Structural Performance of Bamboo: Capacity under Sustained Loads and Monotonic Bending

[摘要] STRUCTURAL PERFORMANCE OF BAMBOO: CAPACITY UNDER SUSTAINED LOADS AND MONOTONIC BENDING Jennifer M. Gottron, M.S.University of Pittsburgh, 2014The exploration of the structural material properties of bamboo is motivated by its potential to serve as an alternative sustainable building material. Although bamboo has been used as a building material for thousands of years, the majority of applications do not conform to any standard design criteria and are therefore considered to be non-, or at best marginally-engineered construction. Nonetheless, as a result of the composite-like structure of bamboo, its mechanical properties are generally superior to those of other natural materials such as timber. The current research addresses the capacity of bamboo under sustained loads and monotonic bending. The sustained loads intend to develop an understanding of the material creep behavior. The effects of creep on radially-cut clear bamboo specimens will be evaluated based on a series of parameters, mainly the ratio of the ultimate load applied to specimen and the orientation of the specimen with respect to the fiber gradation. Specimens were subject to sustained loads for a period of 90 days. Following 10 days of recovery, the residual capacity of the creep specimens was determined. Significant creep-induced plastic deformations and strains were observed in the present work. The orientation of the specimen was found to have a significant effect on both the creep behavior and residual strength of creep-conditioned specimens. The results showed that bamboo loaded with the outer culm-wall in tension (OT) generally exhibited a greater modulus of rupture but reduced apparent modulus of elasticity and residual strength when compared to specimens with outer culm-wall in compression (OC). Additionally the effects of creep conditioning appear to have a strengthening effect on the residual capacity of OC specimens and a detrimental effects on OT specimens. The results of the creep experiments met or exceeded the ASTM 6815 acceptance criteria for wood suggesting that for the structural design of bamboo, a load duration factor similar to that used for wood may be employed. While the creep tests explored only one species of bamboo, the culm bending tests investigated the longitudinal shear capacity of two species. Longitudinal splitting often dominates failure in bamboo components; longitudinal splitting in bamboo is thought to be the result of a mixed-mode shear failure which is influenced by both Mode I tension and Mode II shear failures. The research aimed to understand the mixed-mode shear capacity of full-culm bamboo under four point bending by testing standard span culms with longitudinal notches at midspan and unnotched short span culms. Each of the culm bending tests is designed to provoke a mixed-mode shear failure. The data demonstrated a reduction in the pure Mode II capacity of culms in the presence of Mode I component of distortion. Each of the experiments reported maintains the ultimate goal of standardization; the data collected and results provided intend to aid in the development of a standardized design criteria for bamboo structures.

[发布机构] the University of Pittsburgh