Patent Description:
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 multifunctional 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 (maybe more than <NUM> tonne).

The need for a roofing structure to be strong, especially where required to bridge a large span of say <NUM> 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 500MPa and a density around <NUM>/cm3, whereas aluminium alloy is much lighter, at less than <NUM>/cm3, but its tensile strength is less than 300MPa.

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.

<CIT> discloses a composite beam comprising a first and second elongate member being coupled together.

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:.

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 according to the first aspect of the invention or truss according to the second aspect of the invention.

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:.

Referring first to <FIG>, this shows previously known first and second roofing profiles <NUM> and <NUM> each extruded from aluminium alloy and having a box section with a hollow centre. The first profile <NUM> may in lightweight structures may be mounted at its opposite ends on a support indicated schematically in broken lines at <NUM>, to form a roof beam to support a fabric roof. For this purpose, the first profile <NUM> has at its corners channels <NUM> 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 <NUM> to extend along the length of the roof beam and have flaps that in use extend through the narrow neck 106a of the channels <NUM> to be secured to the fabric, by stitching or preferably welding).

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

Instead of the arrangement of <FIG>, 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>) are connected together along their length, one above the other. This is illustrated by <FIG>, which shows in transverse cross-section a composite roof beam <NUM> comprising said first elongate member <NUM> and said second elongate member <NUM>, each extruded from aluminium alloy.

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

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

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

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

The composite beam <NUM> is both lighter and stronger than the previously known reinforced beam formed as described hereinbefore with reference to <FIG> by sliding the profile <NUM> into the profile <NUM>, 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 <NUM> and <NUM> of <FIG>(and hence of the previously known composite beam formed by sliding one into the other) is off, <NUM><NUM>. The aggregate cross-sectional area of the composite beam <NUM> of <FIG>, with nominal wall thicknesses equal to those of the profiles <NUM> and <NUM>, is <NUM><NUM>. It follows that the weight per unit length of the composite beam <NUM> is nearly <NUM>% 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 <NUM><NUM> kWh of electricity per tonne; and carbon emissions from aluminium production are greater than <NUM> tonne of CO2e (carbon dioxide equivalent, including perfluorocarbons) per tonne of aluminium.

Considering now the strength of the composite beam <NUM>, 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 <NUM> and <NUM> of <FIG> has an area moment of inertia calculated as Iy ≈ <NUM> cm<NUM>. By contrast, the composite beam <NUM> embodying the invention has an area moment of inertia calculated as Iy ≈ <NUM> cm<NUM>. It follows from this that under a given load the deflection of the beam <NUM> under a given load is very much less than that of the known composite beam formed by fitting together the profiles <NUM> and <NUM> of <FIG>. Alternatively expressed, and more significantly, the composite beam <NUM> 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.

<FIG> and <FIG> illustrate a roof truss combining two roof beams according to the invention. As shown in <FIG> and <FIG>, the truss <NUM> comprises an upper roof beam <NUM> and a lower roof beam <NUM> each similar to the roof beam <NUM> of <FIG> and arranged in parallel. The lower roof beam <NUM> has the same orientation as that of the beam <NUM> as depicted in <FIG>, 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 <NUM> 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 <NUM> and (for triangulation) diagonal braces <NUM>. The ends of the braces <NUM>,<NUM> are secured in the second elongate members 302b and 304b by means of rivets such as indicated at <NUM> in <FIG>. 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>.

Calculations indicate that a truss as described above, comprising two roof beams of the kind shown in <FIG>, can be as much as <NUM>% lighter than one comprising two roof beams of the form shown in <FIG>, 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:.

This enables the construction of a roof (a) of very large span (say <NUM>) 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 <NUM> 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 <NUM>) 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.

Claim 1:
A composite roof beam (<NUM>) for a temporary building wherein:
said composite roof beam comprises a first elongate member (<NUM>) and a second elongate member (<NUM>) for reinforcing the first 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 (<NUM>, <NUM>, <NUM>, <NUM>) 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 (<NUM>, <NUM>) 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 composite roof beam.