Bamboo is versatile group of grass, belonging to the subfamily Bambusoideae of the family Poaceae in Asia. It is fast growing, highest yield, low cost, and a renewable natural resource with excellent mechanical properties. To explore its potential as a building and structural material, further research on its properties is needed. In the following, the structure and mechanical properties of bamboo will be introduced. Then, a comparison of the mechanical properties between bamboo and other materials will be made. Previous literature on structural bamboo will be reviewed. In addition, practical considerations in construction uses, defects and protective treatments, and applications of bamboo will be described. Finally, the future development of structural bamboo and the objectives of this study will be stated.
Structure of bamboo
Macrostructure: Bamboo culms are tapered and hollow in shape. The diameter of culm and the internode length vary along the culm. The wall thickness decreases from bottom to up. Microstructure: Bamboo culm is made up of parenchyma cells and vascular bundles consisted of thick-walled fibers and vessels, similar to fiber-reinforced-matrix composite material. Bamboo fibers are parallel to the axis of internode culm, and more concentrated at the upper part of culm and towards the outer layer of the cross section of wall-thickness. As a result, bamboo possesses the optimum capacity for load bearing.
Mechanical properties of bamboo
The mechanical properties of culm depend on the bamboo fiber distribution and orientation, since the fibers are mainly responsible for bearing loads. (i) Orientation
The mechanical properties parallel to the axis of culm with fibers longitudinally oriented are superior to those in other direction. For example, the elasticity modulus E in the tangential direction is about one-eighth of the E in the longitudinal direction (Villalobos, 1993), since no radial fiber strands exist in bamboo internode culm. (ii) Effect of node
The effect of node on mechanical properties of bamboo is different under various load types. The tensile strength of bamboo strips from the internode section is higher than the strength at node, because nodes are the weakest components under tensile load, in which fibers are bent inwards. The tensile strength of nodes was found to be 75-80% of the inrernode section (Wu, 1999), and the tensile strength at node location is only 40% of the strength at internode (Villalobos, 1993). However, node enhances the stiffness and compression capacity and thus strengthens the overall structural performance of a bamboo member. In conclusion, elastic modulus, compressive and flexural properties increase with the number of nodes. (iii) Fiber content
Fiber content increases from bottom to top of culm and from inner to outer layer across the wall-thickness. This results in similar mechanical properties of the bamboo. According to Lo and his colleagues (2004), more closely packed fibers imply high strength capacity of bamboo. (iv) Fiber volume
The wall thickness of culm increases during the growth period of bamboo, which is in the range of 1-5 years. Cellulose content increases mainly in the first year of growth, thus mature bamboo possesses the good structural properties.
Comparison of mechanical properties
Material| Densityρ| Tensile strength σt (MPa)| Elastic modulusEt (GPa)| Poisson ratioυ| σt/ ρ| Compressive strength σc (MPa)| Flexural strength σf (MPa)| Bamboo| 0.8| 88-142| 9-18| 0.35| 100-178| 55-79| 100-300| Hard wood| 1.0| 49| 4-9| -| 49| 24-34| 70-120|
Plywood| 0.8| 12-54| 1.2-4.6| -| 15-67| -| 20-50|
Steel| 7.8| 275-450| 200-210| 0.3| 35-58| 275-450| 275-450| Glass Fiber Reinforced Plastic (GFRP)| 2.0| 294-451| 21| 0.33| 147-226| 137| 223| Table 1 Comparison of mechanical properties between bamboo and other materials...