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Description  |
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TECHNICAL SCOPE
The present invention relates to a cassette made of thin sheet or a similar
material which is intended to constitute a lost form when casting concrete
framework while co-operating with the concrete in the finished framework
in the absorption of forces.
BACKGROUND TECHNOLOGY
It has previously been known how to cast framework with the aid of an
integral form consisting of cassettes arranged next to one another,
whereby the underside of the form constitutes a complete ceiling in the
room under the framework. Such a cassette consists of a U-shaped,
longitudinal unit of thin steel sheet comprising a rectangular bottom with
an edge beam section extending along its respective two parallel
longitudinal sides, substantially at a right angle to the bottom on the
side which is to be turned up. The said edge beam section comprises both a
web rising at a right angle from the bottom and at its upper edge a flange
extending at a right angle away from the web and towards the centre on one
side of the cassette and away from the centre on its other side. This
imparts to the cross-section of the edge beam section a shape enabling
adjacent cassettes to be hooked into one another so as to form a
continuous framework. The flanges are at their free edges provided with a
support edge facing downward, which ensures additional stability and
prevents two adjacent units from sliding apart during the casting process.
When casting a framework with the known cassettes by way of a form, their
ends are made to rest on the shell of the building, which may consist of a
steel shell, temporary support beams resting on temporary piles supporting
it along its length. The cassettes in the form are hooked to one another
in sequence until the entire area of the framework has been covered. Once
the adjacent webs have been joined for instance with the aid of rivets the
concrete is applied.
The webs of the edge beam section are provided with holes and aligned with
one another in two adjacent edge beam sections, as a result of which the
concrete forms a connection along the length of the beams.
The cassettes are subject to tensile forces acting in their plane both
during casting and after hardening and loading of the concrete. It is
therefore important that the cassettes should be joined with great
accuracy. This has proved to be difficult with previously known designs.
Apart from a reduced capacity to absorb such tensile stresses the
cassettes had a tendency to separate owing to indentations about the rivet
heads but also because the fasteners were located too far from the
undersides of the cassettes. Furthermore, if a fire broke out, the edge
beam sections used also to be in part directly exposed to heat, which is
normally not permissible, unless special measures were taken.
Nor are these designs proof against the escape of unbound concrete water
while the concrete is being cast, such water being able to flow down on
the undersides of the cassettes causing such disfigurations that costly
measures could not be avoided.
SUMMARY OF INVENTION
The present invention is intended to provide a framework cassette without
any of the disadvantages of the known cassettes, which is easier to
install and to join and can also be made sound absorbent instead of being
a source for echos. The object has been achieved by the present invention
relating to a framework cassette which comprises a preferably rectangular
bottom, with an edge beam section extending along its respective two
parallel sides, the web thereof being substantially perpendicular to the
bottom and whereby the respective edge reinforcement has a cross-section
substantially identical with that of a shelf at a slightly higher point on
the web. The primary tensile reinforcement consists of the cassette but
the invention is also characterised by the fact that an additional section
can be provided capable of constituting a tensile reinforcement especially
in the transverse direction or constituting an economy device with a view
to reducing the amount of concrete, creating space for larger
installations and having curves in the web projections, susequently
referred to as bulges, so as to bring about a shear connection between the
concrete and the sheet while acting as a reinforcement for flat surfaces
of the web.
The invention is described in greater detail in the subsequent paragraphs,
in the claims and in the attached figures.
DESCRIPTION OF THE DRAWINGS
FIG. 1 showing cassettes in accordance with the invention and resting on a
shell,
FIG. 2 showing a cross-section of the cassettes casting concrete,
FIG. 3 showing a cross-section of the cassettes casting concrete and with
an economy device inserted, and
FIG. 4 showing edge beam sections before and after joining.
DETAILED DESCRIPTION OF INVENTION
The said edge beam section, 2, comprises both a web, 3, and a flange, 5, at
its upper edge as well as a shelf, 6, at a base point of the web, 3,
whereby the flange, 5, and the shelf, 6, extend at right angles away from
the web, 3, shelf 6 towards the centre, 10, of one side of the cassette,
1, and flange 5 away from the centre, 10, on its other side. The
cross-section of the edge beam section, 2, makes it possible as a result
for adjacent cassettes, 1, to be hooked to one another to bring about a
cohesive and tight concrete form. At least the flange, 5, which is facing
away from the centre, 10, of the cassette is at its free edge provided
with an edge reinforcement, 7, facing towards the edge plane, whereby a
reinforcement of the joints between two adjacent cassettes, 1, is
achieved. The said web, 3, also comprises projections or bulges, 8, facing
towards the centre, 10, of the cassette, 1, and constituting the main link
between the cassette, 1, and the concrete cast in the cassette, 1. The
bulges, 8, reinforce also the plane areas of the web, 3, so as to reduce
any danger of buckling.
