Fasteners and wall assemblies

Abstract

A wall assembly (10) comprising top and bottom caps (11) and (12) which are generally U shaped channels and these are secured to a floor (13) and a concrete slab ceiling (14) which comprises in this case the underside of a concrete floor of the next level in a multi-storey building. In these arrangements the ceiling (14) has to be arranged in relation to the wall (15) for deflection of the ceiling (14), consequentially, the track (11) is spaced from the underside surface (16) by a distance of typically 20 mm and a suitable compressible spacer arrangement (17) is located between the upper surface (18) of the track (11) and the underside surface (16). The spacer arrangement (17) may be any suitable infill and one example may be a fire rated double sided adhesive layered expandable/compressible tape or foam. This tape may be applied to the upper outer surface of the channel and its other side adhesively applied to the underside of the concrete.

Claims

1. A wall frame comprising top and bottom tracks secured to top and bottom surfaces, the tracks having channels accommodating spaced studs extending between the top and bottom tracks in fixed spaced relation to form with the top and bottom tracks a rigid frame, inhibiting any vertical movement of the studs relative to the top or bottom tracks, the top track having axially spaced axially extending slots of predetermined length, spaced fasteners used to secure the tracks to the surfaces and with some of said fasteners passing through the slots in the top track, each fastener passing through the slots in the top track comprising a hold section penetrating the top surface, a head and a deflection guide slideway in the form of a cylinder movable up, down and along the respective slot to account for surface deflection, the fastener having a stop comprising one end of the cylinder adapted to set a distance of the head from the top surface and thereby set the track distance from the top surface, the track distance set being for the sole purpose of accommodating vertical displacement of the top surface, the studs being rigid with the tracks to inhibit relative movement between the studs and the tracks while the distance of the head from the top surface and the predetermined length of the slots is selected to accommodate top surface movement by permitting relative movement between the top track and the fasteners due to said surface deflection of the said top surface, the fasteners being chosen such that shear load testing of the stud track and fastener combination demonstrates a stud track and fastener combination demonstrates a stud to track failure at 6 mm-10 mm deflection and ranging from applied loads of 2.5 kN to 7 kN with no effect on the fasteners.

2. A wall frame according to claim 1 wherein the deflection guide slideway extends from a stop face located at one end of the hold section and along the fastener to the head, the effect being that when the stop face is hard up against the top surface the head is at a predetermined distance from the top surface and this distance from the top surface is substantially the same for all the fasteners along the track.

3. A wall frame according to claim 2, wherein the deflection guide slideway is a shank section of the fastener and the stop face comprises a physical stop to limit penetration of the hold section into the top surface, and wherein the head has a flange adapted to be secured in register with the track at a predetermined distance from the top surface determined by the stop face and the shank providing a dowel function enabling sliding movement of the fastener relative to the track in order to take account of deflection of the surface relative to the track.

4. A wall frame according to claim 1, wherein the deflection guide slideway is a shank section of the fastener and the stop comprises a physical stop to limit penetration of the hold section into the top surface, and wherein the head has a flange adapted to be secured in register with the track at a predetermined distance from the top surface determined by the stop and the shank section providing a dowel function enabling sliding movement of the fastener relative to the track in order to take account of deflection of the top surface relative to the track.

5. The wall frame of claim 1 wherein each fastener has a transversely extending stop face at a hold section end of the deflection guide slideway.

6. The wall frame of claim 1 wherein the deflection guide slideway is a dowel section and there is a stop face as an outer edge of one end of the dowel section at a juncture between the dowel section and the hold section.

7. A wall frame according to claim 1 wherein at least one stud has a side wall edge extending across the top track, the side wall edge having an end gap to accommodate a head of a said fastener.

8. A wall frame according to claim 1, wherein the top and bottom tracks define an internal wall height between the top and bottom surfaces, and the slots have a slot length selected according to the internal wall height.

9. An in situ rigid wall assembly comprising an upper track, a lower track, wall frame elements extending between the tracks and being fixed to the tracks, the wall assembly being secured to concrete surfaces, the upper track having axially spaced and axially extending slots of predetermined length and being spaced from an adjacent said concrete surface and being in axial slidable engagement with spaced fasteners passing through each of the slots, each fastener having a deflection guide slideway passing through the track and a stop setting a gap of predetermined width between the track and the adjacent said concrete surface determined by the position of the stop, a filler or spacer arrangement employed in the gap and wall cladding secured to the wall frame elements and to the tracks, the slot length and gap width being selected to accommodate movement of the adjacent said concrete surface, the fasteners being chosen such that shear load testing of the stud track and fastener combination demonstrates a stud track and fastener combination demonstrates a stud to track failure at 6 mm-10 mm deflection and ranging from applied loads of 2.5 kN to 7 kN with no effect on the fasteners.

