Method of manufacturing a joist

Abstract

A method of manufacturing a joist or truss 44 having two timber chords 42,44 connected and separated by web elements 12,14, an initial web element (10, Figs. 1, 2) having 1st and 2nd elongate separable spacer portions 12a,14a arranged at an angle to each other, each end of each spacer portion having a connector portion (12b,12c,14b,14c) for attaching the web element to a chord, two of the connector portions being connected directly to one another, the method including severing the connection between the two directly connected connector portions to provide two web elements, and attaching the two web elements to the timber chords such that the angle between each separated spacer portion is smaller or greater than the original angle prior to severing. Changing the angle allows variation in spacing between chords. The elements may be stamped or pressed metal e.g. steel, aluminium, and may be attached via a frangible weakened groove such that severing can be achieve via bending or flexing to cause failure and snapping of the connection. Alternatively sawing or cutting may be used.

Description

TECHNICAL FIELD The invention relates to a method of manufacturing a joist or a truss. BACKGROUND Bracing elements for connecting and spacing chords of a joist or a truss are known in the construction industry. In particular, bracing elements are known for attaching to parallel upper and lower chords of a timber joist or a timber truss to form a web connecting the chords. Such bracing, or web, elements, which are typically made of pressed metal, extend between the timber chords to provide open joists and trusses, and are commonly used in floor and roof structures as an alternative to solid timber joists and I-joists. Open joists and trusses allow for utilities (piping and wiring, for example) to be passed between the upper and lower chords without the need for drilling or notching, also allow for longer spans compared to solid timber joists, and can reduce material costs compared to solid timber joists. In use, an upper timber chord may be positioned at a predetermined distance above, and generally parallel to, a lower timber chord. Multiple web elements are attached to and extend between the chords, so as to connect the chords to one another and maintain them in spaced relation. Under gravity loads, the upper and lower chords provide compression and tension resistance to overall bending, respectively, while the web elements resist shear forces. Together, the chords and the web elements transfer the loads acting on a joist to supports, for example load bearing walls or columns. Attachment of the web elements to the chords is commonly achieved by way of connector plates, sometimes referred to as nail plates, having protruding nails that embed in the timber chord, for example into a side face of the timber chord. In such arrangements, the connector plates are typically formed integrally to the web element. Moreover, the nails may be formed integrally to the connector plates, for example by being pressed out of the material from which the plates are made. During manufacture of joists or trusses, the nails are driven, for example by a pressing operation, into the side faces of the timber chords to attach the web element thereto and thus form the joist or truss. Various configurations of web elements are known, including l-shaped, V-shaped and W-shaped web elements. Examples of known web elements are disclosed in earlier patent application GB2500030A, the contents of which is incorporated herein by reference, including a web element that is, initially, a V-shaped web element, comprising two separable I-shaped web elements. Each of the separable web elements comprises an elongate spacer portion and connector plates, of which a respective connector plate of each of the separable web elements may be joined to, or formed integrally with, the another. This known web element may be used as a single, V-shaped web element or may be separated to form two distinct, individual l-shaped web elements. It is an object of embodiments of the invention to provide an improved method of manufacturing a joist or a truss, and / or at least mitigate one or more problems associated with known methods. SUMMARY OF THE INVENTION According to an aspect of the invention, there is provided a method of manufacturing a joist or a truss, the method comprising: providing first and second timber chords; providing a web element, the web element comprising: first and second elongate spacer portions between which extends an angle in a plane common to the first and second elongate spacer portions; and first, second, third and fourth connector portions for attaching the web element to the timber chords, a respective one of the connector portions disposed at each end of the first and second spacer portions, and two of the connector portions being connected directly to one another; severing the connection between the two directly connected connector portions to provide two web elements; and attaching the web elements to the timber chords to maintain the timber chords in spaced relation to one another such that the angle between the first and second elongate spacer portions is greater or smaller than the angle prior to the step of severing. The method allows for the web element to be used for a range of spacings between the timber chords. In certain embodiments, the web elements may be attached to the timber chords to maintain the timber chords in spaced relation to one another such that the angle between the first and second elongate spacer portions is smaller than the angle prior to the step of severing. In certain embodiments, the method my comprise positioning one or both of the web elements to span between the timber chords prior to the step of attaching such that the web elements bear onto a surface of the timber chords for transferring a load between the web element and the surface. Additionally, the method may comprise positioning one or both of the web elements to span