BOX-SECTION BUILDING ELEMENT

Abstract: A building element (10) such as a lintel is formed of two members (12,14) engageable by means of complementary projections (26) and slots (31). Preferably both are provided by opposed L-shaped tangs (26) which are hooked behind one another by slight longitudinal displacement. They may be shaped (31) so as to wedge together. Members may have apertured (40) webs (16) to provide keying. They can be made by forming steel strip in a single operation. Preferably, the two members (12,14) are identical so that alternate portions of formed steel strip have merely to be turned through 180°.

Description: The present invention concerns box-section building elements, particularly lintels and other girders, e.g. purlins. A known type of lintel (e.g. GB-A-1 308 560) such as is used in forming an opening in an internal partition wall is basically a box girder of square section. It is formed of two like side-portions, each of which is a channel section member whereof the base forms a side wall and the arms form halves of the top and bottom faces. The mouths of the channels are narrowed by opposed flanges. The two portions are located so that respective flanges abut; and they are joined by a pair of longitudinal welds extending for the full length of the lintel, at the abutting mouths of the channel members. To enable such a lintel to key to plaster, it is conventional to apply expanded metal mesh, possibly to both sides and the bottom, and to secure this by metal bands passing right around the lintel. The manufacture of such a lintel may proceed from standard steel strip which is subjected to the following steps: (1) forming into channel members; (2) locating two channel members in the correct orientation and forming two longitudinal welds; (3) locating the expanded metal mesh, and banding it in position. The connection of the channel members by welding, and the connection of the mesh thereto by banding involve a significant cost of materials, and a much larger cost for labour. Similar considerations apply to other types of lintel, roof purlin etc. formed from two or more parts and/or having keying means applied. In one aspect the present invention provides a building element comprising a box-section, whereof the box-section is formed of two members each of which provides part of the box-section; the members being connected at two longitudinally extending regions by mutual engagement of complementary formations, which formations comprise projections with enlarged heads (e.g. being L- or T-shaped) and openings through which the heads can pass when they are in register. Relative mutual longitudinal displacement of the members then effects said engagement. Preferably the formations are shaped so that the displacement has a wedging and/or deforming effect. The openings may be closed slots. Alternatively they may be open-ended. For example, a pair of complementary formations may both be formed by a like series of alternating L- or T-shaped projections and (inverted) L- or T-shaped openings, the openings of one set being in register with the projections of the other. In a particularly preferred form, at least one (and preferably each) pair of complementary formations comprises, on each member, a series of L-shaped projections or tangs, the tangs on the two members facing opposite ways so that they can hook one another. The two portions for engagement may require resilient deformation to permit engagement, so that their resilience holds them firmly once engaged. The connection may be secured by welds, which require little strength and may be intermittent. The connection of members may be strengthened by deforming engagement portions after (or during) engagement. For example, tangs projecting into the box-section may be bent so as to resist disconnection. Alternatively or additionally at least some of the engagement portions may be shaped to promote wedging. Thus tangs may have heads whose inner edges, extending generally in the longitudinal direction of the lintel, are angled relative to that direction. Engagement slots or openings may be complementarily angled. The two members may be identical. Thus each may have two longitudinal series of L-shaped tangs pointing in the same longitudinal sense. Inversion of one member effectively reverses its tangs. As an alternative, each member may have one portion which provides projections and one portion which provides openings. A lintel for a cavity wall may comprise a portion of box-section for supporting one skin of the wall and possibly bridging the cavity, and a horizontally extending flange for supporting the other skin. One member may provide part of the box-section portion while the other provides the rest of the box-section portion and the flange. This other portion may be formed of a profiled sheet portion that provides the flange, an upright wall portion of the box, and possibly a roof portion of the box; and one or more engagement portions connected to a lower region of the upright portion so as to extend away from the flange. The engagement portion(s) is/are preferably connected only to intermittent regions of the upright portion, to reduce possible heat transfer. Thus an