JP7511866B2 - Metal Expansion Anchor - Google Patents

Description

The present invention relates to a metal expansion anchor that is a post-installed anchor that is fixed into a concrete structure.

Conventionally, a known example of this type of metal expansion anchor is a dowel that is fixed into a fixed bore consisting of a front bore and an enlarged bore formed in a base such as a concrete base, for attaching a workpiece to the base (see Patent Document 1).
This dowel comprises a fixing bolt having a bolt head, a locking part screwed to the tip of the fixing bolt, a gap sleeve through which the fixing bolt passes, a sleeve part and an engaging part. The locking part has a tip member screwed to the fixing bolt and four-part locking elements connected to the tip member via a circumferential groove. The ends of the four locking elements are in contact with an engaging part whose tip is tapered in a conical shape.
When the gap sleeve is driven in through a washer attached to the bolt head, the engaging part advances in the axial direction through the sleeve part, pushing the four locking elements apart. As a result, the four locking elements swing outward around the circumferential groove, i.e., toward the enlarged bore. Next, when the fixing bolt is rotated to attract the locking part, the four locking elements abut against the rear surface of the enlarged bore and are locked, while the sleeve part is deformed so as to be crushed, and the workpiece is fixed and crimped onto the base by the fixing bolt.

JP 60-500966 A

In such a conventional dowel (metal expansion anchor), if the enlarged bore is formed with precision and the effective embedment depth of the dowel is sufficient, the tensile strength of the dowel is determined by the tensile strength of the dowel itself, not by the strength determined by the cone-shaped fracture of concrete, etc. In other words, the tensile strength of the dowel is determined based on the yield strength of the fixing bolt. Specifically, the allowable tensile strength is set to several tens of percent of the yield strength of the fixing bolt, and the design is based on this allowable tensile strength.
In such a case, the fixing bolt will not be destroyed through the workpiece due to an earthquake or the like, but if a load greater than expected, that is, a load exceeding the allowable tensile strength, acts on the fixing bolt, some kind of problem may occur, and it is necessary to investigate the cause of such load for the purpose of inspection and management.However, with conventional dowels, even if a load exceeding the allowable tensile strength acts on such a fixing bolt, it was not possible to know this history from the appearance of the dowel.

Post-installed anchors are broadly divided into metal expansion anchors and adhesive anchors. The tensile strength of metal expansion anchors depends on the wedge effect of the expansion part, while the tensile strength of adhesive anchors depends on the adhesive strength (shear). For this reason, the embedment depth of adhesive anchors is sufficiently deep compared to the embedment depth of metal expansion anchors. Due to this deep embedment depth, it is known that the failure of adhesive anchors does not depend on the cone-shaped failure of the concrete structure, but on a special failure mode in which a mushroom-shaped failure (hereinafter referred to as "mushroom-shaped failure") occurs on the surface of the structure, followed by the pull-out of the anchor bolt.
This mushroom-shaped fracture is believed to occur when a large tensile load acts on an anchor bolt, and the load does not act on the adhesive over the entire depth direction, but instead acts on the adhesive in a concentrated manner in a shallow portion of the body surface due to the elongation of the anchor bolt. Also, when mushroom-shaped fracture occurs, it is believed that the embedment depth of the anchor bolt is insufficient, causing the anchor bolt to come out.

The present invention was developed with a focus on the mushroom-shaped fracture that is unique to adhesive anchors, and aims to provide a metal expansion anchor that can visually detect when a load greater than expected acts on the anchor bolt.

The metal expansion anchor of the present invention is a metal expansion anchor that is fixed into a pilot hole drilled into a concrete structure, and comprises an anchor bolt whose base end supports and fixes an object to be fixed, a fixing mechanism provided at the tip of the anchor bolt and fixing the anchor bolt to the concrete structure at the back of the pilot hole, and an adhesive on the opening side of the pilot hole that adheres the anchor bolt to the pilot hole, the adhesive being filled in a part of the opening side of the pilot hole and causing mushroom-shaped destruction on the surface of the concrete structure when a load exceeding the allowable tensile strength is applied to the anchor bolt .

According to this configuration, the anchor bolt is fixed to the deep part of the pilot hole via the fixing mechanism and is bonded to the opening side of the pilot hole via an adhesive, and the adhesive causes mushroom-shaped fracture on the surface of the concrete skeleton when a load exceeding the allowable tensile strength acts on the anchor bolt. Therefore, when a load exceeding the allowable tensile strength acts on the anchor bolt, a crack indicating the occurrence of mushroom-shaped fracture occurs on the surface of the concrete skeleton. In other words, the fact that a load exceeding the allowable tensile strength has acted on the anchor bolt can be visually detected (confirmed) by a substantially circular crack that occurs on the surface of the concrete skeleton centered on the anchor bolt .

In this case, when the nominal diameter of the anchor bolt is D, it is preferable that the axial dimension of the adhesive is 1D to 3D.

With this configuration, the axial dimension (adhesive area) of the adhesive that leads to mushroom-shaped failure can be adjusted appropriately depending on the concrete density of the concrete body and the nominal diameter of the anchor bolt.

