Journal of the International Association for Shell and Spatial Structure Vol. 60 No. 3, 2019. Access >>
M. Seixas; L.E. Moreira; J. Bina; J.L.M. Ripper
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 presented study investigates a mobile bamboo roof structure with flexible connections. The developed ultralight structural system built with modular space frames, tensile pantographic grids, textile joints in polyester ropes and biocomposites, is capable of supporting itself. Prefabricated hinged flexible connections (HFC), designed for the structure, allow for a deployable mechanism, free of torsional stresses in the bamboo bars. Nonlinear analysis using the finite element method (FEM) was used to determine the forces in the structure. Static loading patterns for wind loads were investigated and it was determined that the applied forces can be safely resisted by the structural members. A numerical model, physical models and full-scale prototypes were used to investigate the complex mechanical behavior of the bamboo structure. Selected design guidelines are also introduced.
