Monday, December 19, 2011

An Arch Never Sleeps. Part 2

A gothic arch was built next, a revolutionary shape in its efficiency, following more closely the catenary shape of the invisible force of gravity. The gothic arch changed everything, walls became thinner and opened up allowing light more light in. The audience were advised to go to Christchurch Cathedral in Dublin and see how in the 12th century they started to build Romanesque with semi-circular arches but then during the course of the building changed to the pointed  gothic arch.

Since Roman times lime mortar was very much a part of arch building and is one reason why so many arches still survive. Why? because lime allows movement; the arch barrel of the bridge moves with traffic and expands and contracts with changes in temperature but these movements mostly occur in the lime mortar joints and not in the stones themselves otherwise they would crack and fail.
Next a segmental arch was built in brick and lime mortar. This is another common arch but it often hides away where we cannot see it behind plasters and renders relieving or taking the weight that would otherwise be applied to the timber lintel underneath.

Lastly a single light round headed window was built with a cill, two sides and a lintel having a semi-circular arch shape cut in it. Not an arch at all but simply an arch shape, beautiful and commonly seen in Irish medieval architecture. Finally the lintel was swapped for an ogee arch shaped lintel to reflect an arch shape common in the 15th and 16th centuries.

If the world was abandoned for a millennium I doubt we would find many surviving examples of modern buildings, the steel would have rusted and destroyed the concrete and anyway very few buildings today are designed to last much more than half a century. Amongst the thick undergrowth stone and lime mortar structures would be found that are historic even in today’s terms and a prominent feature of those structures would be the arch, still working, dutiful, tired but never once in a thousand years having fallen asleep.