WO1992004547A1

WO1992004547A1 - Masonry anchors

Info

Publication number: WO1992004547A1
Application number: PCT/AU1991/000371
Authority: WO
Inventors: Richard John Beton
Original assignee: Ramset Fasteners (Aust.) Pty. Limited
Priority date: 1990-09-10
Filing date: 1991-08-19
Publication date: 1992-03-19

Abstract

A masonry anchor of expansion type comprises a stepped bolt (2) and an expansion sleeve (10) on a smaller diameter portion of the bolt shank (6) part way along the length of the shank (6). The expansion sleeve (10) includes a circumferential array of X-shaped lands (16) which permit the sleeve to collapse axially upon the application of a predetermined torque whereby to permit the anchor to tighten a component firmly against the surface of the masonry. The stepped configuration of the bolt shank permits increased shear strength of the bolt.

Description

MASONRY ANCHORS

The present invention relates to masonry anchors.

One well known form of masonry anchor comprises a split cylindrical expansion sleeve fitted over a bolt which carries a conical expansion element which is drawn into the sleeve by tightening of the bolt in order to expand the sleeve into engagement with the wall of a hole drilled into masonry and into which the anchor is fitted. The sleeve is mounted on the shank of the bolt over a substantial portion of the length of the shank and is of a diameter sized to fit closely within the hole drilled into the masonry. The anchor is normally set into the hole to a setting depth at which the outer end of the sleeve is adjacent to the surface of the masonry. With this configuration, the diameter of the shank is smaller than the diameter of the hole at least by a factor of twice the wall thickness of the sleeve. In such an anchor, the shear strength of the bolt is dependent on the diameter of the bolt shank at the point of entry of the bolt into the masonry and the reduced shank diameter necessitated by the presence of the sleeve leads to a reduction in the possible shear strength of the bolt and in some working situations shear failure can occur in the bolt. Normally if shear failure does occur this will result in bending of the portion of the bolt projecting externally of the masonry which will lead to slippage of the component being fixed, and in extreme cases this can generate a moment tending to withdraw the anchor from the hole.

According to the present invention there is provided a masonry anchor comprising a bolt, an expansion sleeve mounted on the bolt, and an expansion element at an inner end of the bolt, the arrangement being of such that, to set the anchor, the expansion element is drawn into the inner end of the sleeve upon tightening of the bolt whereby to cause circumferential expansion of the expansion sleeve into engagement with the wall of a hole drilled into masonry so as to set the anchor within the masonry, wherein the shank of the bolt is of stepped form to provide at least at its inner end portion a reduced diameter section on which the sleeve is mounted, with the outer diameter of the sleeve being equivalent to the outer diameter of the remainder of the shank, the setting depth of the anchor within the masonry is greater than the length of the sleeve, and the sleeve includes adjacent its outer end portion a series of circumferentially spaced apertures defining a plurality of lands which deform upon application of a predetermined load to the sleeve whereby to permit axial shortening of the sleeve, said lands being substantially of X-shape with the respective limbs of each land being oblique to the longitudinal direction.

Preferably the adjacent X-shaped lands are separated by circumferentially spaced diamond-shaped apertures formed into the sleeve with each land being defined by two adjacent diamond-shaped apertures and further apertures therebetween. These further apertures may be of triangular or of circular form.

Preferably the central area of each X-shaped land projects outwardly to form a protrusion which lies radially outwardly from the body of the sleeve. An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:-

Figure 1 is a side elevation of a masonry anchor in accordance with an embodiment of the invention; Figure 2 shows schematically a bolt of the expansion anchor of Figure 1 ;

Figure 3 is a developed view showing in greater detail the X-shaped lands of the expansion sleeve of the anchor of Figure 1;

Figure 4 is a view similar to Figure 3 and showing schematically the manner in which the lands collapse upon application of a predetermined load to the sleeve; and

Figure 5 is a view similar to Figure 1 of a modified embodiment of the anchor.

