EP1915487B1 - Prestressed planar load-bearing structure made of fiber concrete and textile reinforced concrete - Google Patents

Abstract

Disclosed are thin-walled planar load-bearing structural elements which are made of fiber concrete and textile reinforced concrete and are joined together by prestressing the same so as to obtain disks, plates, and shells, thus making it possible to produce thin-walled structures that behave like monolithic structures when subjected to stress. The planar load-bearing structural elements can be planar or three-dimensionally curved. Prestressing with subsequent bonding and prestressing without bonding are used as prestressing processes.

Description

The invention relates to thin-walled structural elements made of fiber concrete or textile-reinforced concrete according to the preamble of claim 1. Such a surface support element is made DE 27 57 432 A known. Washers, plates and shells are surface structures, with loads of discs exclusively and of shells primarily abolishing via membrane stress states. By definition, plates are loaded normally to the plate mid-plane and the stress is removed via bending stress states.

Such thin-walled surface structures can be used as facade panels, noise barriers or shell structures, for example for the construction of exhibition stands.

The tensile strength of concrete is only about 5% to 10% of the compressive strength. The insertion of reinforcing steel reinforcement into thin-walled concrete elements does not make sense, because with a total thickness of e.g. 4 cm a minimum concrete cover of 2.5 cm to 3 cm for the reinforcement can not be executed and thus no corrosion protection is guaranteed. Thin-walled precast concrete elements are therefore provided with non-metallic fiber reinforcements or textile reinforcements to increase the tensile strength. Suitable materials for the production of textile reinforcements and fiber reinforcements are, for example, alkali-resistant glass fibers or carbon fibers.

Prefabricated structural elements made of fiber-reinforced concrete and textile-reinforced concrete available on the market are fastened to substructures as small-sized elements with dimensions of, for example, 1.25 m by 3.6 m. Larger-sized applications are not possible because of the limited bending and Zugtragfähigkeit the fiber-reinforced or textile-reinforced elements and in the absence of a suitable joining technique.

To improve the bending and tensile load capacity has been proposed to bias the textile reinforcement before the introduction of the concrete (see, eg Markus Krüger: Prestressed Textile Reinforced Concrete, Dissertation, University of Stuttgart, 2004 ). This so-called preload with instant composite allows that Applying a small compressive prestressing of the concrete of, for example, only 1.5 MPa in the above-mentioned dissertation, because the anchoring of the textile reinforcement for applying the bias voltage is problematic.

The invention is based on the object to provide a surface structural element made of fiber concrete or textile-reinforced concrete, which has a higher bending and tensile strength than the known embodiments and which has a suitable connection option for creating thin-walled surface structures of at least two individual surface structural elements.

This object is achieved by a surface-structural element with the features of claim 1. Thus, the production of surface structures succeeds as viable structures of thin-walled, prefabricated surface structural elements, which are substantially larger than the known embodiments. The largest span of doubly curved shell structures made of surface structural elements according to the invention will be between 20 m and 30 m. Simply curved shell structures and planar structures will have smaller maximum spans, which must be determined in the individual case for the given geometry and the actions to be applied. The construction of relatively large, simply curved or planar structures will be possible if the wind action to be applied is low, which would be the case, for example, when constructing a trade fair stand in a closed hall.

Preload is used in civil engineering to create a compressive stress state in the prestressed concrete structure. This state of compressive stress must first be reduced by tensions as a result of external stresses before tensile stresses occur and finally cracking occurs. The tensile and flexural strength of an uncracked, reinforced concrete structure is much higher in the non-cracked state than after cracking. The higher stiffnesses in the non-cracked state cause that non-cracked structures have much smaller deformations than structure, which have cracks. These known advantages of the bias voltage are in the utilized according to the invention surface structural elements to build with the help of the bias thin-walled tensile structures that remain undisturbed under the external effects and thus have a high tensile and bending stiffness and as a result, small deformations. Especially for thin-walled structures whose load-deformation behavior is nonlinear and which can fail at low material stresses as a result of stability problems, the high rigidity of the non-cracked structure and the avoidance of large deformations is of great importance for the support safety.

Advantageous developments of the invention are defined in the subclaims.

The invention will be described and explained with reference to the embodiment shown in the drawing.

Fig. 1

eine Ansicht eines ebenen Flächentragwerkelements, das in einer Richtung vorgespannt ist

Fig. 2

einen Schnitt längs der Linie II-II in Fig. 1

Fig. 3

eine Ansicht eines von geraden Rändern begrenzten Flächentrag- werkelements mit der Form eines hyperbolischen Paraboloids

Fig. 4

einen Schnitt längs der Linie IV-IV in Fig. 3

Fig. 5

ein ebenes Flächentragwerk, das aus mehreren einzelnen Flächentragwerk- elementen besteht, die mittels Vorspannung miteinander verbunden sind.

