Dowel and prefabricated concrete element with same

Description

[0001] The present invention relates to a dowel with a dowel axis for casting into a precast concrete element.

[0002] Such anchors are cast into prefabricated concrete wall elements, for example. During installation, these elements often need to be temporarily supported.

[0003] Publications US 2010 / 0293883 A1, EP 4 134 503 A1, and EP 3 971 360 also show various dowels. Document DE 20 2019 100 898 U1 discloses a dowel according to the preamble of claim 1.

[0004] For example, it is known to erect prefabricated wall elements consisting of two parallel concrete shells spaced apart on a floor surface, insert reinforcing metal between the concrete shells, and then pour in-situ concrete between the concrete shells. To prevent these prefabricated wall elements ("double walls" or "hollow walls") from toppling over during the placement of the reinforcement and in-situ concrete, they are supported by diagonally arranged supports, which are connected to the floor surface on one side and to the prefabricated wall element on the other. Once the in-situ concrete has fully hardened, the supports can be removed.

[0005] The supports are bolted to both the ground and the precast concrete element. To bolt the support to the ground, a hole is drilled in the ground and then the support is screwed to the ground using a concrete screw. Concrete screws have a special self-tapping thread that cuts into the wall of the drilled hole, providing a secure connection. Securing the support to the ground is therefore relatively complex, as a hole must first be drilled and then a thread must be cut into the hole using the concrete screw. Furthermore, this type of fastening is only sufficiently strong if the ground material has already fully hardened.

[0006] In principle, it is possible to use the same fastening method to attach the column to the precast concrete element. However, to save time, it is common practice to cast dowels into the precast concrete element, allowing the column to be secured using a screw that engages the dowel.

[0007] These dowels can have an internal thread into which the screw engages, thereby pushing the dowel radially outwards so that the dowel is squeezed between the screw on the one hand and the prefabricated wall part on the other.

[0008] Therefore, while the column's connection to the ground essentially creates a positive connection, the connection to the precast concrete element is primarily frictional. Therefore, different screw types are used. When installing precast wall elements, it is important to ensure that a concrete screw is used to secure the column to the ground and a conventional screw, such as a wood screw, is used to secure the column to the precast wall element. This is prone to errors.

[0009] If a conventional screw is accidentally used to secure the support to the ground, the worker will immediately notice, as the conventional screw cannot cut a thread into the hole in the ground. The worker will therefore correct their mistake and use the concrete screw.

[0010] However, if a concrete screw is accidentally used to attach the column to the precast wall element, the worker may not notice this, as the concrete screw can be screwed into the anchor, but it does not provide the necessary force-locking connection, and may even destroy it. The connection between the column and the precast concrete element can therefore become loose during the placement of in-situ concrete or reinforcement elements, or during strong wind loads, causing the precast concrete element to collapse.

[0011] The object of the present invention is therefore to mitigate at least some of the disadvantages described.

[0012] According to the invention, this object is achieved by a dowel with a dowel axis for casting into a precast concrete part, which is intended to receive a fastening screw with a screw head and a thread and to hold it in the precast concrete part, wherein the dowel has a head section for receiving the screw head and a fastening section for receiving the thread, wherein the dowel is designed both for use with a concrete screw and for use with a non-self-tapping screw, such as a wood screw. The fastening section has a substantially cylindrical cavity that is open on one side, wherein in every sectional view perpendicular to the dowel axis, the wall thickness of the dowel is greater than 30% and preferably greater than 40% of the diameter of the cavity.

[0013] This measure allows the cheaper wood screw to still be used to attach the column to the prefabricated wall element. However, if a concrete screw is accidentally used, the anchor according to the invention provides a sufficiently strong connection even in this case.

[0014] The relatively large wall thickness of the anchor in every area where the thread of the screw engages with the anchor ensures that there is sufficient anchor material in every area of ​​the fastening section of the anchor, which can be compressed by a conventional screw to achieve a force-locking connection.

[0015] In a further preferred embodiment, the dowel is made of a material with a modulus of elasticity less than 10 GPa and preferably less than 7 GPa. This measure ensures that the dowel has high elasticity, which supports the formation of a force-locking connection.

[0016] In a particularly preferred embodiment, the anchor is made of a thermoplastic material, preferably polycaprolactam and particularly preferably fiber-reinforced polycaprolactam. Polycaprolactam is also referred to as PA-6. Glass fiber-reinforced material, namely polycaprolactam with 30% glass fiber content (PA 6 GF30), is best used.

