Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This inventlon relates to drop-head units for supporting
shuttering members used in the construction of concrete
floors and/or ceilings.
A drop-head which is normally used at the top of a
scaffold member is used to support shuttering members in two
main positions, an upper position in which concrete (or other
settable material) is cast onto the shuttering members, and
a lower position in which the shuttering members are lowered
to be stripped from partially set concrete and then removed
from the drop-head for use elsewhere. The partially set
concrete slab is then supported by spaced fixed head plates
of the drop-head units.
A drop-head unit in accordance with the invention
comprises a shank having a fixed head at one end and the
other end being adapted for connection with a standard
scaffold prop or the like, a drop-head slidably mounted on
the shank and movable between a supporting position adjacent
the fixed head and a "strip" position in which it is spaced
from the fixed head, characterized in that the shank is
provided with a slot extending along its length between the
supporting and fixed positions of the drop-head and a wedge
member movable along the length of the slot between its
supporting position in which a ledge formed on one or both
sides of the wedge engages a shoulder (or shoulders) formed
at one (or both~ sides of the slot to support the drop-head
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in its supporting position and its strip position,, wedge
movement between the supporting and strip position being
enabled by withdrawing the ledge(s3 from the shoulder(s),
means bein~ provided to hold the memher captive
in the slot and to correctly position the drop-head in
its supporting position relative to the fixed head.
In an aspect of the invention a formwork system for
supporting concrete(or other settable material) during
setting on a casting surface comprises a plurality of beams
which in use span horizontally between and are supported by
drop-head units, a plurality of casting panels supported by
the beams and/or drop-head units, wherein each drop-head
unit comprises a shank having a fixed head at one end and
the other end being adapted for connection with a standard
scaffold prop or the like, a drop-head which supports the
beams and/or casting panels slidably mounted on the shank
and movable between a supporting position adjacent the fixed
head and a "strip" position in which it is spaced from the
fixed head, characterized in that the shank is provided with
a slot extending along its length between the supporting and
fixed positions of the drop-head and a wedge member movable
along the length of the slot between its supporting position
in which a ledge formed on one or both sides of the wedge
engages a shoulder (or shoulders~ formed at one (or both)
sides of the slot to support the drop-head in its supporting
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position and its strip position, wedge movement between the
supporting and strip position being enabled by with~
drawing the ledge (s) from the shoulder(s~, the wedge
member having means to hold the member captive in the
slot and the slot being provided with a stop correctly
to position the drop-head in its supporting position
relative to the fixed head so that beams and/or drop~
heads support casting panels to provide a flush casting
surface.
Preferably, the wedge surface of the wedge member
engages a corresponding surface on the drop~head~
The distance between the supporting surface of
the drop-head when in its supporting position and the
fixed head, is preferably equal to the distance between
the top of a beam to be supported by the drop head, and
its support means.
The shank is preferably rectangular in cross-
section and the drop-head preferably has a plate depending
therefrom extending at right angles to the shank and formed
with a lower wedge surface to engage the wedge surface of
the wedge member.
When the drop-head is held by the wedge member in
its supporting position and is to be moved to its strip
position, the wedge is tapered in the direction to lower
the drop-head slightly before the ledges on the wedge
member moves clear of the shoulders so that an initial
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gradual strip of the concrete formwork panels takes place
before the beams and panels are dropped rapidly to the strip
position. Thls helps to reduce stock loads on the partially
set concrete slab and also relieves the wedge member of the
load of the cast concrete.
The drop-head is preferably provided with a member
which also engages in the slot in the shank.
Preferably the means to hold the wedge member
captive in its supporting position comprises a first stop
mounted at one end of the wedge member and a second stop
mounted at the other end of the wedge member such that the
member is held captive in the slot when the Irop-head is
in its supporting or strip positions, and also when the
drop-head unit is in use or in storage or being transferred
from building site to building site. The means on or in
the slot correctly positions the drop-head in its supporting
position such that beams or the drop-heads support casting
panels to provide a flush casting surface.
The invention will now be described, by way of example,
with reference to the accompanying drawings in which:-
Figure 1 is a perspective view of one embodimentof drop-head according to the invention in its support
posltion,
Figure 2 is a corresponding side view of the drop-
head, and
Figure 3 is a side view of the drop-head in the lower
or strip position.
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The drop-head unit 10 shown in the drawings
comprises a rectanyular central shank 12 having a fixed -
upper head 14 and a lower plate 16 for connection
to a standard scaffold prop.