Fig. 6

einen Schnitt längs der Linie VI-VI in Fig. 5

Fig. 7

einen Schnitt längs der Linie VII-VII in Fig. 5

Fig. 8

ein zweifach räumlich gekrümmtes Flächentragwerk mit der Form eines hyperbolischen Paraboloids, das aus mehreren einzelnen Flächentragwerk- elementen besteht, die mittels Vorspannung miteinander verbunden sind

Fig. 9

ein zweifach räumlich gekrümmtes Flächentragwerk mit der Form eines Hyperboloids, das aus mehreren einzelnen Flächentragwerkelementen besteht, die mittels Vorspannung miteinander verbunden sind

Fig. 10

einen Schnitt längs der Linie X-X in Fig. 9

Fig. 11

die auf einer geeigneten Unterkonstruktion angeordneten Flächentragwerke für den untersten Ring des Hyperboloids

Fig. 12

die Flächentragwerkelemente des ersten und zweiten Rings des Hyperboloid

Fig. 13

die Flächentragwerkelemente der ersten drei Ringe des Hyperboloid

It shows

Fig. 1

a view of a planar sheet-metal structural element, which is biased in one direction

Fig. 2

a section along the line II-II in Fig. 1

Fig. 3

a view of a limited area of straight edges Flächenungs- basement with the shape of a hyperbolic paraboloid

Fig. 4

a section along the line IV-IV in Fig. 3

Fig. 5

a flat tensile structure, which consists of several individual Zächentragwerk- elements which are interconnected by means of bias.

Fig. 6

a section along the line VI-VI in Fig. 5

Fig. 7

a section along the line VII-VII in Fig. 5

Fig. 8

a two-dimensionally curved tensile structure with the shape of a hyperbolic paraboloid, which consists of several individual elements that are connected by prestressing

Fig. 9

a two-dimensionally curved surface structure with the shape of a hyperboloid, which consists of a plurality of individual surface structure elements which are interconnected by means of prestressing

Fig. 10

a section along the line XX in Fig. 9

Fig. 11

the arranged on a suitable substructure surface structures for the bottom ring of hyperboloid

Fig. 12

the tensile elements of the first and second ring of the hyperboloid

Fig. 13

the plane structural elements of the first three rings of the hyperboloid

The following is first on the Fig. 1 and 2 Referenced.

A view of a surface structure element 10 according to the invention is shown in FIG Fig. 1 shown. The illustrated rectangular embodiment is planar and biased in one direction with tendons 20 . The edge 30 of the tensile structure element 10 consists of straight sections which are normal to the plate center plane.

A detail with a section through the surface structure element 10 and the tendon 20 shows the Fig. 2 , The tendon 20 consists of a tension member 22, a cladding tube 24 and an anchor 28th

Suitable materials for the tension member 22 are, for example, fiber composites of carbon, aramid or glass fibers in conjunction with a matrix of epoxy resin and stainless steels. For fiber composite materials, there are suitable anchoring systems (described, for example, in US Pat DE 100 10 564 ). Wires, strands and rods made of stainless steel can be anchored to the systems known from prestressed concrete construction, with sleeve anchorages for strands and wires and nuts for threaded rods being particularly suitable for the small cross-sectional dimensions present here. The tensile strengths of the fiber composites are currently between 2000 MPa and 5000 MPa, stainless steels are available with tensile strengths up to 1800 MPa.

In Fig. 2 a cavity 26 is shown, which is formed in the concrete of the surface structure element 10 by the insertion of the cladding tube 24 before or during the concreting process. In this cavity 26 , a tension member 22 is introduced before or after concreting. As a result, the cavity 26 is reduced. After hardening of the concrete, the tension member 22 is biased against the hardened concrete, usually with hydraulic presses. Will the remaining Cavity 26 then pressed with a cement mortar or an epoxy resin, there is a pre-stress with subsequent bond.

Tendons without composite can be subsequently relaxed and removed again. Thus, the production of demountable structures is possible.

Assuming that the surface structure element 10 in Fig. 1 has a thickness of 13 mm, the round tension members 22 have a diameter of 4 mm and a distance of 200 mm and are prestressed with 1000 MPa, so arises in a central region of the roof truss member 10 which is not affected by stress peaks at the anchorage, a tension of tension force (area times tension = 12.6 mm ² times 1000 Mpa = 12570 N) by area (200 mm by 13 mm = 2600 mm ² ) equal to 4.8 MPa. By halving the mutual distance of the tendons 20 from 200 mm to 100 mm, the compressive prestressing of the concrete would rise to twice the value (9.7 MPa).

The tension on the anchor 28 is assumed dimensions of the anchor plate of 13 mm by 30 mm 12570 N by 390 mm ² equal to 32.2 MPa, which is easily absorbed by a textile-reinforced and / or fiber-reinforced concrete. Uniaxial compressive strengths of textile-reinforced and / or fiber-reinforced concrete are between 40 and 160 MPa for 28-day-old test specimens.

