Measuring sleeve and method for measuring a force in an anchor pile

Description

[0001] The invention relates to a measuring sleeve for measuring a force in an anchor pile according to claim 1 and to a method for measuring a force in an anchor pile according to claim 10.

[0002] Anchor piles, which consist of multiple anchor rods, are used for a wide variety of purposes, particularly in specialized foundation engineering. For example, anchor piles are used as tie rods for the back-anchoring of excavation enclosures and floor slabs. Anchor piles can also be used to protect against buoyancy, for example, for underwater structural elements. Their use as micropiles to absorb structural loads is also generally known.

[0003] The anchor rods used to construct an anchor pile are typically between 5 m and 15 m long, although this length is usually determined by transportation constraints. To form longer anchor piles, they are usually bolted together with a connecting sleeve. After being driven into the ground, they are anchored in the surrounding soil by introducing a cement slurry.

[0004] Conventional anchor rods for forming anchor piles are known, for example, from DE 18 13 627 B2. Due to manufacturing technology, the anchor rods do not have a continuous, cut-in external thread. Instead, the external thread is formed by individual thread ribs that are separated from each other, creating an interrupted thread.

[0005] DE 36 36 322 discloses a measuring sleeve for measuring the load on cable tie anchors. The sensors are mounted in four longitudinal grooves on the outside of the measuring sleeve. The signal is transmitted via a hollow threaded anchor. The measuring body, with its longitudinal grooves, is unsuitable for measuring forces in anchor rods with interrupted thread ribs.

[0006] In the case of anchor piles, there is a need to record their load, for example in order to be able to verify that the structure is adequately secured by the anchor piles.

[0007] It is known to attach sensors to anchor piles to measure forces, which can be used to determine the actual forces absorbed by an anchor pile. These sensors can be attached to the anchor rods themselves. However, handling the long anchor rods after the sensors are attached is critical, as the sensitive sensors can be easily damaged.

[0008] When using conventional anchor rods, attaching sensors to the connecting sleeves leads to unreliable and significantly deviating measurement results. The connecting sleeves are provided with a continuous internal thread that extends over the entire axial length. When screwing in the threaded sections of the anchor rods, which are designed with discontinuous thread ribs, an uneven force introduction and loading occurs across the cross-section of the threaded sleeve. The measurement results of a sensor arranged on the connecting sleeve can vary significantly depending on the screw-in position of the thread ribs and thus the relative position to the sensor. For the same load, different measurement values ​​result depending on whether the sensor is located in an area where the partial thread ribs of the anchor rod engage with the thread of the sleeve or in an area where the thread sections in the connecting sleeve are exposed.

[0009] The invention is based on the Task The aim is to provide a device and a method for measuring a force in an anchor pile, with which a force in an anchor pile can be detected in a simple and reliable manner.

[0010] The object is achieved, on the one hand, by a measuring sleeve having the features of claim 1 and, on the other hand, by a method having the features of claim 11. Preferred embodiments of the invention are specified in the dependent claims.

[0011] According to the invention, a measuring sleeve is provided for measuring a force in an anchor pile which has at least two anchor rods, wherein the measuring sleeve comprises a sleeve-shaped base body with a receiving hole, wherein a first internal thread extends from one side and a second internal thread extends from a second side into the base body, the internal threads are each designed to screw in a threaded section of an anchor rod, an annular central section is formed between the first internal thread and the second internal thread, which is free of a thread, and at least one force measuring element is arranged on the central section and is axially spaced from the internal threads.

[0012] A basic idea of ​​the invention is to provide a special measuring sleeve that differs from conventional connecting sleeves with a continuous internal thread. An annular central section is provided on the measuring sleeve, which has no thread cut or formed on either the outside or inside. This central section is designed as a receiving area for accommodating at least one force measuring element. The at least one force measuring element is mounted in this central section, which is kept free of a thread.

[0013] The invention is based on the finding that the significantly deviating measurement results when attaching a force measuring element to a conventional connecting sleeve with a continuous internal thread are primarily due to an asymmetrical thread engagement between the partial thread ribs, which form an external thread on the anchor rods, and the internal thread of the sleeve. This results in uneven force introduction across the circumference and thus an uneven load in the threaded connection area of ​​the sleeve. By providing a central section between two lateral internal threads and arranging the at least one force element in this central section, it is ensured that the force measuring element is not arranged in a sleeve area with uneven force introduction.

