.3 to 30× 103 GPa.day was inferred, corresponding to the linear dashpot n1. These models estimated the bamboo culm deflection over time and predicted failure at a 40% increase in deflection. Overall, this study provided comprehensive insights into the long-term structural behavior of bamboo culms for use in design and engineering applications. 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.
