ROOFING STRUCTURE

Abstract

A roof beam is shown for a temporary building in which the beam comprises a first elongate member and a second elongate member, each comprising a box section with a hollow centre having a length, a width and a depth. The first elongate member is provided at each of two adjacent corners of its box section with a first connector extending lengthwise and comprising a channel closed off from the hollow centre of the first elongate member and open outwards through a neck narrower than the channel. The second elongate member has at each of two adjacent corners of its box section a second connector extending lengthwise and comprising a rib projecting through the neck of a complementary first connector and a flange on the rib held within the channel of the complementary first connector. In addition, the first elongate member and the second elongate member are respectively configured and arranged so that the first and second connector interconnect, with the second connector being a close fit within the first connector, whereby the first and second elongate members are coupled together to form the roof beam.

Description

The present invention relates to a roof beam for a temporary building. The present invention also relates to a method of making a roof beam.

Temporary buildings may be required, non-exclusively, for: events such as concerts (with sound staging) and conventions; educational purposes in schools and colleges; sports facilities (where it is especially desirable to be able to provide a clear span over an area the size of a football pitch); retail purposes; training; military buildings such as a temporary (and possibly camouflaged) hangar for aircraft; vertical farming; humanitarian needs; and corporate multi-functional storage including bonded warehousing. Those skilled in the art will appreciate that most if not all of these uses will require a completely open area under the roof, which means the roofing structures must be supported only at their ends, with no intermediate supporting legs intruding on the covered area. And in addition, the roofing structure must be strong enough to carry lights, screens, loudspeakers and lifting equipment and so forth which are commonly heavy (may be more than 3 tonne).

The need for a roofing structure to be strong, especially where required to bridge a large span of say 100 m without intermediate supports, gives rise to a design problem in that the stronger materials tend to be heavier. Thus, for instance, structural steel has a tensile strength around 500 MPa and a density around 8 g/cm3, whereas aluminium alloy is much lighter, at less than 3 g/cm3, but its tensile strength is less than 300 MPa.

A way tackling this problem in temporary buildings—which are required to be light, for portability—is to use extruded aluminium alloy for a roof beam in the form of a hollow box section. To bridge large spans, it is known to reinforce the roof beam, for instance by means of a reinforcing profile slid into and fitting snugly within the box section of the roof beam. This increases the strength of the beam, but at the cost of increasing its weight.

It is an object of the present invention to reinforce a roof beam such as formed from extruded aluminium is such a way that the gain is strength is proportionately greater than the gain in weight. The invention seeks particularly to provide a roof beam which is both stronger and lighter than those using a reinforcing profile slid into a box section as described above.

Thus, according to a first aspect of the invention there is provided a roof beam for a temporary building wherein:

• • said roof beam comprises a first elongate member and a second elongate member each comprising a box section with a hollow centre having a length, a width and a depth;
  • the first elongate member is provided at each of two adjacent corners of its box section with a first connector extending lengthwise and comprising a channel closed off from the hollow centre of the first elongate member and open outwards through a neck narrower than the channel;
  • the second elongate member has at each of two adjacent corners of its box section a second connector extending lengthwise and comprising a rib projecting through the neck of a complementary first connector and a flange on said rib held within the channel of the complementary first connector; and
  • the first elongate member and the second elongate member are respectively configured and arranged so that the first and second connectors interconnect, with the second connector being a close fit within the first connector, whereby the first and second elongate members are coupled together to form said roof beam.

It will be seen that, like the previously known reinforcing arrangement mentioned above, the present invention provides a roof beam comprising two elongate members each having a hollow box section profile. However, instead of one member being slid inside the other as in the previously known arrangement, the invention locates the reinforcing member (the second elongate member) alongside the first elongate member, rather than within it. As will be described hereinafter, with other features of the invention, this is both stronger and lighter than the previous arrangement.

In a second aspect the invention extends to a roof truss comprising two roof beams according to the first aspect of the invention, wherein said two roof beams are arranged in parallel to one another, one above the other, and the upper roof beam has its said second elongate member below its said first elongate member and the lower roof beam has its said send elongate member above its said first elongate member, with bracing members extending between and secured in said second elongate members.

