Civil Engineering Reference
In-Depth Information
It is the reverse of this state of af airs which is surprising. To roof over in concrete
the expansive halls of monumental public buildings the Roman builders employed
the (hemispherical) dome and the cross vault. When during the i rst century AD
Roman builders constructed domed and cross vaulted concrete rooi ng of ever
larger and larger span, it is popularly assumed that they were always proceeding
on the model of earlier domed and vaulted ashlar masonry construction. However
this is not at all the case. When the Roman builders constructed concrete barrel
vaults they did indeed have the model of Hellenistic ashlar vaulting to guide them.
Such vaulted rooi ng erected on centering was current in the Greek world from
the later 4th century BC onwards—mainly for monumental underground tombs
(cf the Macedonian Royal Tombs at Vergina, v
supra
, pp. 183, 184). However for
the other arcuated forms of rooi ng there was no chronological priority in ashlar
masonry construction (cf R. Mainstone, p. 115). h e earliest surviving ashlar masonry
domes (in Anatolia and in the Levant) are not earlier than the i rst century AD
(v
supra
pp. 189-193). h us ashlar domes are no earlier than Roman concrete
domes (and are much reduced in size). Moreover the lobate dome form (the
umbrella dome, the pumpkin dome) was altogether & novelty of concrete con-
struction. Nothing like it is known in stone or brick masonry. It was, perhaps,
Handrians brain child. As for ashlar cross vaults, the earliest surviving examples
are probably 2nd century AD (from Pergamum, cf Adam, p. 207) whereas cross
vaulted concrete rooi ng appears in Rome during the middle of the 1st century
AD (L.C. Lancaster,
Concrete Vaulted Construction
, p. 106). What the 1st century
AD Roman builders of monumental concrete vaulted rooi ng took from Greek
precedent was not similar structures in ashlar masonry, but familiarity with the
geometry of such forms.
Domes &
Cross
vaults
404-414
C.
Centering and Shuttering
Whatever structural form was adopted by Roman builders for rooi ng large areas,
the basis of the undertaking was the same—the provision of a strong wooden
framing which
Pre-
requisite
carpentry
(1) dei ned the form of the soi te of the concrete rooi ng and
(2) supported the load of the concrete rooi ng until it became a rigid self sup-
porting structure.
Additionally for concrete construction a sheathing of impervious materials was
required immediately below the soi te of the vaulting to prevent the escape of
the liquid content of the concrete while curing. h ese two features, the former
“centering” and the latter “shuttering”, in general are formally and functionally
quite distinct; but in the case of vaulted construction they are conl ated in position,