between the timber chords prior to the step of attaching such that the web elements bear onto opposing surfaces of the timber chords for transferring a load between the web element and the opposing surfaces. In certain embodiments, the step of severing comprises flexing the web element to induce failure in a region of the web element, such as a frangible region. In certain embodiments, the method may comprise positioning one or both of the web elements to span between the timber chords prior to the step of attaching such that an angle between the respective elongate spacer portion and the timber chords is at least 34° up to 40°. In certain embodiments, the angle (0) between the first and second elongate spacer portions may be fixed prior to the step of severing. That is, angle may be set to a predetermined value. In certain embodiments, the step of providing the web element may comprise providing the web element in a first configuration in which the first and second elongate spacer portions are connected to one another. In the first configuration, the angle (0) between the first and second elongate spacer portions may be fixed. In certain embodiments, the step of severing produces a second configuration of the web element in which the first and second elongate spacer portions are separated (i.e. distinct) from one another. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 is a perspective view of an exemplary web element, the web element being in a first configuration; Figure 2 is partial further perspective view of the web element of Figure 1, the web element being in a second configuration; Figure 3 is partial side view of an exemplary truss having the web element of Figure 1 attached thereto and being in the first configuration; and Figure 4 is partial side view of a further exemplary truss having the web element of Figure 1 attached thereto and being in the second configuration. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Embodiments of the invention have particular application for use in manufacturing floor and roof structures, connecting upper and lower timber chords of a joist or a truss, for example to form an open-web joist. However, other applications are contemplated, including use in manufacturing structural walls. Embodiments of the invention are intended for connecting upper and lower timber chords to maintain the chords in spaced relation with one another. Moreover, embodiments of the invention are intended to allow the spacing between the chords to be predetermined prior to their connection, thereby accommodating a range of spacings between the upper and lower chords. Figures 1 and 2 illustrate an exemplary web element 10. The web element 10 is of the V-shaped type, and comprises first and second separable web elements 12, 14 of the l-shaped type, the first and second separable web elements 12,14 being separable in that they are selectively separable from one another. The first separable web element 12 comprises a first elongate spacer portion 12a, together with first and second connector portions, or nail plates, 12b, 12c, between which the spacer portion 12a extends. Each of the spacer portion 12a and the nail plates 12b, 12c are formed as respective sheet-like portions, or plates, and are formed integrally with one another such that all lie in a common plane. As above, nail plates for attaching web elements to the timber chords of joists are known in the art, and are commonly used to attach web elements to timber chords. However, it will be appreciated by the skilled reader that any suitable means for attaching a web element to a timber chord may be used, for example, nails, screws, staples and the like, together with openings, through which such fastening means may extend, provided in the web element 12. In the illustrated example, each of the nail plates 12b, 12c has a plurality of nails, or teeth, 16 formed integrally therewith, by pressing or stamping regions of material from the plates 12b, 12c. The teeth 16 are upstanding from a rear surface of the web element 12. Moreover, respective outer edges 18 of the nail plates 12b, 12c comprise serrations, for embedding into timber chords, which may strengthen attachment of the nail plates 12b, 12c to the chords of the joist. The first separable web element 12 further comprises first and second edge flanges 20 extending along opposing outer edges of the web element 12. The edge flanges 20 are upstanding from the rear surface of the web element 12, each extending along the spacer portion 12a from an outer end 22 of one of the nail plates 12b, 12c to an inner end 24 of the other of the nail plate 12b, 12c. The edge flanges 20 may be upstanding from the rear surface of the web element 12 at an angle of approximately 90° thereto. At the outer end 22 of each of the nail plates 12b, 12c, the flanges 20 terminate in respective locating lugs 26, which may facilitate locating and maintaining correct positioning of the web element 12, as, in use, the locating lugs 26 may contact the timber chords of a joist. The edge flanges 20 may strengthen the web element 12, by increasing its resistance to compressive and / or torsional forces. The first separable web element 12 further comprises a pair of openings 28, about which inner flanges 30 extend, and a rib 32. Each of the openings 28 is delimited by a substantially continuous edge and forms an enclosed hole extending through the elongate spacer portion 12a, i.e. the openings 28 are substantially bounded on all sides by the material of the elongate spacer portion 12a. Each of the inner flanges 30 is upstanding from the rear surface of the web element 12 and may be substantially continuous, defining the periphery of the respective opening 28. Each inner flange 30 may be upstanding from the rear surface of the web element 12 at an angle of approximately 90° thereto. The opening 28 and the inner flanges 30 may be formed by punching through the sheet-like spacer portion 12a. Respective portions 30a (denoted in Figure 2) of the inner flanges 30 may