EP0803020A1

EP0803020A1 - Securing of reinforcing strips

Info

Publication number: EP0803020A1
Application number: EP95938340A
Authority: EP
Inventors: Urs Meier; Martin Deuring; Gregor Schwegler
Original assignee: Eidgenoessische Materialprufungs und Forschungsanstalt EMPA; EMPA
Current assignee: Eidgenoessische Materialprufungs und Forschungsanstalt EMPA; EMPA
Priority date: 1995-01-09
Filing date: 1995-12-12
Publication date: 1997-10-29
Anticipated expiration: 2015-12-12
Also published as: ATE171240T1; DE59503647D1; WO1996021785A1; JPH10512635A; EP0803020B1; US5937606A; ES2122696T3; DK0803020T3; AU3977195A

Abstract

PCT No. PCT/CH95/00298 Sec. 371 Date Nov. 24, 1997 Sec. 102(e) Date Nov. 24, 1997 PCT Filed Dec. 12, 1995 PCT Pub. No. WO96/21785 PCT Pub. Date Jul. 18, 1996An arrangement and method for reinforcing a structural component utilizes an elongated strip or lamina which is applied to the surface of the structural component and which has at least one end which submerges into a recess in the surface of the component and is anchored in that recess. This has been found to greatly increase the reinforcing effect of the strip on the structure.

Description

Fastening reinforcement slats

The present invention relates to an arrangement for reinforcement on a longitudinally extended and / or flat structure or structural part by means of at least one lamella-like reinforcement arranged on the structure or structural part or masonry, a structural part provided for carrier functions, reinforced with an arrangement, a masonry with an arrangement and a method for reinforcing a building or part of a building.

For many years, research and practice have been concerned with the subsequent reinforcement of buildings, such as, in particular, reinforced concrete structures and masonry by applying additional reinforcement. The beginnings of this technique are described in J.Bresson, "Nouvelles recherches et applications concernant 1 'utilization des collages dans les structures. Beton plaque.", Annales ITBTP No. 278 (1971), series Beton, Beton armme No. 115, described and go back to the 1960s. In doing so, Bresson focused his efforts particularly on the research of bond stress in the area of the anchoring of glued steel lamellas.

For around twenty years, existing structures, such as reinforced concrete structures, such as bridges, floor and ceiling slabs, side members and the like, or even unreinforced masonry, have been reinforced by subsequent gluing of steel slats.

The reinforcement of concrete structures and masonry by gluing steel lamellas, for example with epoxy resin adhesives, can be regarded as standard technology today. There are several reasons that require reinforcement:

- increasing the payload,

- Modification of the static system, for example by subsequently removing load-bearing elements such as supports or reducing their support functions,

- reinforcement of components at risk of fatigue,

- increase rigidity,

- Damage to support systems or renovation of existing structures and masonry, as well

- Incorrect calculation or execution of the structure.

Subsequent reinforcements with glued-on steel lamellas have proven their worth on numerous buildings, as described, for example, in the following literature citations: Lad¬ner, M., Weder, Ch.: "Glued reinforcement in reinforced concrete construction", EMPA Dübendorf, Report No. 206 (1981 ); "Reinforcement of supporting structures with glued reinforcement", Switzerland. Bauzei¬ tion, reprint from the 92nd year, issue 10 (1974); "The renovation of the Gizenen Bridge over the Muota", Switzerland. Engineer & Architect, reprint from issue 41 (1980).

However, these reinforcement methods have disadvantages. Steel slats can only be supplied in short lengths, which means that only relatively short slats can be applied. In this way, lamella joints that become compulsory and potential weak points cannot be avoided. The cumbersome handling of heavy steel lamellas on the construction site can also cause considerable design problems for tall or difficult to access structures. In addition, with steel, even with careful anti-corrosion treatment, there is a risk of lateral rusting of the fins or corrosion the interface between steel and concrete, which can lead to detachment and thus loss of reinforcement.

