EP1528173A2 - Prestressed floor with hollow floor slabs - Google Patents

Abstract

The method for the manufacture of a prestressed flat slab floor (1) involves the laying of a number of cored floor slabs (2,3) in a X-Y modular grid. The one side of the cored floor slabs in each case is integrated in a prestressed girder section (4,5) manufactured from in-situ concrete. The unstressed reinforced cored floor slabs has an additional prestressed reinforcement extending in the vertical direction. For the prestressed reinforcement a tensioning cable is laid in the gap (32) between the abutting cored floor slabs. An independent claim is included for a prestressed flat slab floor with cored floor slabs laid in a X-Y modular grid.

Description

The invention relates to a prestressed flat ceiling with hollow ceiling panels and a process for their preparation according to the preamble of patent claim 1.

A prestressed concrete flat cover according to the preamble of patent claim 1 has become known with the CH 535 878.

For making a flat ceiling is on the free upper ends of vertical Supports a flat, non-pointing and flat Schalboden attached. On Depending on the static requirements, this formwork base will be rebars brought in. Become near the column supports of the rebar additional tensioning cables are introduced, which after pouring out the scarf floor and hardening the concrete mass to be prestressed.

It is therefore a monolithic concrete floor, whose Load capacity is improved by the introduction of tension cables. disadvantage This known technique is that a very high basis weight in purchase must be taken. Accordingly, high support loads with given correspondingly strongly dimensioned supports.

Due to the high basis weight must be correspondingly high Ceiling cross-sections are made to ensure stability. In order to However, high production costs are associated. The cost of a such a building are therefore high.

There is also the disadvantage that there is no possibility in the interior to install such a ceiling installations and / or insulation.

With the subject of DE 201 03 059 U1 a hollow ceiling slab is known become, consisting of a lower and a distance above it upper shell, the shells by lattice girders with each other are connected. Although there is the possibility in the interior installations and insulating material, but is not shown as such Suspended ceiling slab in flat ceiling systems according to CH 535 878 could.

The invention is therefore the object of a prestressed flat ceiling after the CH 535 878 educate so that they with substantially low Basis weight and lower production costs can be made.

To achieve the object, the invention is characterized in that that the flat slab consists of individual with their long sides (in Y direction) abutting hollow ceiling slabs which are in the direction of their Longitudinal extent (in the X direction) in a prestressed, in situ concrete manufactured belt strips are integrated.

With the given technical teaching there is the advantage that now very slender dimensioned hollow ceiling slabs with low basis weight can be used because their static load capacity in combination with prestressed belt strips - in which they are involved - is achieved.

It can therefore be very inexpensive and only a small height requiring hollow ceiling panels are used, which only in the narrow Area of a belt strip with a higher-quality in-situ concrete with each other get connected.

This results in significant advantages:

The hollow ceiling panels are cheaper overall than poured Finished ceiling elements and have a much lower basis weight.

The ceiling system according to the invention is about 50% lighter than monolithic ceilings. Such monolithically produced ceilings For example, prefabricated ceilings are used at the construction site corresponding in-situ concrete poured out.

A conventional prefabricated ceiling system of a length of, for example, 8 x 8 meters requires an in-situ concrete quantity of about 19 m ^{3 to} produce the precast ceiling element, which in the final state has a thickness of, for example, 30 cm.

This is where the invention comes in, which provides, based on an area of 8 x 8 m only a relatively thin hollow ceiling slab with a thickness of 2 x 7 cm too use, which preferably consists of two spaced-apart shells, these shells only from a low quality concrete, such as the Goodness B25, insist.

Such a lightweight and low-building hollow ceiling slab is with her Narrow side with each adjoining hollow ceiling slab on the in In-situ concrete bonded belt strips connected.

To produce the belt strip is a higher-quality in-situ concrete, for example used in grade B80 and with the tensioning cables according to the invention prestressed so as to distribute the support forces in one direction.

Regarding the previously mentioned amount of 19 m ³ in situ concrete in the production of a conventional precast ceiling, the ceiling system according to the invention requires only for the production of the belt strip a higher quality concrete, eg grade B80, with an amount of only 2.1 m ² .

It is important that according to the subject of CH 535 878 a distribution the clamping forces in both the X and Y direction took place, what with a extraordinarily high expenditure was connected.

