Civil Engineering Reference
In-Depth Information
as also for chambers overlain by an enormous burden of stone. h e builders soon
became aware that slab rooi ng was inadequate to bear the massive loads, and
they hit on two devices to deal with the situation: corbelling and the triangular
arch. h ey used both devices either to relieve the load above a slab roof or indeed
in place of slab roofs. Both devices proved ef ective structurally, and accordingly
were adopted in a normal building, signii cantly for circulation passages and
corridors. However they gave a rectilinear aspect: in the i rst instance a series of
steps; in the second an isoceles triangle. Where in a massif these devices roofed a
relieving space above a l at slabbed roof not exposed to general view, their aspect
was acceptable—and evidence of them survives. However where these forms were
exposed to view over apartment generally accessible, a new factor intervened,
appearance not construction.
For Egyptians the rooi ng (more properly the ceiling) of a compartment sym-
bolised the sky. In the normal l at slabbed rooi ng, this symbolism was expressed
by painted decoration, e.g. by stars and the sky Goddess Nut hovering in vul-
ture form. However the exposed stepped or triangular form conl icted with this
symbolism. h e matter was adjusted in both instances by carving the soi te into
a continuous curved form—the sky vault. Finally it would seem during the Late
Period (ca 8th century BC and later) Egyptian builders realised the possibility of
directly constructing vaulted rooi ng by the use of radially set blocks with their
faces dressed in curvilinear form (i.e. voussoirs). h is involved the use of some
form of temporary support (centering) for blocks until the construction was com-
pleted. (Specii c instances of all these stages are conveniently illustrated in Arnold,
pp. 183-201, i gs 4.114-4.143.)
Here may be a convenient juncture to mention a very individual example of
Egyptian stone vaulting that in the small funerary chamber of (the god's wife)
Shepenupets I at Medinet Habu, ca 700 BC. Its radially set voussoirs were in the
form of thin slabs set on end so as to comprise a series of arches. h ese arches of
conventional (paraboloid) proi le, however, were not set vertically but were inclined
slightly backward to rest against the upstanding rear wall of the chamber. h is
technique was exactly that of “pitched” vaulting in mud brick which avoided the
necessity of centering by a combination of friction plus quick setting mortar. It is
dii cult, however, to see what structural advantage was aimed at in its use with
i nely dressed stone masonry. Perhaps it was thought that the inclination placed
the voussoirs in some horizontal compression which better held the i nished con-
struction in place (v Wesenberg, i g 6).
h e above discussion of Egyptian rooi ng may seem sui cient to account for
the origin and development of radial stone vaulting in general—however it is
doubtful that it is the complete story in itself. In the i rst instance all the examples
of Egyptian stone vaulting are of very restricted span—two to three metres only.
Arcuated
stone
rooi ng—
Egyptian
vaults
261
262
354, 355,
371