To the cassette may also be added a rectangular top section, 9, intended
for placing between the shelves, 6, and covering the space between the
webs, 3, of the cassette. One side thereof is curved downward and partly
backward and up. The height of the curved part, 12, is prior to mounting
somewhat larger than the distance between the underside of the shelf, 6,
and the upper side of bottom, 11, of the cassette. For in the course of
mounting the curved part, 12, has to be inserted under the shelf, 6, being
resiliently pressed together to some extent so as to join tightly to the
underside of the shelf, 6, the edge beam section, 2, and the bottom, 11,
of the cassette. The opposite side of the top section, 9, is bent up at a
right angle and should after mounting in the cassette, 1, follow the side
of the web, 3, upward to the lower row of bulges, 8, terminating in an
edge bent obliquely inward and upward, i.e. the snap edge, 13, which
advantageously snaps fast under the undersides of the bulges, 8. The top
section, 9, can be designed either with a substantially flat top surface,
17, which after assembly extends between both webs, 3, of the cassette, 1,
or it may have an upward bulging top surface, 18. When casting the
concrete it is intended for the top section, 9, to close off the web, 3,
and the bottom, 11, of cassette, 1, so as to create a cavity below the top
section, 9. The bottom, 11, of the cassette can for instance be perforated
through the enclosure so as to achieve a sound-damping effect. The cavity
between the bottom, 11, of the cassette and the top section, 9, is
advantageously utilised for requisite sound-insulating mats, electricity
and heat and ventilation lines etc. If the top section, 9, is made with a
flat surface, 17, between the webs, 3, of the cassette, 1, the top
section, 9, also acts as a tensile reinforcement in the direction
transverse to the longitudinal direction of the cassette, 1. If the upper
surface of the cassette, 1, is bent upward, 18, the top section's, 9,
capacity to absorb tensile forces is lost but on the other hand space is
gained for installations and a lot of concrete is saved, thus above all
reducing its weight. The main function of the concrete consists after all
in absorbing the pressure loads in the upper sections of the framework and
in forming a surface.
When assembling framework cassettes, 1, in order to cast a framework the
said cassette, 1, is hooked to the preceding one so that the edge
reinforcement, 7, of the upper flange, 5, grips the free edge of the
flange below, 5, as a result of which the respective positions of the
cassettes, 1, are fixed. Any pipes and lines as well as sound-absorbent
mats, 14, are now placed on the bottom, 11, of the cassette, whereupon the
curved part, 12, of the top section, 9, is inserted into the recess below
one shelf, 6, and fixed to shelf, 6, of the opposite web, 3. The top
sections, 9, are secured on the one hand to the horizontal surfaces of the
shelves, 6, and on the other hand to the top sections, 9, of adjacent
cassettes by means of self-cutting and self-tapping screws or possibly
rivets fitted vertically through the shelves, 6, of the said web and two
top sections, 9, on the upper or lower side of the shelf, 6. When the top
section, 9, is exposed to tensile stresses at a right angle to the
longitudinal direction of the edge beam sections, 2, the joint absorbs
this stress as a shear stress acting on the fastener. This inter alia
means that no indentations are formed about the heads in the sheet. As a
result of the arrangement where the webs, 3, and the flanges, 9, are
facing the same direction, room is made for modern assembly tools required
to bring about the vertical joints. It is advantageous to locate the
shelves, 6, at as low a level as possible since, inter alia, projecting
parts of the joint actively take part in the co-operation between the
concrete and the cassettes, 1. A disadvantage of having the shelf, 6, and
the flange, 5, facing in the same direction consists in the fact that the
web, 3, tends to be deflected in that direction and subjected to loading.
This can be avoided by inclining the web, 2, of the cassettes, 1, the
shelf, 6, and flange, 5, of which are located uppermost during assembly,
towards the centre, 10, of the cassette, so that the web, 3, forms an
angle of 70.degree.-89.degree. with the bottom, 11, of the cassette, see
left-hand illustrations in FIG. 4. When the adjacent webs, 3, are joined,
see right-hand illustration in FIG. 4, the assembly is inclined. In the
loaded state the assembly tends to turn in the opposite direction. As a
result the bending resistance of the cassette increases when it is loaded
during the casting process since the controlled bending axis coincides
with the main axis of inertia of the edge beam section, 2.
As a result an otherwise accelerating stress characteristic is obviated
when bending a cassette, 1.
When joining the webs, 3, the bottoms, 11, of the cassettes are bent
slightly upward thus compensating any downward bend when they are loaded
with concrete or if top sections, 9, are used for installations, etc. With
a view to reducing the danger of the bottom, 11, of the cassette buckling,
the latter can be provided with grooves, 19. If required the cassette can
also be made sound-absorbent by providing its bottom with a dense pattern
of holes, preferably also filling the space next to the bottom with an
insulating material, 14, such as mineral wool. The insulation can be so
selected as to ensure fire protection of the cast framework.
Having completed the assembly of the cassettes, 1, a layer of concrete is
poured over the cassettes, 1. After hardening of the concrete a
construction results, which is characterised by high carrying capacity. As
a result of this design, which causes the joints between the cassettes to
be tightly sealed, adjacent webs, 3, are pressed against one another when
they are loaded by the flowing concrete, whereas with previous
conventional designs where holes were provided to join the webs there was
a tendency for the webs to be pressed apart owing to internal excess
pressure on the part of the concrete water.
The cassette, 1, forms a tensile reinforcement in the construction as
regards bending perpendicularly to the longitudinal direction of the
cassette, 1. The top section, 9, constitutes a tensile reinforcement as
regards bending parallel to the longitudinal direction of the cassette, 1,
and this tensile reinforcement is largely retained even in case of a fire.
The bulges, 8, engaging one another and acting as dowels bring about very
good shear connection between the cassette, 1, and the concrete. With this
design there is practically no danger of shear failure in the shear joint.
With correct assembly the casting form will be completely tight. There are
no holes in the web causing the concrete water to run out in the joints
between the reinforcements, and the load exerted by the concrete
compresses adjacent reinforcements, not as used to be the case with
previous designs tending to separate them.
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Description |
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