Mechanical and Morphological Characterization of Full-Culm Bamboo

Full-culm bamboo that is bamboo used in its natural, round form used as a structural load-bearing material, is receiving considerable attention but has not been widely investigated in a systematic manner. Despite prior study of the effect of fiber volume and gradation on the strength of bamboo, results are variable, not well understood, and in some cases contradictory. Most study has considered longitudinal properties which are relatively well-represented considering bamboo to be a unidirectional fiber reinforced composite material governed by the rule of mixtures. Despite the dominance of transverse failure (splitting) of bamboo in load-bearing applications, very little study of bamboo transverse properties has been conducted. The objective of this work is therefore to develop a framework and the tools required to evaluate the material and mechanical properties of full-culm bamboo. The study focuses on transverse properties and recognizes that bamboo is a heterogeneous highly orthotropic functionally graded material rather than a homogeneous fiber-reinforced composite as is often assumed. This framework brings together work conducted in the area of bamboo geometric, morphologic and material characterization to develop a correlation with mechanical properties. The effect of fiber volume ratio and gradation in the bamboo cross-section in the characterization is studied and used as a basis to establish materials- and mechanics-based constitutive models for the behavior of full-culm bamboo. The impact of material variability and uncertainty in the mechanical behavior of the full-culm is investigated and included in the presented models. Experimental, imaging and numerical results from this study indicate that considering the transverse behavior of bamboo as a fiber-reinforced material, governed by the rule of mixtures, is not appropriate. The scope of the work focuses on materials test specimens. This is believed to be the scale at which internal heterogeneity of the bamboo effects experimentally determined data and is also a scale at which complex modeling is still appropriate. The models developed in this work have two primary and related uses: 1) providing a platform for researchers to better understand the results of bamboo material property tests; and 2) providing a platform against which to validate macroelement models suitable for structural evaluation and design

Through-culm wall mechanical behaviour of bamboo

Performance of full-culm bamboo structures is dominated by longitudinal splitting behaviour, often exacerbated by connection details. This behaviour is a function of the transverse properties of this highly orthotropic material. Considerable study of the longitudinal properties of bamboo is available in which it is often concluded that bamboo may be considered as a fibre-reinforced composite material and material properties may be assessed using rule-of-mixture methods. Nonetheless, few studies have addressed the transverse properties of the bamboo culm wall, despite these largely governing full-culm behaviour. This study investigated the transverse material property gradient through the culm wall and attempts to connect the mechanical results to physical observations and phenomena. Most importantly, the study demonstrates that the complex transverse behaviour of bamboo does not appear to behave as a classic fibre-reinforced composite material in the direction transverse to the fibres. In this study, five different bamboo species, Phyllostachys edulis, Phyllostachys bambusoides, Phyllostachys meyeri, Phyllostachys nigra, and Bambusa stenostachya were tested using a modification of the flat-ring flexure test to obtain a measure of the transverse tensile capacity of the bamboo. Microscopy analyses are used to qualitatively describe the culm wall architecture and to quantitatively assess the failure modes through the culm wall thickness.</p