[0014] By spacing the center section from the individual threaded areas on the socket, it is achieved that stresses or a force flow within the socket can be compensated in the center section, so that a reliable and uniform measured value can be recorded by the at least one force measuring element regardless of the rotational position of a screwed-in anchor rod in the center section.

[0015] In principle, the internal threads can be designed differently and implemented according to the intended anchor rods to be screwed in. According to one embodiment of the invention, it is preferred that the two internal threads be designed identically. The internal threads can have the same thread direction, the same thread pitch, the same thread type, and / or the same inner diameter.

[0016] The force-measuring element can, in principle, be attached to any suitable location on the central section. According to one embodiment of the invention, it is particularly expedient for the at least one force-measuring element to be attached to the central section on an outer side of the base body. This makes it possible, in particular, to very easily provide the force-measuring element with a data and / or power line.

[0017] the receiving hole is formed as a through hole which extends over the entire axial length of the base body. A further advantageous embodiment of the invention consists in that in the receiving hole the central section protrudes radially inwards and protrudes radially from the internal thread or recesses radially outwards and forms an annular groove. This achieves a clear spacing of the two lateral internal threads from one another. If it protrudes radially inwards, the central section can also serve as an axial stop when screwing in the threaded sections of the anchor rods. The base body of the sleeve-shaped measuring sleeve preferably has a cylindrical outer contour. The central section can also be solid, with the receiving hole being formed by two separate blind hole areas.

[0018] To achieve uniform or repeatable measured values, the invention provides that the central section is formed with a smooth surface on its outer and inner sides with the same wall thickness. In such a uniformly formed, in particular annular, central section, stresses caused by an uneven application of force from the anchor rods across the circumference in the axially adjacent threaded sections of the sleeve can be compensated. In this way, a largely uniform elastic and / or plastic deformation of the central section can develop in the central section. These changes, which are largely uniform across the circumference of the central section, can thus be recorded reliably and with good repeatability, regardless of the rotational position or relative rotational orientation of the force measuring element to the threaded ribs of the anchor sections.

[0019] In principle, any suitable sensors can be used as the force measuring element. According to one embodiment of the invention, it is particularly advantageous and efficient to provide at least one strain gauge as the force measuring element. A strain gauge can be permanently attached, in particular glued, to the central section. Strains in the central section caused by a force applied to the central section or the measuring sleeve can be detected by the strain gauge and converted into an electrical signal. The electrical signal can be amplified if necessary and forwarded to an evaluation device. This can be done wired or wirelessly.

[0020] The invention further comprises an anchor pile with at least two anchor rods, which have a threaded portion at at least one end, wherein the threaded portions are screwed into a measuring sleeve according to the invention and the anchor rods are connected to one another by the measuring sleeve. Preferably, the anchor rods can be formed with threaded portions at their two free ends or with a thread over their entire length. Furthermore, the anchor pile can also be constructed from more than two anchor rods, wherein a connecting sleeve is arranged between each two adjacent anchor rods. One or more sleeves can be designed as measuring sleeves according to the invention.

[0021] The anchor pile with the at least two interconnected anchor rods can be inserted into a borehole to create a bored or anchor pile. A measuring line can extend from the at least one force measuring element along an outer side of the thus formed anchor pile. The measuring line can be designed to conduct data and preferably also electrical current.

[0022] According to a further embodiment of the invention, at least one threaded section of an anchor rod is designed with thread ribs that form an interrupted thread. The anchor rod with the thread can thus be manufactured in a particularly efficient manner, for example by hot rolling and / or cold rolling. Such anchor rods are commercially available and can be purchased inexpensively. Despite the design of the threaded sections with individual thread ribs and thus without the formation of a continuous external thread, reliable measured values ​​regarding the actual force absorption of an anchor pile can be achieved in conjunction with the measuring sleeve according to the invention. This is advantageous for reliably testing and ensuring correct anchoring, for example of a structure in the ground or a body of water.

