EP0190989B1 - Intermediate anchor arrangement for the prestressing of construction elements which are built in many stages, and method for setting up such an intermediate anchor arrangement - Google Patents

Description

The invention relates to an intermediate anchor arrangement according to the preamble of patent claim 1 and to a method for producing an intermediate anchor arrangement according to the preamble of patent claim 5.

In prestressed concrete construction, the "prestressing with subsequent bond _{" is known} , in which the tendons are guided longitudinally in cladding tubes and tensioned after the concrete has hardened. The empty spaces remaining in the cladding tubes are then filled with grout the respective tendons achieve a bond between them and the concrete surrounding them, which provides additional security both when broken and when an anchor fails.

In addition to the «prestressing with subsequent bond» mentioned above, «prestressing without bond» has recently been increasingly used for concrete ceilings and other concrete components. Pre-stressing without bond prevents the tendon from coming into direct contact with the concrete. The tendon surrounded by a layer of permanent corrosion protection grease is located in a plastic tube. After the concrete has hardened, the tendons are prestressed without creating a bond with the surrounding concrete over the entire length between the two anchors.

In such constructions, in particular with long tendons that pass through several ceiling fields, it is disadvantageous that if one ceiling field is destroyed locally, the directly adjacent ceiling fields may be affected.

It can also happen that if an anchoring point of a single tendon fails, the remaining intact tendons must compensate for the lost prestressing force of the single tendon, which will inevitably lead to a reduction in the breaking resistance of such a section.

Efforts were therefore made to install additional reserves by means of additional intermediate anchors, preferably in the area of the supports, which become effective if one of the end anchors fails and only a part of the ceiling panels is damaged.

Another advantage of these intermediate anchors is that the increase in tension is increased in relation to the reduction in the free expansion length of the tendons and that the breaking force is increased accordingly.

DE-B-1 147740 describes an intermediate anchorage, which is referred to as a tendon joint, in which two adjacent tension anchors are firmly connected to one another by threaded bolts before the second construction stage is concreted. The two tension anchors hold the adjacent ends together of two tendons arranged one behind the other, the threaded bolts being loaded with at least the prestressing force of the tendons. To avoid overloading the plate-shaped tension anchor parts, an annular fitting is inserted between them and a rubber plate between the clamping wedges and the two tension members. This means that when the high-strength screws are tightened, the clamping wedges are only pressed into the anchor cone with part of the full pretensioning force of the two tendons, which part is sufficient so that no slippage occurs when these links are pretensioned, and the high-strength, prestressed screws practically do not be stretched more. This known intermediate anchorage has the disadvantages that high-strength threaded screws must be used, which together have to withstand the tension of the tendons, tightening the nuts screwed onto the threaded bolts requires great skill and must be carried out very carefully, since at least four high-strength screws are tightened at the same time and, finally, the section between the tendons in the area of the butt joint is not pretensioned on the concrete by the rigid and inextensible tendon joint. This means that the construction section in the area of the butt joint is in danger of cracking in use and must be dimensioned according to other static criteria than that of the prestressing without bond.

US-A-4 368 607 describes an intermediate anchor which has two tension anchors with associated clamping wedges. The clamping wedges of each tension anchor are assigned an actuating member with a tube piece surrounding the tension member and a hood surrounding the thicker ends of the clamping wedges and part of the tension anchor. An external thread is present on the pipe sections and a tubular pressing member provided with opposing internal threads is screwed onto this external thread of the opposite pipe sections of the actuating members. The central area of the pressing member is hexagonal so that the pressing member can be rotated about its longitudinal axis with the help of a wrench, whereby the actuating members are pressed apart and the clamping wedges are pressed into the frustoconical recess in the tensioning anchors. This known intermediate anchor arrangement is foamed as a whole between the two anchor plates with polystyrene and thus forms a cuboid plastic recess block, the actuating element being in a position in which the clamping wedges only partially protrude into the aforementioned frustoconical recess and which enables the individual tendons to be subsequently threaded.

