As a person native to the seismically active region of my country, earthquakes have been a part of my life ever since I can remember. So have the traditional houses which are specifically designed to withstand the dangerous shaking brought in by these earthquakes. Traditional houses are generally made of locally available materials and in my region bamboo is a material found in abundance. Now, for any kind of house the frame of the building is very crucial as it takes up the load applied and transfers it to the ground below. For houses built in earthquake prone areas an added parameter of flexibility of the frame along with load carrying capacity is needed, because rigid structures when vigorously shaken by an earthquake break more easily as compared to structures which are flexible. This is where the humble bamboo steps in. Bamboo has been known since ages to be a flexible yet strong material having the capacity to take up dead, imposed and as well as seismic loads. The cheap and easy availability of bamboo made it a popular building material among the masses. Moreover in seismic zones the building materials used are supposed to be lightweight so that if during an earthquake any of the members break and fall they don’t cause fatal accidents. The bamboo along with the other indigenous building materials passes this test.
For the construction process bamboo poles are used as the frame of the house with a shallow foundation. Once the bamboo columns are erected next is the construction of the walls. The walls are built with a material called “Ikora”. The Ikora are laid vertically and woven together into a form of a mat with thin pieces of bamboo. Next is the plastering of the walls for which mud mortar is used. The mud mortar is prepared simply by mixing soil and water until the mixture becomes plastic enough to be laid over the Ikora walls. The walls are plastered on both sides with a decent number of coats of mortar. After the mortar has dried a finishing coat made from a mixture of mud and cow dung is applied over the walls.
For the roof the idea is to make it even lighter as compared to the rest of the structure with the obvious speculation that it might fall on the inhabitants during an earthquake. The material used is either corrugated iron sheets or hay depending upon the choice of the dwellers. For the hay roof again the same technique as the Ikora walls is applied. The hay is woven together with thin bamboo pieces. The roof is made a sloping one to drain off the rain water and is laid on a king post truss made of either timber or bamboo. Apart from the lightweight materials used, earthquake resistant construction practices such as use of seismic bands at the roof, lintel and plinth level make these houses safer.
Assam has a history of massive earthquakes with magnitudes shooting up to 8.6 on the Richter scale (1950 Assam earthquake). The traditional bamboo and mud houses have stood the testimony of time but with the evolution of human choices these houses have been replaced with high rise concrete buildings thus compromising the safety during earthquakes. Studies are being conducted to make the modern day high rise buildings safer but the fact remains that in India most buildings constructed are not earthquake resistant and hence remain vulnerable to damage.