[0017] In a further preferred embodiment, it is provided that the fastening section has a plurality of elevations on the outer side, which are designed such that each elevation, when cast into the precast concrete part, is positively connected to the precast concrete part in such a way that a relative movement between the elevation and the precast concrete part is positively connected both in the direction of the longitudinal axis and in the circumferential direction.

[0018] Particularly when the anchor is used together with a concrete screw, which cuts a thread into the anchor and does not press the anchor walls outwards against the precast concrete element, the elevations give the anchor more hold within the precast concrete element. Therefore, on the one hand, the elevations are designed in such a way that, when cast in, i.e., when the anchor is arranged within the precast concrete element, relative movement of the anchor along the anchor axis is prevented. This is because both the precast concrete element and the anchor have corresponding active surfaces that lie on top of one another and prevent both movement of the anchor towards the precast concrete element and movement of the anchor out of the precast concrete element through form closure.

[0019] On the other hand, the elevations are also designed in such a way that, when cast in, a relative movement of the dowel around its circumferential direction, i.e. a rotation of the dowel within the precast concrete element around its axis, is prevented, since then both the precast concrete element and the dowel have corresponding active surfaces which lie on top of one another and prevent both a right and a left rotation of the dowel within the precast concrete element by means of form closure.

[0020] The elevations can, for example, be dome-shaped or button-shaped. Cuboid-shaped elevations are also conceivable. Ribs that encompass the outer surface of the anchor like a flange merely provide a positive connection in such a way that relative movement between the elevation and the precast concrete element in the direction of the longitudinal axis is prevented, while rotation of the anchor about its axis is not prevented. Similarly, a rib arranged on the outer side of the anchor in the direction of the anchor axis could merely prevent rotation of the anchor, but not movement of the anchor towards the precast concrete element or out of the precast concrete element. Circumferential ribs or ribs extending along the entire outer surface of the fastening section in the direction of the anchor axis are therefore not elevations in the sense used here.

[0021] In a particularly preferred embodiment, two elevations are arranged axially spaced from each other. This improves the anchor's fixation within the precast concrete element.

[0022] In another particularly preferred embodiment, four elevations are arranged at a distance from one another in the circumferential direction. This measure also significantly improves the fastening of the anchor within the precast concrete element.

[0023] For example, four pairs of elevations can be arranged spaced apart from one another in the circumferential direction, with each pair having two elevations spaced apart from one another in the direction of the dowel axis.

[0024] In a further preferred embodiment, the fastening section has a plurality of ribs on the outside, each rib extending in the axial direction, with each rib ideally extending over the entire fastening section. This measure also supports the stability of the dowel against rotational movement around the dowel axis.

[0025] In a further preferred embodiment, the head section has a diameter that is larger than the diameter of the fastening section. The head section therefore has a larger surface area that can be used as an adhesive surface during the production of the precast concrete element. The anchor is thus glued to a formwork with its head section, and the concrete is added. After the concrete has set, the formwork can be removed.

[0026] In a preferred embodiment, the head section has a recess for receiving a nut, preferably with a hexagon socket. Machine screws can then be screwed into this nut on site instead of concrete or wood screws.

[0027] In a further preferred embodiment, the head section has a recess which is designed in the shape of a double-bit lock.

[0028] For certain applications, it may be advantageous to have a shank section between the fastening section and the head section, which is designed to accommodate a shank located between the thread and the head of the screw. Screws with such a shank exist, but the shank does not have an external thread.

[0029] In this case, it may be advantageous if the outer diameter of the shaft section is smaller than the outer diameter of the fastening section, wherein preferably the outer diameter of the shaft section is smaller than the outer diameter of the head section, whereby an annular groove is formed on the outer surface of the anchor, which is filled by the concrete of the precast concrete element when cast in and thereby provides additional hold of the anchor within the precast concrete element.

[0030] Furthermore, the present invention also relates to a precast concrete element with at least one plate-shaped section into which the dowel according to the invention is cast. The invention is described below with reference to a plate-shaped wall element as a precast concrete element, even though the precast concrete element does not, in principle, have to be completely plate-shaped.

[0031] The anchor can be dimensioned to have a length that exceeds the thickness of the slab section, so that when cast in place, the fastening section protrudes from the slab section at its end facing the head section. Especially when the precast concrete element itself is used as formwork for a wall to be cast, it is particularly advantageous if the anchor extends into the area that will later be filled with in-situ concrete, so that the anchor then holds not only the precast concrete element but also the final concrete wall.

[0032] Particularly preferably, the fastening section has a circumferential flange on its outer side, which is flush with the plate-shaped section. Furthermore, it is advantageous if the head section of the anchor is flush with a surface of the plate-shaped section.

