Civil Engineering Reference
In-Depth Information
Erec-
tion of
columns
by clean
lit ing
In this way the head of the hoist can be brought directly above any position
within the area covered by the tower, so that the drums wherever situated on
the ground can be attached, hoisted alot and then brought directly over the
column emplacement.
No evidence of such a device is known from the ancient world, and its
existence has never been discussed. It is possible, however, that something
like it might have been developed in imperial Roman times.
(2) Moveable jib arm. h is device is now familiar on all construction sites where
powerful cranes with long jibs are in operation. h e jib can be rotated into any
direction and the lit can be moved outwards or inwards any distance up to
the length of the jib. Such a device may have been available in ancient times,
with a wooden jib controlled by ropes. h e limitation here is the strength of
the wooden jib to resist the bending moment of a heavy load on a long arm.
(3) Attachment to multiple hoisting units. A scaf olded tower is arranged to
cover the area of the operation and at the top of the tower several hoists
can be positioned so that the drum can be lit ed by one hoist to a convenient
height, then attached to the other hoist, and by dif erential control of the hoists,
the drum can be brought vertically above the column emplacement. Such a
device could have been arranged in antiquity. Skilful control of the hoists is
necessary, otherwise the load can swing dangerously on occasion.
(4) h ere is also a makeshit proceedure when the load is not great. h e drum can
be lit ed from any convenient position by a hoist, raised to the required height,
then dragged into position above the column emplacmeent by ropes fastened
to it, and then lowered into position by the hoist. h is, at best, is a hit and
miss operation with risk of chipping and jarring. It would not be employed
for heavy loads or positioning i nely dressed masonry.
h is outline can be super-imposed over what is known of ancient Greek and
Roman lifting devices. Representations of these occur in Roman decorative
reliefs (Adam, pp. 46-47, i gs 87-90) and the subject is discussed by Vitruvius
(X.2) and in a treatise by Hero of Alexandria (Mechanicorum fragmenta III ed,
Nix-Schmidt, Leipzig, 1900). Both sources classify lit ing devices according to the
supports or frames to which the hoist (pulley block) is attached—enumerating the
single leg (limb)
monokōlos
; the two legged/biped
dikōlos
; the three legged/tripod
trikōlos
; and the four legged/quadruped
tetrakōlos
. h e discussion indicates that
the
monokōlos
and
dikōlos
devices were stayed in position by auxilliary guy ropes,
so that the lit ing head could be pre-set at a distance from the base of the device,
i.e. directly above a given emplacement. Nowhere, however, does the discussion
clearly indicate arrangements by means of such ropes for changing the position of
88-91
85, 86,
89