Accordingly, in the publication by U. Meier, "Bridge renovations with high-performance fiber composites", Material + Technik, 15th year, volume 4 (1987), and in the publication by H.P. Kaiser, Diss. ETH No. 8918 from ETH Zurich (1989), proposed replacing the steel fins with carbon fiber reinforced epoxy resin fins. Slats made of this material are characterized by a low bulk density, very high strength, excellent fatigue properties and excellent corrosion resistance. It is therefore possible to use light, thin, carbon fiber-reinforced plastic lamellae instead of the heavy steel lamellae, which can be transported to the construction site almost endlessly in the rolled-up state. Practical investigations have shown that carbon fiber lamellas with a thickness of 0.5 mm are able to absorb a tensile force which corresponds to the flow force of a 3 mm thick FE360 steel lamella.

The carbon fiber lamellas mentioned have also proven their worth when reinforcing masonry in seismic zones. Report 229 of the Federal Materials Testing and Research Institute (EMPA), Dύbendorf, by G. Schwegler, entitled "Reinforcement of masonry with fiber composites in seismic zones", particularly suggests that existing masonry shear walls or walls in the facade area Reinforcing seismically endangered buildings with fiber composite lamellae. Masonry can thus be decisively strengthened in terms of shear and tensile strength compared to masonry that has not been reinforced. It is proposed, for example, to glue the reinforcement slats diagonally and crosswise to a push wall, such as a facade wall, whereby it is has shown that the final slat anchorage, for example in concrete slabs, is decisive for increasing the shear resistance.

Particular attention must be paid in all the cases described to the formation of shear cracks in the concrete or masonry. Shear cracks that occur lead to an offset on the reinforced surface, which generally results in the reinforcing lamellas being peeled off or detached. The formation of shear cracks is thus also an essential dimensioning criterion, both with regard to the load-bearing capacity of the unreinforced structural part and also with a possible risk of the subsequently arranged reinforcement lamellae becoming detached.

In international patent application WO93 / 20 296 a method is described by means of which structural parts provided for supporting functions are reinforced against shear forces occurring, in that the above-mentioned reinforcing lamellae are each pressed onto the outside of the end area by means of clamping elements in order to prevent detachment. The slats are arranged in such a way that the distance from the slat end to the support or the concrete slabs arranged at the end with push walls is as small as possible. The anchoring zone must be dimensioned such that the lamella tensile force can be anchored and the transmission of the force to a support or the concrete slabs enclosing a thrust wall is ensured.

In practice, however, it has now been shown that anchoring of the reinforcement lamellae in the area of the supports as a result of coves and shoulders is not always possible, which leads to an increase in the distance. Even when reinforcing push walls, it is usually difficult and time-consuming Anchoring reinforcement slats in the concrete slabs arranged at the top and bottom of these walls. Furthermore, for handling reasons on construction sites, it is advantageous if reinforcement lamellae do not have to be too long, but this automatically results if, for example, reinforcement lamellae have to extend from support to support when reinforcing bridges.

It is therefore an object of the present invention to propose a measure by means of which a largely constant reinforcement on structures can be achieved with shortened anchoring lengths on reinforcement lamellae.

According to the invention, the object is achieved by means of an arrangement according to the wording according to claim 1.

An arrangement is proposed for reinforcement on a longitudinally extended and / or flat structure or structural part by means of at least one lamella-like reinforcement arranged on the structure or structural part in a slack or prestressed manner, wherein according to the invention the at least one slat used for reinforcement is inserted into the structure or at least at one end The building part is anchored running into it.

It is proposed that at least one slat end, preferably at least almost continuously bent, be deflected into the building or masonry in order to be anchored in the building or masonry.

In this way it is possible to achieve a similar or almost the same reinforcement to a structure or masonry with short anchoring lengths as with longer anchoring lengths, which result from the fact that the reinforcement lamella practically extends from support to support. ger runs and anchoring of the slat ends in the area of the supports is easily possible. Experiments, which will be discussed in more detail below with reference to the attached figures, have shown that reinforcement lamellae which have only been arranged on the structure to be reinforced by a relatively short anchoring length beyond the load introduction and, according to the invention, are anchored so as to protrude into the structure part , result in almost the same reinforcement on the structure as when the corresponding slat end is anchored into the area of the support.

The arrangement or anchoring of a slat end, which projects into the structure or masonry, proposed according to the invention, is of course suitable for any known reinforcing slats, such as steel slats, glass fiber or carbon fiber reinforced slats, for example produced with epoxy resins or polyester ¬ resins, extruded reinforcing lamellae from a thermoplastic, etc.