[0023] The anchor pile formed from the at least two anchor rods and the connecting sleeve can be used in a variety of ways. According to a further development of the invention, it is particularly expedient for the anchor pile to be designed as a micropile, a tension anchor, or a buoyancy anchor. The insertion of the anchor pile into a vertical borehole can be used to form a micropile in the ground. The micropile can absorb vertically directed forces both upwards and downwards, for example from a structure, and transfer them into the ground. Furthermore, the anchor pile according to the invention can also be used to create a tension element or tension anchor, for example for anchoring a retaining wall in the ground or for enclosing an excavation pit. The anchor pile according to the invention can also be used in particular underwater and particularly preferably in offshore applications.The anchor pile can also be formed from more than two anchor rods, with at least one measuring sleeve and, if necessary, further conventional connecting sleeves being arranged.

[0024] The anchor pile can thus be inserted into the bed of a body of water and used, for example, as a buoyancy protection element for underwater structures or foundations. To form the respective element, the anchor pile is preferably inserted into a borehole, with the surrounding free space being filled with a hardenable suspension, particularly a cement suspension.

[0025] The method according to the invention for measuring a force in an anchor pile is characterized in that an anchor pile according to the invention is formed, and measurement data for tensile and / or compressive forces are generated by the at least one force measuring element. For this purpose, the measuring sleeve according to the invention is used on the anchor pile. In addition to the tensile and / or compressive forces, shear or torsional forces, as well as other forces that may be of interest, can also be measured via the measuring sleeve.

[0026] A preferred method variant according to the invention consists in measuring continuously or at discrete times. In particular, measuring can be carried out not only during the construction of the anchor pile, but especially after it has been inserted into a soil area at a considerable time interval after construction. This can, for example, also enable long-term structural monitoring. The at least one force measuring element is connected to an evaluation unit, which can transform the recorded measurement signals into corresponding data for force application. The evaluation unit can also emit a warning signal, which can be used to indicate to monitoring personnel when predetermined limit values ​​have been exceeded.

[0027] To achieve particularly accurate measurement results, a further development of the invention provides that the measuring sleeve, with the anchor rods screwed in, is subjected to a defined test force at least once to calibrate the at least one measuring element. For calibration, identical or different test forces can be applied to a formed anchor pile several times. Based on this one or more defined test forces, the resulting signals of the at least one force measuring element can then be calibrated. This increases the subsequent measurement accuracy.

[0028] The invention will be further described below with reference to preferred embodiments, which are schematically illustrated in the drawings. In the drawings: Fig. 1 is a schematic half-cross-sectional view through a measuring sleeve according to the invention; Fig. 2 is a front view of the measuring sleeve of Fig. 1; Fig. 3 is a side view of a threaded portion of an anchor rod; and Fig. 4 is a partial side view of an anchor pile according to the invention.

[0029] According to the embodiment according to the Figures 1 and 2 A measuring sleeve 10 according to the invention has a sleeve-shaped base body 12 with a receiving hole 14, which can be continuous. A first internal thread 16 is formed in a first section on one side of the base body 12, while a second internal thread 18 is formed in a second section on the opposite side of the base body 12. The first internal thread 16 and the second internal thread 18 can be identical or different depending on the anchor rods to be screwed in.

[0030] Between the first internal thread 16 and the second internal thread 18, an annular central section 20 is formed in a central region of the base body 12. This section can be produced, for example, by screwing in an annular groove 22. The two internal threads 16, 18 are axially spaced from one another by the central section 20. A wall thickness in the annular central section 20 can be uniform over the circumference.

[0031] At least one force measuring element 40 is mounted on a preferably cylindrical outer side of the measuring sleeve 10 in the circumferential region of the central section 20, preferably in an axial center. The force measuring element 40 can, in particular, be a so-called strain gauge, which is glued to the outer side of the base body 12. The force measuring element 40 can detect changes in the shape of the central section 20 as a measure of the acting forces and transmit them to an evaluation device.

