Journal of the International Association for Shell and Spatial Structure Vol. 58 No. 3, 2017. Access >>
M. Seixas; J. Bina; P. Stoffel; J.L.M. Ripper; L.E. Moreira; K. Ghavami
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. The present paper describes the design process of a textile hybrid bamboo amphitheater dome built in the tropical climate of Brazil, employing a mobile free-form space structure spanning a 17 x 12m area. The structural system is designed applying pantographic gridshells pre-stressed by acrylic membranes and braced by self-stressed active bending beams reinforced by steel cables and strut scissors, avoiding buckling of the members. The structural system consists of an adaptable supporting space structure using hinged bamboo bipods. The connection of the structural modules on a free-form geometry has a self-stabilizing behavior, therefore reducing the use of heavy foundations. Flexible hinged lashed joints with textile-based techniques were developed. A form-finding method based on the developed physical models established the topology of the building site, generating the assembly procedure. The full-scale model was constructed on the inclined site at the banks of the Rainha River at the campus of the Pontifical Catholic University of Rio de Janeiro, PUC-Rio. The modular space structure was mounted in stages on the ground, then erected with the aid of lifting bipods, without the need of cranes and heavy machinery. The 200m² built structure had a weight of 14 kN corresponding to 0,07 kN/m², consisting a sustainable ultra-lightweight space structure.