extend along or adjacent the inner ends 24 of the nails plates 12b, 12c, which may facilitate locating and maintaining correct positioning of the web element 12, as, in use, the portions 30a, like the locating lugs 26, may contact the timber chords of a joist. The rib 32 is an elongate depression formed in the spacer portion 12a, for example by embossing. Like the edge flanges 20, each of the inner flanges 30 and the rib 32 may strengthen the web element 12, by increasing its resistance to compressive and / or torsional forces. One or both of the locating lugs 26 may, in use, bear onto a surface, for example and upper and / or lower surface, of a timber chord when in use. Similarly, the portions 30a may, additionally or alternatively, bear onto surface of a timber chord. Such bearing features, or portions, may facilitate load transfer between the web elements 12,14 and the timber chords, thereby increasing web capacity of a joist or a truss. The second separable web element 14 comprises a second elongate spacer portion 14a and third and fourth nail plates, 14b, 14c, between which the spacer portion 14a 12 09 24 extends. As can be seen in Figure 1, the second separable web element 14 is symmetrical to the first separable web element 12. The second separable web element 14 may comprise all of the features, functionality and associated properties described herein with reference to the first separable web element 12, with like features being 5 denoted in the figures using reference numerals offset by a factor of 100. An angle 0 (denoted in Figures 3 and 4) extends between the first and second elongate spacer portions 12a, 14b in a plane common to the first and second elongate spacer portions 12a, 14a. io The web element 10 comprises a connection 34 between the separable web elements 12, 14. As such, the first and second web elements 12, 14 may be formed integrally with one another. In the illustrated example, the connection 34 connects adjacent connector plates 12c, 14c of the first and second web elements 12, 14 such that the adjacent connector plates 12c, 14c are formed integrally with one another. As shown 15 in the illustrated example, the adjacent connector plates 12b, 14b may be the second and fourth connector plates 12c, 14c. In certain situations, it may be desirable to use the first and second web elements 12, 14 as distinct, individual web elements, by dividing the web element 10 in two. This separation may be achieved by severing the connection 34 between the first and second separable web elements 12, 14. 20 Separating the first and second web elements 12, 14 from one another may be achieved by cutting means, for example a saw. However, in certain embodiments, this separation may be achieved by hand, by flexing the web element 10 about the connection 34—more specifically, about an axis extending in the plane common to at least the first and second elongate spacer portions 12a, 14a and that delineating the 25 adjacent connector plates 12c, 14c from one another—to induce work hardening, also known as strain hardening, thereby reducing the ductility of the material at the connection 34 to point of brittle failure. This separation may be facilitated by the inclusion of a frangible region of the connection 34. The frangible region may take the form an area of reduced cross section of material forming the connection, and may 30 comprise, for example, a necked region, a groove, an aperture, or multiples and / or combinations thereof. Separation allows variation of the angle 0, by which the web element 10 is capable of accommodating a range of spacings between the upper and lower chords of a joist, when the web element 10 is attached thereto. In embodiments of the invention, the web element 10 may be formed / manufactured by one or more of folding, bending, stamping, punching and / or pressing operations. During manufacture, the web element 10 may be initially formed as a sheet metal blank, which is subsequently punched and folded into the desired configuration of the web element 10. Suitable materials for the web element 10 include galvanised steel materials, and aluminium or aluminium alloys. Figures 3 and 4 show the web element 10 attached to and extending between parallel first and second chords 40, 42 of a timber joist 44, in which the first chord 40 may be an upper chord and the second chord 42 may be a lower chord. More specifically, Figure 3 shows the joist 44 wherein the web element 10 is attached to the chords 40, 42 in a first configuration, in which the web element 10 is used as a single web element, and Figure 4 shows the joist 44 wherein the web element 10 is attached the chords 40, 42 in a second configuration, in which the web element has been divided into two distinct, individual web elements. In the second configuration the angle 0 between the first and second elongate spacer portions 12a, 14a is smaller than it was prior to severing the connection 34. By virtue of varying the angle 0, the web element 10, i.e. each of the separable web elements 12, 14, is capable attachment to the chords 42, 44 while bearing against a surface, for example a lower surface, of the first chord 40 and a further surface, for example an upper surface, of the second chord 42 over a range of values for the spacing S. In the first configuration, the web element 10 bears against the timber chords 42, 44 by the locating lugs 26 and the portions 30a of the inner flange 30. In the second configuration, the web element 10 bears against the timber chords 42, 44 by the locating lugs 26 only, as in the second configuration the portions 30a do not contact the chords 42, 44, due to the decrease in the angle 0. The range of spacings possible will depend upon exact size of the joist or the truss desired. It is contemplated that typical values of the spacing S will be at least 126 mm up to 151 mm. Particularly suitable values of the spacing S will be at least 146 mm up to 151 mm. Varying the spacing S varies an angle a between the elongate spacer portion 12a and the timber chords 