[0032] According to Fig. 3 1 shows a threaded section 32 of an anchor rod 30. The external thread on the anchor rod 30 is formed by separate thread ribs 34, which are separated from one another by axially extending flat areas 36. In this way, the thread ribs 34 form an interrupted thread 38 on the anchor rod 30. Such an interrupted thread 38 can be produced more efficiently than a continuous thread, whereby anchor rods 30 with high tensile strength can be achieved overall. The threaded section 32 can extend over the entire length of an anchor rod 30 or be formed only at the end regions of an anchor rod 30.

[0033] With at least two anchor rods 30 and a measuring sleeve 10 according to the invention, a Fig. 4The partially illustrated anchor pile 50 according to the invention can be formed by screwing a first anchor rod 30a into the first internal thread 16 and a second anchor rod 30b into the second internal thread 18. The threaded connections do not extend into the central region 20 of the measuring sleeve 10, since this is held free of an internal thread on its inside.

[0034] Due to the uneven introduction of tensile and / or compressive forces from the anchor rods 30 into the measuring sleeve 10 in the threaded sections caused by the interrupted thread ribs 34, reliable force measurement can hardly be carried out in these areas, since the force measurement is highly dependent on the rotational position of the screwed-in anchor rod 30 relative to the measuring sleeve 10. On the other hand, in the free central section 20, a uniform force and stress distribution results across the circumferential cross-section, so that a particularly reliable measured value for an axial force acting in the anchor pile 50 can be recorded by an applied force measuring element 40.

[0035] By means of a measuring line 42, which extends from the force measuring element 40 along a longitudinal axis of the anchor pile 50 to a measuring and evaluation device (not shown), a reliable data transmission and evaluation of the recorded measured values ​​can be achieved.

Claims

1. Measuring sleeve for measuring a force in an anchor pile which has at least two anchor rods (30), wherein the measuring sleeve (10) comprises a sleeve-shaped base body (12) with a receiving hole (14), wherein - a first internal thread (16) extends from one side and a second internal thread (18) extends from a second side into the base body (12), - the internal threads (16, 18) are each designed for screwing in a threaded section (32) of an anchor rod (30), - between the first internal thread (16) and the second internal thread (18) an annular central section (20) is designed which is free from a thread, and - on the central section (20) at least one force measuring element (40) is arranged which is axially spaced apart from the internal threads (16, 18), characterized in that on its external side and its internal side the central section (20) is of smoothsurfaced design and is designed with the same wall thickness.

2. Measuring sleeve according to claim 1, characterized in that the two internal threads (16, 18) are of the same design.

3. Measuring sleeve according to claim 1 or 2, characterized in that the at least one force measuring element (40) is mounted on the central section (20) on an external side of the base body (12).

4. Measuring sleeve according to any one of claims 1 to 3, characterized in that in the receiving hole (14) the central section (20) protrudes radially inwards and projects radially with respect to the internal thread (16, 18) or recedes radially outwards and forms an annular groove (22).

5. Measuring sleeve according to any one of claims 1 to 4, characterized in that as force measuring element (40) at least one strain gauge is provided.

6. Anchor pile with at least two anchor rods (30) which have a threaded section (32) on at least one end, characterized in that the threaded sections (32) are screwed into a measuring sleeve (10) according to any one of claims 1 to 5 and in that the anchor rods (30) are connected to each other by the measuring sleeve (10).

7. Anchor pile according to claim 6, characterized in that a measuring line (42) is provided which extends from the force measuring element (40) along the anchor pile (50).

8. Anchor pile according to claim 6 or 7, characterized in that at least one threaded section (32) of an anchor rod (30) is designed with threaded ribs (34) which form an interrupted thread (38).

9. Anchor pile according to any one of claims 6 to 8, characterized in that the anchor pile (50) is designed as a micropile, a tension anchor or an uplift anchor.

10. Method for measuring a force in an anchor pile, characterized in that an anchor pile (50) according to any one of claims 6 to 9 is formed and in that for measurement measuring data on tensile and / or compressive forces are generated by the at least one force measuring element (40).

11. Method according to claim 10, characterized in that the measurement takes place continuously or at discrete points in time.

12. Method according to 10 or 11, characterized in that when the anchor rods (30) are screwed in, a defined test force is applied at least once to the measuring sleeve (10) to calibrate the at least one force measuring element (40).