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The mechanical behaviour of bamboo is greatly influenced by its transverse properties, which are not easily measured by experiment. This study develops a framework and the computational tools required to evaluate the material and mechanical properties of bamboo in its full-culm form. A numerical model of bamboo as a transversely isotropic material with functionally graded material properties in the radial direction is developed. The random field method was introduced as a means of quantifying the measured uncertainty of bamboo with respect to the mechanical characterisation of its full-culm state. Four increasingly complex approaches to model circumferential compression tests of bamboo are presented: a theoretical evaluation using Castigliano’s theorem; an orthotropic model neglecting the graded nature of the culm wall; and, two models—one discrete and one continuum-based that define a transversely isotropic graded material. Output from each model is compared, calibrated and validated with experimental results. While the models developed were robust, their application has drawn into question the fundamental hypothesis that the functionally graded behaviour of bamboo can be captured using the rule of mixtures.

Bamboo has been in the focus of attention as a re-discovery of an old and available material to solve environmental problems in the construction industry. The use of full-culm bamboo in the built environment, however, depends on proper quality control/assurance of its mechanical and physical properties. In this work, a quality assessment in terms of treatment control and mechanical properties of a small production of Phyllostachys edulis bamboo poles treated with disodium octaborate tetrahydrate (DOT) was performed. A comparison between two commercial preservatives used for exterior and interior applications, chromated copper borate (CCB) and DOT respectively, in terms of the effect on the mechanical properties and treatability behaviour was also investigated. Penetration and retention analyses showed satisfactory results for the samples treated with CCB, with retention of 7.2 kg/m3, while lower values of retention for the samples treated with DOT by the immersion method (2.2 kg/m3) was observed. Microstructural and EDS analyses revealed a much higher concentration of chromium and copper from the CCB solution in the bamboo large vessels. The mechanical characterization performed by compression, shear, tension, coupon three-point bending, and flat ring flexure tests showed that the difference between the two treatment conditions was small and, in most cases, not statistically relevant. Low coefficients of variation were observed in all the investigated mechanical tests, suggesting a uniform distribution of mechanical properties within the batch of P. edulis bamboo used in this study. The full characterization schedule combined with digital image correlation analyses enabled the calculation of the characteristic values of the mechanical properties, useful for structural design, complementing the treatability and quality assessment.

The withdrawal capacity – as determined by a modified ASTM D1761 test – of screws embedded in Phyllostachys edulis bamboo culm walls is presented, demonstrating capacities and behaviour suitable for structural load bearing applications. This study considers twelve screw type-size combinations and considers whether these are predrilled or the screws are inserted without predrilling, resulting in 20 screw type-size-predrill combinations. For the better-performing screws, average withdrawal parameters exceeding fax = 40 N/mm2 were achieved; twice that determined for three-ply plywood having comparable thickness. Comparison with a comparable dataset of screw withdrawal tests from Guadua angustifolia Kunth bamboo indicates that the value of fax is likely species-dependent. In order to mitigate splitting upon screw insertion into bamboo, screw diameters generally less than 6 mm were required unless the screws are inserted into predrilled holes. There was no advantage observed to using self-drilling screws.

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.

Bamboo is often described as a functionally graded unidirectional fibre-reinforced composite material. As such, the Rule of Mixture (RoM) is often reported as an appropriate method of capturing longitudinal material and mechanical properties. However the dominant failure mode of bamboo is associated with longitudinal splitting of the culm and is therefore affected by transverse material properties. The efficacy of RoM in the longitudinal direction suggests its adoption in the transverse direction. It is concluded that the transverse behaviour of bamboo is not adequately captured using the often-adopted RoM approach. Experimental, morphological and numerical approaches are presented to better understand the reasons for bamboo not behaving as a unidirectional fibre reinforced material as is uniformly described in the literature. The approach has identified possible causes of the deviation of the observed behaviour – all which require further study.

Image analysis is used to quantify the distribution of fibre volume ratio, Vf, in strips of P. edulis bamboo obtained from two commercially available glue-laminated bamboo beam products. In total, 58 cross sections containing more than 3500 19 × 6 mm strips were analysed. Simple digital manipulation techniques were found to work well in establishing fibre volume data from the 1200 dpi source images. Total fibre volume for each strip was established and was found to vary in a linear manner through the strip thickness. The observations presented indicate significantly different bamboo source (feedstock) material used by the two manufacturers. Autocorrelation analysis was used to demonstrate that the orientation of the individual strips in each beam section was not random. The impact of a non-random distribution of strip orientation in a section subject to flexure is relatively small but does result in variation from analyses that assume a homogenous distribution of mechanical properties. Finally, nodes, a weak location in glued-laminated bamboo members were observed to represent 3–4% of all strips in a given cross section. The distribution of nodes appeared to be random.