Building an arch

The earliest brick arches were built possibly around the Mesopotamian civilisation, more than 3,000 years ago. Both abroad and in India, we still see arches standing tall, often bereft of the roofs, open to rain and sun, yet lasting for centuries.

19HAB-greensens_19_1851562gIt is strange to see how the horizontal and straight line has come to dominate building construction, especially in lintels, beams and roofs. Most of us may not know that early humans did not create shelters only with the horizontal, instead built sloping roofs, conical forms, domed profiles, arched windows, corbelled projections, vaulted shelters and a range of such forms where there were ideas beyond the horizontal and this continued until a few hundred years ago. Of course there are region-specific exceptions where long timber members or stone lengths were available; however the idea of horizontal lintel and beam has been gaining universal application only for a few centuries.

The simple example to discuss the effectiveness of a curved lintel is to hold a book horizontal and place a weight in the centre – of course it will bend down in the centre, or deflect, as a technical person may explain. If it is held in a curved profile, the same book will take the weight.

Depending upon the type of curve, masonry material, construction skills, strengths of the side walls, columns holding the arch and such others, the clear width of the arch gets decided by expert masons and engineers. The load gets transferred to the sides, enabling a support-free space under the arch.

Free standing

The earliest brick arches were built possibly around the Mesopotamian civilization, more than 3,000 years ago. Both abroad and in India, we still see arches standing tall, often bereft of the roofs, open to rain and sun, yet lasting for centuries. Arch is among the few forms around us that can be free standing unlike a vertical post and horizontal beam which may fall sideways. Hence many gates, bridges and openings in forts were arch shaped.

Unbelievable but true – many hundreds of years ago, many masonry bridges in stone and bricks were built with many hundreds of feet clear width!

Arch performs under a concept termed as load transfer by compressive method, where the weight of the building comes on the arch, trying to push it down, but ends up moving along the curved profile to the edges, creating a side thrust there. Thicker the arch and stronger the side wall, the wider can be the arch with greater load. Accordingly, people in the past used very thick walls; however, with the advent of modern technologies today an arch can be built with steel and cement spanning across thousands of feet.

Most Indian buildings predominantly use masonry materials even today, though concrete and steel buildings are making inroads mainly for larger complexes. With the load bearing wall anyway in place, it makes tremendous sense to support the roof over an arch. Even in a house with RCC framed system, arches can be judiciously introduced at appropriate places to reduce the cost. We only need to re-consider it as a viable option.

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Posted on April 19, 2014, in concepts, designs and tagged . Bookmark the permalink. Leave a comment.

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