GB2269609A - Shearhead with inclined surfaces - Google Patents

Abstract

A shearhead for column to slab reinforcement comprises a substantially coplanar arrangement of pairs of beams (2, 4) for horizontal containment within a concrete floor slab (18). The beams define juxtaposed surfaces (12) at lateral boundaries of a central aperture which is void of any shearhead component and which corresponds to the cross-section of the column (14). At least some of the juxtaposed surfaces (12) are inclined, eg. by the provision of wedges (20), relative to respective planes perpendicular to the plane of the beam arrangement. The wedges (20) may intrude into the column cross-section, possibly as far as reinforcement (16). <IMAGE>

Description

This invention relates to shearhead reinforcement.

In our published European Application No. 0414484 there is described a shearhead for column to slab reinforcement comprising a horizontally disposed arrangement of pairs of beams for containment within a concrete floor slab. These beams have vertical webs, the surfaces of which define the lateral boundaries of a central aperture which is void of any member of the shearhead and which corresponds to the cross-section of the column supporting the shearhead. Upon erection of the respective building the shearhead is supported at the top of a column with the slab reinforcement by formwork and concrete is cast around the shearhead and between the pairs of beams thereof to form the laterally extending floor slab and to extend the column therethrough.

As shown in Figure 3 of the aforesaid publication, the webs of the beams may be built up within the central aperture by means of bodies which resemble flat plates oriented in the vertical plane.

These plates may be offset from or welded onto the webs or otherwise attached thereto and they may be on all or some of the vertical faces of the beams. These built-up portions assist in ensuring that the concrete in the column which is essentially supporting the floor slab is maintained in compression.

It is now found that the performance of the shearhead is enhanced by the use of members to define the central aperture which are angled in the vertical plane. This may be achieved by building up the webs with vertically oriented, downward-pointing wedges.

These wedges may totally replace the previous disclosed plates, or parts thereof, and may be provided on all or some of the vertical faces defining the aperture. Preferably they have a wedge angle of around 4 to 5 degrees and a maximum thickness (at their upper end) such that at the thickest part thereof they substantially penetrate the concrete cover of the column. Alternatively the flanges of the beams may be offset so that the webs are angled out of the vertical plane. In yet another arrangement the members may comprise regions struck out from the webs.

Hereinafter the invention is described by way of example and with reference to the accompanying schematic drawings, wherein: Figure 1 is a plan view of a shearhead assembly embodying the invention; Figure 2 is a sectional elevation taken on line II-II of Fig. 1; Figure 3 is a perspective view of another shearhead assembly according to the invention; and Figure 4 is a view similar to Figure 2 showing another shearhead of the invention.

The shearhead shown in Figure 1 comprises two pairs of parallel steel beams (2, 4) of "C" or channel section with flanges (6, 8).

The beams (2, 4) are cut and welded together to form the cruciform shape shown so that the upper and lower flanges (6, 8) of the beams (2, 4) face outwardly and lie on the same two horizontal planes. The webs of the beams are thus juxtaposed in pairs to define an enclosed space open at the top and bottom through which the column (14) passes. The periphery of the space corresponds substantially to the cross-sectional envelope of the column. As shown, the column (14) is provided with vertically extending reinforcement rods (16). On the juxtaposed surfaces (11, 12) and within the enclosed space formed by the beams there are provided planar members (20) which extend into the volume of the space. These members may be attached to the beams by any suitable means such as welding or by fasteners, or they may be formed as offsets in the respective vertical webs.

Referring now to Figure 2, it is seen that the members (20) are wedge-shaped in cross section with the narrow part of the wedge shape oriented downwards.

When installing a shearhead of the kind shown in Figures 1 and 2, the shearhead is positioned at the head of a column (14) and supported generally on suitable shuttering or formwork which will define the lower surface of the eventual cast lateral concrete floor slab (18). Prior to pouring the concrete and at suitable stages in the assembly the lower and upper slab reinforcements are provided with the shearhead positioned therebetween. The concrete is poured over the shuttering around the extending beams and within the centrally enclosed volume defined by the juxtaposed surfaces (10, 12) such as to simultaneously form the slab (18) and continue the column upwards through the shearhead.

In a second embodiment (28) of the invention shown in Figure 3 beams (30) are arranged in two orthogonally disposed pairs, each pair being in longitudinal axial alignment so as to define a space between the facing ends thereof to accommodate the column (14).