The masonry anchor shown in the accompanying drawings comprises a bolt 2 having a head 4 at its outer end and a shank 6 which is threaded at its inner end portion. The head 4 may be integrally formed with a washer 8 or a separate washer may be mounted on the shank 6 adjacent the head. The shank 6 of the bolt carries a cylindrical expansion sleeve 10, but unlike in conventional masonry anchors of this general type, the sleeve 10 extends from the inner end of the shank 6 only part way along the setting depth D of the anchor. As shown, the sleeve 10 extends from the inner end of the bolt shank 6 to a position approximately midway along the length of the shank 6. In the zone of the shank 6 on which the sleeve 10 is fitted, the shank 6 is stepped down in diameter in order to pass through the interior of the sleeve. The stepping down in diameter is clearly shown in Figure 2 and defines a circumferential abutment surface 6a against which the outer end of the expansion sleeve 10 abuts. The portion 6b of the bolt shank 6 outwardly of the expansion sleeve 10 is of a diameter which corresponds to the outer diameter of the sleeve 10 and hence to the diameter of the hole into which the anchor is fitted. With this configuration the portion of the bolt shank within the outer part of the hole and projecting beyond the hole is of a maximum diameter corresponding to the diameter of the hole which provides significantly increased shear strength in comparison with a comparable anchor in which the entire bolt shank is reduced in diameter in order to accommodate the sleeve. A conical expansion nut 12 carried at the inner end of the shank 6 is drawn into the sleeve 10 upon tightening of the bolt in order to cause setting of the anchor into the hole within the masonry. In an alternative configuration, the bolt may also be threaded at its outer end to form a stud the anchor being set by rotating the stud by any convenient means (for example a pipe wrench) and the fitting being secured by means of a nut and washer on the outer end of the stud.

The expansion sleeve 10 is a pressed metal sleeve which is shaped into cylindrical form from a flat blank to define a slot 14 extending the length of the sleeve whereby the sleeve can expand circumferentially as the expansion nut 12 is drawn into the inner end of die sleeve 10. The sleeve 10 is also formed with additional circumferentially spaced slots extending longitudinally from the inner end of the sleeve to positions part away along the length of the sleeve as will be described subsequently. The inner end portion of the sleeve 10 is provided with a chamfer on its inner surface to provide a conical inner surface which approximately matches the conical outer surface of the expansion nut 12 so that the nut 12 is partially seated within the sleeve 10 upon insertion into the masonry. This provides an increased initial bearing area between the inner end portion of the sleeve 10 and the expansion nut 12 and thereby prevents possible stalling of the nut by digging of the end of the nut into the sleeve when the bolt is tightened to set the anchor. The nut 12 is itself hardened in order to prevent its inner end from closing onto the bolt thread during setting of the anchor as the torque increases.

During setting of an anchor of this type it is necessary for the expansion sleeve to be able to shorten or collapse axially without a significant increase in the tightening torque so as to enable the component being fitted to be "drawn down" firmly against the surface of the masonry. For this purpose it is conventional in masonry anchors of this general type to incorporate within the expansion sleeve apertures which form lands which can deform upon tightening of the bolt in order to permit the necessary shortening of the expansion sleeve.

Hitherto in the design of such anchors there has not been substantial consideration given to the point at which axial collapse of the sleeve occurs and with most commercially available anchors the axial collapse usually occurs at around 25 to 50 percent of the recommended setting torque of the anchor. However, if the axial collapse occurs before the anchor has been properly set into the hole by expansion of the inner end portion of the sleeve, the commensurate shortening of the sleeve can take place by displacement of the inner end of the sleeve outwardly along the hole rather than by displacement of the outer end of the sleeve inwardly into the hole. Displacement of the inner end of the sleeve outwardly upon collapse of the sleeve will reduce the setting depth of the anchor within the hole which is not desirable as the overall anchoring force is dependent on the setting depth. The applicants consider that, desirably, collapse should take place when a significant amount of the recommended setting torque has been applied, preferably around 75 percent or higher, to ensure that collapse does not take place until the inner end of the sleeve has been firmly set within the hole whereby collapse will take place only by inwards displacement of the outer end of the sleeve.

