Mechanical Properties of Timber Bamboo
Natures Strongest Botanical Fiber
Whole bamboo has often been called “vegetative steel” and in some mechanical characteristics, like its surface tensile strength, in internodal sections is stronger than steel (582 MPa v. ~350 MPa). (Shao et al., 2010) As reflected in the figure below, when compared on an equal density basis, timber bamboo has been shown to be comparable to steel in strength tests and stronger than wood or concrete, depending on specific species and test protocols. Relative to stiffness, whole bamboo can test stronger than concrete, steel or wood, again depending on specific species and test protocols. (Janssen, 2000).
In another study, when compared on an equal density basis, whole bamboo requires more pressure perpendicular to the grain to rupture (higher Modulus of Rupture (MOR)) than Loblolly pine, Douglas fir, cast iron, or structural steel. (Mahdavi 2011) A study from an MIT team compared the mechanical properties of Chinese Moso bamboo with four North American kinds of wood, three of which are commonly used in U.S. building construction: white pine, Douglas fir, and white spruce. The study examined three mechanical properties: compression, bending, and stiffness. The chart below plots the three mechanical properties of Moso bamboo relative to the four kinds of wood.
In compressive strength bamboo was superior to all four kinds of wood, ranging from 38% greater compared to Douglas fir to 109% greater compared to white pine. In bending strength, bamboo again showed superior strength to all four kinds of wood, ranging from 31% stronger compared to northern red oak to 120% stronger compared to white pine. In stiffness, the bamboo was stronger by 10% and 24% compared to white spruce and white pine, respectively and less stiff by 21% and 16% than Douglas fir and northern red oak, respectively. Having somewhat less stiffness than other structural building materials can be a benefit in high wind and earthquake prone areas. “Bamboo is strong in tension and compression. The tensile strength of Bamboo is much greater than that of steel. Bamboo exhibits great bending capacity. Its elasticity makes it a great material for construction in earthquake areas.” (Laroque, 2007)
Based on growing interest in using bamboo in Western style building, engineers and researchers are now studying a wide range of mechanical properties for laminated bamboo lumber and panels. Researchers at the University of the Andes in Bogota, Colombia actively study Guadua bamboo, which grows natively in Colombia and throughout much of Latin America. Through a series of published research, they have examined many aspects of using Guadua in structural bamboo products, including laminating strength, sustainability, and mechanical properties. In 2008 they concluded, “the mechanical properties obtained in this research with the corresponding data reported around the world indicate that GLB (glued laminated Guadua) can be suitable for construction and design of structural elements.” (Correal, 2008) In 2013, a study from the University of Cambridge reported that laminated bamboo lumber from Moso bamboo, has superior bending strength (MOR) compared to laminated veneer wood lumber (15% better) and parallel strand wood lumber (19% better) but less stiffness (Modulus of Elasticity (MOE)) than laminated veneer wood lumber (17% less) and parallel strand wood lumber (22% less). (Mulligan & Ramage) See figure below.