Engineering Structures Vol. 265, 15 August 2022, 114457. Access >>
N. B. Albuquerque; C. M. R. Gaspar; M. Seixas; M. V. B. Santana; D. C. T. Cardoso
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. In this work, an experimental and numerical study of the behavior of a tensegrity structure constructed with natural materials is presented. Firstly, it is shown the concept of tensegrity structures, highlighting its emergence, current context, and applications within Civil Engineering. The design of a bio-based tensegrity structural module is investigated as object of study. Initially, a prototype of a single module of the structure is built in 1:25 scale. Subsequently, a prototype on a 1:5.65 scale is built using Phyllostachys aurea bamboo culms for the struts and sisal (Agave sisalana) ropes for the cable nets. Both non-destructive static and dynamic testing were performed on the module to investigate the level of prestress right after assembly of the structure and also considering the relaxation of the cable networks under laboratory conditions. The results obtained from the experimental tests are compared with the numerical predictions by means of a relative error parameter regarding the static stresses and the natural frequencies. Thus, it was possible to indirectly determine the level of prestress applied in the sisal ropes of the tensegrity module. The prestress level was equal to 15% in both static and dynamic approaches, which indicates a good agreement between them and points to the robustness of the proposed methodology. The use of bamboo as a suitable material for strut-cord joints is proposed to avoid metal components and consider the end-of-life biodegradability of the structure in the design of joints. The study deploys bio-based materials for tensegrity structures and the kit of parts as a whole, contributing to the development of extremely lightweight and sustainable structural systems.