10. An in situ rigid wall assembly according to claim 9 wherein each said track ranges in width from 64 mm to 150 mm with a base metal thickness ranging from 0.5 mm-1.5 mm and with guideways comprising axially spaced slots with a slot length ranging from 60 mm-310 mm.

11. An in situ rigid wall assembly according to claim 9 wherein each slot has a defined slot length and in multistory buildings the relationship between the distance between storeys, the internal wall height and slot length is such that the slot length is longer for greater distances between storeys.

12. A method to secure a wall track to an underside of a surface comprising: preparing a wall frame track with axially spaced guideways through which respective deflection guide slideways can pass for predetermined movement in concert with the surface and within the guideways; providing fasteners, each having a hold section, a head and a deflection guide slideway; securing the track using the hold section of the fasteners with the deflection guide slideway of each fastener being able to move in its respective guideway to account for surface deflection, the fastener automatically setting track spacing from the surface, the fasteners being chosen such that shear load testing of the stud track and fastener combination demonstrates a stud track and fastener combination demonstrates a stud to track failure at 6 mm-10 mm deflection and ranging from applied loads of 2.5 kN to 7 kN with no effect on the fasteners.

13. The method of claim 12 further comprising: using a track connector bracket between sections of track; the track connector bracket coinciding in use at a location with a one of said vertical frame elements.

14. The method of claim 12 further comprising: using a track connector bracket between sections of track; the track connector bracket coinciding in use at a location with one of said vertical frame elements, said one of the vertical frame elements being secured to the said section of track through gaps in a said connector bracket.

15. The method of claim 12 further comprising: using a track connector bracket between sections of track; the track connector bracket coinciding in use at a location with a vertical frame element, locating a track end first over a connector bracket and securing the track end and connector bracket to a concrete roof; and sliding an end of a further track over the already fastened track section and bracket and subsequently securing the further track with the track section in alignment using said fasteners along the further track and also securing it to the bracket.

16. A method according to claim 12 including the further step of having a head of a said fastener position in a gap in an end of a vertical frame element.

17. A multi-storey building comprising a rigid wall assembly according to claim 9 in a multi-storey building where the wall assembly is an internal wall, wherein the track ranges in width from 64 mm to 150 mm with a base metal thickness ranging from 0.5 mm-1.5 mm and with guideways comprising axially spaced slots with a slot length selected according to the following table depending on distance between storeys and internal wall height: TABLE-US-00009 Internal wall height - Required slot length - Distance between Assuming 300 mm including 9 mm Bolt storeys (mm) slab (mm) diameter (mm) 2000 1700 69 2100 1800 72 2200 1900 75 2300 2000 78 2400 2100 81 2500 2200 84 2600 2300 87 2700 2400 90 2800 2500 93 2900 2600 96 3000 2700 99 3100 2800 102 3200 2900 105 3300 3000 108 3400 3100 111 3500 3200 114 3600 3300 117 3700 3400 120 3800 3500 123 3900 3600 126 4000 3700 129 4100 3800 132 4200 3900 135 4300 4000 138 4400 4100 141 4500 4200 144 4600 4300 147 4700 4400 150 4800 4500 153 4900 4600 156 5000 4700 159 5100 4800 162 5200 4900 165 5300 5000 168 5400 5100 171 5500 5200 174 5600 5300 177 5700 5400 180 5800 5500 183 5900 5600 186 6000 5700 189 6100 5800 192 6200 5900 195 6300 6000 198 6400 6100 201 6500 6200 204 6600 6300 207 6700 6400 210 6800 6500 213 6900 6600 216 7000 6700 219 7100 6800 222 7200 6900 225 7300 7000 228 7400 7100 231 7500 7200 234 7600 7300 237 7700 7400 240 7800 7500 243 7900 7600 246 8000 7700 249 8100 7800 252 8200 7900 255 8300 8000 258 8400 8100 261 8500 8200 264 8600 8300 267 8700 8400 270 8800 8500 273 8900 8600 276 9000 8700 279 9100 8800 282 9200 8900 285 9300 9000 288 9400 9100 291 9500 9200 294 9600 9300 297 9700 9400 300 9800 9500 303 9900 9600 306 10000 9700 309

