Damages to life and property due to natural disasters like earthquakes and cyclones have become a regular feature in our country. The massive earthquake that struck Gujarat on the Republic day has stirred the country, with mounting fears about more earthquakes being eminent. India in the past decade has witnessed a number of major and minor earthquakes and cyclones. The prime ones being - the Latur earthquake in 1993 claiming over 10,000 lives (Southwest India), the Uttarkashi earthquake in 1991 (North India), often occurring tremors in Jabalpur (Central India), Bhavnagar (West India), and foothills of Himalayas (Northern India). The northeast region of our country continuously experiences vibrations of minor intensities. Metros in India like Delhi and Mumbai are under continuous threat of earthquakes. A major cyclone affected Kandla port in Gujarat state a couple of years ago. The great Super cyclone of the year 1999 on the Orissa coastline caused heavy devastation and as the region is prone to cyclones another big one cannot be entirely ruled out.

As evident from the above, with the fear of the natural disasters attacking almost all parts of the country, we cannot afford to ignore the issue. Certain measures need to be imbibed in regular construction so that the damage gets minimised. Instead of especially designing for earthquakes, or cyclones, certain minimal features need to be standardized and incorporated in all parts of the country so that a minimum level of resistance against these damages is achieved. While we can do very less to stop the forces of nature, what needs to be done is to create solutions which move along with the forces and in the process reduces its impact on human life.

Nature provides its own solutions and we need to learn....... A tree is embedded into ground and sways with high winds, - and regains its original position after the winds have stopped. It does not fight against stopping the winds affecting it - it is made to resist the forces of certain intensity. A similar approach needs to be incorporated while designing the macro and microenvironment for resisting disasters - the built form has to be conducive to the forces of nature.

The wisdom of resisting these disasters need not be invented. Our ancestors have done so in the past very consciously. It is we, in the process of modernising our principles, who have forgotten the basics and are suffering because of it. Our ancient structures are still standing the tests of time because of their sound geometry and clear structural behaviour responding to all the natural forces.Even in the case of the most recent earthquake in gujrat, buildings using latest construction practises and methodologies fared very badly when compared to buildings of yesteryears. And in case of previous big quake in Latur, none of the ancient Indian temples or mosques collapsed.

A study of the ancient domes existing in temples / mosques all across the country reveals a standard building system which is designed to withstand horizontal movements and wind forces of certain minimum intensities. As shown in the photograph enclosed, a system of triangulation is used in which the lateral forces are distributed to perpendicular walls. The structure behaves as one and does not disintegrate or collapse in any nature of movements
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In the mosques also, the system of dome construction was adopted using squinch arches in the corners. This system converted the square plan to eight sides, then to sixteen and eventually into a circular one for the base of the dome. It also braces the corners of the structure following the triangulation system. The squinches helped to reduce the slenderness ratio of the walls horizontally as well as vertically thus increasing the lateral stability in plan. In section, the horizontal thrust is transferred on to the arches, which in turn transferred the lateral forces to the adjacent walls.

Squinch* An arch or a corbelling system of concertrically wider and gradually projecting arches, placed diagonally at the internal angles of towers to support a polygonal or round superstructure

Even the walls of the structure were baffled which increased the lateral stability of the structure. The structures in the past were simply supported structures, where the material of the roof behaved as a cladding material over the support system. Our Vastu Vidya divides the working components to two types viz. Cladding system and the support system.

This emphasises the need to re-examine thecontinuity of structures as is the case in R.C.C. Using of continuous beams proves economical but simply supported structures may well prove their worth in the eventual analysis
So, where have we forgotten what we already knew? Instead of reinventing the wheel let us look into our past and try and understand how our forefathers designed and built.

Before that let us glance through what is it that makes a structure vulnerable in earthquakes or cyclones and what are the bare essentials needed to make a structure resistant of these.

EARTHQUAKE / CYCLONE RESISTANT FEATURES IN CONSTRUCTION
An earthquake subjects any structure on ground to horizontal movements whereas a cyclone, apart from high lateral forces, also subjects the building to uplift.The structures therefore should be able to withstand these forces of average magnitude. In cases of higher intensity disasters (as in case in Gujrat) they should be able to resist these distructive forces till the time its inhabitants are safely out of them.What is critical is the behaviour of the entire structure as one. For it not to collapse all the elements of a structure (walls, roof, columns, beams, doors, windows etc) should behave as one, when subjected to these forces

And therefore what is important are the junction details, places where two different materials or elements meet each other. A collapse occurs wherever the joint splits.

To get an idea about the above-, we go through the common damages during disasters:
1. Corner splaying
2. Buckling of walls
3. Diagonal cracks in the wall
4. Diagonal cracks from corners of openings
5. Cracks wherever material change was observed
6. De-lamination of plaster
7. Walls giving away because of roof load in a load bearing structure

A closer look at all the above problems reveals the incorporation of two or more materials / technologies / elements. e.g.

During Cyclones, the various components of buildings such as boundary walls, electric polls etc are severely damaged owing to uplift. This happens due to very high suctions and pressure exerted by high velocity winds

Types of damamges

• Roof sheets or tile fly off.
• Joints and connections are broken.
• Anchorage of roof gets broken and whole roofs fly off.
• Frames collapse due to jointing failures.
• Even entire timber houses are lifted off.

Thus the main cause of damages as observed are:
1. Asymmetrical volumes both in plan and elevation
2. Non performance of the structure as one

Let us briefly go through some case studies to understand the relevance of our traditional knowledge related to disaster resistance.
Also we should try and see how they can lead us to try and evolve innovative concepts for disaster resistant structures.

CONTINUE.....

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