A view of a second embodiment of the surface structure element 10 according to the invention is shown in FIG Fig. 3 shown. The surface support element 10 has straight edges 30 and has the shape of a hyperbolic paraboloid 62. The surface support element 10 is prestressed with two tendons 20 , which are arranged approximately orthogonal to one another. In the Fig. 3 and in the associated section in the Fig. 4 is a state after the hardening of the concrete and before the insertion of the tension members 22 shown. By means of the cladding tubes 24 , cavities 26 are created for the later connection of a plurality of such surface-area supporting elements 10 by means of prestressing.

A flat tensile structure 50, which according to the invention consists of a plurality of surface structural elements 10 , which by means of tendons 20 with each other are connected in Fig. 5 and in detail in Fig. 6 and Fig. 7 shown. Rectangular, planar surface-structural elements 10 with tendons 20, which are arranged orthogonal to each other, are joined together by means of prestressing to form a planar surface structure 50 . For the sake of clarity, in Fig. 5 only some of the tendons 20 located . The flat surface structure 50 could be used as a facade panel or noise barrier. The tendons 22 extend in cladding tubes 24 and are anchored at the edge 30 of the flat surface structure 50 with suitable anchorages 28 .

The edge 30 of the planar surface structure 50 has according to Fig. 6 a thickening 32 for better absorption of the anchors 28 of the tendons 20 . Between the individual surface structural elements 10 is a strip of soft material 34, for example of epoxy resin or extruded polystyrene, which leads due to a low modulus of elasticity and / or due to its pronounced creep to a reduction of the edge pressures, the tensioning of the tendons 20, the at the edges 30 of the surface structure elements 10 due to inaccuracies in the production of the surface structure elements 10 occurring stress peaks decrease.

The Fig. 8 Figure 3 shows a spatially-curved surface structure 60 in the form of a hyperbolic paraboloid 62 with straight edges 30. Two of the four edges 30 are non-slidably supported. The hyperbolic paraboloid 62, which could be used as an event hall or as a roof of an exhibition area, is composed of individual area-structural elements 10 , which likewise have the shape of hyperbolic paraboloid 62 and are already in the FIG. 3 and FIG. 4 have been described. By tensing the tendons 20 , the individual surface structure elements 10 are connected to a two-dimensionally curved surface structure 60, which corresponds in its carrying behavior of a monolithic structure.

The Fig. 9 shows a spatially curved surface structure 60 in the form of a hyperboloid 64. Along the edge 30 , the hyperboloid 64 is non-displaceably supported. The individual surface structure elements 10 or flocks 11, 12, 13 of surface structure elements 10 are frictionally with tendons 20 connected with each other. The sake of clarity in Fig. 9 Tensioning members 20 , not shown, according to the invention are located in the surface structure elements 10 and are used to connect the individual surface structure elements 10 together. The individual surface support elements 10 can be shaped exactly according to the shape of the hyperboloid 64 to be built or only approximate this shape. If, for example, plane surface structural elements 10 are used to construct the hyperboloid 64 , angles 36 are formed along the edges 30 between the edge 30 and the center plane of the surface structural element 10 which are different from 90 °. The detail in Fig. 10 shows such a situation in which two tensile structure elements 10 meet along an edge 30 at angles 36 which are greater than a right angle.

A method for the construction of two-dimensionally curved surface structures 60 of surface-tensioning elements 10 is in the Figs. 11, 12 and 13 shown. According to Fig. 11 For example, a first group 11 of surface supporting elements 10 is fixed on a suitable support along an edge 30 .

According to Fig. 12 is a second family 12 of tensile structure elements 10 with tendons 20 with the first share 11 positively connected. For the sake of clarity, is in Fig. 12 and Fig. 13 only one clamping member 20 shown.

According to Fig. 13 Subsequently, a third group 13 of surface structure elements 10 with tendons 20 with the first blade 11 and the second share 1 2 is connected. In this process, the tendons 20 are either to be coupled or a part of the laid in the second step clamping members 20 is to be relaxed and replaced by longer tendons 20 . The provision of cavities 26 for all later to be added tensile structure elements 10 in the first installed flocks 11 and 12 according to the procedure in the cantilever method in bridge construction would also be possible.

By attaching further surface support elements 10, which is not shown in the drawing, finally, the shell in the form of a hyperboloid 64 is completed.

Is low when this method is that the use of a falsework is not necessary, because the weight of the appended Tensile structure elements 10 is predominantly removed via membrane tensions in the biased spatially curved surface structure 60, which is formed by the already installed surface structure elements 10th

In the examples, the preparation of a flat tensile structure 50, a hyperbolic paraboloid 62 and a hyperboloid 64 has been described. The surface support elements 10 according to the invention, however, can also be used for other shell formwork of any shape, not shown here.