18. A wall frame comprising top and bottom tracks secured to top and bottom surfaces, spaced studs extending between the top and bottom tracks in fixed spaced relation to form with the top and bottom tracks a rigid frame, spaced fasteners used to secure the tracks to the surfaces and to account for surface deflection each fastener comprising a hold section, a head and a deflection guide slideway in axial slidable engagement with the top track to account for surface deflection, the fastener having a stop adapted to set the distance of the head from the top surface and thereby set the track distance from the top surface, the studs being rigid with the tracks to inhibit relative movement between the studs and the tracks while permitting relative movement between the top track and the fasteners due to said surface deflection of the said top surfaces; wherein at least one stud has a side wall edge extending across the top track, the side wall edge having an end gap to accommodate a head of a said fastener.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the present invention may be more readily understood and be put into practical effect reference will now be made to the accompanying drawings which illustrate preferred embodiments of the invention as applied at the top of a vertical wall but it will be appreciated that the top track may be at the bottom of the wall and wherein:—

(2) FIG. 1 is a cutaway view illustrating a wall assembly according to one aspect of the present invention;

(3) FIG. 2 is a close up of the top section of a typical wall assembly;

(4) FIG. 3 is a drawing illustrating application of the present invention to a curved wall;

(5) FIG. 4 is a part view showing part of a typical assembly process;

(6) FIG. 5 is a possible next step;

(7) FIG. 6 is a further possible next following the view of FIG. 5;

(8) FIG. 7 is a possible final view;

(9) FIG. 8 is a view of a typical fastener;

(10) FIG. 9 is a side view of the fastener of FIG. 8;

(11) FIG. 10 is a top view of the fastener of FIG. 8;

(12) FIGS. 11 and 12 are to a further embodiments similar to FIGS. 1 and 3 where cladding is secured to the outside of a typical track using spaced fasteners at any location along the tracks;

(13) FIG. 13 is a connector bracket that may be used to secure to section of track;

(14) FIG. 14 is a drawing showing use of the connector bracket at the juncture of two track ends and a stud;

(15) FIG. 15 is an exploded view of an alternative fastener; and

(16) FIG. 16 as a graph which is exemplary of the displacement of a stud track interface according other present under applied load.

METHOD OF PERFORMANCE

(17) Referring to the drawings and initially to FIG. 1 there is illustrated a wall assembly 10 comprising top and bottom caps 11 and 12 which are generally U shaped channels and these are secured to a floor 13 and a concrete slab ceiling 14 which comprises in this case the underside of a concrete floor of the next level in a multi-storey building.

(18) In these arrangements the ceiling 14 has to be arranged in relation to the wall 15 for deflection of the ceiling 14, consequentially, the track 11 is spaced from the underside surface 16 by a distance of typically 20 mm and a suitable compressible spacer arrangement 17 is located between the upper surface 18 of the track 11 and the underside surface 16. The spacer arrangement 17 may be any suitable infill and one example may be a fire/acoustic rated single sided adhesive layered expandable/compressible tape or foam. This tape may be applied adhesively to the upper outer surface of the channel and its other side compresses against the underside of the concrete.

(19) The lower track 12 is secured using concrete screws 19 which are located at spaced intervals along the track 12. In order that the track 11 may be secured in place fasteners 20 according to the present invention secure the track at spaced intervals along the track into the concrete slab 14.

(20) Referring now to FIG. 2 the top of the wall assembly 10 is illustrated in close up view whereby there is shown a stud 21 which fits inside the track 11 and then there is outer cladding 22, 23 applied to complete the assembly. The fastener 20 includes a hold section in this case in the form of a thread 24, there is a deflection guide slideway in the form of cylindrical shank 25 and there is a flanged head 26 of conventional hex form, the shank 25 having a stop face comprising in this example as an annular shoulder 27 which as can be seen serves as a stop to set the spacing between the underside 16 of the concrete slab and the top 28 of the track 11.

(21) Referring to FIG. 3 there is illustrated application of the present invention to a curved wall assembly which in this case employs a track 30 made up of individual segments 31 which have a flexible bridge 32 and are interconnected by a flexible strap 33 so that a curved track may be formed. Studs 34 are secured into the track as shown with fasteners 20 as previously described located at stud centers to secure the track to the concrete or other deflectable surface in fixed spaced relationship according to the length of the shank of the fastener 20.

