Bamboo can be utilized as a building material for scaffolding, bridges, houses and buildings. Bamboo, like wood, is a natural composite material with a high strength-to-weight ratio useful for structures.[1] Bamboo's strength-to-weight ratio is similar to timber, and its strength is generally similar to a strong softwood or hardwood timber.[2][3]
In its natural form, bamboo as a construction material is traditionally associated with the cultures of South Asia, East Asia, the South Pacific, Central and South America. In China and India, bamboo was used to hold up simple suspension bridges, either by making cables of split bamboo or twisting whole culms of sufficiently pliable bamboo together. One such bridge in the area of Qian-Xian is referenced in writings dating back to 960 AD and may have stood since as far back as the third century BC, due largely to continuous maintenance.
Bamboo has also long been used as scaffolding; the practice has been banned in China for buildings over six stories, but is still in continuous use for skyscrapers in Hong Kong.[4] In the Philippines, the nipa hut is a fairly typical example of the most basic sort of housing where bamboo is used; the walls are split and woven bamboo, and bamboo slats and poles may be used as its support. In Japanese architecture, bamboo is used primarily as a supplemental and/or decorative element in buildings such as fencing, fountains, grates and gutters, largely due to the ready abundance of quality timber.[5]
In parts of India, bamboo is used for drying clothes indoors, both as a rod high up near the ceiling to hang clothes on, and as a stick wielded with acquired expert skill to hoist, spread, and to take down the clothes when dry. It is also commonly used to make ladders, which apart from their normal function, are also used for carrying bodies in funerals. In Maharashtra, the bamboo groves and forests are called Veluvana, the name velu for bamboo is most likely from Sanskrit, while vana means forest. Furthermore, bamboo is also used to create flagpoles.
In Central and South America, bamboo has formed an essential part of the construction culture.[6] Vernacular forms of housing such as bahareque have developed that use bamboo in highly seismic areas. When well-maintained and in good condition, these have been found to perform surprisingly well in earthquakes.[7]
Over the past few decades, there has been a growing interest in using bamboo round poles for construction, primarily because of its sustainability. Famous bamboo architects and builders include Simón Velez, Marcelo Villegas, Oscar Hidalgo-López, Jörg Stamm, Vo Trong Nghia, Elora Hardy and John Hardy. To date, the most high-profile bamboo construction projects have tended to be in Vietnam, Bali (Indonesia), China and Colombia. The greatest advancements in structural use of bamboo have been in Colombia, where Universities have been conducting significant research into element and joint design and large high-profile buildings and bridges have been constructed.[6] In Brazil, bamboo have been studied for more than 40 years at the Pontifical Catholic University of Rio de Janeiro PUC-Rio for structural applications. Some important results are the tensegrity bamboo structures, the bamboo bicycles, the bamboo space structure with rigid steel joints, the deployable bamboo structure pavilions with flexible joints [8][9] and the bamboo active bending-pantographic amphitheater structure [10][11] developed by Bambutec Design company.
The first structural design codes for bamboo in-the-round were published by ISO in 2004 (ISO 22156 Bamboo - structural design, ISO 22157-1 Bamboo – Determination of Physical and Mechanical properties part 1 and ISO 22157-2 Bamboo – Determination of Physical and Mechanical properties part 2: Laboratory manual. Colombia was the first country to publish a country-specific code in the structural use of bamboo (NSR-10 G12). Since then, Ecuador, Peru, India and Bangladesh have all published codes,[12] however the Colombian code is still widely considered to be the most reliable and comprehensive.
