Note: Descriptions are shown in the official language in which they were submitted.
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True translation of PCT/DE2008/000928 as filed on June 03, 2008
SP09248US(PCT)
GIRDER ELEMENT FOR CONCRETE FORMWORK COMPRISING A
STRUCTURE FOR AUTOMATICALLY COMPENSATING BENDING STRAINS
The invention relates to a girder element for a concrete formwork, in
particular a ceiling girder element, having a girder for accepting external
forces, a traction band, which runs behind the girder, and at least one
length-adjustable tensioning device, which is situated between the girder
and traction band, using which the local spacing between the girder and
traction band is settable.
Such a girder element is known, for example, from the brochure "Column
Hung System" of HI-LITE Systems, division of JASCO Sales Inc.,
Mississauga, Ontario, Canada, 2001.
Formwork technology is frequently used for manufacturing buildings. A
building structure to be manufactured, such as a wall, column, or ceiling,
has formwork elements built around it ("erecting formwork") and is filled
with liquid concrete. The concrete is subsequently permitted to harden.
The formwork elements, which have a formwork skin subjected directly
to the liquid concrete, have a girder construction built behind them,
which keeps the formwork elements in a desired position. A girder
construction typically comprises a plurality of girder elements, which are
partially fixedly connected to one another (longitudinal girders and
crossbeams), and are partially fastened or supported on fixed structures
(such as already finished building parts, for example, a story column or a
story floor).
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Girder elements can be deformed by the intrinsic weight of girder
elements, and above all by the weight of further girder elements and
liquid concrete resting or pressing thereon. Deformed girder structures
fundamentally result in undesired dimensional deviations of the
manufactured concrete structure from the desired concrete structure.
An example in this regard: during manufacturing of a story ceiling having
an area of 10 m x 10 m in formwork technology, weights of
approximately 10 tons for the formwork and approximately 75 tons for
liquid concrete typically occur. Upon fastening of the girder structure to
four corner story columns, with typical girder elements, a sag of
approximately 7 cm occurs under load.
Through a sufficiently large number, i.e., density, of fastening and
support points, deformations in the girder construction may be reduced.
However, a high density of support points is associated with a high outlay
for work and material during construction of the formwork. Furthermore,
adequately solid structures for supporting or fastening a girder
construction are simply not available to a sufficient extent for many
concrete structures to be manufactured. For example, during
manufacturing of story ceilings, the manufacturing of the next higher
story ceiling is often already to have begun before the story ceiling
underneath is completely hardened; the next higher story ceiling and/or
the girder construction thereof must then exclusively be fastened to
already hardened story columns.
In order to be able to construct a desired concrete structure, even with a
low density of fastening and support points of a girder construction, the
most rigid possible girder elements are used. Girder elements for a
ceiling formwork construction are known from the cited brochure
"Column Hung System", which have a framework-like frame having two
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parallel chords and partially inclined spokes running between the chords.
The upper chord is used as the support for other girder elements and/or
formwork girders and formwork elements. A traction band runs below the
lower chord. A tensioning device is situated between the lower chord and
the traction band (trussed framework girders). These known girder
elements are very rigid, but are very heavy and are therefore difficult to
handle on the construction site and are expensive to produce because of
the large steel consumption. In addition, the deformation problems can
be reduced, but not completely eliminated using these girder elements.
Attempts have also been made to initially calculate the bending
deformation of girder elements under the expected load. The girder
elements are prepared (for example, using cambering brackets) so that
without load they have a curvature which is initially undesired for the
structure to be manufactured, but a desirable shape for the concrete
structure to be manufactured results under load. However, prior
calculation of the bending deformation is time-consuming and difficult
and must be performed for each concrete structure to be manufactured
and also individually and newly for each girder element. A specially
prepared girder element is typically only usable for a single concrete
structure to be manufactured at a specific point of the girder
construction. Furthermore, maintaining the desired ceiling thickness is
difficult, because the formwork sag changes during the concrete casting
procedure.
Object of the Invention
It is the object of the present invention to propose a girder element with
which arbitrary concrete structures may be exactly and cost-effectively
manufactured.
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Brief Description of the Invention
This object is achieved by a girder element of the type above-mentioned
type which is characterized in that the length-adjustable tensioning
device is implemented as a length-adjustable compensation device
having a motorized drive for setting the length of the compensation
device and a measuring unit is provided, by which the position of the
girder in the area of the compensation device relative to a target position
can be determined, and with a control unit by which the length of the
compensation device can be regulated as a function of the position of the
girder.
It is the fundamental idea of the present invention to also determine and
set the shape of a girder element, and in particular the curvature of the
girder of the girder element, through a length-adjustable compensation
device. The length of the compensation device is selected in dependence
on the external forces which act on the girder so that the desired shape
(typically a linear shape) of the girder results. According to the invention,
the length of the compensation device can also be set under load by the
motorized drive, in particular readjusted.