(22) It will be appreciated by reason of the shank 25 and the self drilling capability of the thread on the fastener 20 that it is a simple matter to utilise the fastener 20 which is in the form of a heavy duty fastener at stud centers along the length of the track. This provides a very secure arrangement for simply and easily marking out centres and drilling and then securing the track in position while at the same time catering for the shank to enable the deflection allowance as prescribed for this type of assembly.

(23) FIGS. 4 through 7 illustrate typical assembly arrangements of a wall assembly according to the present invention utilising a fastener 20. The track 36 has been secured in place by fasteners 20, screwed into the slab 37 and studs 38 have also been secured, in this case the studs 38 have service holes 39 and these are aligned along the wall assembly. The fastener 20 operates as a deflection screw bolt inserted through the head track and fixed into the slab with the anchor points at stud centers. Screws 40 secure the track to the studs. After the top and bottom tracks and studs have been located then a plasterboard is secured as shown with sheet 41 suitably secured.

(24) The plasterboard is secured with screws. An open cell compressible backing rod 42 is secured and located in the 20 mm gap 43 and then a sealant 44 is applied to fill the gap between the top of the plasterboard and the underside of the slab. The plasterboard may typically be fire rated as is the sealant. This is repeated as illustrated in FIGS. 6 and 7. As additionally shown in FIG. 7 an additional sheet of plasterboard may be utilised at 45 as may other cladding be used depending upon the requirements of the space as is a custom in the usual way.

(25) Referring now to FIGS. 8 through 10 the preferred form of fastener 20 is illustrated which in this case has a total length of 75 mm and most importantly the shank 25 is in this case set at 20 mm from the flange 26 so that the stop shoulder 27 may operate to secure a track at this preset distance so that it is a simple matter to rapidly and quickly utilise ordinary tooling and equipment to put a track in position.

(26) Referring now to FIG. 11 another embodiment is illustrated. Like numerals illustrate like features. As in the previous embodiment it will be understood the track 11 secured to upper ends of the studs 34 at 46 on opposite sides. In this case the track 47 differs from the track 11 in so far as the holes 48 are elongated in the axial direction of the track. This permits limited movement in the axial direction. This is particularly useful in case of ground movements as in for example, during an earthquake. In all other respects the track is the same. The fasteners 20 are at the same centres as the studs. Fastener spacing may vary depending on the track material thickness.

(27) FIG. 12 illustrates a track arrangement 49 that may be used at the lower end of a ceiling bulkhead or the like of the type customarily involving a frame. The upper end not shown may correspond to the preceding drawings in FIGS. 1-11. One frame member of the ceiling underside frame is shown at 50 to which plasterboard or other cladding may be fixed in the usual way. The track 49 has a strap 51 passing through flange section 52 but there is no corresponding flange and strap on the inside. In all other aspects this is the same track. It may have elongated holes. It is fixed to the studs as shown.

(28) In each of the embodiments the track material may be made from lesser or thicker and stronger metals as may be desired by the application. In some cases it may be desirable to make the track self holding from thicker material one example being 0.75 mm Zincalume (registered trade mark of Bluescope Steel) or similar may be used and in this case it is possible to omit the straps 51 altogether. In this case the fastener spacing may be further apart but of course the fastener spacing may be selected according to need.

(29) In order for track sections to be joined a connector bracket illustrated in FIG. 13 may be used in the arrangement of FIG. 14. In FIG. 14 only part of the bracket has been shown in phantom to show its position as have the ends of the respective tracks and the ends of the stud. Referring to FIGS. 13 and 14 a connector bracket 53 fits inside and is secured to track 54 which together are secured to roof 55 using spaced fasteners, one being shown at 56, passing through slots 57. This mode of connecting the track 54 is effectively the arrangement of the previous embodiments, so the roof may float above the track. A vertical internal wall with studs 58 is rigidly connected back to the floor.

(30) It will be appreciated that once the bracket 53 and the track section 54 is secured then the end 59 of a second track section 60 may be manually located above the bracket 53 to abut with the end of track section 54 and before securing the track 60 to the bracket 53, the track section 60 may be secured at its far end using a fastener 56. Further fasteners 56 may be added. The stud 58 may be added later. It will be appreciated that the installation of the track sections in this case can then be a single man operation. A bracket similar to bracket 53 may be employed with curved track sections.