The axial collapse of the sleeve is primarily determined by the axial strength of the lands between the apertures in the sleeve. In a conventional masonry anchor of this general type in which the sleeve extends substantially for the whole of the setting depth there is a large available length at the outer end portion of the sleeve for accommodation of the apertures which define the lands. Conventionally, the apertures are in the form of longitudinal slots whereby the lands are in the form of longitudinal columns. While the applicants believe it would be a comparatively straightforward matter to "tune" the column strength to achieve collapse at the desired high torque setting by varying the length and width of the columns, such tuning in the anchor of the invention is somewhat more difficult because the length of the sleeve over which the apertures are able to extend is considerably more restricted as the sleeve itself only extends for part of the overall setting depth of the anchor. In particular, it is desirable for the part of the sleeve forwardly of the apertures to be as long as possible because in circumstances where the anchor is used in relatively soft concrete or in concrete with voids, the expansion nut may need to be drawn a substantial distance into the sleeve before full setting occurs. In these circumstances, proper setting could not occur if the apertured area were to extend for such an axial length that the expansion nut was likely to enter that area during certain setting conditions because, in this case, proper circumferential contact between the expanded sleeve with the wall of the hole would not take place. Accordingly, it is desirable for the length of the apertured area to be as short as possible.

The applicants have determined that effective "tuning" of the axial collapse can be achieved, whilst maintaining a short apertured axial length, if the apertures are so configured as to define a series of circumferentially spaced lands 16 of a substantially X-shaped configuration, with the limbs 18 of the X extending obliquely to the longitudinal direction of the sleeve. This is clearly shown in the developed view of Figure 3. With this X-shaped configuration the lands 16 act more like beams than columns and deformation occurs by bending as illustrated schematically in Figure 4. Within a relatively small required axial length, this X-shaped configuration is capable of significant tuning in order to provide the axial collapse at the required high torque level. This can be achieved by varying the number of X-shaped lands (typically from 2 to 4 lands), the width of d e limbs 18, the size of the central area 20 of the "X", the length of the limbs 18 and the inclination of the limbs 18 to the longitudinal.

The X-shaped lands 16 are formed by stamping diamond shaped apertures 22 into the sleeve and, between each adjacent pair of diamond shaped apertures 22, triangular apertures 24. However, to facilitate manufacture, the triangular apertures can be replaced by circular apertures which are easier to stamp and which will, in conjunction with the diamond shaped apertures still provide X-shaped lands. This alternative configuration is shown in Figure 5 in which the circular apertures are designated 26. The further longitudinal slots in the sleeve 10 as referred to earlier, extend from the inner end of the sleeve longitudinally to the adjacent innermost triangular or circular aperture 24 or 26 as illustrated in Figure 4, the slots being designated 28 in that figure and further facilitate the circumferential expansion of the inner end portion of the sleeve 10.

During forming of the sleeve 10 from the flat blank, the central area 20 of each X-shaped land 16 is preferably pressed so as to extend slightly radially outwardly from the body of the sleeve 10 so as to form a protrusion which can key into the wall of the hole whereby to prevent rotation of the sleeve within the hole during initial tightening of the bolt. This radial extension or bulging of the central area also promotes collapse of the X-shaped lands 16 outwardly relative to the bolt so that the lands do not collapse into the bolt and bind the bolt which would significantly increase the torque required to fully set the anchor.

The embodiment has been described by way of example only and modifications are possible within the scope of the invention.

Claims

1. A masonry anchor comprising a bolt, an expansion sleeve mounted on the bolt, and an expansion element at an inner end of the bolt, the arrangement being of such that, to set the anchor, the expansion element is drawn into die inner end of the sleeve upon tightening of the bolt whereby to cause circumferential expansion of the expansion sleeve into engagement with the wall of a hole drilled into masonry so as to set the anchor within the masonry, wherein the shank of the bolt is of stepped form to provide at least at its inner end portion a reduced diameter section on which the sleeve is mounted, with the outer diameter of the sleeve being equivalent to the outer diameter of the remainder of the shank, the setting depth of the anchor within the masonry is greater than the length of the sleeve, and the sleeve includes adjacent its outer end portion a series of circumferentially spaced apertures defining a plurality of lands which deform upon application of a predetermined load to the sleeve whereby to permit axial shortening of the sleeve, said lands being substantially of X-shape with the respective limbs of each land being oblique to the longitudinal direction.

2. A masonry anchor according to claim 1, wherein the adjacent X-shaped lands are separated by circumferentially spaced diamond-shaped apertures formed into the sleeve, with each land being defined by two adjacent ones of said diamond-shaped apertures and further apertures therebetween.

3. A masonry anchor according to claim 2, wherein said further apertures are of triangular or of circular form.

4. A masonry anchor according to any one of claims 1 to 3, wherein the central area of each X-shaped land projects outwardly to form a protrusion which lies radially outwardly from the body of the sleeve.