Heat and pressure is sometimes traditionally used to form curved shapes in bamboo.[13]
A typical bamboo shows a nonlinear stress-strain behaviour. It can restrain strain of up to 0.05 until it breaks at which the stress level can be about 300 MPa.[14]
Bamboo is more susceptible to decay than timber, due to a lack of natural toxins [15] and its typically thin walls, which means that a small amount of decay can mean a significant percentage change in capacity. There are three causes of decay: beetle attack, termite attack and fungal attack (rot).[16][17] Untreated bamboo can last 2–6 years internally, and less than a year if exposed to water.[16][15]
In order to protect bamboo from decay, two design principles are required:[16]
Both principles must be applied to a design in order to protect bamboo. Boron by itself is inadequate to protect against rot, and it will wash out if exposed to water.[16]
Modern fixed preservatives may be used as alternatives to boron such as copper azole, however little bamboo has been reliably tested using these methods to date. In addition, they tend to be more hazardous for the treatment workers and the end user, and therefore are less appropriate for developing countries, which is where bamboo is currently mostly used.[16]
Natural forms of bamboo treatment such as soaking in water and exposing to smoke may provide some limited protection against beetles, however, there is little evidence to show they are effective against termites and rot, and are therefore not typically used in modern construction.[18]
Bamboo can be cut and laminated into sheets and planks. This process involves cutting stalks into thin strips, planing them flat, and drying the strips; they are then glued, pressed and finished. Long used in China and Japan, entrepreneurs started developing and selling laminated bamboo flooring in the West during the mid-1990s; products made from bamboo laminate, including flooring, cabinetry, furniture and even decorations, are currently surging in popularity, transitioning from the boutique market to mainstream providers such as Home Depot. The bamboo goods industry (which also includes small goods, fabric, etc.) is expected to be worth $25 billion by 2012.[19] The quality of bamboo laminate varies among manufacturers and varies according to the maturity of the plant from which it was harvested (six years being considered the optimum).
There are a number of common myths and misconceptions surrounding the use of bamboo for construction.
This misunderstanding may have occurred due to the following reasons:[3]
In reality though, even if some fibres of some species show relatively high strengths, following international practice, the design strength that can be safely used is closer to 5–10% of this value, to account for the variability of the strengths.
As described above, bamboo needs to be kept dry in order to protect it from rot, and many existing bamboo structures are showing signs of rot because they did not follow the principles of durability by design.[20]
Bamboo is a brittle material and therefore by itself unable to absorb energy in earthquakes. There is also no advantage of its low stiffness in terms of the performance of bamboo buildings in earthquakes Instead, bamboo structures are primarily good in earthquakes because:
Plain bolted connections can show brittle behavior due to longitudinal splitting of bamboo culms. Providing confinement to bamboo culms at the connection zones increases resistance to this failure mode and brings significant improvement to strength and ductility.
More importantly, bolted connections display predictable yielding.[22][23][24] This is vital for performing a rational engineered design.[25] The bolts are also widely available, easy-to-use and versatile.[26]
This misconception stems from the original idea that bamboo is stronger than steel, and hence could simply replace steel in reinforced concrete.
In reality, bamboo does not function well as a replacement for steel in concrete for the following reasons:[27]
Bamboo was used for the structural members of the India pavilion at Expo 2010 in Shanghai. The pavilion is the world's largest bamboo dome, about 34 m (112 ft) in diameter, with bamboo beams/members overlaid with a ferro-concrete slab, waterproofing, copper plate, solar PV panels, a small windmill, and live plants. A total of 30 km (19 mi) of bamboo was used. The dome is supported on 18-m-long steel piles and a series of steel ring beams. The bamboo was treated with borax and boric acid as a fire retardant and insecticide and bent in the required shape. The bamboo sections were joined with reinforcement bars and concrete mortar to achieve the necessary lengths.[28]
Bamboo has been used successfully for housing in Costa Rica, Ecuador, El Salvador, Colombia, Mexico, Nepal and the Philippines.[2][20][29] An appropriate way of using bamboo for housing is considered to be "bahareque encemendato", or "improved bahareque"/"engineered bahareque".[30] This method takes the Latin America vernacular construction system bahareque (a derivative of wattle and daub and engineers it, making it considerably more durable and resistant to earthquakes and typhoons.
Bamboo used for construction purposes must be harvested when the culms reach their greatest strength and when sugar levels in the sap are at their lowest, as high sugar content increases the ease and rate of pest infestation.
Harvesting of bamboo is typically undertaken according to the following cycles:
