GB2158481A - Cavity wall ties for timber frame construction - Google Patents

Abstract

A wall tie (13), for joining the timber inner wall (10) and the masonry outer wall (11) of a cavity wall construction to allow for considerable differential shrinkage therebetween, comprises two parts (14, 16) connected by a connection which allows for relative movement therebetween in the plane of the cavity (12). One part (14) is fixed to the timber inner wall (10) and has a spigot or head (21) which is received in an elongate slideway (20) formed in the other part (16), the latter having one end (17) remote from the slideway (20) embedded in the mortar 18 of the masonry outer wall (11). <IMAGE>

Description

SPECIFICATION Cavity wall ties for timber frame construction The invention concerns cavity wall ties for timber frame construction, hereinafter called "frame ties".

In buildings comprising an innerwall of preassembled timber frames and an outerwall of masonry difficulty is experienced in providing the degree of connection therebetween necessary to ensure integrity of the total structure in view of differential movements which occur between the inner and outerwalls, whether on drying outofthe building after its completion or otherwise. Furthermore conventional wall ties cannot be used since there are no mortar joints in the innerwall in which such conventional wall ties can be embedded.

In addition corrosion of conventional wall ties has been a major problem and galvanised mild steel has been replaced by stainless steel orcertain plastics materials in orderto overcome this problem. However, none ofthe proposed wall ties have completely overcome the above-mentioned problems or have been entirely satisfactory from a strength, corrosion resistance, cost, and ability to accommodate the relative movement ofthe timber inner and masonry outer walls during drying out.

The object of the present invention is to provide a wall tie which will allow ofthe relative movement between inner and outerwalls due to differences in rates ofthermal expansion and such like yet which will maintain the structural integrity thereof at all times.

According to the present invention there is proposed a frame tie as hereinbefore defined comprising first and second parts adapted for attachment to inner and outer walls respectively of a cavity wall, and means connecting the first and second parts together so asto bridge a cavity between the said inner and outer walls, the connecting means being adapted to allow of limited relative movement between the parts in the plane of the cavity.

According to a preferred feature, the permitted relative movement between the first and second parts is a translational movementtherebetween, and may be transversely of a generally axial direction of said tie.

Said first part may comprise a first member which may have an elongate slidewaytherein adapted to receive a slide part of said second part comprising a second member, said slideway extending transversely of said axial direction. Said slideway may comprise a first undercut formation and said slide part may comprise a second undercutformation cooperable with that of said slideway. Said slideway may comprise a slot and said slide part may comprise a spigot.

Said second member may have a base adapted to abutthetimberframe innerwall, a neck portion and a head providing said second undercut formation, and the base may have a projected area in the plane ofthe inner wall which is greaterthan that of said head.

The second member may have a single central hole for receiving a fastening to secure itto a timberframe.

The hole may be countersunk in the head.

The first member may have one or more watershedding formations thereon positioned so as to lie withinthewall cavity in use.

One end ofthefirst member may have mortar keying formations thereon. These formations may comprise ribs or other projections, openings or depressions in the material ofthe member.

The elongate slideway ofthe first member may have a closed end, intended to face upwardly in use.

The general axis of the tie may pass through the elongateslidewayata position spaced from said closed end, whereby initial shrinkage ofthetimber frame and resultant movement ofthe head of the second member along the slideway will tend to align the axis of the second memberwith that ofthe first member.

In an alternative form, the second member may comprise an undercut bar and the first member may comprise an undercut slider engageable with the bar.

The members may be made of a high-tensile synthetic plastics material, for example polypropylene. Alternatively they may be made of a corrosion resistant metal, for example stainless steel.

The invention will now be described further, byway of example only, with reference to the accompanying drawings illustrating several embodiments thereof and in which: Fig. lisa first embodiment ofthe invention shown in diagrammatic perspective view; Fig. 2 is a plan view ofthe embodiment of Fig. 1 in use, Fig. 3 is a sectional view on line 3-3 of Fig. 2, Fig. 4 is an end elevation ofthe embodiment of Fig.

1, Fig. 5 is a view corresponding to Fig. 1 of a second embodiment, Fig. 6 is a view corresponding to Fig. 1 of a third embodiment, Fig. 7 is a plan view of a fourth embodiment, Fig. 8 is a view corresponding to Fig. 1 of a fifth embodiment, Fig. 9 is a side elevation of a sixth embodiment, and Fig. loins a plan view of a modified form of the embodiment of Fig. 1.

Referring firstlyto Figures 2 and 3 of the drawings, a timber frame cavity wall comprises a timberframe inner leaf 10, a masonry outer leaf 11, and a central cavity 12. In currenttimberframe construction, the cavity may vary in size between about 30 mm and about 50 mm.The frame tie illustrated is shown in use in a 40 mm cavity but is equally suitable for use in a cavityofa smallerora larger size.

The frame tie itself is generally indicated at 13 and, as will be seen in Figure 3, consists oftwo main parts.

A button part 14 is secured by means of a single nail or screw fixing 15 to the studding ofthe timber frame 10.

Asecond member which will be referred to as the "tail member" 16 is engaged by cooperating interfitting formations with the button 14. The free end of 17 of the tail 16 is embedded in a mortar coursing joint 18 ofthe outer masonry leaf 11 of the cavity wall.

Further details ofthe frame tie can be seen in Figure 1 ofthe drawings, which is an exploded perspective view. Atthe end ofthe tail 16 which is remote from the part 17 inserted in the masonry, there is provided an undercut formation 19 in the form of a slideway 20 which can receive a head 21 and a neck 22 ofthe button 14 as a sliding fit. An extreme end face 23 of the undercutformation 19 bears againsta base 24 ofthe button 14.

Referring again to Figure 3 ofthe drawings, it will be seen thatthe base 24 ofthe button 14 has a greater projected area in the plane ofthetimberframe inner leafthan the head 21. This provides a large bearing area so that compressive forces can be transmitted through thetieto the inner leaf. Figure 3 also illustrates the shape of the slideway 20 of the undercut formation 19 on the tail member 16.

The remainder ofthe tail has a general axis of elongation which is somewhat belowthe upper end of the slideway 20, as best seen in Figures 3 and 4 ofthe drawings. The upper end of the slideway 20 is closed off at 25.

In use, the button 14 is secured to thetimberframe 10 by the fastener 15 passing through a pre-formed central axial hole 26 which may be countersunk. A single fastener is used since, where two or more fasteners are used the design load is shared between them. If one ofthe fasteners should have to takethe whole design load at any stage, then it might not be capable of doing so safely because itwas not designed to take such a load. Where a single fastener is used, it is designed to take the full load safely.

When the button 14 has been secured to the studdingofthetimberframe 1 the outer masonry leaf ofthewall 11 is built up to the level ofthetie and the tail 16 is attached to the button by sliding it downwardly into a position where the button lodges snugly in the closed upper end 25 ofthe slideway 20. The free end 17 ofthe tail is then embedded in the mortar coursing joint 18 ofthe outer leaf 11. It will be seen that the tail 17 has mortar keying formations. In the example shown, these include a circular through hole 27 and at least two ribs 28 extending completelyaroundthetie.

A series of such ribs is provided around the tie and some ofthese may be embedded in the mortar. Others such as the rib 29 may be positioned in the cavity 12 in use and will assist in shedding water droplets which may condense on the tie.

The overall shape ofthe tie changes from the undercut end, where it is generally circular in cross section at30,to theflaKened wedge-like shape ofthe free end 17. This shape is selected for ease of injection moulding in a synthetic plastics material such as polypropylene.

Adjacentthe circular cross section 30 of the tie, there is provided a main circular drip rib 31. It will be seen thatthe wall tie tapers as viewed in Figure 3, in both directions from this rib 31 which is intended to shed water, preventing it from penetrating to the inner leaf ofthe cavitywall. It will be seen that with the medium size cavity shown in Figure 3 ofthe drawings, the main drip rib 31 is positioned more or less centrally in the cavity. For a narrow cavity, it will be relatively closerto the outer leaf 11 The rib 29 is also within the cavity. For a broader cavity, more ofthe ribs 28may occur in the cavity and each will act to shed any water condensing on the tie.

Further, the lower end ofthe undercut formation 19 will also act to shed any water droplets which may form. The undercut 19 is spaced from the inner leaf 10.

Referring now to Fig. 5, a frame tie comprises a first elongate member 41 for location in and retention by a masonry wall 42 during the construction thereof and a second member43 for attachmentto the timber frame (not shown) or inner wall as by screw means 44. The frame tie further includes means 45 connecting the first and second members 41,43 together in such manner as to allow relative movementtherebetween in the plane ofthe cavity.