Each beam is physically separated from its neighbour and comprises a facing pair of "C" section beams which are spaced apart and has a bridging "C" channel member joining their ends to define one of the surfaces (12) in each juxtaposed pair. Fastened to these surfaces or formed thereon are the vertically oriented wedge-shaped members (20) arranged as disclosed in the previous embodiment.

The four composite beams referred to in Figure 3 may comprise separate members which are suitably arranged on formwork prior to casting the concrete and which only become an integrated assembly when the concrete has hardened. Alternatively, the members may be linked together, for example by means of a hoop bar which surrounds and is attached to the outer ends of the beams.

As before, the inner ends (12) of the beams are disposed generally at the outer perimeter of the column (14) such that the wedges (20) penetrate the cover of the column.

The wedges (20) in both the above embodiments and in other arrangements embodying the invention may take the form of single wedge-shaped members attached to or deformed from the beams (e.g. by deforming each beam so that the web at the central aperture is angled out of the vertical plane) or they may be formed by spaced-apart bars attached to the webs generally defining the wedge shape required, or by discrete spaced-apart masses which may be machined to conform with the envelope of the wedge shape. In respect of the second embodiment described above they may also be effectively provided by attaching bridging "C" channel members at the proximal ends of the composite beams in which the respective webs are angularly offset from the vertical plane.

The general requirement is that the member (20), however constructed, should conform to the envelope of a vertically oriented wedge having its thinnest part facing downwards and its thickest part, being the upper edge, penetrating the cover of the concrete of the column by about 3 to 312 cm and with a wedge angle of about 5 degrees. The vertical dimension of the wedge may vary around 15 to 40 cm, depending upon the depth of the floor slab.

Figure 4 illustrates an embodiment of the invention in which the members (20) are not required as separate elements attached to the beams (2, 4). In this embodiment, the beams themselves are adapted to provide the desired wedge shape in the webs (36). Thus, the cross-section of the beams has the overall shape of a parallelogram, with the webs (36) inclined upwardly and inwardly relative to the column (14). As with the members (20) the inclined webs (36) substantially penetrate the column cover, almost to the reinforcement rods (16). In some instances, actual contact with the rods (16) can be made, by the webs (36), or the members (20).

Claims (14)

1.- A shearhead for column to slab reinforcement comprising a substantially coplanar arrangement of pairs of beams for horizontal containment within a concrete floor slab, the beams defining juxtaposed surfaces at lateral boundaries of a central aperture which is void of any shearhead component and which corresponds to the cross-section of a said column, wherein at least some of the juxtaposed surfaces are inclined relative to respective planes perpendicular to the plane of the beam arrangement.

2. A shearhead according to Claim 1 wherein the inclined juxtaposed surfaces are on web sections of the beams.

3. A shearhead according to Claim 2 wherein the inclined juxtaposed surfaces are regions of the web sections struck out from the plane thereof.

4. A shearhead according to Claim 1 wherein the inclined juxtaposed surfaces are on built-up portions forming wedges on web sections of the beams.

5. A shearhead according to Claim 4 wherein the built-up portions comprise spaced bars attached to the webs and defining said wedges.

6. A shearhead according to Claim 1 wherein the beam arrangement comprises convergent beam pairs of which each pair is connected at their inner ends by a web section, said inclined juxtaposed surfaces being defined at the web sections.

7. A shearhead according to Claim 6 wherein the inclined juxtaposed surfaces are on built-up portions forming wedges on the web sections.

8. A shearhead according to any preceding Claim wherein the angle of inclination of the juxtaposed surfaces is in the range 4 to 5 degrees.

9. A shearhead according to any preceding Claim wherein all of the juxtaposed surfaces are inclined relative to respective planes perpendicular to the plane of the beam arrangement.

10. A shearhead for column to slab reinforcement substantially as described herein with reference to Figures 1 and 2, Figure 3, or Figure 4 of the accompanying drawings.

11. A shearhead assembly between a substantially vertical reinforced concrete column and a substantially horizontal concrete slab, comprising a shearhead according to any preceding Claim disposed around the column with the juxtaposed surfaces thereof inclined downwards and away from the column axis.

12. An assembly according to Claim 11 wherein the upper edges of the juxtaposed surfaces substantially penetrate the concrete cover of the column.

13. An assembly according to Claim 12 wherein the upper edges of the juxtaposed surfaces make contact with the column reinforcement.

14. A shearhead assembly substantially as described herein with reference to Figures 1 and 2, Figure 3, or Figure 4 of the accompanying drawings.