To create, for example, a concrete ceiling that extends over several fields, the plastic foam recess block is preferably arranged above the supports. Normal known tension anchors are placed at both ends of the tendon and then the entire ceiling is concreted. After the concrete has hardened, the foam surrounding the intermediate anchor arrangements is removed so that the pressing members are accessible. The tendons are then tensioned over their entire length in a known manner. Then the pressing member of each intermediate anchor arrangement is actuated in such a way that the clamping wedges are pressed into the frustoconical recess of the tensioning anchors and thus the relevant area of the tendon is firmly clamped in the tensioning anchor so that the tendon can no longer move in its longitudinal direction. Finally, the recesses created by removing the plastic are filled with concrete.

In the intermediate anchor arrangement described above, the plastic has to be removed after the concrete has hardened and the resulting cavities in the concrete have to be filled up again after the compression members have been tightened, which is associated with considerable additional work. The pressing member must be tightened with great care, because if the tightening is insufficient, the clamping effect is too small and the intermediate anchor arrangement is not effective.

Another disadvantage is that the recesses in the concrete are only filled with concrete mortar after the prestressing work has been completed, thereby forming places that are not prestressed.

It is an object of the invention to provide an intermediate anchor arrangement which does not have the disadvantages mentioned above and whose use is problem-free.

The intermediate anchor arrangement according to the invention is characterized by the features stated in the characterizing part of patent claim 1.

The inventive method for producing an intermediate anchor arrangement is characterized by the features listed in the characterizing part of claim 5.

• Fig. 1 die stark vereinfachte Darstellung einer Betondecke im Schnitt,
• Fig. 2 einen Längsschnitt durch ein Ausführungsbeispiel der erfindungsgemässen Zwischenankeranordnung, wobei einer der Spannanker bereits einbetoniert ist,
• Fig. 3 Klemmteile der Anordnung gemäss der Fig. 2 im Längsschnitt, mit einer zweiten Ausführungsform des Abstandhaltemittels,
• Fig. 4 einen Schnitt entlang der Linie IV-IV der Fig. 3,
• Fig. 5 einen Schnitt entlang der Linie V-V der Fig. 3,
• Fig. 6 Klemmteile der Anordnung nach der Fig. 2 im Längsschnitt, mit einer dritten Ausführungsform des Abstandhaltemittels und
• Fig. 7 einen Schnitt durch einen der Spannanker der Zwischenankeranordnung, wobei der Spannanker in einer Vorbereitungsphase nach dem Betonieren der vorangehenden Bauetappe dargestellt ist.

The invention is explained in more detail below with reference to the drawing, for example. Show it

• 1 shows the greatly simplified representation of a concrete ceiling in section,
• 2 shows a longitudinal section through an embodiment of the intermediate anchor arrangement according to the invention, one of the tension anchors having already been concreted in,
• 3 clamping parts of the arrangement according to FIG. 2 in longitudinal section, with a second embodiment of the spacing means,
• 4 shows a section along the line IV-IV of FIG. 3,
• 5 shows a section along the line VV of FIG. 3,
• Fig. 6 clamping parts of the arrangement of FIG. 2 in longitudinal section, with a third embodiment of the spacer and
• 7 shows a section through one of the tension anchors of the intermediate anchor arrangement, the tension anchor being shown in a preparation phase after concreting the preceding construction phase.

In Fig. 1, a component, in particular a concrete ceiling 1, is very simplified and shown in section so that one of the tendons 2 extending through the concrete ceiling 1 is visible. The ends of the concrete ceiling are supported on outer walls 3 which are only partially shown. Between the outer walls 3, pillars 4, metal supports or partitions are provided, on which the concrete ceiling 1 is additionally supported. At both ends of the tendon 2, which can be, for example, a tension cable made of steel wires, an end tension anchor 5 is provided. To prevent the prestressing force from being lost over the entire length of the tendon in the event of any loosening of one of the end tendons 5 or a break in the tendon 2, so-called intermediate anchor arrangements 6 are preferably arranged in the area above the pillars 4. The invention described below relates to the design and manufacture of such an intermediate anchor arrangement 6.