The connecting means 45 is defined by a generally horizontally disposed hook formation 46 integral with the first member 41 and a generally vertically dis- posed plate 48 integral with the second member having an elongate slot47 therein to receive the hook formation 46, and to allow relative vertical movement between thefirst and second members41,43.

As will readily be apparent, relative movement is also possible betweenthefirstand second members 41,43 horizontally both in the plane of the cavity and axially ofthe tie 41 within limits imposed by the dimensions ofthe slot 47 and thickness of the second member43 in relation to the thickness and dimensions ofthe hook formation 46, and thus the frame tie will serve to hold the inner and outer walls together in the event of differential expansion or contraction as between the individual walls, and will thus assist in maintaining the structural integrity ofthewall as a whole. Thearrangementwill therefore serve to accommodate relative movement between the walls in any direction within the general plane ofthe cavity between inner and outer walls.

In the arrangement shown in Fig. 6, the free end of thefirst member 51 is extended to provide an upwardly directed flange 52 lying in a plane parallel to the innerwall,there being an elongate slot 53 in such flangefreelyto receive the shank 54 of a screw or bolt 55 therethrough, the screw or bolt 55 being engaged with the innerwall (not shown) through a washer 56 having an aperture 57therein of lesser dimension than the shank 54 and thus providing forfree movement of the flange 52 on the shank 540f the screw or bolt 55 within limits determined bythe dimensions of the elongate slot 53, engagement between the slot 53 and screw or bolt 55 being maintained by the head 56 of the latter.

In a fourth embodiment, see now Fig. 7,the means connecting the first and second members 61,62 comprises a part-cylindrical channel 63 formed integrally with the first member 61 at the free end thereof and a spherical or like formation 64 formed integrally with or extending from the second member 62, the spherical formation 64 being engageable with the channel 65 at an end thereof and being freely movable in the axial direction of such channel on relative movement between the inner and outer walls in an appropriate sense.

In a further embodiment, see now Fig. 8, the end of the first member71 is provided with an upstanding flange 72 arranged in parallel spaced-apart register with the upstanding flange 73 on the second member 74, there being elongate slots 75 in each upstanding flange to receive the respective opposite ends of a coupling element 76 of C-shape into engagement therewith.

It is to be appreciated that the frame tie will be of such length as properly to bridge the cavity between inner and outer walls.

The invention is not restricted to the exactfeatures ofthe embodiments hereinbefore described and illustrated, since alternatives will readily present themselves to one skilled in the art. For example, as is shown in Fig. 9, it may be found convenient, in some instances, to provide the tie 81 with a region of corrugated configuration 82 to permit of a limited flexing (and perhaps elongation) thereof or relative movement between the inner and outer walls, such feature being relied upon to accommodate such movement or being included in conjunction with the connecting means herein described and illustrated.In the event that the corrugation 82 provides a sufficient elongation characteristicto satisfy normal requirements the ties 81 can be of one piece construction, the opposite ends 83, 84thereof being adapted for attachment to the inner and outer walls respectively, in the mannerof anyone ofthe previously described embodiments.

In Fig. lOan alternative form of the embodiment of Fig. 1 is shown, corresponding parts being designated with the same numerals. In this case the shape of the "tail" has been modified from that shown in Fig. 1.

Obviouslythe shape of the tail may be incorporated into any one of the previously described embodiments.

The shape ofthe tail assists in preventing wet mortarfrom adhering readily to the tie if it should fall onto the tie from a position at a higher level where a bricklayer is working. The rounded shape ofthe part 30 and the relatively narrow adjoining portions ofthe tie mean that there is little purchaseforsuch wet mortar which will tend to fall off. This reduces the problem of mortar bridging between the innerand outer leaves ofthe wall, which can lead to damp penetration through to the inner leaf.

In use, the frame tie is required to withstand both tensile and compressive forces tending to separate or push togetherthe inner and outer leaves 10 and 11 of the wall. The tie must therefore be fairly rigid within the cavity and must be anchored secu rely to both the inner and the outer leaves so as to be able to transmit the forces oftension and compression. However in a timberframe construction, it is to be expected that the inner timber frame leaf will undergo rather greater shrinkage than the outer masonry leaf on the completion ofthe building. This means that the inner leaf will tend to settle more rapidly.