This is where the invention begins, which provides that the support forces only in the Y direction on the belt strips are introduced while in the X direction a Such introduction with prestressed tensioning cables is eliminated. This will be the Cost of the clamping system significantly reduced.

The ceiling system is also applicable as a multi-field carrier.

According to the upper shell of the respective hollow ceiling slab in Belt strip area shortened, so that there is a larger recessed area results. There can therefore by in-situ concrete additions a continuous property the upper shell can be reached. It is therefore a complete one continuous, jointless and without joists and falls provided flat ceiling.

Another advantage of the invention is that because of the use of Hollow ceiling panels now for the first time the possibility exists, over completely continuous ceiling lengths and widths installations and insulating material in the To bring flat ceiling.

With the given technical teaching, there is the advantage that one create large-area ceiling systems with the flat ceiling according to the invention can, in particular, for commercial buildings, office buildings, apartment buildings and the like are usable. With much lower basis weight and lower production costs can be spanned very large ranges. It can thus grid systems of up to 12 to 12 meters can be achieved, which in the prior art only with much higher Basis weights and heights were possible.

It is also a fast transport and installation of low-building and low-weight hollow ceiling slabs at the construction site possible. The necessary Construction refers to the pouring of in-situ concrete to form the relatively narrow belt strips, for example, 40 cm wide. It does not need one large-scale concreting work and the associated large scarf Support work more.

Where previously large formwork panels with appropriate support beams had to be installed, it is sufficient now, only in the area of the narrow Belt strips to shed the in-situ concrete.

The above-mentioned inventive teaching is that the load transfer of Flat slab with hollow slabs over the prestressed belt strip in In-situ concrete and above the slackly reinforced slabs Hollow ceiling panels takes place. This formulation applies to standard blankets a column grid of Ix, Iy up to about 10.0m.

After an extension of this technical teaching is provided that both the smaller spans as well as the large spans also covered become:

For belt stiffeners with a wingspan of 5 - 7 [m], the load capacity can be adjusted Also make sure with a limp armor. Only from a span of I > 8 m, a preload is required and from a span of I> 10.0 absolutely necessary. The hollow ceiling slabs with the already in the precast plant inlaid limp reinforcement have a scope of up to approx. 8m span. Are in this direction larger spans than about 8m too overcome, the slack reinforced hollow ceiling slabs to one Prestressing reinforcement added. It uses the gap between the individual Plate strip within which a tensioning cable must be placed locally.

These tension cables intersect the belt strip of in-situ concrete and lead i.d.R. above several fields. In contrast to the in the belt strips of in-situ concrete arranged, concentrated bias voltage is called the regular Distance in the joints arranged tensioning cable as a distributed bias.

Due to different span ratios are any combinations of "limp reinforced" and "prestressed reinforced" possible. From the execution ago possible is a short span for the belt strip and a large span for the hollow ceiling slab and vice versa. Accordingly, the short would Span flabby reinforced and the large span performed biased.

The subject invention of the present invention is not only evident the subject matter of the individual claims, but also from the Combination of the individual claims among themselves.

All disclosed in the documentation, including in the abstract Information and features, in particular those shown in the drawings Spatial training, are claimed as essential to the invention, as far as they are individually or in combination with the prior art are new.

In the following, the invention will be described with reference to only one embodiment illustrative drawings explained in more detail. Here are the drawings and its description further features essential to the invention and advantages of Invention forth.

Figur 1:

schematisiert die Draufsicht auf eine Flachdecke nach der Erfindung;

Figur 2:

ein Schnitt durch die Flachdecke nach Figur 1 gemäß der Linie A-A;

Figur 3:

ein vergrößerter Schnitt durch den Anschluss von zwei Hohldeckenplatten im Bereich eines Gurtstreifens bei Herstellung eines Gurtstreifens;

Figur 4:

der Schnitt ähnlich wie Figur 3 vor Herstellung des Gurtstreifens;

Figur 5:

vergrößert ein Schnitt durch ein Hüllrohr mit daran angeordneten Spannkabeln;

Figur 6:

ein vergrößerter Schnitt nach Figur 2 mit Darstellung weiterer Einzelheiten;

Figur 7:

eine weitere Vergrößerung der Darstellung nach Figur 6;

Figur 8:

ein Schnitt gemäß der Linie VIII-VIII in Figur 6;