The girder has a (typically linear) front side, upper which the external
forces can act. For example, other girder elements or formwork girders
rest or press on this front side. A traction band runs above the opposite
side of the girder, typically slightly inclined with respect to the girder.
The
outer ends of the traction band and girder are typically connected to one
another; the outer ends of the girder are typically also fastened on fixed
structures. There is usually a further connection between the girder and
traction band at the compensation device. The traction band is under
tensile stress, while the girder and optionally further compression rods
are under compressive stress. If an external force acts on the girder,
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which attempts to deform it (push-in), a spreading force can be exerted
between the girder and the traction band using the compensation device,
which keeps the girder in the present shape. The compensation device
causes a redistribution of the elastic deformation in the girder element
under load, namely from the girder to the traction band.
The deformation of the girder by external forces, such as the weight force
of liquid concrete, and also by the intrinsic weight of the girder element,
thus has a superimposed deformation of the girder by the compensation
device. The shape of the girder is monitored in that a measured actual
position of the girder is compared to a target position. The target position
of the girder is predetermined absolutely by the concrete structure to be
constructed; the actual position of the girder, in contrast, is a function of
the applied load, the intrinsic weight of the girder element, and the
length setting of the compensation device. A measuring unit is used to
determine the position of the girder and relays its measuring results
(typically in electronic form) to a control unit (also usually electronic). If
the actual position of the girder deviates from the target position, a
length change of the compensation device is activated to bring the girder
closer to its target position. The girder can always be kept at the target
position completely automatically by continuous regulation.
A desired shape of the girder of the girder element can be maintained at
fundamentally arbitrary loads by setting the shape of the girder using a
measuring and regulation system. Prior calculations of the load are not
necessary (within a maximum strain of the girder element). The girder
element does not have to be particularly rigid as a whole, because a
deformation of the girder is prevented by the length-adjustable
compensation device. The girder element according to the invention can
thus be relatively light and have little material, whereby it is easy to
handle during the construction and teardown of formwork. In comparison
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to typical girder elements, weight reductions of up to 50% may be
achieved.
It is typically sufficient to describe the formwork deformation of a girder
by the position of one measuring point of the girder and to compensate
for the deformation of the girder using one compensation device (per
girder element). However, multiple measuring points and/or multiple
compensation devices per girder/girder element may also be provided
within the context of the invention in order to increase the compensation
precision. One measuring point is then preferably provided for each
compensation device. A measuring point is preferably as close as possible
on the girder/girder element to the associated compensation device.
An additional advantage of a girder element according to the invention is
simplified stripping of formwork elements. The girder element can be
lowered and/or retracted by actuating the compensation device (lowering
the pressure).
It is typically sufficient within the context of the invention, if the length-
adjustable compensation device can build up pressure (for example, can
apply a spreading force between girder and traction band) in one
direction (piston side), for example, a plunger cylinder can be used here.
However, in specific cases, double-acting cylinders can also be useful, for
example, for compensation of deformations of taller formwork in strong
wind.
Preferred Embodiments of the Invention
In a preferred embodiment of the girder element according to the
invention, the motorized drive comprises an electric drive, in particular a
linear motor. Such a drive is simple and easy to maintain.
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In an alternative embodiment, which is also preferred, the motorized
drive comprises a hydraulic drive or a pneumatic drive. Particularly large
forces may be applied using a hydraulic drive. Water and oil can
preferably by used as hydraulic media, Water does not cause any
damage on the construction site in the event of leaks. Typical high-
pressure cleaning devices (and/or the assemblies thereof) can be used
for providing and maintaining pressure with water because of the slow
pace of deformation pathways during concrete casting. A joint provision
of pressure for a plurality of compensation devices, in particular also of
various girder elements, can be performed with hydraulic or pneumatic
drives; the force regulation at the individual compensation devices is
performed by locally controllable valves, either in the supply lines of the
compensation devices or directly at the particular compensation device.
It is to be noted that the motorized drive can comprise a mechanical
adjustment unit (for example, having gear wheels, spindles, or wedges),
which is driven by the motorized drive.
An embodiment is also preferred in which the measuring unit comprises a
spacer bar or a cable having a deflection roller and ballast or a laser
distance meter. A spacer bar and a cable having ballast are very simple
measuring units. A laser distance meter is particularly simple to install.
An embodiment of a girder element according to the invention in which
the compensation device is length-adjustable in a direction which extends
essentially perpendicular to the girder is particularly preferred. This
ensures effective and uniform force introduction into the girder.
In another preferred embodiment, the girder element has fasteners for
the girder element at two opposing ends of the girder, in particular for
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fastening on story columns. This embodiment is suitable above all for
ceiling formwork, with greater distances (typically 7 m to 10 m) being
spanned by a girder construction. In this embodiment, no further
fastening or support points are provided except at the opposing ends of
the girder. Alternatively, the fasteners may also be implemented for
fastening on other girders.