~ drop-head 18 is mounted on the shank for
sliding movement between an upper"supporting"position
in which it is located adjacent the fixed head 14 (see
Figures 1 and 2) and a lower "strip" position as seen
in Figure 3.
The shank is provided with a slot 20 which
extends along the length thereof between the fixed head
and a position adjacent the lower plate 16. A wedge
member generally indicated at 22 is held captive within
the slot whilst being free to slide up and down the
slot between a supporting position as shown in Figures
: . 1 and 2 and strip position shown in Figure 3.
In the supporting position a ledge 24 which
is provided on each side oi the wedge member,engages
against a shoulder 26 cut out in each side of the slot
as can clearly be seen in Figure 1. When in this position
the wedge member is prevented from sliding down the
slot and its upper wedge or tapering surface 28 is
engaged agalnst a corresponding tapered surface 30 formed
on the lower edge of a plate 32 extending through the
. 25
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slot transversely to the shank and forming part of the drop-
head 18. It will thus be appreciated that the drop-head is
held fixed in its upper supporting position.
When in this position beams, such as that illustrated
at 33 which engage on upstanding knib 34 on the drop-head so
as to be supported, thereby span between adjacent units with
the top surfaces 35 of the beams flush with the top surface
of the fixed heads 14 of the drop-head units. Formwork
panels 36 are supported either by the upper surfaces 56 of
beams 37, by ledges 52 of beams 33 or by drop-heads 18.
Various alternative arrangements of beams 33, 37 and panels
36 are described in co-pending British Application No.
8117524.
A cut-out 54 is provided in the top surface of
the web to receive a pin, nail or the like to lock the
wedge in the supporting position during casting.
A concrete slab 38 (see Figures 2 and 3) is then
cast over the panels, the top surfaces of which are flush
with the top surfaces of the beams 33 and fixed heads, to
produce a unitary slab.
~ hen the concrete slab is partially set the drop-
heads are lowered resulting in the lowering of the beams
33, 37 and panels 36 leaving the partially set concrete
- slab supported (as shown in Figure 3) by the fixed heads
14 of the drop-head units. The beams and panels can then
be re-used elsewhere.
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In order for the drop-heads to be lowered on the
shanks the wedge members 22 are moved to the right (as shown
in the drawings). ~uring this movement the drop-head moves
gradually down due to the tapering of the corresponding
surfaces 28 and 30 of the wedge member 22 and plate 32.
This means that the initial strip of formwork panels and
beams from the concrete is gradual which helps to avoid
shock loads and the wedge is relieved of the load of the
concrete.
Once the wedge member is moved to the positlon
shown in Figure 3 in which the ledges 24, which only extend
partially along the length of each side of the wedge member,
are clear of the shoulders 26 in the slot, the wedge member
is free to fall down the slot thus enabling the drop-head
and the beams and panels supported thereby, also to drop
down the slot to the strip position shown in Figure 3.
The wedge member 22 is further provided with means
to hold the member captive in the slot 20. This means
comprises a first stop 40 at the smaller end of the member
22 and a second stop 50 at the larger end. These two stops
40 and 50 prevent any possibility of the wedge being lost
either when the drop-head 18 is in its supporting or strip
position, or when the drop-head unit 10 is in use, in storage,
or being transferred from one position to another.
A stop 51 is positioned on the shank 12 in slot 20
such that when the drop-head is in its supporting position the
stop 51 engages the upper face of the head 18 (see Figllre 2?, the
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upper surface 35 of the beam 33 and top surface of the panel 36
are automatically flush with the upper surface of the head 14.
Accordingly a flush casting surface is achieved simply and
efficiently by knocking the wedge member 22 along the ledges
24 until the stop 51 contacts the head 18.
The plate 30 attached to the drop-head is provided with
two projecting pins 42 on each side which engage the sides
of the shank to help to provide rigidity and to prevent the
drop-head twisting relative to the shank. The drop-head
is further provided with two downward projecting flanges
43 attached to two edges of the plate 30 to provide rigidity
to the plate 30.
In accordance with standard practice the drop-head
unit 10 may either be supported on the top plate of a
standard prop which may be bolted to the plate 16 of the
drop-head unit, or alternativelv a screwed shank 44 which
extends down fro~ the plate 16 may be engaged by a nut
member formed with a circular hub 46 which fits over the
top of a standard tubular scaffold prop 48. This enabies
height of the top plate 14 of the drop-head unit to be
adjusted relatively to the prop, for alignment and to ensure
that the surfaces of the top plate 14 and of the beams 33
and panels 36 are at the desired level.