Figur 9:

Schnitt durch eine weitere Ausführungsform einer Flachdecke, hergestellt aus Halbfertigteilen (Elementplatten) mit bauseitigem Überbeton;

Figur 10:

Schnitt gemäß der Linie A-A in Figur 9;

Figur 11:

Schnitt durch eine weitere Ausführungsform einer Flachdecke bestehend aus vorfabrizierten Wingdecken-Elementen;

Figur 12:

Schnitt gemäß der Linie A-A in Figur 11;

Figur 13:

Schnitt durch eine weitere Ausführungsform einer Flachdecke, bestehend aus sogenannten Bubbledeck-Elementen;

Figur 14:

Schnitt gemäß der Linie A-A in Figur 13;

Figur 15:

Schnitt durch ein weiteres Ausführungsbeispiel einer Flachdecke mit Spannbeton-Hohlplatten;

Figur 16:

Schnitt gemäß der Linie A-A in Figur 15.

Figur 17:

Draufsicht auf eine weitere Ausführung der Flachdecke mit Vorspannung in den Fugen zwischen den Hohldeckenplatten

Figur 18:

Schnitt B-B in Figur 17

Figur 19:

Detail Y aus Figur 18 - Darstellung eines Hüllrohres im Schnitt

Figur 20:

Tabelle mit Darstellung der Kombination unterschiedlicher Bewehrungsarten

Show it:

FIG. 1:

schematizes the plan view of a flat ceiling according to the invention;

FIG. 2:

a section through the flat ceiling of Figure 1 along the line AA;

FIG. 3:

an enlarged section through the connection of two hollow ceiling panels in the region of a belt strip in the manufacture of a belt strip;

FIG. 4:

the section similar to Figure 3 before the production of the belt strip;

FIG. 5:

enlarges a section through a cladding tube with tensioning cables arranged thereon;

FIG. 6:

an enlarged section of Figure 2 showing further details;

FIG. 7:

a further enlargement of the representation of Figure 6;

FIG. 8:

a section along the line VIII-VIII in Figure 6;

FIG. 9:

Section through a further embodiment of a flat ceiling, made of semi-finished parts (element panels) with on-site overburden;

FIG. 10:

Section along the line AA in Figure 9;

FIG. 11:

Section through a further embodiment of a flat ceiling consisting of prefabricated wing ceiling elements;

FIG. 12:

Section along the line AA in Figure 11;

FIG. 13:

Section through a further embodiment of a flat ceiling, consisting of so-called Bubbledeck elements;

FIG. 14:

Section along the line AA in Figure 13;

FIG. 15:

Section through another embodiment of a flat ceiling with prestressed concrete hollow slabs;

FIG. 16:

Section along the line AA in Figure 15.

FIG. 17:

Top view of another embodiment of the flat ceiling with prestress in the joints between the hollow ceiling panels

FIG. 18:

Section BB in FIG. 17

FIG. 19:

Detail Y from FIG. 18 - illustration of a cladding tube in section

FIG. 20:

Table showing the combination of different reinforcement types

According to Figures 1 and 2, the flat ceiling 1 consists of the X-Y grid laid hollow ceiling panels 2, 3, each abutting one another on the longitudinal side. she form longitudinally a joint area 32, which is closed on site.

The front side are in the X direction to each other continuing Hollow ceiling panels 2, 3 via belt strips 4, 5 interconnected. The Belt strips 4, 5 are made of in-situ concrete at the construction site.

In the area of the belt strips, supports 6 are arranged at a mutual distance.

In the space between the abutting hollow ceiling panels 2, 3rd will be described with reference to Figures 6 and 7 in more detail Reinforcing baskets 18, 32 introduced and with corresponding, in Figure 4 shown, ducts 8 and arranged therein tensioning cables 9 connected.

The reinforcement plant produced in this way is cast with in-situ concrete according to FIG. 3, wherein on the underside of the abutting hollow ceiling panels 2, 3 a Schaltisch 7 is created.

The gap is then in a conventional manner with in-situ concrete poured out, so that the representation of Figure 3 results.

FIG. 5 shows that the tensioning devices laid in the belt strip 4, 5 are shown in FIG consist essentially of cladding tubes 8, which are at a mutual distance are arranged in a grid pattern to each other, each cladding tube from a Plastic or metal shell is made and in the interior one or more Clamping cables 9 are arranged.

This tension cable 9 can be made of a cable-shaped metal or a Be plastic material. It is also possible to use (multicore) stranded cables become.

From Figures 6 and 7 go further details of the structure of the respective Belt strip 4, 5 out.

First, each hollow ceiling slab 2, 3 consists of a lower shell 10 Concrete. In the lower shell 10 are in a conventional manner Reinforcing iron or mats arranged.

The rebars are in the form of spaced apart Reinforcing rods 11 several times from the material of the lower shell 10th led out and reach the area of the respective belt strip 4, 5, according to FIG. 7.

The end 12 of the respective reinforcing rod 11 engages in the free space into it, which later forms the belt strip 4, 5.

In the same way, the upper shell 13 is formed, each in turn a plurality of reinforcing bars 14, which also in the X direction run and their free ends 15 in turn intervene in the gap, which later forms the belt strip 4, 5.

The space between the lower and the upper shell 10, 13 of the respective hollow ceiling slab 2, 3 is, for example, with an insulating material 16th filled.

FIG. 6 also indicates that lattice girder 17 is arranged in the intermediate space are, with their upper and lower ends in the respective shells 10, 13th are cast in order to ensure a static surface load capacity.

It is important that each belt strip 4, 5 of one or more Reinforcing baskets 18, 23 is completed. Instead of the two shown here Reinforcing baskets 18, 23 can also only a single reinforcement cage available be.

Each reinforcing cage 18, 23 consists of a grid mesh that extends longitudinally the entire length of the respective belt strip 4, 5 extends and as a loose Part is spent at the construction site. There it will be in the space between the adjoining hollow ceiling panels 2, 3 inserted.

The outer reinforcement cage 18 is made up of a plurality of ones mutual spaced U-shaped rods 19, in the X direction are connected by longitudinal bars.

Each U-bar 19 consists of an upper horizontal leg 20 which in a Vertical leg 21 passes, which in turn into a lower horizontal Base leg 22 passes.

The U-bar 19 is exactly mirror-symmetrical with respect to a longitudinal center line, so that the outer reinforcement cage 18, the two end faces of Hollow ceiling panels 2 and the protruding ends 12, 15 of the Reinforcing rods 11, 14 interconnected.

Similarly, a smaller, inner reinforcement cage 23 is provided, which, in turn, consists of a large number of mutually parallel ones consists of mutually arranged U-rods.

Each U-bar has an upper horizontal leg 24, which in a Vertical leg 25 and this merges into a horizontal leg 26.

The above reinforcing baskets 18, 23 with their rods are about corresponding longitudinal bars 27 connected to each other.

There is still an upper, horizontally extending connecting rod 28 is present the ends 15 of the upper reinforcing bars 13 connects to each other.

In addition to the lower longitudinal bars 27 and upper longitudinal bars 29 are present.

FIG. 8 schematically shows the arrangement of the tensioning device as it is was explained with reference to FIG. It consists of the parabolic laid Cladding tubes 8 with the tensioning cables 9 arranged therein, as shown in FIG. 5 is shown.

The respective cladding tube 8 is connected via cable holder 31 with the respectively assigned Reinforcement cage 18, 23 connected. It will be in the direction of its longitudinal extension wave or parabolic laid, as shown in Figure 8 is shown.

After the concrete in the belt strip 4, 5 poured out and cured takes place a bias with a tensioning device not shown on the free ends of the ducts 8 with the tensioning cables 9 arranged therein in the opposite arrow directions 30. The tensioning device is after removed a certain time of bias application again.

In this way, it succeeds, the support forces, which in the flat ceiling in both X and also in the Y direction, only in the Y direction on the narrow Belt strips 4, 5 initiate, while in the X direction, the carrying capacity of Hollow ceiling slab 2 with reinforcing bars arranged therein the load capacity takes over.

This results in a significant cost advantage because the belt strips 4, 5 the Take up bearing forces only in one single direction (in Y direction) have to.

The invention is not based on the use of hollow ceiling panels 2, 3 limited. It can also all other known ceiling systems instead of the Hollow ceiling panels 2, 3 are used. These are for example local folded solid ceilings, slack animated or prestressed hollow floorboards, Element ceilings, bubble latch systems and so on.