engagement portion may comprise an elongate plate that at one side has projections welded to the upright portion and at the other side has engagement formations, preferably L-shaped tangs. Alternatively there may be a plurality of cleats longitudinally spaced along the lintel. In another aspect the invention provides a building element comprising a box-section having web portions which are apertured to provide keying formations. Preferably it is formed from two members with complementary formations, as described above in relation to the first aspect. Such members can be produced with a single punching tool or step, which produces both the keying apertures and the complementary engagement formations. In another aspect the invention provides a method of making a building element as described above. Some embodiments of the invention will now be described in greater detail with reference to the accompanying drawings in which: Fig. 1 is a sectional view through a box lintel embodying the invention; Figs. 2,3 and 4 are like views of pairs of edge regions of lintel portions having three types of complementary formations; Fig. 5 is an elevation, viewed in the direction of arrow IV in Fig. 1; Fig. 6 is a schematic plan view of apparatus for producing lintel portions; Fig. 7 is an end elevation of another type of lintel embodying the invention; Fig. 8 is a detail of a cleat portion of the Fig. 6 lintel; Fig. 9 is a view similar to a section on A-A in Fig. 7 but showing a modified embodiment; and Fig. 10 is a detail of an edge region for explaining a modification of those shown in Fig. 2. Fig. 1 shows a box lintel 10 preferably formed from identical right and left members 12,14. Each of these members is a channel member of thin steel sheet, having a base 16 which forms a side of the lintel; and upper and lower arms 18,20 which extend for a little more than half of the width of the lintel. Adjacent the base 16, the arms extend at right-angles to it (in the finished lintel). But outer portions 22 extend inwardly at an angle, so that the lintel 10 has recesses 24 in its top and bottom faces. The two outer portions 22 of one lintel portion 12 engage the corresponding angled outer portions 22 of the other lintel portion 14 with complementary formations. These may be as shown in Fig. 2. Thus each outer portion 22 may be formed with a series of L-shaped tangs or projections 26, having wedge-shaped heads 28 on stems 30. (The inner edges 31 of the heads are inclined so that the heads are thicker adjacent the stems.) On each member, the heads 28 at each outer portion 22 face in the same longitudinal direction. Since the two members 12,14 are facing opposite ways, their heads 28 face in opposite directions. Thus they can be pushed into engagement whereafter the lintel portions, 12,14 can be relatively displaced to a small extent longitudinally, so that the heads 28 lock behind one another. Furthermore they wedge, so that force would be required to reverse the displacement. One alternative is shown in Fig. 3. One portion 22 has tangs 26 as before. Its complementary portion 22 has slots 32 through which the heads 28 can pass. Once again, longitudinal displacement leads to wedging. Preferably the two lintel portions, 12,14 are identical (for economy of production). Thus each may have projections 26 on one of its outer portions 22, and openings 32 in its other one. A further alternative formation is shown in Fig. 4. In this, each of the engaging outer portions 22 has an identical formation of alternating T-projections and T-slots out of phase with each other. Thus in the assembly configuration as shown, the projections 34 of one set are adjacent the openings 36 of the other. One set of projections 34 can be passed through the other set of openings 36, whereafter, as in the previous case, a slight longitudinal movement of one lintel portion locks them together. It is desirable that the two lintel portions 12,14 should be exactly in register in the finished lintel, without one projecting beyond the other to any great extent at either end. With the configuration shown in Fig. 4 there is perhaps a greater risk that portions will be engaged in a less preferred configuration, so that relatively large mis-matching occurs. Preferably each lintel portion 12 or 14 is resiliently urged to form a more widely open channel shape than in the engaged configuration shown in Fig. 1. Thus engagement of the complementary formations involves resilient bending of the lintel portions 12,14. Consequently in the engaged configuration each is slightly stressed, so that the portions are not loose. They are made even more stable if they wedge as previously described. Nevertheless it is preferable to apply one or more spot welds just to lock the portions in the longitudinally displaced configuration in which the complementary formations cannot disengage. As can be seen in Figs. 1 and 5, the lintel 10 has openings and recesses. The openings are to provide keying formations and comprise horizontally extending rows of holes 40 in the side walls, and openings 42 in the underside. The holes 40 are preferably vertically staggered as shown, so as not to take too much steel out of the cross-section. The