This specification concerns undercut anchors for securing objects to concrete.
Undercut anchors are used for securing objects to a concrete surface, wherein undercut anchors have a higher pull out strength than other types of mechanical anchors such as drop-in anchors, screw anchors and expansion anchors.
A hole 10 is drilled in a concrete surface using a hammer drill like in
With further reference to
An object can then be fastened to the concrete using a nut 26 and washer 24 in conjunction with the installed undercut anchor. The upper part of the threaded rod 16 is caused to extend through a hole in the object to be secured. The washer 25, and subsequently the nut 26, are placed on the upper part of the threaded rod 16. Upon tightening the nut 26 against the washer 25, and thereby the object to be secured, the expansion feature 18 is urged in a pull-out direction, which further urges the expansion portion 22 against the conical surface defined by the undercut region 12. It will thus be appreciated that the expansion feature 18, the expansion portion 22 and the conical surface defined by the undercut region 12 of the hole 10 cooperate to resist pull-out of the undercut anchor 14.
The undercut angle θ illustrated in
Some undercut anchors like the HDA-P™ and HDA-T™ (undercutanchors available from Hilti) form their own undercut region during installation. A drill is only required to form a cylindrical hole in a concrete surface for receiving the HDA-P™ and HDA-T™ undercut anchors. During installation, while drawing its expansion feature against its expansion sleeve, the HDA-P™ and HDA-T™ undercut anchors are themselves rotated whereby such rotation causes the anchor to cut its own undercut region in the concrete. Undercut angles θ capable of being achieved with the HDA-P™ and HDA-T™ undercut anchors can reach around 55 degrees, however, such anchors are highly engineered and so are complicated to manufacture compared to traditional undercut anchors which require a pre-drilled undercut region. What is needed therefore is a compromise, namely an undercut anchor solution that can achieve undercut angles θ greater than 30 degrees while remaining simpler to manufacture than an undercut anchor which forms its own undercut section during an installation process.
Due to improvements in drilling technology undercut drilling bits are now commercially available that can form undercut regions having undercut angles up to about 40 degrees (e.g., measured between opposite surfaces of the hold). As an example, the DEWALT® branded undercut drilling bits DFX21381, DFX21121, DFX21581 and DFX21341 can reliably drill undercut regions in concrete having an undercut angle up to about 40 degrees. Applicant has discovered that certain cleverly designed anchors may have significantly improved capacity when under cut holes have angles of 31 degrees or larger when measured between opposite sides of the cone shaped portion of the hole. For example, there are significant unexpected load capacity improvements between about 37 and about 43 degrees and between about 36 and about 43 degrees and between about 35 and about 43 and between about 34 and about 43 degrees.
Aspects of the present invention relate to an undercut anchor which is designed to function in holes having an undercut angle θ up to about 40 degrees (in particular, about 37 degrees to about 43 degrees).
According to the present invention this is provided an undercut anchor according to claim 1, wherein optional features thereof are defined in dependent claims 2 to 7.
Various aspects and embodiments of the invention will now be described by way of non-limiting example with reference to the accompanying drawings, in which:
The undercut anchor 140 can be made of carbon steel such as A36 carbon steel or B7 carbon steel. In some embodiments the carbon steel is zinc plated.
Alternatively, the undercut anchor 140 can be made of 316 stainless steel, wherein the 316 stainless steel version is particularly suitable for exterior use and other applications where a high level of corrosion resistance is required.
A threaded rod 160 is fixed relative to an expansion feature 180. With reference to
Referring to
The expansion portion 122 has a plurality of axially extending slots 1231 to 1236 evenly circumferentially arranged around the sleeve 120, which defines a plurality of fingers 1251 to 1256. The width of each slot 1231 to 1236, in other words the distance between adjacent fingers 1251 to 1256 is WSLOT. The fingers 1251 to 1256 have the same length LFINGER. A weakened portion 1271 to 1276 of the sleeve 120 is located at the proximal end of each of the fingers 1251 to 1256, only three of which are shown in
With particular reference to
It is known to categorise different sized undercut anchors as ⅜″, ½″, ⅝″ and ¾″ varieties, wherein these figures are indicative of the outer thread diameter DROD (these values being denoted in inches, namely 0.375″, 0.5″, 0.625″ and 0.75″). For each of these four categories the applicant has determined from experimentation the optimum parameters listed in the table 1 below which give optimum use performance of the heretofore described undercut anchor 140 in holes in concrete with an undercut angle up to 40 degrees. Such enhanced performance is characterised by maximising pull-out resistance of the undercut anchor 140 for the respective dimension of the outer thread diameter DROD.
Parameters of the undercut anchor 140 not listed in the above table 1 can be varied depending on the usage context and specific user requirements. For example the length LSLEEVE of the sleeve 120 (see
Table 2 below expresses the experimentally determined ranges of parameters which give acceptable use performance of the undercut anchor 140 in holes in concrete with an undercut angle up to about 40 degrees. Such acceptable use performance is characterised by maximising pull-out resistance of the undercut anchor 140 for the selected dimension of the outer thread diameter DROD.
It is here stated that the respective sets of unexpected, parameters in Table 1 for the different anchor sizes fall within the scope of the range expressed in Table 2.
Performance data of the heretofore described undercut anchor 140 relative to a prior art undercut anchor is illustrated in
It will be appreciated that whilst various aspects and embodiments have heretofore been described, the scope of the present invention is not limited thereto and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the spirit and scope of the appended claims.
In some embodiments the expansion feature 180 has a different shape.
In some embodiments the expansion feature 180, 280 is welded to the threaded rod section 160 after such features are threadably engaged instead of using adhesive.
In some embodiments the expansion feature 180, 280 does not have a threaded opening 182 and is welded to the threaded rod section 160.
The threaded rod section 160 does not need to be threaded along its whole length and only needs to be threaded sufficiently far along its length in order to enable a nut to be threadably engaged with it in order to secure an object to a concrete surface after anchor installation.
In some embodiments expansion sleeve 120 may have more or less than six fingers 125 provided that the dimensions of LFINGER, LRAMP and WSLOT remain within the ranges set out in table 2.