FIG. 9 shows a section through such as an exemplary embodiment Embodiment of a flat ceiling, consisting of element plates, in turn from a concrete shell with a thickness of about 5 to 8 cm and incorporated therein Lattice girders, which determine the rigidity of these element plates for transport and ensure the assembly.

Such element plates are used with the invention processed high strength prestressed in situ concrete strip at the construction site, the previously stated proof baskets in the belt strip remain completely alike and only the connection to the element plates shown here accordingly is provided.

The advantage of using such element plates is their cost-effective Production and their easy transport to the construction site.

In known manner then the element plates - as in Figure 9 shown - cast with in-situ concrete, at the same time the high-strength-prestressed belt strips can be poured with.

Figures 11 and 12 show as another embodiment, the use of so-called wing-ceiling elements in conjunction with the Flat cover according to the invention.

The wing cover element consists of a narrower shell of about 5 to 8 cm and piecewise attached thereto stronger shell elements, the material integral with the narrower shell elements are connected and have the corresponding weight saving reasons cavities. The Thickness of the larger shell elements corresponds to the thickness of the finished ceiling.

Such wing ceiling elements are also spent at the site and poured with in-situ concrete and in the manner previously described with the high-strength prestressed in-situ concrete strips connected.

In Figures 13 and 14 is the use of so-called bubble-beat elements shown. Such Bubbledeck elements consist of a narrow shell of about 6 to 8 cm thickness, such an element in the consists essentially of the element plates shown in FIGS. 9 and 10, in the space corresponding hollow body were inserted. These Hollow bodies consist of round plastic hollow bodies which are filled with air and the corresponding weight savings when pouring in-situ concrete should provide.

Also, this ceiling element is like the previously described ceiling elements connected to the high-strength prestressed in-situ concrete strip.

In contrast to the embodiment of Figure 13 and 14, a Bubbledecke also without element plates according to Figures 9 and 10 produced become. Such a production is carried out by an on-site sub-formwork, on which are placed in a conventional manner lattice girders, in whose Intermediate spaces are inserted from the existing hollow plastic body.

In the figures 15 and 16 is a further embodiment, a flat ceiling with Prestressed hollow slabs are shown.

A prestressed concrete hollow plate consists of two at a distance from each other arranged flat ceilings with a thickness of about 6 to 8 cm each and Connecting webs that form intervening cavities. The cut according to the line A-A in Figure 15 is a section through a cavity, so that So outside of this cavity, the connecting webs 35 (see also Figure 18) between the upper plate shell and the lower plate shell available.

Such a prestressed concrete hollow plate is in the previously described Way connected to the high-strength prestressed in-situ concrete strip.

In the embodiment of Figures 17 - 20 is an extension of the above described clamping concept described.

In contrast to the embodiment described first, FIG. 17 shows that in addition to the bias in the main direction (in Figure 17 in horizontal Direction- arrow 33) also a perpendicular thereto extending bias in the secondary direction (in Figure 17 in the vertical direction - arrow 34) can be made.

For the attachment of the bias in the secondary direction (arrow 34) used the same means and measures as stated above for the Preload in the main direction (arrow 33) were described. Therefore The same reference numbers apply to the same parts.

The hollow ceiling slabs 2, 3 with the already inserted in the precast plant flaccid Reinforcement have a range of up to approx. 8m wingspan. are in this direction to overcome larger spans than about 8m, so are the limp reinforced hollow ceiling slabs 2, 3 supplemented by a prestressing reinforcement. It uses the joint 32 between the individual plate strips, within the locally a tensioning cable, consisting of a cladding tube 9 with there inserted Steel ropes 9, insert is. This is shown in Figure 18, wherein from Figure 19 to can be seen how the inserted in the joint area steel rope on average is designed. It consists of a cladding tube 8, which has a number of Clamping cables 9 encloses.

From Figure 17 it can be seen again that in the arrow directions 34th running and inserted in the joint areas 32 tensioning cable 8, 9 the Belt strips 4, 5 intersect from cast-in-place concrete and i.d.R. over several fields of Hollow ceiling panels 2, 3 lead.

In contrast to that arranged in the belt strips 4, 5 of in-situ concrete, concentrated prestressing is called the periodically in the Joints 32 and extending in the direction of arrow 34 tensioning cable 8, 9 as a distributed Preload.

