SCREW WITH ENLARGED HEAD PORTION FOR PLASTER BOARD BRACING SYSTEM The present invention relates to improvements in and relating to a screw for fixing plaster board, which is used in bracing a framed wall and a bracing system using such screws. For simplicity the present invention will be described particularly in respect of its use in respect of a plaster board bracing system but it will be appreciated by those skilled in the engineering arts that the screw of the present invention could also have benefit in its use with other materials.

Various proposals have been put forward in the past for achieving a strong screw fixing into plaster board. These proposals have included the "drywall"plaster board screws of for example United States Patent 3,942,405 which have been marketed under the trade mark GRABBER.

Typically these drywall screws have had a head diameter of the order of 8mm.

Such"Grabber"drywall screws have performed well for general fixing of plaster board. However, an improved screw fixing has been sought by the applicant in order to achieve improved shear diaphragm performance of a plaster board lined building element.

In using plaster board to brace a framed wall, in New Zealand, nails or clouts and washers have been used for this purpose.

In New Zealand an important consideration is"NZS3604: 1990 Code of Practice for light timber frame buildings not requiring specific design", and its subsequent amendments, which requires a building to be braced, typically with shearwalls, against lateral loads imposed by wind and earthquake actions. This has required a shearwall, or"bracing element"to have in-plane racking resistance to wind and earthquake loading. Similar regulations and codes exist of course in other countries. The performance of proprietary wall bracing elements have been evaluated in a series of full- scale reversed cyclic loaded in-plane racking tests, described in the published paper"BRANZ Technical Paper P21: 1979 (revised 1982,1987,

1988). A wall bracing test and evaluation procedure", which is incorporated herein in its entirety insofar as appropriate. The bracing element performance is measured in"BU/m" ("Bracing Units per metre) where 20 BU = 1 kN and the length (metre) measurement is plan length of the wall system. Other design (engineering) methods are featured in other codes in New Zealand and overseas.

Although particularly developed for use in New Zealand where wind and earthquake ratings for structures are specified in the appropriate building code the equivalent rating requirements are present in other countries so that it is believed that the present invention will have application outside of New Zealand, as a general shearwall or shear diaphragm component. Although described particularly in respect of a wall, it is envisaged that the present invention could be used in respect of floors and ceilings.

The term plaster board is intended to include within its scope other sheet material such as reprocessed wood or fibre cement.

OBJECTS OF THE INVENTION It is thus an object of one embodiment of the present invention to provide a screw for constructing a braced structure and particularly, but not exclusively, a plaster board lined, timber or steel framed structure, including a shearwall or shear diaphragm.

It is an object of a further embodiment of the invention to provide a method of bracing a structure and/or a braced structure which avoids or reduces problems or difficulties in previous methods or structures or which at least will provide the public with a useful choice.

Further objects of this invention will become apparent from the following description.

BRIEF SUMMARY OF THE INVENTION According to one aspect of the present invention there is thus provided a screw for constructing a braced structure having a head portion and a shank portion, the shank portion including along at least part of its length a thread and said head portion having a diameter of at least 9.5mm.

Preferably the diameter of the head portion is at least 10mu.

Preferably the head portion is bugle headed.

In one embodiment of the invention as defined in any one of the three paragraphs immediately above, the shank is provided with a thread along only part of its length and a portion of the shank adjacent the head portion is without a thread.

According to a further aspect of the present invention, a method of bracing a plaster board lined structure includes fixing the plaster board to a framed structure about its perimeter using spaced apart screws each having a head portion and a shank portion, the shank portion including along at least part of its length a thread and said head portion having a diameter of at least 9.5mm.

According to a further aspect of the present invention, there is provided a braced plaster board lined structure having plaster board fixed to a framed structure about its perimeter with spaced apart screws each having a head portion and a shank portion, the shank portion including a thread along at least part of its length and said head portion having a diameter of at least 9.5mm.

According to a further aspect of the present invention there is provided a screw substantially as herein described with reference to Figure 2 or Figure 3 of the accompanying drawings.

According to a still further aspect of the present invention, there is provided a method of bracing a plaster board lined structure and/or a

braced plaster board lined structure substantially as herein described with reference to Figure 4 of the accompanying drawings.

According to a still further aspect of the invention, there is provided a bracing system incorporating a sheet panel fixed to at least one side of a framing member by a plurality of screws each having an enlarged head of a diameter of at least 9.5mm.

Further aspects of this invention which should be considered in all its novel aspects will become apparent from the following description given by way of example of possible embodiments of the invention and in which reference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1: Shows an example of a"prior art"screw; FIGURE 2: Shows diagrammatically a screw according to one possible embodiment to the invention; FIGURE 3: Shows diagrammatically a screw according to a further embodiment to the invention; and FIGURE 4: Shows diagrammatically a braced plaster board lined wall structure according to one possible embodiment of the invention.