An embodiment in which the girder is implemented as telescoping is very
particularly preferred. The girder element can thus be set to a length to
be spanned.
An embodiment which provides that the girder has fasteners for fastening
a plurality of formwork girders on the girder is also preferred. This
increases the safety of the overall construction.
In another advantageous embodiment, multiple length-adjustable
compensation devices are provided, which are distributed over the length
of the girder. A more precise compensation of a deformation of the girder
can thus be achieved, in particular if an asymmetrical deformation (for
example, with one-sided fastening of the girder element) is to be
compensated for. Each compensation device preferably has a separate
measuring and control unit. Furthermore, an essentially uniform
distribution of the compensation devices over the girder element is
preferred.
An embodiment is also advantageous in which a signal device is
provided, which outputs a warning signal if a limiting value for the
position of the girder is exceeded, in particular an acoustic, optical, or
electronic warning signal. Through the warning signal, in the event of
overload of the compensation device (i.e., deformation compensation is
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not possible or is no longer entirely possible), safety measures may be
initiated.
The use of girder elements according to the invention for constructing
concrete formwork, in particular for implementing ceiling formwork, is
also within the context of the present invention. This concrete formwork
has a high manufacturing precision and, in particular, can be used free of
formwork deformation. Because girder elements of lighter construction
may be used universally, the construction and teardown of the formwork
according to the invention requires little work and is thus cost-effective.
A use of a girder element according to the invention for the continuous
compensation of bending deformations of the girder, a changeable
external force acting on the girder, in particular the external force on the
girder being caused by the weight of concrete, is also within the context
of the present invention.
Further advantages of the invention result from the description and the
drawing. According to the invention, the above-mentioned features and
the features listed hereafter may also be used individually or in multiples
in arbitrary combinations. The embodiments shown and described are not
to be understood as an exhaustive list, rather have exemplary character
for description of the invention.
Drawing and Detailed Description of the Invention
The invention is illustrated in the drawing and is explained in greater
detail on the basis of embodiments. In the figures:
Figure 1 shows a schematic side view of an embodiment of a girder
element according to the invention for a ceiling formwork;
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Figure 2a shows a girder construction for a ceiling formwork having
girder elements according to the invention, in a schematic
perspective view; and
Figure 2b shows the girder construction of Figure 2a with applied
formwork girders and formwork elements, in a schematic
perspective view.
Figure 1 shows an embodiment of a girder element 1 according to the
invention, which is used for the construction of a ceiling formwork
(compare also Figures 2a, 2b in this regard) and is fastened on two story
columns 2, 3. A level, horizontal ceiling is to be manufactured, for
example.
The girder element 1 has an upper girder 4, on the front side 14 of which
(on top in Figure 1), further girder elements or also formwork girders or
formwork elements may be laid and/or fastened (not shown). The girder
4 is preferably implemented as telescoping and comprises one or more
steel profiles, for example. A traction band 5, which is stretched in a V-
shape, runs behind the girder 4 (below the girder 4 in Figure 1). The
traction band 5 is fastened in the middle to a lower end of a length-
adjustable compensation device 6. The outer ends of the traction band 5
are connected via fasteners 7a, 7b to the outer ends of the girder 4. The
traction band 5 (and/or each section of the traction band) is implemented
as a wire cable or as a solid rod and/or as a steel pipe, for example. The
fasteners 7a, 7b are additionally also connected to one another using a
pressure rod 8. The pressure rod 8 can be implemented as a solid steel
rod or as a steel pipe, for example (it is to be noted that the girder 4
itself can also or does also act as a pressure rod). Furthermore, the
girder 4 is connected in the middle to the upper end of the compensation
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device 6 via a connection element 13 (e.g., rod, bar, plunger of a
cylinder). The compensation device 6 is length-adjustable in the vertical
direction by a force-driven drive in Figure 1.
The girder element 1 is fixedly connected to the story columns 2, 3 via
the fasteners 7a, 7b (i.e., the outer ends of the girder 4 are also fixed
under load). There is no direct fastening or support of the girder element
1 on an already manufactured story ceiling (i.e., the floor) 9, for
example, because the story ceiling 9 has not yet sufficiently hardened. In
addition, the girder element 1 may be supported close to a story column
2, 3 via a support on the floor, because a premature strain of a story
ceiling is possible in these areas. The girder element 1 spans the
intermediate space between the story columns 2, 3.
If external forces 10 are introduced into the girder 4 (from above in
Figure 1), in particular by the weight force of formwork girders, formwork
elements, and liquid concrete resting thereon, the middle of the girder 4
begins to sag downwardly. In other words, the spacing x between the
girder 4 and the floor 9 decreases.