The invention extends to a method of making a roof beam or truss as defined hereinafter.

Other features of the invention will be apparent from the following description, which is made by way of example only and with reference to the accompanying drawings which are schematic and in which:

FIG. 1 illustrates in transverse cross-section two hollow box sections extruded from aluminium alloy of which one is configured and arranged to fit snugly within the other so as to form a reinforced roof beam as previously known;

FIG. 2 illustrates in transverse cross-section a roof beam embodying the present invention;

FIG. 3 is an isometric view of a roof truss two roof beams of the kind shown in FIG. 2; and

FIG. 4 shows, enlarged relative to FIG. 3, a detail of the roof truss of FIG. 3.

Referring first to FIG. 1, this shows previously known first and second roofing profiles 100 and 102 each extruded from aluminium alloy and having a box section with a hollow centre. The first profile 100 may in lightweight structures may be mounted at its opposite ends on a support indicated schematically in broken lines at 104, to form a roof beam to support a fabric roof. For this purpose, the first profile 100 has at its corners channels 106 for receiving keders to hold the fabric roof in place. (The keders are not shown in the drawings, but those skilled in the art will know that they are slid into the channels 106 to extend along the length of the roof beam and have flaps that in use extend through the narrow neck 106a of the channels 206 to be secured to the fabric, by stitching or preferably welding).

For heavier structures, and especially for longer spans (say L>10 m) the profile 100 is reinforced by having the profile 102 slid into the hollow centre of the box section of the profile 100, to extend along the length of the profile 100. The profiles 100 and 102 are respectively configured and arranged so that the profile 102 is a snug fit within the profile 100. Thus:

• • The profiles 100 and 102 are of equal length;
  • The profile 102 has an external width W2e slightly less than the internal width W1e of the profile 100;
  • The profile 102 has an external depth D2e slightly less than the internal depth D1e of the profile 100; and
  • The corners of the profile 102 are arcuately formed with inwardly directed curves 108 to accommodate the projection of the channels 106 into the hollow box section of the profile 100.

Instead of the arrangement of FIG. 1, in which one roofing profile is slid inside another to provide a composite roof beam, in the present invention two profiles (called herein a first elongate member and a second elongate member, to distinguish the invention more clearly from the prior art of FIG. 1) are connected together along their length, one above the other. This is illustrated by FIG. 2, which shows in transverse cross-section a composite roof beam 200 comprising said first elongate member 202 and said second elongate member 204, each extruded from aluminium alloy.

The first elongate member 202 comprises a hollow box section the same as that of the profile 100 of FIG. 1, with channels 206, 208, 210 and 212 at its four corners. The two lower channels 210 and 212 as seen in FIG. 2 receive keders to hold a fabric roof in place. (It may be noted here that the composite beam 200 may in use be inverted relative to FIG. 2 so that the second elongate member 204 is below the first elongate member 202 and the keder-receiving channels 210 and 212 are at the top of the composite beam 200). The upper channels 206 and 208 as seen in FIG. 2 do not receive keders but are used for a different purpose as will now be described.

The second elongate member 204 comprises a rectangular hollow box section with its sides somewhat thickened at 214 for extra strength. The first and second elongate members 202 and 204 are of equal length and equal width. The second elongate member 204 has a depth somewhat less than half that of the first elongate member 204.

As seen in FIG. 2, the second elongate member 204 has at its two lower corners arcuately-formed ribs 216 and 218 extending outwardly and then curving back to extend into the upper channels 206 and 208 of the first elongate member 202, the ribs 216 and 218 being dimensioned and arranged to fit through the narrow necks of the channels 216 and 218. The free ends of the ribs 216 and 218 are formed with enlarged heads 220 and 222 respectively that do not fit through the necks of the channels 216 and 218. Rather, each of the rib-head 15 formations 216, 220 and 218, 222 is configured and arranged so that the heads 220 and 222 are each close against the inside of their respective channels 206 and 208.