2 shows a longitudinal section through an exemplary embodiment of such an intermediate anchor arrangement 6, which comprises two tension anchors 7 and 8, which can also be used individually as the above-mentioned end tension anchors 5 at the two ends of the tension member 2. Each tension anchor has a support body 9 or 10 with a radially outwardly projecting flanges 11 or 12 and a support rib 13 or 14 also projecting outwards. Following the support ribs 13 and 14, the support body 9 and 10 has a cylindrical projection 15 and 16 respectively. A passage consisting of a cylindrical part 17 or 18 in the area of the shoulder 15 or 16 and a frustoconical part 19 or 20 extends through the support body 9 or 10, through which the tendon 2 extends. The frustoconical part 19 is intended for receiving two clamping wedges 21, for example, and the frustoconical part 22 is intended for receiving two clamping wedges 22, for example. The clamping wedges 21 and 22 are provided on their inside with sawtooth-shaped ribs 23 which, when the clamping wedges are brought into the operative position, at least partially penetrate into them to hold the tendon 2 in place.

Between the large end faces 24 of the clamping wedges 21 and 22 is a tubular rigid element 25, for. B. a pipe section arranged. The inner diameter of the tubular element 25 is larger than the outer diameter of the tendon 2 so that it can move freely within the tubular element 25.

Screws 26, e.g., distributed evenly over the circumferential area of the flanges 11 and 12. B. four, extend through holes in the flanges. The task which the screws 26 have to be performed is described in more detail below.

3 shows only a part of the tendon 2 and the clamping wedges 21 'and 22' of the intermediate anchor arrangement. The clamping wedges 21 'and 22' are rigidly connected to one another via a web 27, which web takes over the function of the above-mentioned tubular element 25. FIG. 4 shows a section through the web 27 and FIG. 5 shows a section through the clamping wedges 22 '. The web 27 is designed such that it does not touch the tendon 2 in the assembled state.

6 likewise shows only the tension member 2 and the clamping wedges 21 and 22 "of the intermediate anchor arrangement. The clamping wedges 21 are of the same design as the clamping wedges 21 which are shown in FIG. 2. The clamping wedges 22" each have an extension 28, the free ends of which are intended to rest against the end face 24 of the clamping wedges 21. The extensions 28 are designed such that they do not touch the tendon 2 in the assembled state of the clamping wedges. This embodiment is the most advantageous of the three above-mentioned embodiments of the means for holding the clamping wedges at a predetermined distance.

FIG. 7 shows a part of the intermediate anchor arrangement according to the invention after concreting the preceding construction phase. Before concreting the preceding construction stage, the tendon 2 was pushed through the tension anchor 7 and the tension anchor 7 was fastened by means of screws 26 to a formwork board 29 which is only partially shown, the tension anchor 7 being replaced by a filler 30, e.g. B. of polystyrene, is kept at a distance from the formwork board 29. The concrete filled in during the first construction phase is designated by 31.

Since the intermediate anchor arrangement described above is used to create components such as concrete ceilings, floor slabs, rugpists, bridge slabs, etc. with «pre-stressing without bond», the sections of the tendon 2 which extend through the concrete are of a protective cover, not shown, or one Surround protective tube. So that the concrete does not penetrate into the interior of the tension anchor 7, a sleeve 32 is provided which forms a protective transition between the end of the protective cover (not shown) and the cylindrical extension 15.