42, 44. It is contemplated that typical values of the angle a will be at least 34° up to 40°. Particularly suitable values of the angle a will be at least 38° up to 40°. In embodiments of the invention, the joist 40 may be formed / manufactured by a pressing operation to drive the nails 16 into surfaces of the timber chords 42, 44, for example side surfaces, to attach the web element 10 to the timber chords 42, 44. Prior to attachment, an operator moves the first and second elongate spacer portions 12a, 14a relative to one another to provide a predetermined value of the angle 0 between the first and second elongate spacer portions, the predetermined value of the angle 0 corresponding to a desired spacing S between the timber chords 42, 44. It has been found to be particularly advantageous to maintain the connection between the first and second web elements 12, 14 when manufacturing a joist or a truss. This is because using the web element 10 as a single web element has been found to facilitate locating and maintaining correct positioning of the web element 10 before and during pressing operations to attach the web element 10 to the chords of the joist or the truss, at least being superior to using the first and second web elements 12, 14 as distinct, individual web elements once separated. Locating and maintaining correct positioning of the web element 10 may enable optimum load transfer between the web elements 12, 14 and the timber chords being achieved, thereby increasing web capacity of the joist or the truss. However, it has been found that the web element 10 may be used as a single, V-shaped web element, or may be separated at the connection 34, severing the connection between the first and second separable web element 12, 14 to be used two distinct, individual web elements, while providing suitable load transfer between the web elements 12, 14 and the timber chords 42, 44 in either case. When separated, the web elements 12, 14 may be spaced apart along a length of the timber chords 42, 44. The invention is not restricted to the details of any foregoing embodiment. For example, while the illustrated embodiment shows the web element 10 to be of the V-shaped type, other shapes are contemplated, including S-shaped, W-shaped and L-shaped. Indeed, the embodiments of the invention may be formed as any web element shape known in the field. Features serving to strengthen the web elements 12, 14, including the edge flanges 20, the inner flanges 30 and the ribs 32 are optional and may be present only in certain embodiments, either individually or collectively. Certain embodiments may comprise one or both of the web elements 12, 14 comprising one or more of any of the edge flanges 20, the inner flanges 30 and the ribs 32, any of which may be provided continuously or discontinuously. Certain embodiments may comprise one or both of the web elements 12 comprising one or more of the openings 28. Moreover, each of the teeth 16, the serrations, and the locating lugs 26 are optional and may be present only in certain embodiments, either individually or collectively. The nail plates 12b, 12c need not lie in the same plane as the spacer portion 12a, nor one another, and in certain embodiments maybe offset. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps 5 are mutually exclusive. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 10 Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A method of manufacturing a joist (44) or a truss, the method comprising: providing first and second timber chords (40, 42);providing a web element (10), the web element comprising:5                    firstand second elongate spacer portions (12a, 14a) between whichextends an angle (0) in a plane common to the first and second elongate spacer portions; andfirst, second, third and fourth connector portions (12b, 12c, 14b, 14c) for attaching the web element to the timber chords, a respective one of 10            the connector portions disposed at each end of the first and second spacerportions, and two of the connector portions being connected directly to one another;severing the connection between the two directly connected connector portions (12c, 14c) to provide two web elements (12, 14); and15            attaching the two web elements to the timber chords to maintain the timberchords in spaced relation to one another such that the angle between the first and second elongate spacer portions is greater or smaller than the angle prior to the step of severing.20   2. A method according to claim 1, wherein the two web elements are attachedto the timber chords (40, 42) to maintain the timber chords in spaced relation to one another such that the angle between the first and second elongate spacer portions (12a, 14a) is smaller than the angle prior to the step of severing.25   3. A method according to claim 1 or 2, wherein the method comprisespositioning one or both of the two web elements (12, 14) to span between the timber chords (40,42) prior to the step of attaching such that the two web elements bear onto a surface of the timber chords for transferring a load between the web element and the surface.

4. A method according to claim 3, wherein the method comprises positioning one or both of the web two elements (12, 14) to span between the timber chords (40, 42) prior to the step of attaching such that the two web elements bear onto opposing surfaces of the timber chords for transferring a load between the web element and the opposing surfaces.

5. A method according to any preceding claim, wherein the step of severing comprises flexing the web element (10) to induce failure in a region of the web element.

6. A method according to any preceding claim, wherein the method comprises positioning one or both of the two web elements (12, 14) to span between the timber chords (40, 42) prior to the step of attaching such that an angle a between the respective elongate spacer portion (12a, 14a) and the timber chords is at least 34° up to 40°.

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