“Bamboo is close to an ideal structural material.” This statement by Neil Thomas during his talk at Bamboo U, which took place in November 2017 in Bali, really caught my attention. Neil is the founding director of atelier one, a London office of structural engineering, whose outstanding projects include stage and scenography for the Rolling Stones, Pink Floyd, and U2; art installations by Anish Kapoor and Marc Quinn; the Gardens by the Bay, in Singapore, among many others. From the last few years, the engineer has exhaustively studied about bamboo, its structural properties and its most diverse potential.
According to him, bamboo is close to the ideal structural material, beginning with its tubular shape. An open section, such as a channel, is weaker than a closed one because the edge can bend much more easily. Just think of a sheet of paper and how it becomes stronger when we roll it up like a tube, preventing it from bending so much.
In addition, it has another feature that improves its resistance. The bamboo culm has longitudinal fibers that span the entire length, called vascular bundles. Closer to the exterior of the culm wall, these bundles have a higher density, making them stronger. So, the stronger part of the section is further away radially from its centroids, making the overall section stronger. And this is the main difference compared to a wooden trunk, which has its strongest material in the center of its section. Another peculiarity is its speed of growth. Unlike hardwood, which can take more than 30 years to be exploited, bamboo can be cut and used between 3 to 5 years, then growing again.
In laboratory tests bamboo also achieves impressive structural capabilities. Its compressive strength is equivalent to concrete. Clearly, this can range according to the species – more than 1500, which grow naturally on almost all continents, especially in regions with higher temperatures.
Even so, there is some resistance to the use of the material, since it requires another type of thinking and the breaking of certain paradigms so rooted in architecture. One of them is the fear of using the material in its rough form, with its irregularities and natural forms, where the beauty of bamboo lives.
There are, of course, some issues that need to be considered, such as the chemical treatment of bamboo prior to its use for construction, to prevent rotting and insects infestation. Another issue when constructing with bamboo is the fact that its components should be very well protected from the sun and rain, for adequate durability. This also includes the pillars, which cannot be in direct contact with the ground. This is usually solved by adding a piece of rock over the shallow foundation.
The detailing of bamboo and its connections has been historically developed, being passed from one generation to the next through artisan builders, evolving through the understanding of the material itself. In the 21st century, with all the technology we have available, it is possible to better understand the specific forces in different conditions (strain, compression, bending, shear) and apply modern technologies, so that it is possible to optimize the material and to use other materials and techniques, such as shells and membranes, to achieve even more ambitious structures.
Neil concluded by stating that bamboo is the most sustainable natural building material on the planet and that we are certainly at the beginning of its use in a much broader way. However, his main teaching is that we should not try to adjust the bamboo to the existing rules, but change the rules to suit the bamboo.
By Eduardo Souza. Translated by Guilherme Carvalho.