After the concrete 31 has hardened, the formwork board 29 and the filler 30 are removed. The latter leaves a niche 33 (see FIG. 2) into which the tension anchor 7 partially protrudes. Thereafter, the clamping wedges 21 are inserted into the frustoconical part 19 of the passage of the tension anchor 7 and the section of the tendon 2 extending through the hardened concrete 31 is prestressed to the desired value by means of a known and therefore not described prestressing device. After the prestressing has been carried out, the clamping wedges 21 assume the position shown in the figure within the tension anchor 7 and prevent the section of the tension member 2 from being able to relax.

Now the tubular element 25 and then the tension anchor 18 are first pushed onto the tensioning element 2 without the clamping wedges 22 until the element 25 rests on the end face 24 of the clamping wedges 21. Then the clamping wedges 22 are inserted into the frustoconical part 20 of the passage in the tension anchor 8 and this is pushed in the direction of the already embedded concrete anchor 7 until the end face 24 of the clamping wedges 22 abut the tubular element 25 and the screws 26 pass through the flange 12 of the Extend tension anchor 8. The tension anchor 8 is held coaxially to the tension anchor 7 by means of screw nuts 34 screwed onto the ends of the screws 26, which are only moderately tightened. The screw nuts 34 are only tightened to such an extent that all the clamping wedges 21 and 22 lie snugly against the tubular element 35 and the clamping wedges 22 are not completely inserted into the frustoconical part 20 of the passage in the tensioning anchor 8 and thus only a very slight clamping effect on the tendon 2 exercise. This state is shown in FIG. 2.

After attaching a further sleeve 32 at the end of the shoulder 16 of the tension anchor 8 and a corrosion protection tape 35 around the joint 36 between the two tension anchors 7 and 8, the subsequent construction section is concreted. The niche 33 is also filled with concrete. The anti-corrosion tape 35 prevents concrete from entering the space between the clamping wedges 21 and 22.

After the concrete filled during the subsequent construction phase has hardened, the relevant section of the tendon 2 is prestressed to the desired value mentioned above. At the end of this section, an end tie rod 5 or the tie rod 7 of a subsequent intermediate anchor arrangement can be arranged. Because the clamping wedges 22 of the tension anchor 8 have practically no clamping action on the tendon 2, the prestressing of the second section of the tendon 2 affects the part of the tendon 2 clamped by the clamping parts 21, whereby the tendon 2 at least approximates its entire length is pre-stressed evenly, regardless of the number of intermediate anchor arrangements located between the end points of the tendon 2.

Even after the subsequent section of the tendon 2 has been prestressed, the tension anchors 7 and 8 and the clamping wedges assigned to them are in the position shown in FIG. 2, ie the clamping wedges 21 of the tensioning device 7 exert their full clamping action on the tendon 2 while the clamping wedges 22 of the tendon 8 have almost no clamping action exert the tendon 2.

A major advantage of the intermediate anchor arrangement described above enables the prestressed tendon 2 over its entire length, i. H. is preloaded practically evenly in the area of the intermediate anchor arrangements.

If the tension anchor 5 at the other end of the first section of the tension member 2 suddenly releases or the tension member breaks in the first section, the clamping wedges 21 of the tension anchor 7 are pulled to the right in relation to FIG. 2 by the prestressing in the remaining part of the tension member 2 . This movement is instantaneously transmitted via the tubular element 25 to the clamping wedges 22 of the tension anchor 8, whereby the clamping wedges 22 inevitably come into their operative position, i. H. be pushed completely into the frustoconical part 20 of the passage in the tension anchor 8. As a result, the clamping action is transmitted from the clamping wedges 21 to the clamping wedges 22.

If the anchoring in the following section is released, the pretensioning in the preceding section of the tendon 2 is maintained by the clamping wedges 21 of the tendon 7 that are already in the clamping position.

As already mentioned with reference to FIGS. 3 and 6, instead of the clamping wedges 21 and 22 and the tubular element 25, the clamping wedges 21 'and 22' can be used, which are rigidly connected to one another via the web 27, or preferably can Wedges 21 and 22 "are used, the wedges 22" having the extension 28. This latter embodiment of the spacer means is characterized by an assembly which is simpler than that of the tubular spacer.