The at least one end of the reinforcing lamella, or both ends of the reinforcing lamella, are preferably embedded in a continuously curved manner running into the building, wherein the inserted end can each be covered by concrete and / or a polymer-reinforced material, such as, in particular, an adhesive. In the case of, for example, carbon fiber reinforced epoxy resins, it is advantageous to use an epoxy mortar or an epoxy resin reinforced concrete polymer in order to anchor or cover the end of the lamella embedded in the masonry or concrete.

Of course, it is also possible that the slat end protruding into the masonry or concrete structure is additionally, as suggested in WO93 / 20296, with a plate, lamella to press len- or belt-like element against the building or the building part in order to achieve a further reinforcement against shear forces. A wedge covering the slat end is also suitable for this purpose.

Instead of these pressing means, however, it is also possible to anchor the slat end additionally in the building or building part or masonry by means of pre-tensioned or non-tensioned mechanical fastening means, such as in particular screws, rivets, pins, loops, and the like.

The arrangement proposed according to the invention is suitable for a building or a building part provided for supporting functions, which is reinforced with one or more reinforcing lamellae against shear forces occurring. But also for the reinforcement of any building or masonry by means of one or more reinforcing slats, it is advantageous to anchor the slat ends, as proposed according to the invention, running into the building or part of the building or masonry. For example, when reinforcing masonry in seismically endangered zones, it is possible to anchor the slat ends into the masonry by means of GRP slats, which eliminates the need to insert the slats into the concrete slabs or cover slabs that are respectively arranged end to the masonry to extend for anchoring, which is a significant simplification when applying such reinforcement lamellae.

For the reinforcement of buildings and masonry, the method according to one of claims 9 or 10 is proposed in the further process.

The invention will now be explained in more detail, for example with reference to the accompanying figures. Show:

1 schematically shows in longitudinal section a reinforced concrete bridge by means of a reinforcing lamella,

2 in side view shows a masonry or a push wall reinforced by means of reinforcing lamellae, for example suitable for a seismically endangered area,

3 schematically shown in longitudinal section, the arrangement and anchoring of a slat end according to the invention running into the masonry or building,

4a schematically shown in longitudinal and transverse and 4b section a concrete beam or a test arrangement, by means of which the terminal anchoring according to the invention is compared with a conventionally anchored slat end,

5a is a top view of a test arrangement with and 5b the concrete beam from FIG. 4 with a conventionally glued-on reinforcement lamella,

6a shows a test arrangement similar to that in FIGS. 4 and 6b and 5, but with an extended slat end,

7a, again the same experimental arrangement as in FIGS. 7b and 7c, FIGS. 4 to 6, but anchored with a slat end, as suggested according to the invention, running into the concrete beam, 8 shows, in diagram form, the deflection in the three test arrangements according to FIGS. 5, 6 and 7,

9a the slat expansion at the slat end at different and 9b different force levels and in the center of the beam in the test arrangement according to FIG. 5,

10a shows the elongation at the slat end at different and 10b force levels and in the middle of the support in the test arrangement according to FIG. 6,

11a shows the elongation at the slat end at different and 11b force levels and in the center of the beam in the experimental arrangement according to the invention

Fig. 7,

12a shows a longitudinal section and a top view schematically, and FIG. 12b shows a method for anchoring a slat end according to the invention,

13a shows a longitudinal section and a top view of the arrangement of a and 13b end anchor wedge on a slat end anchored according to the invention,

14a the problem on the basis of a haunch in longitudinal section and 14b the arrangement of a reinforcing lamella and the corresponding solution according to the invention, and

Fig according anchored. 15, a further building arrangement which ^¬ preference, with a reinforcement lamina, erfindungs¬ is amplified.

In Fig. 1 is a schematic longitudinal section of a reinforced concrete bridge ^¬ 1 shown, comprising a concrete slab 3, which is supported or held by two pillars 5 on the respective supports 7. As a result of aging, this concrete bridge was reinforced by means of a reinforcing lamella 10 arranged between the two supports 7. The reinforcing lamella 10 extends between the two supports 7 and is glued over its entire length, for example with an epoxy resin adhesive, the lamella also being glued to the concrete slab 3 in the area A ', as is customary in the conventional way. It is possible, as proposed in WO93 / 20296, to additionally anchor the slat ends by means of additional belts or steel plates, or to press them against the concrete plate 3.