The table in FIG. 20 gives an overview of the possible type of reinforcement different spans. Due to different span ratios All combinations are limp-reinforced and harnessed possible. From the execution is possible a short span for the Belt strips 4, 5 and a large span for the hollow ceiling slab and vice versa. Accordingly, the short span would be flabby reinforced and the large span biased performed.

drawing Legend

1

flat ceiling

2

Hollow ceiling panel

3

Hollow ceiling panel

4

Belt strips (out situ concrete)

5

belt strips

6

support

7

formwork table

8th

cladding tube

9

span cable

10

Lower shell

11

rebar

12

The End

13

Upper shell

14

rebar

15

The End

16

insulation

17

girder

18

Reinforcement cage (outside)

19

U-bar

20

leg

21

leg

22

base leg

23

Reinforcement cage (inside)

24

leg

25

leg

26

base leg

27

longitudinal bars

28

connecting rod

29

longitudinal bars

30

arrow

31

cable holder

32

joint area

33

bias direction (Main area

34

bias direction (Low range)

35

connecting web

Claims (15)

Method for producing a prestressed flat ceiling (1) with ceiling panels, in which a switching table (7) is mounted on the free upper ends of vertical supports (6) on which reinforcing bars (11, 14, 18, 23, 27, 28, 29 ) and introduced in the vicinity of the support support tensioning cable (9), which are biased after pouring the scarf floor and hardening of the concrete mass, characterized in that a plurality of hollow ceiling panels (2, 3) are laid in the XY grid, and that each one side of the hollow ceiling panels in a prestressed, made of in-situ concrete belt strips (4, 5) are integrated. A method according to claim 1, characterized in that the (in the direction of arrow 33) slack reinforced hollow ceiling panels (2, 3) is associated with an additional, in the vertical direction (arrow 34) extending biasing reinforcement. A method according to claim 2, characterized in that for prestressing reinforcement in each case a tensioning cable (9) in the joint (32) between the adjoining hollow ceiling panels (2, 3) is inserted. Method according to one of claims 1 to 3, characterized in that the hollow ceiling slabs (2, 3) in the Y direction with their longitudinal sides are pushed abutting and that the directed in the X direction narrow sides in each case in the belt strips (4, 5) involved become. Method according to one of claims 1 to 4, characterized in that for the production of in-situ concrete strip (4, 5) a higher-grade concrete, for example of grade B80, is used, and that for the shells (10, 13) of the hollow ceiling slabs (2, 3 ) a low-grade concrete, eg grade B25, is used. Method according to one of claims 1 to 5, characterized in that in the space between the adjoining hollow ceiling slabs (2, 3) Reinforcing baskets (18, 32) are introduced, which are connected and with tensioning cables 9. Prestressed flat ceiling, characterized in that it consists of hollow ceiling panels (2, 3), which are laid in the XY grid and in the region of one side in a made of in-situ concrete belt strips (4, 5) are integrated. Prestressed flat ceiling according to claim 7, characterized in that the belt strips (4, 5) are biased in the direction of their longitudinal extent. Prestressed flat ceiling according to one of Claims 7 to 8, characterized in that an additional prestress is introduced perpendicular to the prestressed belt strips (4, 5). Prestressed flat ceiling according to claim 9, characterized in that the additional prestressing takes place by means of tensioning cables (9), which are inserted between the joints (32) of adjoining hollow ceiling slabs (2, 3). Prestressed flat ceiling according to claim 10, characterized in that the tensioning cables (9) intersect the belt strips (4, 5) of in-situ concrete and lead over a plurality of fields of the hollow ceiling slabs (2, 3). Prestressed flat ceiling according to one of claims 7 to 1.1, characterized in that it is produced according to at least one of claims 1 to 6. Prestressed flat ceiling according to one of claims 1 to 12, characterized in that in the intermediate space of the hollow ceiling slab (2, 3) installations and / or insulating material is introduced. Prestressed flat ceiling according to one of claims 1 to 13, characterized in that in the space between the adjoining hollow ceiling panels (2, 3) reinforcing cages 18, 32 are arranged, which are connected to a tensioning device. Prestressed flat ceiling according to claim 14, characterized in that the clamping device consists of cladding tubes (8) arranged tensioning cables (9) which are laid wave-shaped in the direction of their longitudinal extension and pointwise connected to rods of parallel to each other reinforcement cages (18, 23) ,

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