The intermediate anchor arrangement described above is also effective in the event of a fault if, for example, when prestressing the subsequent construction phase, a greater pretension is applied to the tendon 2 than the above-mentioned setpoint. In this case, the clamping wedges 21 of the tensioning anchor 7 can be moved a little to the right in relation to FIG. 2, as a result of which the clamping effect of the clamping wedges 21 is reduced. However, the tubular element 25 transmits the displacement movement of the clamping wedges 21 to the clamping wedges 22 in such a way that the clamping effect of the wedges 22 increases to the extent that the clamping effect of the clamping wedges 21 decreases. As a by-product of this, the tendon 2 is again subjected to tensile stress over its entire length. Should a defect occur on one or the other side of the intermediate anchor arrangement, the clamping wedges react in the same way as already described above, i. H. in the event of a fault, those clamping wedges that face the faulty area are always automatically brought into their full operative position.

Because the screws 26 serve on the one hand to hold the formwork board 29 during the concreting in of the tension anchor 7, to hold the tension anchor 8 during assembly and to fit the tubular element 25 or the extension 28 against the end face of the clamping wedges, they are not a major burden exposed and therefore normal screws can be used.

Claims (5)

1. Intermediate anchor arrangement for prestressing structural components, particularly concrete ceilings, which are produced in several phases of construction, by means of at least one prestressing element (2) extending through the structural members, with two prestressing anchors (7, 8) having at least one clamping wedge (21, 22) each, and with screws (26) for holding the two prestressing anchors together after the carrying-out of the preceding phase of construction and during the following phase of construction, at least one rigid spacer means (25 ; 27 ; 28) being disposed between the clamping wedges (21, 22) of the two prestressing anchors (7, 8) for communicating the clamping effect of the clamping wedges of the one prestressing anchor to the clamping wedges of the other prestressing anchor, and the dimension of the spacer means (25 ; 27; 28) in the direction of the prestressing element (2) being so chosen for keeping a distance between the clamping wedges that either only the clamping wedges of the one prestressing anchor are in full clamping effect or the clamping wedges of both prestressing anchors are only partially in clamping effect.

2. Intermediate anchor arrangement according to claim 1, characterized in that the spacer means is a tubular rigid element (25) having a larger inside diameter than the outside diameter of the prestressing element, that the tubular element surrounds the prestressing element (2), and that the tubular element (25) is disposed between the opposite end faces (24) of the clamping wedges of the two prestressing anchors.

3. Intermediate anchor arrangement according to claim 1, characterized in that the rigid means are formed by extensions (28) on the clamping wedge (22") of one of the prestressing anchors, and that the said extension does not touch the prestressing element.

4. Intermediate anchor arrangement according to claim 1, characterized in that the rigid means are formed by a crosspiece (27) rigidly connecting the clamping wedges (21', 22') of the prestressing anchors, and that the crosspiece is so formed that it does not touch the prestressing element.

5. Process for prestressing structural components which are produced in several phases of construction, having an intermediate anchor arrangement according to claim 1, by embedding the first prestressing anchor (7) of the intermediate anchor arrangement in concrete during the preceding phase of construction and by prestressing the respective section of the prestressing element after the setting of the concrete, characterized in that thereafter the second prestressing anchor (8) traversed by the prestressing element is so fastened by means of screws (26) to the first prestressing anchor (7) embedded in concrete that the clamping wedges (21, 22) of the two prestressing anchors rest against the spacer means (25 ; 27 ; 28), that the said screws are tightened only to the extent that the second prestressing anchor remains stationary during the concreting of the following phase of construction and the clamping wedges (22) of the second prestressing anchor are in the starting phase of the clamping position, that after the setting of the concrete poured during the following phase of construction the associated section of the prestressing element (2) is prestressed like the preceding section during the preceding phase of construction.

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