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)
(part two tomorrow)