Also, the allowable tensile strength is preferably 20 to 100 % of the yield strength of the anchor bolt.

According to this configuration, the metal expansion anchor (its tensile strength) is designed based on the allowable tensile strength (strength) set based on the yield strength of the anchor bolt. Therefore, the axial dimension of the adhesive is also determined based on this allowable tensile strength. Therefore, if mushroom-shaped fracture occurs, appropriate countermeasures can be taken, such as rechecking the object to be fixed or re-installing the metal expansion anchor, before a defect (complete fracture, etc.) occurs in the anchor ring.

FIG. 2 is a structural diagram of the metal expansion anchor according to the first embodiment in an installed state. 1A is a plan view of a metal expansion anchor in a state where mushroom-shaped fracture has occurred, and FIG. 1B is a cross-sectional view thereof.

Below, we will explain a metal expansion anchor according to one embodiment of the present invention with reference to the attached drawings. This metal expansion anchor is a so-called "post-installed anchor" that is driven into a pilot hole (anchor hole) drilled in a concrete structure. In addition, this metal expansion anchor has the function of visually detecting when a tensile load that exceeds the expected load acts on the anchor bolt, which is the main body of the anchor.

[First embodiment]
Fig. 1 is a structural diagram of the metal expansion anchor according to the first embodiment in an installed state. As shown in the figure, an anchor hole AH (pilot hole) with an expanded diameter portion AHa formed in the inner part is drilled in a concrete structure C, and a metal expansion anchor 10 is fixed by being driven into this anchor hole AH. The metal expansion anchor 10 fixed in the anchor hole AH (concrete structure C) has a base end of its anchor bolt 11 protruding from the surface of the concrete structure C, and a base plate Sa of a fixing object S is fastened by a fixing nut N screwed into this portion via a washer W.

The metal expansion anchor 10 comprises an anchor bolt 11, the base end of which supports and fixes the object to be fixed S, a fixing mechanism 12 that fixes the tip of the anchor bolt 11 to the expanded diameter portion AHa (concrete body C) of the anchor hole AH, and an adhesive 13 that bonds the anchor bolt 11 to the anchor hole AH on the opening AHb side of the anchor hole AH. The anchor bolt 11 and the fixing mechanism 12 are made of steel, stainless steel, or the like.

The anchor bolt 11 and the fixing mechanism 12 have the original anchor function of the metal expansion anchor 10, which supports and fixes the fixed object S to the concrete structure C. Meanwhile, the adhesive 13 that bonds the anchor bolt 11 to the anchor hole AH (concrete structure C) near the opening AHb of the anchor hole AH has a function unique to this embodiment, which is to detect when a load greater than the expected load (a load greater than the allowable tensile load) is applied to the anchor bolt 11 (details will be described later).

The anchor bolt 11 is composed of a fully threaded bolt, and the diameter of this fully threaded bolt is the nominal diameter of the metal expansion anchor 10. In the metal expansion anchor 10 of this embodiment, when the nominal diameter is D, the embedment depth (the length between the upper end of the expanded portion AHa and the opening AHb) is 9D, and the length of the anchor bolt 11 is about 14D. Note that the anchor bolt 11 may have male threads only at the base end and the tip end.

The fixing mechanism 12 has an expansion nut 21 screwed onto the tip of the anchor bolt 11 and a driving sleeve 22 arranged to surround the anchor bolt 11. The expansion nut 21 is integrally formed with a nut body 24 in the lower half shown in the figure that screws onto the anchor bolt 11, and an expansion part 25 in the upper half shown in the figure that is divided into four parts by slits 25a. A cone part 26 is formed at the tip of the driving sleeve 22, and the expansion part 25 of the expansion nut 21 expands radially outward by driving the driving sleeve 22. The expanded expansion part 25 expands toward the peripheral wall of the expansion part AHa and is fixed to the expansion part AHa. The anchor bolt 11 exerts a wedge effect due to the cooperation between the expansion part 25 and the expansion part AHa.

The adhesive 13 is preferably one used in adhesive anchors for post-installed anchors, and in this embodiment, a two-component epoxy resin adhesive is used. The adhesive 13 fills the gap between the anchor bolt 11 and the anchor hole AH on the opening AHb side of the anchor hole AH. A ring-shaped backup material 31 is attached near the opening AHb so as to abut against the base end of the driving sleeve 22, and this backup material 31 adjusts the filling depth (axial dimension) of the adhesive 13.

Although details will be described later, in this embodiment, the adhesive 13 filled on the opening AHb side of the anchor hole AH is designed to cause mushroom-shaped fracture in the concrete body C when an unexpected tensile load acts on the anchor bolt 11. For this reason, when the nominal diameter of the anchor bolt 11 is D, it is preferable that the axial dimension of the adhesive 13 is 1D to 3D, and in this embodiment, the axial dimension of the adhesive 13 is about 1D.

On the other hand, mushroom-shaped failure is a unique failure phenomenon that occurs in adhesive anchors. Due to the deep embedment depth of adhesive anchors, instead of cone-shaped failure of the concrete body C, the failure mode may be mushroom-shaped failure in which a thin layer of the surface of the concrete body C peels off, followed by the anchor bolt 11 coming loose.