[0033] Further features, advantages, and possible applications of the present invention will become clear from the following description of preferred embodiments and the accompanying figures. They show: Figures 1a - 1e show various views of a first embodiment of a dowel according to the invention, Figures 2a - 2c show various views of a second embodiment of a dowel according to the invention, Figures 3 - 5 show various schematic views showing the use of the dowel of the first embodiment together with a precast concrete part, and Figures 6a and 6b show examples of a concrete screw and a wood screw.

[0034] In the Figures 1a -1e a plurality of different views of a first embodiment of the dowel according to the invention are shown. Figure 1a shows a side view of the dowel. Figure 1b shows a corresponding sectional view. The anchor is aligned along a anchor axis A, which is Figures 1aand 1b runs vertically. Dowel 1 has a fastening section 2, a head section 3, and a shaft section 4 connecting the head section 3 and the fastening section 2.

[0035] The anchor has a cavity 5 that is open on one side and serves to accommodate a screw. The external thread of the screw is intended to come into contact with the inner wall of cavity 5 of the fastening section. As soon as the screw is accommodated in the anchor, the screw head is located in the head section 3. The anchor shown is intended for a screw that has a shaft without a thread between the screw head and the thread. Therefore, the anchor 1 has a corresponding shaft section 4. So that the anchor can be used not only together with concrete screws, but also provides sufficient fastening when using wood screws, the wall thickness of the anchor in the fastening section is > 30% of the diameter of the cavity.Even if, in the embodiment shown, the wall thickness increases toward the end of the fastening section 2 facing away from the head section 3, the wall thickness of the fastening section itself meets the required minimum thickness at the end facing the head section 3. Only in the area of ​​the shaft section 4, which does not come into contact with the thread, can the wall thickness be made smaller, as shown in particular in FIG. Figure 1b is clearly visible.

[0036] The wall thickness of the anchor and its face, which is in the Figures 1 and 1b The cavity facing upwards can be made significantly smaller, as it does not come into contact with the thread. The cavity is sealed on this end face only so that the anchor can be cast into a precast concrete element without the risk of concrete penetrating the cavity via the end face and preventing subsequent insertion of a screw.

[0037] The dowel 1 has a plurality of elevations 7 on its outer surface. In this embodiment, a total of eight elevations 7 are provided. The elevations provide active surfaces in all directions perpendicular to a normal on the outer wall of the dowel, which, in interaction with the precast concrete element into which the dowel is to be cast, provide a positive connection both in the direction of the dowel axis A and in the circumferential direction, i.e., a rotational movement of the dowel 1 about the axis A.

[0038] In the example shown, a pair of two elevations 7 is arranged in the direction of the dowel axis A, with four such pairs being arranged in the circumferential direction at a distance of 90°, as can be seen from the perspective views of the Figures 1d and 1e is clearly visible.

[0039] The anchor further comprises ribs 8, which extend substantially over the entire fastening section in the direction of the anchor axis A. The embodiment shown comprises four such ribs, which are always arranged between two pairs of elevations 7. The anchor here additionally comprises a circumferential flange 9.

[0040] The dowel 1 has a double-bit lock-shaped recess 6 at its head section end.

[0041] In the Figures 2a to 2c Three views of a second embodiment of the invention are shown. The dowel 101 is shown here in comparison to the Figures 1a - 1eshown embodiment is significantly smaller. Here, too, the dowel has a fastening section 102 and a head section 103. The dowel has a cavity 105 for receiving a screw, with a recess in the form of a hexagon socket 106 provided in the head section 103, which is intended to receive a corresponding nut.

[0042] Here, too, there are elevations 107 and ribs 108 provided between each pair of elevations 107 arranged along the dowel axis A.

[0043] In the Figures 3 - 5The intended use of the anchor is explained schematically. First, the anchor is glued with its head section 3 onto a formwork 10 so that the fastening section 2 extending along the anchor axis A is aligned perpendicular to the formwork 10. Concrete can now be applied to the formwork 10 to produce the precast concrete element, so that the concrete forms the precast concrete element 11. The flange 9 forms a flush boundary to the upper surface of the precast concrete element. As soon as the concrete is sufficiently solid, the formwork 10 can be removed. In this state, the wedge of the fastening section 2 facing away from the head section 3 is not arranged completely within the concrete layer 11, but protrudes beyond the outer surface on the inside of the concrete layer, which is filled with in-situ concrete on the construction site.In this case, after the wall has been constructed, the anchor 1 is arranged partly in the precast concrete element 11 delivered to the construction site and partly in the in-situ concrete poured on the construction site.

[0044] After removing the head section 3 from the concrete layer 11, the resulting depression must be filled with concrete after removing the support.