(31) The bracket 53 has a crown 61, corner flanges 62 used to secure the track sections and stud openings 63 used to enable the tracks to be secured directly to the stud 58. There are also cut outs 64 in the bracket and U-shaped cut out 65 (shown in phantom in FIG. 14) in the stud 58, these being to accommodate the head 26 of fasteners 56 to the full length of adjustment or movement available from slots 57. This gap 65 caters for the variable position of the studs and their alignment with the fasteners at these locations.

(32) Referring now to FIG. 15 there is illustrated an alternative fastener 66 formed from an internally threaded head end 67 and a complementary nail end 68. The ends are shown separated in FIG. 15 but it will be appreciated that they are screwed together to form the fastener. The nail end is a standard threaded concrete nail for use with a nail gun so that the nail end may be fired into position and then the head end is used to secure the tracks in position. It will be appreciated that any equivalent form of concrete connection may be employed.

Examples

(33) The below is what has been tested at the testing facilities to date with all (BMT) Base Metal Thickness of the tracks. Track length is typically 2400 mm upwards, stud spacing, and fastener spacing and plasterboard applied according to industry norms.

(34) TABLE-US-00002 64 mm Width Track, 0.55 mm, 0.75 mm, 1.15 mm (BMT) 110 mm slot 235 mm slot

(35) TABLE-US-00003 76 mm Width Track, 0.55 mm, 0.75 mm, 1.15 mm (BMT) 110 mm slot 235 mm slot

(36) TABLE-US-00004 92 mm Width Track, 0.55 mm, 0.75 mm, 1.15 mm (BMT) 110 mm slot 235 mm slot 309 mm slot

(37) TABLE-US-00005 150 Width Track, 0.75 mm, 1.15 mm (BMT) 110 mm slot 235 mm slot 309 mm slot

(38) All elongated slots are 10 mm wide in all track widths (64 mm, 76 mm, 92 mm, 150 mm). All setup passed the AS 1170.4-2007 as set out below. Applicant is confident of compliance with other standards. Present commonly used arrangements do not comply.

(39) With the present invention one can cut elongated slots up to 309 mm long. In the present examples these specific lengths in testing (110 mm, 235 mm 309 mm slots) were testing the strengths for the most commonly use track width (64 mm, 76 mm, 92 mm, 150 mm) and (“BMT”) Base Metal Thickness, 0.55 mm, 0.75 mm, 1.15 mm in the field taking into account the inter-story drift limits required to be satisfied with typical government legislation, to gauge the strength of the system. It was found that the present invention produced greater strength in sheer than present systems (which do not satisfy current standards) but with lower base metal thickness, thus providing overall long term savings in metal used while at the same time meeting safety standard for floor and roof deflection.

(40) In the examples a 110 mm slot will cover walls up to 3.0 m in height, a 235 mm slot will cover walls up to 7.2 m in height and a 309 mm slot will cover walls up to 10.0 m in height.

(41) Of course other options are possible, for example one could produce a 150 mm slot as this will cover most commonly used height walls of up to 4.5 m. This may cover approximately 80% of walls being built in the market.

(42) Typically, slots from 80 mm in length through to 309 mm in length (as per the table below) will cover all wall systems that can be constructed as per typical legislation, for example Australian Standard AS 1170.4-2007, that walls must cater for a inter-story drift of up to 1.5% of the storey height for each level. AS 1170.4-2007 (Incorporating Amendment Nos 1 and 2) Structural design actions Part: Earthquake action in Australia 54.4 Drift The inter-storey drift at the ultimate limit state calculated from the forces determined in Clause 5.4.2 shall not exceed 1.5% of the storey height for each level (see Clause 6.7.2).

(43) The table below sets out approximate slot lengths for wall height using 9 mm fasteners through the slots at nominal 600 mm centres as described above with standard stud and fastener locations and 13 mm plasterboard fitted to each side of the wall. Foam sealant was applied in the 20 mm gap between the top track and the underside of the concrete. The tests were repeated with foam strips.