underside's openings 42 may be longitudinal slots, since the slight weakening effect does not matter because the underside is likely to be in tension in use, and not to have to withstand substantial stresses. The openings provided by the engaged complementary formations 22 at the underside also serve for keying, as does the lower recess 24. The upper side of the lintel will not generally have keying formations. However, the recess 24 can have a keying function similar to the frog of a brick. This can reduce the known tendency of bricks or blocks to slide on top of a flat top of a conventional box lintel. Recesses 44 are desirable for stiffening the side walls 16 of the lintel. They can be most easily formed as continuous longitudinal channels, as shown. Instead of one large recess 44, there may be a pair of smaller longitudinal recesses, vertically spaced. This may be easier to manufacture. Fig. 6 shows plant for forming lintel portions 12,14. A coil 60 of steel strip is unwound and flattened by rollers 62. It passes through a forming press 64, past a shear 66 and on to a collecting table 68. A photoelectric detector 70 detects when the strip reaches it, and actuates the shear to cut it. The sensor 70 may be displaceable on rails, to vary the lengths of products being cut off. Within the forming press 64 there is a punch assembly which may act across a transverse region of the strip to form a line of holes 40 and openings 42, as well as the complementary edge formations 26,32 or 34,36. Downstream of this there may be a hammer for producing the stiffening recesses. Further downstream is a bending assembly for forming the strip into the channel section. At some stage the strip is cold-rolled to produce a recess 44 along its length. By way of example, such lintels may be formed of steel strip of thickness 1.6,2.0 or 2.5mm, in lengths of from about 1 metre to a few metres. The complementary formations as shown in Fig. 3 may comprise slots 32 of length 20mm, and projections 26 whose heads are 18mm wide. Locking of two lintel portions 12,14 may then be effected by a relative displacement of about 5mm. As compared with the production of conventional lintels, with two welds extending for the full length and with expanded metal mesh applied by banding, lintels according to the present invention may be produced with a cost for materials and labour which is reduced by 40%. The labour is much reduced by the great reduction in welding and the avoidance of the application of the mesh. Expanded metal mesh is quite expensive, and its costs can be saved in its entirety, as can the cost of the banding material. It is obviously convenient to be able to use the same tooling for several different articles. However, if a punch is producing engagement formations, e.g. as shown in Fig. 2, in sheet material of different thicknesses, there is a risk that not all articles will engage firmly. As shown in Fig. 10, if the formations are tangs 26 whose angled edges 31 define slots of minimum width T , a formation of another portion 12 can engage wedgingly only if its thickness t exceeds T . The minimum slot thickness T could be made so small that this would be the case for all likely materials, but this would require a punch with very fine, easily damaged punch heads. A more practicable alternative is to produce slots whose edges E opposite the tang edge 31 are also angled. Thus the minimum width of a slot is great enough to allow the punch head to be robust. A portion 12 engaging therewith is bent (downwardly in Fig. 10), provided its thickness t is less than the dimension T . This deformation produces a very firm engagement. Engagement can be further strengthened by post-deformation. Thus a tool can be passed along the box-section to bend inwardly projecting tangs outwardly. (The box-section may be externally supported.) If the tangs or other engagement formations are adequately deformed, subsequent welding is unnecessary. Fig. 7 shows a lintel 80 having a box portion 82 and a horizontal flange 84. It comprises two members 86,88 which engage much as the members 12,14 of the lintel previously described. The outer member 86 may be just the same as the members 12,14. The inner member 88 is formed of an approximately Z-shaped sheet steel portion 90, and a multiplicity of cleats 92. The Z-portion 90 has a lower limb that provides the flange 84, a vertical wall 94, an inclined wall 96, a horizontally extending upper portion 98, and an angled outer portion 100 with complementary formations for engaging formations of the outer member 86. The lower limb 102 of the outer member 86 has a series of complementary formations as shown in Fig. 2 or Fig. 3. The inner member 88 has a corresponding series of spaced cleats 92 secured to a lower region of its vertical wall 94. (For example, the spacing of the centres of the cleats (and of the openings 32) may be a dimension in the range 100-150 mm.) Each cleat 92 has a horizontally extending elongate L-section inner portion 104 (whose inner end is secured to the wall 94, suitably by stud welding 105), and an inclined outer planar portion 106 seen in plan in Fig. 8. This terminates in an L-shaped projection 108 having a wedge-shaped head 