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In this section, each month Dreamghar.com would review a building or a discuss a topic which is related to construction or good living. This Month the topic of discussion is : INNOVATIVE SOLUTIONS FOR DISASTER RESISTANT STRUCTURES ( Author - Ar. Anil Laul)



MARATHWADA ARCHITECTURE OF LATUR (SOUTHWEST INDIA)

Marathwada has had severe earthquakes since around 400 years ago. The master masons of that time had perfected the art of building and construction with respect to earthquakes using the local materials such as stone and mud)

Structure and Material usage in Marathwada Architecture :

If observed closely, the Marathwada houses basically had a post and beam construction. Earthquake resistance demands a framed structure (non load bearing walls) so that the load of the roof is not transmitted to the walls. The logic is that the structure can sway in case of horizontal movements and come back to its original position. Walls just act as fillers which in case of damage could be repaired or reconstructed.
Traditionally, timber was abundantly available and as a result the posts, beams, tie members (for triangulation) etc. of the frame were made out of it. Roof insulation and water proofing was done with locally available clayey soil and grass was grown on top of the roof for added insulation. The walls were basically filler walls of mud. Since the walls, in stone were kept of 45 cms. minimum, good bonding could be achieved. It was a structure, which performed well in earthquakes. The openings were very small (also because of extreme hot and dry climate), the plans were more or less symmetrical and the structures were not more than two stories high.
With time and with no major earthquakes for a large duration, slowly people started making modifications as per climate controls. The structure changed from a non-load bearing one to a load bearing one. The thickness of both roof and walls started increasing for insulation purposes and hence walls started taking the load of the roof instead of being independent as fillers.
In case of a quake, therefore, the heavy load of the roof caused it to sway. Since the roof was supported on the walls, the walls collapsed. Walls were very thick and no bonding existed between various masonry units. The wall did not act as one. Besides there were no buttresses or cross walls to support the walls and hence the entire structure collapsed.

Following were the prime damages observed:
1. The walls were not interlocked at the corners. Wherever corner stones were used and interlocking was achieved, the masonry withstood the horizontal movement.
2. Wherever there was an expansion or a change of materials, no interlocking was done in the old and new walls. While the two structures needed to stay independent and self stable, the masonry needed to be continuous.
3. As described earlier, the presence of through stones in walls were absent. The stones acted like cladding on the intermediate layer of mud and boulders and the layer just peeled off during the quake. In the gateways the masonry was always done very carefully and the best stones used. Result : Most of the gateways of houses in all the affected villages withstood the quake. Another reason for the gateways to be standing was that their edges were always baffled which acted like buttresses.

4. The joint between the column and the beams in most of the cases was retained as the traditional one with a dowel joint which allowed for movement and still held the members together. However wherever this was not followed, the roof joint gave away.

Had the ancient system of construction been retained, the damage would have been far lesser. In no way are the materials to be blamed for the poor performance, it is the structural design and the poor quality of masonry which led to the heavy toll.
This is what Latur case-study tells us about quake resistant construction which we can adopt using local resources and modified skills :

 

TRADITIONAL CONSTRUCTION IN THE HILLS - UTTARKASHI (NORTH INDIA)

The foothills of Himalayas have since ages been experiencing tremors of varying magnitude every now and then. Earthquake resistance is therefore imbibed in the traditional construction system.
The traditional house form incorporates sloping roof with houses not more than two stories high. The local materials out there are stone and timber. Scarcity of water has led to dry construction. A composite form of masonry is practiced using the two materials - stone and timber. Slate stone on timber understructure is the most common roofing system with walls done in composite masonry of stone and timber. All these are local materials of the region. Walls are thick which help in keeping the house warm in the cold climate of the region. Sloping roofs help to drain off snow.

The main features of the local construction, which incorporates EQ resistance, are:

With time, however, bricks and concrete replaced the local materials. Also the fine skills slowly are vanishing and artisans are turning to mediocre construction practices since quality is a very scarce criterion for earning. These features therefore are getting diminished in the structures, which led to collapse of the houses.

1. No interlocking in walls led to bulging of stonewalls and resultant delamination.
2. Absence of timber / stone through stones in corners led to corners giving away.
3. Improper stone masonry and joints not staggered properly led to vertical cracks in the walls.
4. Lesser bearings on openings resulted in diagonal cracks.
5. Missing wall plates led to roof disintegration and collapse.
6. No proper ties at the roof level caused the triangular portion of the gables to collapse.

LEARNINGS FROM UTTARKASHI

VERNACULAR CONSTRUCTION IN NORTH-EAST PARTS OF INDIA

In continuance with the Himalayan foothills, the North east parts of India also experience continuous vibrations. The traditional construction out there has therefore been using Bamboo since it is a commonly available local material. Bamboo is used as a frame with infill walls of lighter materials (Wattle and daub etc.). The entire structure stands on stilts, which are anchored deep into the ground. With ground movement, the entire structure moves and then regains its original position. Also during severe intensity earthquakes, the structure may collapse, but would cause minimal damage because of a lightweight structure. It is also easy to assemble.
The distinct feature of this construction is the use of bracing as the effective structural element for stability and flexibility. Even the wattle and daub mat is laid diagonally so as to reinforce the frame of the walls properly.

LEARNINGS FROM THE NORTH - EAST



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