(44) TABLE-US-00006 TABLE 1 Internal wall height - Required slot length - Distance between Assuming 300 mm including 9 mm Bolt storeys (mm) slab (mm) diameter (mm) 2000 1700 69 2100 1800 72 2200 1900 75 2300 2000 78 2400 2100 81 2500 2200 84 2600 2300 87 2700 2400 90 2800 2500 93 2900 2600 96 3000 2700 99 3100 2800 102 3200 2900 105 3300 3000 108 3400 3100 111 3500 3200 114 3600 3300 117 3700 3400 120 3800 3500 123 3900 3600 126 4000 3700 129 4100 3800 132 4200 3900 135 4300 4000 138 4400 4100 141 4500 4200 144 4600 4300 147 4700 4400 150 4800 4500 153 4900 4600 156 5000 4700 159 5100 4800 162 5200 4900 165 5300 5000 168 5400 5100 171 5500 5200 174 5600 5300 177 5700 5400 180 5800 5500 183 5900 5600 186 6000 5700 189 6100 5800 192 6200 5900 195 6300 6000 198 6400 6100 201 6500 6200 204 6600 6300 207 6700 6400 210 6800 6500 213 6900 6600 216 7000 6700 219 7100 6800 222 7200 6900 225 7300 7000 228 7400 7100 231 7500 7200 234 7600 7300 237 7700 7400 240 7800 7500 243 7900 7600 246 8000 7700 249 8100 7800 252 8200 7900 255 8300 8000 258 8400 8100 261 8500 8200 264 8600 8300 267 8700 8400 270 8800 8500 273 8900 8600 276 9000 8700 279 9100 8800 282 9200 8900 285 9300 9000 288 9400 9100 291 9500 9200 294 9600 9300 297 9700 9400 300 9800 9500 303 9900 9600 306 10000 9700 309

(45) Sheer load testing of the various track, stud and fastener combinations in the above BMTs for the tracks demonstrated stud to track failure, at displacement of 6 mm-10 mm and ranging from applied loads of 2.5 kN for the thinner tracks to 7 kN for thicker tracks. These tests employed a 600 mm test rig with tracks of the type shown in FIG. 3 top and bottom, two studs and fasteners at 300 mm centres. There were no effects on the fasteners at stud to track failure.

(46) Graph 1. Shown in FIG. 16 is exemplary of the displacement of the stud track interface under applied load for 51 mm ID wide track at 0.55 mm thick and matching studs at 51 mm wide and 0.5 mm thick.

(47) The next test involved testing straight track sections to determine the deformation of the slots about the fastener connections. A small test rig was used to apply sheer to a section of track until the track deformed about the fastener.

(48) The test results are shown in Tables 2 and 3 using a track and 9 mm fastener of the type illustrated in FIGS. 1 and 2. Table 2 shows the track dimensions and Table 3 shows the results confirming that the use of the present invention achieves loading beyond the requirements of the established standards while in combination optimising the thickness of the materials employed.

(49) TABLE-US-00007 TABLE 2 Test Channel Width Channel Thickness Slot length Designation (mm) (mm) (mm) 1 64 0.7 80 2 64 0.7 80 3 76 0.7 80 4 76 0.7 80 5 92 0.7 80 6 92 0.7 80 7 150 0.7 80 8 150 0.7 80 9 64 1.15 80 10 64 1.15 80 11 76 1.15 80 12 76 1.15 80 13 92 1.15 80 14 92 1.15 80 15 150 1.15 80 16 150 1.15 80 17_300 mm 92 1.15 300 18 64 0.7 80

(50) TABLE-US-00008 TABLE 3 Test Width Thickness Ultimate Load Designation (mm) (mm) (N) Failure Mode 1 64 0.7 2 888 Flange buckling 2 64 0.7 2 697 Web and flange buckling 18 64 0.7 2 980 Flange buckling 3 76 0.7 3 275 Flange buckling 4 76 0.7 3 403 Flange buckling 5 92 0.7 3 951 Web buckling 6 92 0.7 4 046 Web buckling 7 150 0.75 3 926 Web buckling 8 150 0.75 3 834 Web buckling 9 64 1.15 5 602 Flange buckling 10 64 1.15 5 750 Flange buckling 11 76 1.15 6 681 Flange buckling 12 76 1.15 6 899 Flange buckling 13 92 1.15 8 714 Flange buckling 14 92 1.15 8 884 Flange buckling 15 150 1.15 8 402 Web buckling 16 150 1.15 8 150 Web buckling 17 (30 mm 92 1.15 5 006 Web buckling slot)

(51) Whilst the above has been given by way of illustrative example many variations and modifications will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as set out in the appended claims.