2 shows a push wall 11 of a building which is located in a seismically endangered area. The masonry 13 is reinforced with laterally glued-on reinforcement lamellae 20, the lamellae usually being anchored in the end in the concrete slabs arranged below and above the thrust wall 13 or in the floor and ceiling slabs 15 and 17. In this case, for example in area A ", the slat end is led into the concrete slab 17 in order to be anchored therein. The generation of this anchoring is complex and requires a great deal of work.

3 now shows, according to the invention, how the slat ends can be anchored more easily and effectively in the areas A 'and A ". This enables the slat end in the area A' not to run close to the support 7 has and in the area A "it is not absolutely necessary that the slat end has to extend into the concrete ^slab 17. 3, the lamella end 22 of the reinforcement lamella 10 or 20 extends into the concrete slab 3 or the masonry 13, and is accordingly covered in this area by concrete or cement mortar. Of course, it is also possible to carry out the covering 23 by means of a polymer adhesive, such as an epoxy resin mortar or a polyurethane or silicone formulation. The optimal choice of the material to be used depends, for example, on the material from which the reinforcing lamella is made.

On the basis of the following figures, it is now to be shown that the insertion of the slat end into the building or into the masonry, which is shown schematically in FIG. 3, can achieve a decisive shear reinforcement on the building, even if the slat length is not as usual is chosen from support to support or from concrete slab to concrete slab. In particular, the experimental arrangement described below is intended to show that with the same slat length, an increase in the reinforcement can be achieved if the slat end (s) are anchored in the building or part of the building or masonry.

4a shows a longitudinal section of a concrete girder 3 analogous to that of FIG. 1, which is used for the following test arrangements. The concrete beam 3 rests on the supports 7 and comprises a steel reinforcement 4. In addition, the concrete support 3 has been reinforced on its lower side 8 by means of a CFRP lamella 10, one end 11 of the lamella practically extending to the corresponding support 7 ¹ , whilst outputting the opposed fins being spaced ^¬ end 13 from the other supports 7 ". Fig. 4b shows the concrete beam of Fig. 4a in cross-section.

Various test methods are now used on the concrete beams shown schematically in FIGS. 4a and 4b. Orders bending tests carried out, a force F being introduced at the two points 15 each indicated by an arrow.

The experimental arrangement, shown in FIG. 5a, shows the reinforcement lamella in a top view of the concrete beam 3 to be reinforced, the one lamella end 11 extending up to the support 7 ', while the opposite lamella end 13' extends a distance above the corresponding one 5a extends. The dimensioning of the test arrangement is shown in the illustration in FIG. 5a, the slat end 13 'correspondingly extending 20 cm beyond the force introduction point 15 ". 5b schematically shows the measuring points 29 which are provided on the lamella end 13 'for determining the forces or the occurring expansion. Point 24 in Fig. 5a marks the center of the concrete beam 3, where a measuring point is also arranged.

In order to prevent failure of the lamella 10 in the region of the end 11, a pressure plate, not shown, is also provided. The slat end 13 'is anchored in a conventional manner to the underside of the concrete beam.

6a and 6b show an analog test arrangement, however the slat end 13 "extends 30 cm beyond the corresponding force introduction point 15" and thus extends closer to the corresponding support 7 ". Again in the area of the end are 13 "Several measuring points are provided, as well as in the middle at point 24 on the concrete beam 3.

A test arrangement is shown in FIG. 7, the slat end 13 ′ ″ now running into the structural part is anchored, which is shown schematically in the longitudinal sectional view of FIG. 7c. The lamella end 13 '' again extends only 20 cm beyond the corresponding force introduction point 15 '', that is to say it is 10 cm more apart from the corresponding support 7 ", compared to the test arrangement according to FIGS. 6a and 6b. The anchoring of the The slat end 13 '"runs along a distance of 10 cm, the continuously curved end piece 13a''' extending in the concrete beam 3 being schematically shown in longitudinal section in FIG. 7c. Above the slat in the area 23 was in the anchoring zone of the end section 13a an epoxy resin mortar is applied. 7b schematically shows a number of measuring points 29 which have been arranged on the lamella 10. A measuring point was also arranged on the reinforcement lamella 10 at the point 24 in the middle of the concrete beam 3.