Because of the slidable connection between the two parts oftheframe tie, this differential movement between the inner and outer leaves of the wall can be accommodated while the tie can still sustain the necessarytensile and compressive forces because of the interfitting undercut formations. The tie is initially positioned as shown in Figures 3 and 5 but, after some differential movement has taken place, the part attached to the inner wall will slide downwardly relative to the other part and is likelyto be roughly aligned with the axis of elongation of the tie. The typical dimensions ofthe parts allow for about 5 mm off-set between the axis ofthetwo parts in the initial position.Itwill be appreciated that if the part attached to the innerwall moves beyond the axis ofthe other part, it will still be securely held thereby so as to be able to transmit both tensile and compressive forces.

The tapering free end portion 17 of the tie will be relatively flexible because of the thickness of its material. However, the large surface area and the gradually increasing width ofthis portion of the tie aids in embedding the tie more firmly in the mortar 18, reducing the risk ofthetie becoming insecure and being pulled outtowardsthe cavity under load.

Various modifications oftheframetie may be envisaged. In particular,thearrangementofthe interfitting formations may differ. For example, it would be possible to secure an elongate upright slideway member to the studding and have a cooper ating slider on the adjoining end of the tail member.

The advantage ofthe "button" arrangement of Fig. 1 and the ball arrangement of Fig. 7 illustrated is that it may permit slight pivoting movement about the general axis ofthetail 16which may occur because of uneven settlement in the building. It is therefore preferred that, if the reverse arrangement is adopted, the slider on thetie should be relatively small in size since otherwise there might be a tendency for slight pivoting movement ofthe parts to cause the slide to jam.

The material of which the tie is made may be other than polypropylene or a similar high tensile plastics material. For examplethetie may be made of metal. In this case, the shape may differ somewhat from the exact details shown because of different methods of manufacture and mechanical properties ofthe materials used.

Claims (21)

1. Aframe tie as hereinbefore defined comprising first and second parts adapted forattachmentto inner and outer walls respectively of a cavity wall, and means connecting said first and second parts together so as to bridge a cavity between the said inner and outerwalls, the connecting means being adapted to allow of limited relative movement between the parts in the plane of the cavity.

2. Aframetie according to claim 1 wherein said relative movement is translational movement.

3. Aframe tie according to claim 2 wherein said relative movement is transversely of a generally axial direction of said tie.

4. A frame tie according to any one of claims 1 to 3 wherein said first partcomprisesafirst member having an elongate slideway therein.

5. Aframe tie according to claim 4wherein said slideway is closed at an upper end thereof in use.

6. Aframetie according to claim 4Orclaim 5 wherein said slideway is adapted to receive a slide part of said second partwhichcomprisesasecond member.

7. Aframetie according to any one of claims 4 to 6 wherein said slideway extends transversely of a generally axial direction ofsaidtie.

8. Aframetie according to any one of claims 4to 7 wherein said slideway comprises a first undercut formation.

9. Aframetie according to claim 8when dependent on claim 6, wherein said slide part comprises a second undercutformation cooperable with that of said slideway.

10. Aframe tie according to claim 6 or any claim dependent thereon, wherein said slideway comprises a slot and said slide part comprises a spigot.

11. Aframe tie according to claim 9, wherein said second member comprises a base adapted to abut the inner wall, a neck portion and a head providing said second undercut formation.

12. Aframetie according to claim 11 wherein said base has a projected area in the plane of said inner wall which is greater than that of said head.

13. Aframetieaccording to claim 11 orclaim 12 wherein said second member has a single hole for receiving a fastening for securing itto said innerwall.

14. Aframe tie according to any one of claims 1 to 13wherein said first memberhas at least one water-shedding formation thereon positioned so as to lie within the wall cavity in use.

15. Aframetie according to any one ofclaims 1 to 14wherein said first member has mortar keying formations thereon.

16. Aframetie according to claim 15 wherein said mortar keying formations comprise ribs.

17. Aframetie according to claim 15 wherein said motor keying formations comprise apertures.

18. Aframetie according to claim 6 wherein said slideway comprises a channel of part circular crosssection, and said slide part comprises a spherical member.

19. Aflame tie according to claim 4 or claim5 wherein said first and second parts comprise first and second members each having an elongate slideway therein,said tie also comprising a connecting member having opposed ends adapted to be received each in a respective slideway.

20. A frame tie according to any one of claims 1 to 3 comprising first and second parts and a connecting part being of corrugated form to permit flexure thereof.

21. Aframetie substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9 or any one of the aforementioned figures when modified in accordance with Fig. 10.