The distance x of the girder 4 to the floor 9 (i.e., the position of the
girder 4) is monitored using a laser distance meter 11 and compared to a
target distance xs in a control unit 12. The target distance xs
corresponds to the position of the non-deformed, linear girder 4. The
laser distance meter 11 is situated in an area of the compensation device
6.
If the distance x falls below the target value xs, the control unit 12
orders an enlargement of the length L of the compensation device 6. This
results in lifting of the girder 4 and pressing down of the traction band 5
(more strongly or weakly depending on the modulus of elasticity of the
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traction band) in the middle area in proximity to the compensation device
6. The girder 4 can thus be kept at a uniform level.
The position of the girder 4 is typically kept at the target position during
the entire concrete casting and hardening of the ceiling to be
manufactured, i.e., the distance x is kept at the target distance xs. The
girder 4 thus always remains nearly linear, and the ceiling receives the
desired, level shape.
Figures 2a and 2b illustrate the use of girder elements according to the
invention in a girder construction for ceiling formwork for manufacturing
a story ceiling.
Figure 2a shows an already finished, but not yet completely hardened
story ceiling (floor) 9, from which four story columns 2, 3, 51, 52 project.
The story columns 2, 3, 51, 52 are already completely hardened.
The new story ceiling to be manufactured is to be erected, the associated
ceiling formwork only being fastened and/or supported on the story
columns 2, 3, 51, 52, but not on the floor 9, which cannot yet be fully
loaded. For this purpose, a girder construction having a total of five
girder elements 53-57 according to the invention and a further girder 58
is used.
Only the two girder elements 53, 54 are fastened at the outer ends of
their girders 4 to fixed structures, namely the story columns 51, 2 and/or
52, 3 (and thus with these outer ends always fixed, even under load).
The fastening is performed using anchors in the particular column body
and a support on a frame 62, which encloses the particular column base.
The girders 4 of the girder elements 53, 54 are also referred to as yoke
girders.
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According to the invention, the girders 4 of the three further girder
elements 55, 56, 57 are laid (supported) and fastened on the yoke
girders of the girder elements 53, 54. The girders 4 of the girder
elements 55-57 are also referred to as crossbeams; they are
implemented as telescoping (i.e., changeable in their length). The girders
4 of the girder elements 53, 54 and 55, 56, 57 intersect at right angles.
According to the invention, each girder element 53-57 has a length-
adjustable compensation device 6 with a motorized drive (not shown in
greater detail) for setting the local spacing of a traction band 5 from the
girder 4, i.e., the distance (measured perpendicular to the girder 4) in
the area of the compensation device 6. The girders 4 and the traction
bands 5 of each girder element 53-57 are fastened to one another in the
middle via the particular compensation device 6, a connection element 13
(bar, rod), and optionally (only for the girder elements 55-57) the
installed, intersecting girder 58.
A spacer rod 59 is provided at the lower end of each of the compensation
devices 6 for measuring the position of the girder 4 of the particular
girder element 53-57. The spacing of the lower end of the length-
adjustable compensation device 6 from the floor 9 is measured directly.
Together with the current length setting of the compensation device 6
(and the dimension of connection element 13 and optionally the girder
58), the current position and thus the degree of sag of the particular
girder 4 can thus be concluded. By adjusting the length of the
compensation device 6, the position of the girder 4 under load can be
regulated separately on each girder element 53-57 (as described in
greater detail under Figure 1).
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Figure 2b shows the girder construction of Figure 5a in a later stage of
construction. Formwork girders 60 have been laid on the girders 4 of the
girder elements 53, 54 and on the girder 58. These formwork girders 60
have a slightly greater overall height than the adjacent girders 4 of the
girder elements 55-57 (alternatively, the overall height of the girders 4 of
the girder elements can also be equal to the overall height of the
formwork girders 60). Ceiling formwork plates 61 (alternatively ceiling
formwork elements having formwork skin directed upward) are situated
on the formwork girders 60 and optionally the girders 4 of the girder
elements 55-57, on which liquid concrete is poured in the context of the
concrete casting of the story ceiling to be erected. Only a part of the
formwork elements 61 is shown in Figure 2b for simplification.
It is to be noted that the formwork area, defined by the story columns in
Figures 2a, 2b, typically has an edge length of approximately 7 m to 10
M.
In summary, the present invention describes a compensation device for a
girder or bolt, the sag of the girder being settable by the compensation
device by tension against a traction band running behind the girder. The
traction band is spaced apart from the girder in an area of the
compensation device, the outer ends of the traction band engaging
directly on the girder. Using the invention, a sag of the girder under
intrinsic weight and/or external load can be counteracted. Load
deformations of the girder which arise through the concrete load and
through the intrinsic weight may be compensated for using the means
according to the invention.