8 now shows in diagram form the deflection of the test beams measured in the center of the beam with the three test arrangements used according to FIGS. 5, 6 and 7. The deflection δ (mm) is shown as a function of the force (KN) introduced at the points 15, it being shown separately for the three test arrangements by the deflection.

FIGS. 9, 10 and 11 each show the lamella expansions at the lamella end at different force levels for the three test arrangements of FIGS. 5, 6 and 7 in the corresponding FIG. A, and the elongation in the respective FIG. B in the middle of the beam.

In Table 1 below are for the three Versuchsan¬ orders of the measured bearing resistance, the medium Lamel ^¬ lenspannung in carrier center, as well as the failure mode, the carrier listed.

Carrier F _maχ [kNm] σ _L (F) [N / mπr] *) failure

Fig. 5 65 456 (60) slats start

Fig. 6 65 628 (65) slats start

Fig. 7 75 1'063 (75) slats start

*) Medium slat tension in the middle of the beam

Discussion of the results or the diagrams according to FIGS. 8 to 11 and of Table 1:

The maximum load and in particular the maximum slat expansion in the test arrangement according to the invention according to FIG. 7 could be significantly increased compared to the supports of test arrangements 5 and 6. 5 and 6 show similar behavior despite different anchoring lengths in the area of the ends 13 'and 13 ". Approximately the same strains are registered in the central area of the girder. Each time the flow load is reached, the lamellae shear off Slat end down.

The blade of the carrier according to the present invention ^pre-¬ chosen arrangement in Fig. 7 is "embedded at one end 13 'in Be¬ tinge 3 and covered with adhesive 23. The maximum lamellae strains were compared with the above-be ^¬ signed attempts in connection with the 5 and 6. The behavior can probably be justified as follows:

- Redirection of the resulting tension components perpendicular to the glued lamella. So that the lamella is pressed, which creates compressive stresses in the concrete. With a correspondingly ideal and optimized geometry of the end section 13a '"which runs into the carrier 3, the lamella can be pressed against the carrier, which is comparable to the effect of the transverse stress described in the international patent application WO 93/20296.

The adhesive on the lamella or a pressure wedge according to FIG. 3 or the following FIGS. 13a and b prevents the slat end from coming off prematurely, which is caused by the vertical tension component which is directed away from the carrier.

By means of the test arrangements in FIGS. 5 to 7 it can be shown impressively that the inventive anchoring of the reinforcement lamella, which anchors into the structure, results in a substantially increased reinforcement on the structure compared to a reinforcement lamella of the same length or length , the corresponding end of which is not anchored in accordance with the invention as it runs into the building, but rather, as is known from the prior art, is glued to the building along an essentially longer anchoring path or is anchored thereon.

12a and 12b schematically show a method of how the inventive anchoring of a reinforcing lamella 10 is possible in a relatively simple manner. As a rule, it is not possible to grind, mill or grind into the structure, so that, as shown in FIGS. 12a and 12b, it is now proposed that the end of the reinforcement lamella end 22 run into the structure by means of so-called stepped core bores to accomplish. So in the terminal The area of so-called core bores 31 is stepped into the concrete 3 to be reinforced by means of, for example, a conventional drilling machine, the first bore being only a small depth away from the slat end, while the last core bore 31 has a great depth in the area of the slat end. Such core bores can have, for example, a hole diameter of 10 or more cm, depending on how wide the reinforcement lamella 10 to be anchored is. After arranging the slat end 22 into the building, an anchoring wedge 23 can be arranged again, as already shown in FIG. 3.

Such an anchoring wedge is also shown in FIGS. 13a and 13b, with additional fastening means 33 now being arranged, which may be, for example, screws, bolts, loops, etc. By means of these fastening means 33, the anchoring effect of the wedge 23 on the slat end 22 is additionally reinforced. 13a shows the wedge 23 in longitudinal section, while FIG. 13b shows a plan view of the wedge 23.

14a and 14b show a concrete structure 32, such as a supporting structure for galleries or parking halls, in which structure the ceiling plate 35 and the side wall 37 are connected to one another via a so-called haunch 39 in the corner area. Now, if the Un¬ underside of the ceiling is to reinforce 35 by means of a reinforcing plate 10, seen in Fig. 14a shows that anchoring the lamella end 13 in the area of the haunch is unfavorable because Melle upon the occurrence of tensile forces on the Verstärkungsla ^¬ 10, this is replaced in the corner area 36. For this reason, as shown in FIG. 14b, it is proposed according to the invention to anchor the reinforcing lamella 34 or its end 22 in the corner region 36 running into the concrete ceiling 35. When the concrete ceiling 35 is loaded, the tensile stress component resulting from the bending moment on the slat in the end region of the slat is deflected into the ceiling, so that the slat end 22 is not detached.