110. Thus the two members 86,88 are engageable in the same manner as for the lintel previously described, and may be locked together by spot or tack welds, to suit the intended loading. There may be keying formations of similar types. The use of spaced cleats 92 can be rather expensive, because of the individual welding steps. They can be replaced by a single plate 120 as shown in Fig. 9. This has intermittent projections 122 along its outer edge by which it is welded to the wall 94. Its inner edge has tang formations 124 for engaging complementary formations 126 of the member 86. The plate 120 and adjacent limb 102 have keying openings 142. The gaps 144 between the outer projections 122 may also assist keying, but primarily they are to reduce 'cold bridging' heat loss. The pitch of the welded projections 122 is selected in response to the intended loading conditions. It is intended that the lintel 80 should be built into a cavity wall whose inner skin is supported on the flange 84. The cavity is bridged by part of the box portion 82 including the inclined wall 96. The outer skin is supported on the horizontal upper portions 98,112. Of course much variation is possible. For example the box-section could be more nearly rectangular, without the inclined wall 96. The cleats could be shorter, the lower limb 102 of the outer member 86 being correspondingly lengthened. Two part lintels or other building elements embodying the invention may be provided with thermal breaks by interposing insulating material between the complementary formations. This can conveniently be effected by applying tough plastics coatings to marginal edge regions that provide the formations.

Claims: A building element (10;80) comprising a box-section (82), whereof the box-section is formed of two members (12,14;86,88) each of which provides part of the box-section (82); the members being connected at two longitudinally extending regions by mutual engagement of complementary formations (26;32;34,36;108;124,126) characterised in that said formations comprise projections with enlarged heads (26;34;108;124,126) and openings (31;32;36) which permit passage of the heads when they are in register, whereafter relative mutual longitudinal displacement of the members effects said engagement. A building element according to claim 1 wherein both the projections and the openings are provided by like series of alternating L- or T-shaped projections and (inverted) L- or T-shaped openings (26;34,36;124,126). A building element according to claim 1 or claim 2 wherein two portions (22;100,106) for engagement require resilient deformation to permit engagement, so that their resilience holds them firmly once engaged. A building element according to any preceding claim wherein at least one said engagement portion comprises a series of projections (26;108;126) having engagement surfaces (31) which are angled so that said mutual displacement of members to effect engagement promotes wedging. A building element according to claim 4 wherein the member having said angled surfaces (31) has adjacent angled edge portions (E) defining angled slots with said angled projection surfaces, such that an engagement portion (12) being engaged therewith by said mutual displacement is deformed. A building element according to any preceding claim wherein the two members are substantially identical. A building element according to claim 6 wherein each member has two longitudinal series of L-shaped projections (26) pointing in the same longitudinal sense so that inversion of one member relative to the other effectively reverses its projections and provides said complementary formations. A building element according to any of claims 1 to 5 wherein at least one of the complementary formations of at least one connection region is provided by engagement means (106;120) which form part of the box-section and have said complementary formation (108;124) at one side, the other side being connected to another part of the box-section at longitudinally intermittent regions (105;122) so as to reduce thermal bridging. A building element according to any preceding claim wherein the box-section has web portions which are apertured (40) to provide keying formations. A pair of members assemblable together to produce a building element according to any preceding claim. A method of making a building element according to any preceding claim which comprises forming said two members (12,14) from steel strip; locating said members face to face and relatively displacing them so that said projections (26) of one member project through openings (31) of the other member; and effecting said relative mutual longitudinal displacement so that the formations become engaged. A method according to claim 11 in which after said engagement the projections (26) are deformed to restrain disengagement. A method according to claim 11 or 12 wherein the forming includes a step of cutting the strip, thereby simultaneously defining the complementary formations (26) and producing apertures (40) in a web portion to provide keying formations.

Inventors: WILLIAMS, IEUAN
Applicants: ALPHA-KEM LIMITED
Application year: 1987
Main classification: E04C3
IPC codes: E04C3