Civil Engineering Reference
In-Depth Information
a brief review of stone rooi ng may be presented under two headings: trabeated
rooi ng and arcuated rooi ng.
Trabeated
stone
rooi ng
(a)
Trabeated Rooi ng
h is type of rooi ng was limited to monumental buildings in stone, since the great
load of the massive rooi ng units necessitated very strong supporting masonry. To
all intents it was limited to Megalithic Building (l oruit ca 4,500 BC-2,500 BC in
Western Europe); and to Pharaonic Egyptian Building (l oruit ca 2,500 BC-150
AD)—the former out of rude (or roughly shaped) slabs, and the latter from i nely
dressed masonry.
250-252
253-259
(i) Megalithic Rooi ng
h e characteristic form of Megalithic rooi ng is the rude stone slab supported
by similar slabs as walling (= the Dolmen). h e burden of some Megalithic slabs
is very great, indeed up to 100 tons (e.g. the Mount Brown dolmen in Ireland).
Bearing in mind that dolmens were not as a rule “al fresco” structures but were
the interior component of earth tumuli, the method of construction appears evi-
dent. Earth slopes as starters of the tumulus were heaped around the designated
emplacement of the dolmen. h e wall stones/slabs were then hauled up these slopes
base i rst and slid down into position, to be raised vertical with raw-hide ropes.
Next the chamber was i lled with earth to consolidate the standing stones and the
rooi ng slabs were hauled up the earth slopes and across the i lled chamber to be
set into position capping the wall stones. Finally the chamber was emptied of its
earth i ll and the enveloping earth tumulus completed. (A proceedure which was
essentially that of Egyptian Pharaonic masonry construction in general.) Many
such megalithic structures have survived over the millenia to the present day. And
while many more have collapsed, there is little evidence of the capstones failing in
bending (tension) to break apart and fall. h e reason for this is probably that the
spans involved were restricted (say 3 m or so, in gallery graves). Where greater
spans were involved (e.g. for the circular chambers of passage graves) some form
of corbelling was adopted (cf New Grange in Ireland), but the construction pro-
ceedure remained essentially unchanged).
259
154, 251
252
(ii) Pharaonic Egyptian Rooi ng
Here the rooi ng dif ered from Megalithic rooi ng in two essentials: the blocks
were finely dressed, and the spans required were on occasion considerable,
ca 4 m-7 m. h e lesser spans, e.g. of pylon chambers, were roofed by contiguous
slabs spanning directly from wall to wall. h ese slabs of necessity were of consider-
able depth (verging up to 1 m) to provide the strength in tension to resist the bend-
ing stresses. h e greater spans (e.g. that of Hypostyle Halls) required “double” roofs,
255
257, 258