15 finally shows a further structure arrangement, for example once again a supporting structure, comprising a concrete ceiling 41 and a partition wall or a longitudinal pillar 43, the ceiling 41 again being reinforced by means of a reinforcement lamella 10. In the corner area 45, between the ceiling 41 and the pillar 43, the slat end 22 is anchored according to the invention running into the ceiling.

The auxiliary line 53 shown in FIG. 15 shows the curve of the bending moment in relation to the building part or to the system center plane 47 running through the ceiling. This clearly shows the passage through a zero point at a distance x from the pillar 43 near the corner area 45 and a subsequent sharp increase. By anchoring the slat end 22 according to the invention in the spacing area x, where no tensile force occurs, it is possible to fully absorb the tensile stress subsequently created by the reinforcing slat 10, starting from the zero point. In the case that the reinforcing plate 10, as glued conventionally, would be anchored in the corner region 45, a collecting entste ^¬ Henden tension would ^¬ rich 45 possible only at a distance greater than x from Eckbe, whereby the risk of shearing of the sipe 10 of the concrete slab 41 is given. 1 to 15 serve only for a more detailed explanation and illustration of the idea according to the invention, and a terminal anchoring of reinforcing slats proposed according to the invention can of course be chosen in any desired manner. The material used for the reinforcing lamellas can also be any, for example a lamella made of sheet iron, steel, aluminum, a reinforced polymer, such as, in particular, GRP-reinforced epoxy resin, etc. Essential to the invention is the fact that a reinforcement lamella attached or attached to a structure or masonry is anchored at least with one end running into the structure or masonry, whether a reinforcement wedge is used or not is not primarily essential and depends on the Requirements and the location.

Claims

Claims:

1. Arrangement for reinforcement on a longitudinally extended and / or flat building (3) or building part or a masonry (13) by means of at least one lamellar reinforcement (10, 20) arranged slackly or prestressed on the building, building part or masonry, characterized in that the at least one lamella used for reinforcement is anchored at least at one end (13 '", 23) into the building, part of the building or the masonry.

2. Arrangement, in particular according to claim 1, characterized gekenn¬ characterized in that the slat end is deflected deflected anchored in the building running.

3. Arrangement, in particular according to one of claims 1 or 2, characterized in that the at least one lamella for reinforcing the structure, part of the structure or masonry with at least one end of the lamella is largely continuously curved into the structure or masonry, the recessed end is covered by concrete, cement, mortar and / or a polymer-reinforced material, such as an adhesive in particular.

4. Arrangement, in particular according to one of claims 1 to 3, characterized in that the at least one reinforcing lamella made of a metal-like material, such as in particular iron, steel, aluminum or a reinforced plastic, such as in particular a glass, Carbon, aramid, etc. fiber-reinforced polymer.

5. Arrangement, in particular according to one of claims 1 to 4, characterized in that the slat end extending into the building or building part or masonry is also pressed against the building or masonry with a wedge, plate, lamella or belt-like element.

6. Arrangement, in particular according to one of claims 1 to 5, characterized in that the slat end is additionally anchored in the building or masonry by means of mechanical fastening means, such as in particular screws, rivets, pins and the like.

7. Structural part intended for support functions, reinforced with an arrangement according to one of claims 1 to 6.

8. masonry with an arrangement according to one of claims 1 to 6.

9. A method for reinforcing a longitudinally extended and / or two-dimensional building, building part or masonry by means of at least one lamellar reinforcement arranged slackly or pretensioned on the building or masonry, characterized in that at least one of the slat ends is deflected into the building or building part or masonry is arranged running in.

10. The method, in particular according to claim 9, characterized in that the lamella end running into the building or masonry is covered by means of concrete, cement mortar and / or a reinforced polymer, such as polymer concrete or an adhesive material.

11. The method, in particular according to claim 9, characterized in that the deflected slat end is pressed or driven against the building or masonry by means of a wedge, by means of a plate or by means of slat-like or belt-like elements.