This mushroom-shaped fracture is believed to occur when a large tensile load acts on the anchor bolt 11, not over the entire depth direction, but instead acts concentratedly on the adhesive 13 in a shallow portion of the body surface due to the elongation of the anchor bolt 11. This embodiment focuses on the mushroom-shaped fracture as a precursor phenomenon to complete fracture of the metal expansion anchor 10, and aims to detect abnormalities occurring in the metal expansion anchor 10 by causing mushroom-shaped fracture when a large tensile load acts on the anchor bolt 11.

On the other hand, in this type of metal expansion anchor 10 (expanded base anchor), the tensile strength is designed based on the tensile strength (strength) taking into account the yield strength of the anchor bolt 11. In other words, even if a load that reaches the yield strength acts on the anchor bolt 11, the anchor bolt 11 will not break, but in cases where a large load is repeatedly applied (e.g. vibration) or where a constant hanging load is applied, it is necessary to take into account an appropriate safety factor. Therefore, it is preferable to set the tensile strength of the anchor bolt 11 to 20 to 100% of the yield strength for each fixed object S, and to design the anchor bolt 11 (metal expansion anchor 10) based on this.

The tensile strengths used in design include long-term allowable tensile strength (approximately 20-30% of the yield strength) and short-term allowable tensile strength (approximately 40-50% of the yield strength). For example, if the fixed object S has a drive unit, is subject to wind pressure or vibration, or is a suspended object, it is preferable to take the long-term allowable tensile strength into consideration. Also, if there is a possibility of metal fatigue in the anchor bolt 11 in relation to the fixed object S, it is preferable to set the tensile strength at 20% of the yield strength.

In the present embodiment, the metal expansion anchor 10 defines a load that exceeds the long-term allowable tensile strength, i.e., a load that exceeds the long-term allowable tensile load (hereinafter simply referred to as the "allowable tensile load"), as a load that exceeds the expected load (unexpected load).

In other words, in this embodiment, when a load exceeding the allowable tensile load (allowable tensile strength) acts on the anchor bolt 11, the adhesive 13 causes mushroom-shaped fracture in the concrete body C around the anchor bolt 11. In this case, the mushroom-shaped fracture is a phenomenon that occurs before the anchor bolt 11 comes loose, and appears on the surface of the concrete body C as a crack that is approximately concentric with the anchor bolt 11.

Here, with reference to Figs. 2(a) and 2(b), a case where a load exceeding the allowable tensile load acts on the anchor bolt 11 will be described.
When a load exceeding the allowable tensile load acts on the anchor bolt 11, the anchor bolt 11 is stretched between the fixing nut N and the expansion nut 21. When the anchor bolt 11 is stretched, a shear force acts on the adhesive 13, but the adhesive force of the adhesive 13 to the anchor bolt 11 and the concrete body C becomes stronger, and mushroom-shaped fracture occurs in the concrete body C.

Mushroom-shaped fracture occurs when the surface of the concrete body C peels off thinly in a mushroom shape concentric with the anchor bolt 11 (see FIG. 2(a)), and appears as a roughly circular crack on the surface of the concrete body C (see FIG. 2(b)). In the embodiment, cracks are visible on the surface of the concrete body C away from the base plate Sa, and it is visually confirmed that a load exceeding the allowable tensile load has acted on the anchor bolt 11.

As described above, according to this embodiment, when a load exceeding the allowable tensile load acts on the anchor bolt 11, mushroom-shaped fracture occurs on the surface of the concrete body C, so that it is possible to visually detect (confirm) that a tensile load exceeding the expected load has acted on the anchor bolt 11. This allows the cause of the tensile load exceeding the expected load to be identified and the metal expansion anchor 10 to be re-installed, etc.

The metal expansion anchor 10 in this embodiment is a so-called sleeve-driven type, but the present invention can also be applied to metal expansion anchors that use driving methods such as mandrel-driven and body-driven types, and even metal expansion anchors that use a tightening method.

10...metal expansion anchor, 11...anchor bolt, 12...fixing mechanism, 13...adhesive, AH...anchor hole, AHb...opening, C...concrete body, S...fixing object,

Claims (3)

A metal expansion anchor that is fixed in a pilot hole drilled in a concrete structure,
An anchor bolt for supporting and fixing an object to be fixed at a base end thereof;
a fixing mechanism provided at a tip of the anchor bolt and fixing the anchor bolt to the concrete body at a deep portion of the prepared hole;
an adhesive for adhering the anchor bolt to the pilot hole on the opening side of the pilot hole,
The adhesive is filled into a portion of the opening side of the pilot hole, and causes mushroom-shaped damage to the surface of the concrete body when a load exceeding the allowable tensile strength is applied to the anchor bolt . The metal expansion anchor described in claim 1, characterized in that the axial dimension of the adhesive is 1D to 3D when the nominal diameter of the anchor bolt is D. 3. The metal expansion anchor according to claim 1, wherein the allowable tensile strength is 20 to 100 % of the yield strength of the anchor bolt.

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