[0045] In a further embodiment, the dowel can also be placed without the head section 3 onto a holder (for example a "magnet") already located on the formwork 10 before the precast concrete element 11 is manufactured.

[0046] In this description, the terms "machine screw", "concrete screw" and "wood screw" are used.

[0047] A machine screw is a screw with a metric thread which is screwed into a corresponding counter thread, e.g. in a nut.

[0048] A concrete screw is a screw that has a special thread with which it can be screwed into concrete or masonry by cutting its own counter thread.

[0049] A wood screw is a screw that can only cut its mating thread into wood. Otherwise, it is used with a dowel with an internal thread.

[0050] In the Figures 6a and 6b are examples of a concrete screw ( Figure 6a ) and examples of a wood screw ( Figure 6b ) is shown. The concrete screw, which is Figure 6a The screw anchor shown is sometimes called a screw anchor and features a self-tapping thread. The screw can be screwed directly into a pre-drilled hole in concrete without the use of an anchor, with the thread then cutting a thread into the hole.

[0051] The Figure 6bThe wood screw shown has a conical tip and therefore ensures that when the wood screw is screwed in, the dowel used or the material into which the screw is screwed is expanded. Therefore, while the Figure 6b The screw shown essentially provides a force connection due to the radial material displacement, is Figure 6a The concrete screw shown does not displace any material, but rather cuts a corresponding counter thread, which results in a positive connection. List of reference symbols

[0052] 1 Dowel 2 Fastening section 3 Head section 4 Shaft section 5 Cavity 6 Double-bit lock-shaped recess 7 Elevation 8 Ribs 9 Flange 10 Formwork 11 Concrete layer 101 Dowel 102 Fastening section 103 Head section 105 Cavity 106 Hexagon socket 107 Elevation 108 Ribs

Claims

1. A dowel having a dowel axis (A) for being cast into a precast-concrete element, which dowel is intended to receive a fastening screw having a screw head and a thread and to hold the fastening screw in the precast-concrete element, the dowel comprising a head section (3) for receiving the screw head and a fastening section (2) for receiving the thread, the dowel being configured both for use with a concrete screw and for use with a wood screw, and the fastening section having a one-sided open, substantially cylindrical cavity (5), characterised in that, in every sectional view perpendicular to the dowel axis, the wall thickness of the dowel is greater than 30 %, and preferably greater than 40 %, of the diameter of the cavity.

2. The dowel according to claim 1, characterised in that it is manufactured from a material having a modulus of elasticity of less than 10 GPa and preferably less than 7 GPa.

3. The dowel according to claim 2, characterised in that it consists of a thermoplastic material, preferably polycaprolactam and particularly preferably fibre-reinforced polycaprolactam.

4. The dowel according to any one of the preceding claims, characterised in that the fastening section has, on its outside, a plurality of projections (7) which are configured such that, in the state cast into the precast-concrete element, each projection (7) is in a positively locking connection with the precast-concrete element in such a manner that relative movement between the projection (7) and the concrete is prevented both in the direction of the dowel axis (A) and in the circumferential direction, preferably with two projections (7) arranged spaced from one another in the axial direction.

5. The dowel according to claim 4, characterised in that four projections (7) are arranged spaced from one another in the circumferential direction.

6. The dowel according to any one of the preceding claims, characterised in that the fastening section has, on its outside, a plurality of ribs (8), each rib (8) extending in the axial direction and preferably extending over the entire fastening section (2).

7. The dowel according to any one of the preceding claims, characterised in that the head section has a diameter which is greater than the diameter of the fastening section.

8. The dowel according to any one of the preceding claims, characterised in that the head section has a recess for receiving a nut, the recess preferably being of internal-hexagonal configuration.

9. The dowel according to any one of the preceding claims, characterised in that the head section has a recess which is of double-bit-lock shape.

10. The dowel according to any one of the preceding claims, characterised in that a shank section is provided between the fastening section and the head section, which shank section is intended to receive a shank arranged between the thread and the head of the screw, the outside diameter of the shank section preferably being smaller than the outside diameter of the fastening section and particularly preferably smaller than the outside diameter of the head section.

11. A precast-concrete element having at least one plate-like portion, characterised in that a dowel according to any one of the preceding claims is cast into the plate-like portion.

12. The precast-concrete element according to claim 11, characterised in that the fastening section projects from the plate-like portion at its end facing away from the head section.

13. The precast-concrete element according to claim 12, characterised in that the fastening section has, on its outside, a circumferential flange (9) which terminates flush with the plate-like portion.

14. The precast-concrete element according to any one of claims 11 to 13, characterised in that the head section of the dowel terminates flush with a surface of the plate-like portion.