San
Giovanni Rotondo is one of the most-visited Catholic pilgrimage
destinations in
The
dome is supported by twenty two arches made from local limestone. The
largest
arch is 16 meters high and 50 meters long.
The
geometry of the roof is a combination of a central dilation and a
rotation
about the same center. This
type of surface of revolution, employing both translation and rotation,
is
called a spiral symmetry. Each bay, consisting of an inner and outer
arch, is
rotated 20 degrees and reduced in scale to 96%. Continuity between the
secondary members and the props joining the secondary structure from
bay to bay
is derived from joining corresponding vertices. With a spiral symmetry
geometry
there is no physical repetition of elements. Each bay and every element
within
the bay are a different size. However the bays are geometrically
identical in
all aspects other than scale.
The
design was developed to take advantages of new stonecutting
manufacturing
techniques. The arches are made up from a number of shaped limestone
blocks cut
on a three-axis milling machine. The numerically controlled machine can
cut as
many different shapes as it is programmed to, therefore repetition is
not essential.
Each arch corresponds to its adjacent arch at a scale ratio of 96%. The
secondary structural members in laminated timber are simple straight
elements.
Being a range of section sizes and all of different length is a problem
of site
logistics rather than a problem of manufacturing complexity or cost.
The roof
covering is standing seam copper and as this is material is hand worked
on site
and does not need to follow a rigidly prescribed geometry.
Images Copyright RPBW