A half scale model of a two and a half story house of stone, mud and wood, like the ones in the hill regions of Uttarakhand and Nepal, survived several powerful shocks in a shock table test that was conducted by us recently at the Nirma University, Ahmedabad, under the guidance of a close friend and renowned expert, retired professor KS Jagadish of the Indian Institute of Science. It was no ordinary house. It was made earthquake resistant with a relatively less known scheme called “Containment Reinforcement”, a concept developed by Jagadish more than 20 years ago.
The model had absolutely no use of cement and steel. The model was reinforced with 4mm GI and aluminum wires placed vertically on the inside and outside faces of all the walls, along with Weld Wire Mesh (WWM) straps placed horizontally in the wall masonry in the form of bands also in mud mortar at different levels. A total of 14 shocks were given with a 2 meter high 1.5 ton pendulum to the platform on wheels on which the house was built. There were several shocks in which the base acceleration was 1g or greater.
This is roughly equivalent to a full-scale building receiving 0.5g to 0.6g base acceleration. This is comparable to the ground motion of some of the major earthquakes. The fact that the two and half story building did not suffer any major damage in a total of 14 shocks is indicative of the effectiveness of the concept of Containment Reinforcement in conjunction with multiple horizontal bands in making the structure earthquake resistant.
This test was a sequel to a shock test of one and half story house (half scale model) with the same specifications as this model. The first test had showed damage at the base and in the parapet wall above the attic floor. The care was taken to tackle these shortcomings in the second model along with better quality of the construction
In the distant settlements situated in the hilly regions of Uttarakhand, Kashmir, Himachal Pradesh, and of course Nepal, the houses are most commonly built using stone and earth, and some timber. Historically people made them earthquake resistant incorporating much timber in the stone masonry walls horizontally and vertically. But timber scarcity has rendered this option very difficult to exercise, if not impossible.
So the use of timber is typically limited to floor and roof understructure. In the hills large number of settlement are not connected by motorable roads, and hence, taking in heavy material like cement, is unwieldy and heavy material like steel add too much to the cost and invite logistical nightmares. But wire bundles and weld mesh rolls are relatively easy to carry in, even by people or on mules. Unlike cement they do not deteriorate with time and exposure.
In short, the option of containment reinforcement in conjunction with the bands of weld wire mesh straps in stone-earth houses can bring safety to a large number of people living in remote hilly regions through a viable and easy to execute option.
Further test are planned to come up with greater technical understanding and to evolve the technical guidelines about how to build a disaster resistant house with containment reinforcement.