In the examples shown, the tendons 20 were anchored to the edges 30 of the surface structure elements 10 . Other possibilities, such as the anchoring of tendons 20 to pilasters or the coupling of tendons 20, which are proven techniques of prestressed concrete, can be used mutatis mutandis to bias the surface structure member 10 of the invention.

LIST OF REFERENCE NUMBERS

10

Tensile structure element

11

first set of surface structural elements

12

second group of surface structural elements

13

third group of surface structural elements

20

tendon

22

tension member

24

cladding tube

26

cavity

28

anchoring

30

edge

32

thickening

34

Strip of soft material

36

Angle between the edge and the median plane of the surface structure element

50

flat tensile structure

60

spatially curved surface structure

62

hyperbolic paraboloid

64

hyperboloid

Claims (16)

1. A plane load-bearing element (10) as a prefabricated element made of fibre concrete or textile-reinforced concrete, wherein the plane load-bearing element (10) has a thickness of between 8 mm and 36 mm and is prestressed with prestressing elements (20) without bond or with prestressing elements (20) with post-tensioning, characterized in that the respective prestressing elements (20) comprise a jacket tube (24) with an inserted tension member (22) and the bond can be produced by grouting the hollow space (26) remaining between the jacket tube (24) and the tension member (22).
2. A plane load-bearing element according to claim 1, characterized in that the plane load-bearing element (10) preferably has a thickness of between 10 mm and 22 mm.
3. A plane load-bearing element according to claim 1 or 2, characterized in that the tension members (22) for prestressing the plane load-bearing element (10) are made of a composite fibre material.
4. A plane load-bearing element according to claim 1 or 2, characterized in that the tension members (22) are made of stainless high-grade steel.
5. A plane load-bearing element according to claims 1 to 4, characterized in that the plane load-bearing element (10) has no curvature.
6. A plane load-bearing element according to claims 1 to 4, characterized in that the plane load-bearing element (10) has a single curvature.
7. A plane load-bearing element according to claims 1 to 4, characterized in that the plane load-bearing element (10) has a double curvature.
8. A plane load-bearing element according to claims 1 to 7, characterized in that, on at least one edge (30), the plane load-bearing element (10) has an enlargement (32) for receiving the anchors (28) of the prestressing elements (20).
9. A plane load-bearing element according to claims 1 to 8, characterized in that at least one edge (30) of the plane load-bearing element (10) has an angle from the centre plane of the plane load-bearing element (10) which is different from 90°.
10. A plane load-bearing element according to claims 1 to 9, characterized in that the jacket tubes (24) for receiving the prestressing elements (22) are inserted already during the manufacture of the plane load-bearing elements (10).
11. A plane load-bearing element according to claims 1 to 10, characterized in that suitable anchors (28) for anchoring the tension members (24) are inserted on at least one edge (30) of the plane load-bearing element (10).
12. A plane load-bearing element according to claims 1 to 11, characterized in that prestressing elements (22) are laid in the plane load-bearing element (10) which are arranged approximately parallel to each other.
13. A plane load-bearing element according to claims 1 to 11, characterized in that prestressing elements (22) are laid in the plane load-bearing element (10) which are arranged approximately orthogonal to each other.
14. A plane load-bearing element according to claims 1 to 13, characterized in that at least two plane load-bearing elements (10) are positively linked with prestressing elements (22).
15. A plane load-bearing element according to claims 1 to 14, characterized in that strips of a soft material or a material capable of creep (34) are arranged between the edges of the plane load-bearing elements (10).
16. A process for manufacturing a double-curved shell (60) with plane load-bearing elements (10) according to claims 1 to 15, characterized in that

    a) jacket tubes (24) are laid in a straight or curved fashion in plane load-bearing elements (10) close to the centre plane so that hollow spaces (26) of approximately circular cross-sections are present in the plane load-bearing elements (10) and that each hollow space (26) comprises a beginning located at an edge (30) of the plane load-bearing element (10) and an end located at another edge (30),

    b) the second plane load-bearing element (10) is connected to the first plane load-bearing element (10) by means of at least one prestressed tension member (22) which is guided in a hollow space (26) and anchored to an edge (30) of the first plane load-bearing element (10) and an edge (30) of the second plane load-bearing element (10),

    c) further plane load-bearing elements (10) are attached which, in each case, are interconnected with at least one prestressed tension member (22) arranged in the hollow spaces (26) of at least two plane load-bearing elements (10) and anchored to the edges (30),

    d) that the double-curved shell (60) formed by the assembly of the plane load-bearing elements (10) is able to carry the weight of a further plane load-bearing element (10) to be attached primarily via membrane tensions in the double-curved shell (60).

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