To couple the first and second elongate members 202 and 204 together to form the composite beam 200, they are first laid end-to-end, when the rib-head formations 216, 220 and 218, 222 are aligned with respective channels 206 and 208. Then the first and second elongate members 202 and 204 are relatively moved lengthwise so that the rib-head formations 216, 220 and 218, 222 slide through the respective channels 206 and 208. This relative lengthwise movement is continued until the ends of the first and second elongate members 202 and 204 mutually coincide, and the composite beam 200 is formed. The opposite ends of the composite beam 200 are then secured to vertically-extending supports to support a raised roof of fabric connected to the beam 200 by keders in the usual way.

The composite beam 200 is both lighter and stronger than the previously known reinforced beam formed as described hereinbefore with reference to FIG. 1 by sliding the profile 102 into the profile 100, as will now be explained.

In each case, the weight of the beam is proportional to its cross-sectional area. Rounded off, the aggregate cross-sectional area of the profiles 100 and 102 of FIG. 1 (and hence of the previously known composite beam formed by sliding one into the other) is off, 75 cm². The aggregate cross-sectional area of the composite beam 200 of FIG. 2, with nominal wall thicknesses equal to those of the profiles 100 and 102, is 62 cm². It follows that the weight per unit length of the composite beam 200 is nearly 20% less than that of the previously known beam. Further, lighter roof beams do not need such strong supports, offering an additional reduction in the amount of aluminium (or possibly other material) required.

Importantly, the weight reduction from use of the invention also delivers a substantial environmental benefit by reducing both energy consumption and carbon emissions, because aluminium production is both energy intensive and carbon intensive. Aluminium production demands about 17000 kWh of electricity per tonne; and carbon emissions from aluminium production are greater than 6 tonne of CO2e (carbon dioxide equivalent, including perfluorocarbons) per tonne of aluminium.

Considering now the strength of the composite beam 200, building safety dictates—by design and/or by regulation—that deflection shall not exceed some specified amount in use, which in turn defines a safe working load for the beam. As is well known, on a specified axis the deflection of a beam under a given load is inversely proportional to the area moment of inertia with respect to that axis. The known composite beam formed by fitting together the profiles 100 and 102 of FIG. 1 has an area moment of inertia calculated as Iy≈5197 cm⁴. By contrast, the composite beam 200 embodying the invention has an area moment of inertia calculated as Iy≈8265 cm⁴. It follows from this that under a given load the deflection of the beam 200 under a given load is very much less than that of the known composite beam formed by fitting together the profiles 100 and 102 of FIG. 1. Alternatively expressed, and more significantly, the composite beam 200 can safely carry a much greater working load than the prior art.

It is to be understood that a composite beam embodying the invention may have dimensions somewhat different from those indicated by the drawings hereof. And weight reduction and strength increase can be balanced against one another according to specific needs.

FIGS. 3 and 4 illustrate a roof truss combining two roof beams according to the invention. As shown in FIGS. 3 and 4, the truss 300 comprises an upper roof beam 302 and a lower roof beam 304 each similar to the roof beam 200 of FIG. 2 and arranged in parallel. The lower roof beam 304 has the same orientation as that of the beam 200 as depicted in FIG. 2, so the first elongate member 304a, which has a depth substantially greater than that of the second elongate member 304b is below the second elongate member 304b. The upper roof beam 302 is inverted relative to this, that is, with the deeper first elongate member 302a above the less deep second elongate member 302b. Thus, the second elongate members 302b and 304b face each other.

The second elongate members 302b and 304b are formed respectively to receive upper and lower ends of braces comprising orthogonal braces 306 and (for triangulation) diagonal braces 308. The ends of the braces 306, 308 are secured in the second elongate members 302b and 304b by means of rivets such as indicated at 310 in FIG. 4. It will be understood that the number of braces, and their spacing, will depend upon the length of the truss, of which only a short part is shown in FIG. 3.

Calculations indicate that a truss as described above, comprising two roof beams of the kind shown in FIG. 2, can be as much as 34% lighter than one comprising two roof beams of the form shown in FIG. 1, therefore offering further reductions in energy consumption and carbon emissions.

