Civil Engineering Reference
In-Depth Information
Groined “cross vaulting” was developed in the Graeco-Roman World to pro-
vide for the intersection of two vaults or for the change in direction of a vault.
Additionally its structural virtues became apparent so that the device was used
not only for these purposes but also as a solution in itself to roof a rectangular
(square) space, where it functions in parallel to the dome.
h is may be the occasion to note roof construction involving arches which is
dii cult to classify. Although rib arches did not play a signii cant rôle in stone
cross-vaulting, they appeared in connection with barrel vaults. Here, however,
questions of terminology arise. With early (5th cent BC) instances at Ephyra and
Delos (v Boyd,
diss
, p. 180, i g 14; p. 183, i g 17; also
AJA
82, 1978, pp. 96, 97,
i g 13) and a famous manifestation at the Temple (Fountain House) of Diana at
Nîmes (Robertson, pp. 237-38), examples of this type of construction pass from
the category of vaulting to a type of slab rooi ng. Nonetheless the structural basis
remains the same: a succession of arches (v Besenval, pp. 68-69 for comparative
structural analysis). In the i rst instance the lacunae between the arches is covered
by stone vaulting, so that the more solid arches break the vaulting up into smaller
compartments giving additional (lateral) seating to these compartments, and in
the overall provide a stif ening to the entire vault. h is construction is clearly a
(reinforced) barrel vault. h ere is then the well known construction at Nîmes,
where the bays between the arches are covered by slabs, spanning from one arch
to another. Whether these slabs function in any way as vaulting in themselves is
not clear. h ey are certainly slabs, but slabs carried by arches not beams and thus
have the proi le of a barrel vault. h ere is i nally a type of rooi ng which became
common in the basalt region of Jordan and the Hauran, during Nabataean and
Late Antique times (Robertson, pp. 238-40, 314). Here the arches were built up
at the spandrels to give a horizontal seating for the slabs set between them. h us
the rooi ng is a l at slabbed roof, and can not be considered vaulting.
Since consideration has been returned to the barrel vault, a i nal development
in this connection may be mentioned. h e passages and corridors in buildings of
public assembly (theatres, amphitheatres etc.) were very clearly an important factor
in the development of barrel vaulting. Moreover in the functional nature of such
buildings these passages were frequently not horizontal but inclined. h e vaulting
was thus rooi ng to stairways (and equally support for stairways above). h ere were
two solutions to this problem: to build the barrel vaults as a stepped succession
of horizontal vaults (stepped vaulting) or to build the vaulting continuous on the
incline (ramped vaulting). Both solutions were adopted, the simpler construction
of stepped vaulting being more commonly preferred.
Arcuated
stone
rooi ng—
rib arches
278, 279
414
273
273
274
