Abstract
Structural sections of laminated bamboo can be connected using methods common in timber engineering, however the different material properties of timber and laminated bamboo suggest that the behaviour of connections in the two materials would not be the same. This study investigates the dowelled connection, in which a connector is passed through a hole in the material, and load is resisted by shear in the connector and embedment into the surrounding material. Steel dowels were used in a connection between a laminated bamboo member and a steel plate in a central slot in the bamboo, and the behaviour of this connection was compared with a similar connection in timber. The laminated bamboo was made from Moso bamboo (Phyllostachys pubescens) which had been treated by one of two preservative processes, either bleaching or caramelisation. Following testing, substantial qualitative differences between the bamboo and timber specimens were observed: the bamboo failed most often by the formation of a shear plug whereas the timber failed by a single split. The two preservative treatments resulted in different behaviour: the bleached bamboo had a degree of ductility roughly twice that of the caramelised bamboo. Digital image correlation provided full-field strain measurements, which gave further insight into the differences between the materials, particularly between bamboo and timber. Shear strain is dominant in the bamboo, compared with tensile strain perpendicular to grain in the timber. Numerical modelling showed that this difference in the strain field could be explained by the different orthotropic elastic and frictional properties of the two materials.
Highlights
The embedment behaviour of laminated bamboo loaded by a steel bar through a drilled hole was studied
The models suggest that the shear properties of the material and the friction coefficient are key to the performance of the connection. This experimental study has highlighted the difference in embedment and fracture behaviour of dowelled connections in Sitka spruce and laminated bamboo, and has shown that there are substantial differences in the same properties between bamboo treated by bleaching and caramelisation
Fracture in laminated bamboo tends to be by formation of cracks at the locations of maximum shear stress, and failure may be by a single one of these cracks or by a shear plug
Summary
The embedment behaviour of laminated bamboo loaded by a steel bar through a drilled hole was studied. This form of connection is widely used in timber construction, and is known as a dowelled connection. Plastic theory by Johansen [1] allows prediction of the load-carrying capacity of these types of connections, and forms the basis of design standards such as Eurocode 5 [2]. The diameter and yield strength of the steel dowel are required, in order to calculate the work done in the plastic hinges formed in the dowel at failure. The rules in Eurocode 5 Ref. [2] relate embedment strength to density based on a series of tests carried out by Whale et al [3]
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