It will now be understood that a roof beam or truss embodying the invention may be made by a method:

• • wherein there is provided a first elongate member and a second elongate member each having a hollow centre along its length and, outside said hollow centre, a pair of slides extending along the length of the respective elongate member;
  • wherein the slides on the second elongate member are configured and arranged to fit slidingly within the slides on the first elongate member; and
  • wherein the slides are fitted together and the second elongate member is slid along the length of the first elongate member and secured thereto.

This enables the construction of a roof (a) of very large span (say 100 m) without intermediate supports and (b) able to carry very large loads (several tonne, compared with only a few hundred kilograms heretofore).

By means of the invention the internal underslung payload (that is, the weight of equipment that can be hung from any point in the roof) is greatly increased. Present calculations indicate that a central load of over 3 tonne can be hung from the underside of a truss embodying the invention, with two hollow-form elongate members slidingly engaged with one another to be adjacent top to bottom.

The slide-on arrangement not only provides greater strength than heretofore. It also reduces the weight per metre of length; and by removing the need for reinforcing inserts within a roof truss or beam the weight of the truss or beam (and thereby also of supporting legs) there is a further reduction in weight and of material required.

The invention has major benefits in the construction of very large structures that require great intrinsic strength to facilitate very large widths (up to 100 m) without internal supports and the ability to carry a large payload. This is a step forward from existing large structures that are currently manufactured mostly from steel sections. At the same time the invention maximizes internal space while minimizing external impact.

Finally, it will be understood that the invention is of particular value in extending the capacity of existing designs of roof beams and trusses including keder connections.

Claims

1. A composite roof beam wherein: said composite roof beam comprises a first elongate member and a second elongate member, each comprising a rectangular box section with a hollow centre having a length, a width and a depth;the first elongate member is provided at each of two adjacent corners of its box section with a first connector extending lengthwise and comprising a channel closed off from the hollow centre of the first elongate member and open outwards through a neck narrower than the channel;the second elongate member has at each of two adjacent corners of its box section a second connector extending lengthwise and comprising a rib projecting through the neck of a complementary first connector and a flange on said rib held within the channel of the complementary first connector; andthe first elongate member and the second elongate member are respectively configured and arranged so that the first and second connectors interconnect, with the second connector being a close fit within the first connector, whereby the first and second elongate members are coupled together to form said composite roof beam.

2. The composite roof beam of claim 1, wherein each rib of said second connector is of arcuate form and extends outwardly from its corner location and then inwardly through the neck of the respective first connector.

3. The composite roof beam of claim 1, wherein the box section of the second elongate member has either or both of: a length and a width equal respectively to the length and width of the box section of the first elongate member; anda depth less than the depth of the box section of the first elongate member.

4. The composite roof beam of claim 3, wherein the depth of the box section of the second elongate member is not more than half the depth of the box section of the first elongate member.

5. The composite roof beam of claim 1, which, in use, is supported on columns at its opposite ends, with no additional supports between said ends.

6. The composite roof beam of claim 5, configured and arranged to be higher between said ends than at said ends.

7. The composite roof beam of claim 1, comprising an extrusion of aluminium alloy.

8. The composite roof beam of claim 1, further comprising additional connectors configured and arranged to hold edges of sheeting material extending width-wise of the composite roof beam to form a roof.

9. The composite roof beam of claim 8, wherein said additional connectors are keders.

10. A roof truss, comprising two roof beams according to claim 1 arranged in parallel with one another, one above the other in use, wherein: the upper of said two roof beams in use has its second elongate member below its first elongate member; andthe lower of said two roof beams in use has its second elongate member above its first elongate member, with bracing members extending between and secured to said second elongate members.

11. The roof truss of claim 10, wherein the second elongate members are formed to receive ends of said bracing member within the hollow box sections of said second elongate members.

12. The roof truss of claim 11, wherein said ends of the bracing members are secured within the hollow box sections of said second elongate members by means of rivets.

13. The roof truss of claim 10, wherein some of said bracing members are orthogonal to said roof beams and others of said bracing members are inclined relative to said roof beams.

14. A method of making a composite roof beam or truss as claimed in claim 1: wherein the second connectors on the second elongate member are configured and arranged to fit slidingly within the first connectors on the first elongate member; andthe connectors are fitted together and the second elongate member is slid along the length of the first elongate member and secured thereto.