BRIEF DESCRIPTION OF POSSIBLE EMBODIMENTS Referring firstly to Figure 1 a"prior art"screw 1 is shown with a bugle head 2 and a threaded shank 3.

Typically for use in fixing in a drywall plaster board structure the prior art screw 1 has had a head diameter of the order of 8-9mm. The thread 3 can be of any suitable type depending on the use of the screw 1 and for attaching plaster board to metal the thread would be typically self

tapping while for fixing to heavy gauge metal the thread would be typically self drilling.

However, in bracing a plaster board lined wall structure about the perimeter of the wall frame, nails or clouts and washers have been used to fix the plaster board, but without providing totally satisfactory results.

Referring now to Figure 2 a screw 11 according to one embodiment of the invention is shown with a head portion 12 and a threaded shank portion 13 leading to a point 16. Typically the shank 13 may be 6 gauge or 8 gauge although any suitable diameter shank 13 may be used. In the preferred embodiment the head portion 12 is bugle headed as shown and may also, as shown, include a ridge or rim 15 about the bugle head which may assist in the seating of the head portion 12 in the plaster board of a drywall structure. However, in all embodiments of this invention this ridge or rim may be omitted.

In contrast to the head 2 of the prior art screw the diameter D of the enlarged head portion 12 of the present invention is at least 9.5mm, preferably at least 10mm. 10.5mm approximately may be particularly suitable in some instances. It is envisaged that the diameter D could perhaps be of the order of 15mm.

Surprisingly the applicant has found in testing that by increasing the head diameter D to be approximately 10.5mm a significant improvement in bracing performance can be achieved in wall racking tests. The applicant believes that a commensurate improvement would be similarly achieved for head diameters D of at least 9.5mm.

The table below provides the P21 test results for two wall elements constructed using two screws of the present invention compared with wall element constructed using a prior art screw. It is seen that in earthquake resistance the screws of the present invention have respectively a 52% and a 56% improvement while for wind resistance a 29% and a 31 % increase was achieved.

LINING FASTENERS EQ. Improv-WIND Improv- MATERIAL BU/m ement BU/m ement GIB@ Standard drywall 62-86- Braceline'screws @ 150mm centres to perimeter GIB23 6g Bracing screw 97 56% 113 31% Braceline'@ 150mm centres to perimeter GIBUS 8g Bracing screw 94 52% 111 29% Braceline"@ 150mm centres to perimeter The applicant has noted that the performance of the 6 gauge screw was better than the 8 gauge screw and therefore believes that there may be a relationship between the performance of the screw of the present invention and the ratio of the shank gauge and the head diameter.

Accordingly, while in the screws of the present invention as identified in the above tests a particular head diameter and shank gauge was used it is to be appreciated that subject to the head diameter being at least 9.5mm and preferably at or above 1 Omm any suitable shank gauge could be used.

Referring now to Figure 3 of the accompanying drawings the same reference numerals have been used as in Figure 2 to relate to the equivalent integers. However in the screw 11'of Figure 3 the thread on the shank 13 terminates some distance before the head portion 12. It is envisaged that in some uses the screw 11'may have advantages. It is also envisaged that the smooth portion 14 may be of a different diameter relative to the diameter of the rest of the shank 13, either greater or lesser.

As mentioned previously, the rim 15 shown in Figure 3 could be omitted.

Referring now to Figure 4, a plaster board lined braced wall structure is referenced generally by arrow 17. It is shown very diagrammatically as including by way of example a sheet of plaster board 23, or other sheet material, which is fixed to the end studs 19 and the top

and bottom plates 21 of the wall frame by enlarged head screws 18 of the present invention about its perimeter at suitable spacings, suitably for example at 150mm centres. For the intermediate studs 20, nails or clouts 28 may, for example, be used at 300mm centres. The wall 17 may be associated with suitable flooring 22 of particle board or the like. The sheet panels 23 can be provided on one or both sides of the studs 19,20. The studs 19,20 can be of wood, metal or other materials.

As mentioned previously, the use of the enlarged head bracing screws of the present invention, as part of the braced wall structure, enables the required bracing to be achieved and has been found to minimise fastening popping and thus enhancing the quality of the resultant finish.

For the avoidance of any doubt, it is specifically mentioned that while the screw of the present invention has been described in the context of the P21 test method, it could of course be used in any type of shearwall or shear diaphragm and pursuant to other engineering methods or codes of New Zealand or other countries.

Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope of the invention as defined in the appended claims.