Sunday, December 18, 2011

An Arch Never Sleeps Part 1

An article sent to me by my good friend Patrick McAfee (shown here in the photo)

Building Limes Forum Ireland (BLFI) in conjunction with Drimnagh Castle, Dublin ran a Heritage Week event over the course of three mornings in August called ‘An Arch Never Sleeps’. The aim was to introduce the general public to the wonderful world of arches having a brief look at their history and then to experience in practice how they were built.

If children were to assist in the building process then the arches or the separate stones (voussoirs) in the arches had to be light in weight.  It was either build mini-arches using stone or use a lightweight material and build full scale. Quinnlite blocks were selected; these are lightweight and easily cut to shape using traditional stonecutting tools.

The expression ‘an arch never sleeps’ is attributed to the Arab world and beautifully sums up what an arch does, it safely transfers its own weight and applied forces down its sides, it is therefore ‘alive’ dynamic, relentlessly working.

Facing each days audience were the many arch shapes of Drimnagh Castle itself. As one member of the audience said ‘It is only when you really look that you see arches everywhere’, this is equally true of our cities, towns and villages.

The limitations of the beam was explained and demonstrated by Lisa Edden, a structural engineer and member of BLFI. The problem with the stone lintel Lisa explained is that it is weak in tension. The magic of the arch is that it eliminates this weakness, it has no tension, just compression and this is where stone is at its strongest. Further explanation of how forces run down an arch was explained by holding a rope between her two hands forming an inverted curve called a catenary arch displaying the shape of these forces.

Pat McAfee, stonemason and also a member of BLFI started with the building of a semi-circular arch. The semi-circular arch was beloved of the Romans and used extensively by them throughout their empire. It has been popular here in Ireland from at least the Romanesque period of architecture.

Each day a young volunteer/s from the audience came forward to assist with building the arches. When the final stone of each arch (keystone) was laid and the timber centre removed the arch came alive, it was as if suddenly something magic had occurred and it had, not only in the eyes of the young helpers but also amongst the adults in the audience. Something taken for granted and not thought about until now became something to think and marvel about. The response from the audience was always the same, spontaneous applause, with the young helper/s taking a bow. 

(part two tomorrow)

1 comment:

  1. Shameless self promotion: please check out my post on stone arches for more examples- I enjoy your blog especially when you get technical. Thanks.