STRUCTURAL SUPPORT SYSTEM

The present invention relates to a structural support system. More particularly the invention relates to a modular system that facilitates assembly of a structural support.

Support structures are used in a variety of applications such as road sign supports, gantries, traffic signal supports, lampposts, camera supports ^' and stage lighting supports. It is known to use an open frame type of system in which structural elements include panels or box-frames having longitudinal members (for example tubes) interconnected by a lattice of rods or bars, usually in a zigzag or diagonal pattern. An example of such a structure is shown in Figure 1. This type of support structure has a relatively high load-bearing capacity and a relatively low weight. However, one problem with these known support systems is that the structural elements are of a welded construction. This means that once a structural element has been welded together it can only be used in that particular form and size. Also, the open structure of the welded elements means that they are relatively bulky for transportation.

Another problem arises with the use of support structures in roadside applications where there is a possibility of a vehicle striking the structure in the event of an accident. In that case, it is desirable for the support structure to absorb the impact in a manner that results in minimizing the risk of harm to the occupants, or to nearby pedestrians. European standard EN 12767 defines three categories of structure: non- energy absorbing (NE); low-energy absorbing (LE); and high-energy absorbing (HE). These categories are defined by the reduction in exit speed of a vehicle after impact with the structure. The higher the exit speed the lower (or no) energy is absorbed, while the lower the exit speed the higher the energy absorbed. Most support systems, particularly those of the type shown in Figure 1, are NE. However, particularly for taller structures, and for use in urban areas, HE, or at least LE structures would be preferable. A difficulty can arise in designing structures to meet these standards, because they often have to withstand significant wind loadings, while at the same time being designed to absorb energy from an impact.

Another problem with known support structures arises with longevity of use. Fatigue cracks may appear in a structure. For welded structures, such as that shown in Figure 1, it is either necessary to cut away the affected part and replace it by welding, or it is necessary to replace an entire structural element, or in some cases an entire support.

It is an object of the present invention to provide a structural support system that alleviates the aforementioned problems.

According to a first aspect of the present invention there is provided a structural support system comprising: at least one support member that includes a plurality of chord elements, wherein each chord element extends substantially the full length of the support member and includes a plurality of axially aligned keyways of substantially equivalent cross-sections; and at least one expandable panel having a length defined by a pair of continuous opposing edge members interconnected by lattice members, the edge members having a substantially uniform cross-section at least a portion of which is of a shape and size corresponding to the keyways so as to be insertable into the keyways to facilitate construction of a structural support.

In embodiments of the invention, the panels are formed as one-piece integrated expandable metal panels. The panels may be formed in a closed condition, with the edge members initially close together so that the panels can be expanded to a required width by pulling the edge members apart. The panels may be lengths cut from an extruded section. The panels are preferably formed of a low density metal such as aluminium.

The chord elements may have key-ways that are orientated to facilitate insertion of panel element edge members such that the panel elements are at substantially 90 degrees to one another. Two, three or four keyways may be provided in the chord element.- In this arrangement, the use of four chord elements facilitates the construction of structural member having a box section. Alternatively, the key-ways may be orientated such that the panels are at a different angle, for example 60 degrees to one another, facilitating construction of a structural member having a triangular section.

Conveniently, the chord elements are cut to a required length from a length of extruded section. The extruded section is preferably formed of a low density metal such as aluminium.

Embodiments of the invention have the advantage that a support structure can be constructed on-site from a set of basic elements that include chord members and panels. The panels can be expanded to a required width on site and their edge members inserted into the keyways of a set of chord elements. No welding is required. Furthermore, the assembly of the structure in this way means that the component elements can be transported to site in a low-bulk form, for example as a flat-pack.

A further advantage is that the structure can just as easily be disassembled. As no welding was required in the assembly, no cutting or breaking of welded joints is required. This has a further advantage in that should a part of the structure become damaged, or if fatigue cracks should appear, then only the damaged/fatigued panels need to be replaced.

In one embodiment panels are provided in a range of predetermined standard lengths so that the support member can be built up in a modular fashion by selecting suitable length panels. It is an advantage that the length of the panels can be selected to suit a particular application.

Still another advantage arises because the edge members extend the full length of the panel element so that when inserted into the keyways the edge members significantly increase the stiffness of the chord elements. This means that a relatively lightweight and open cross-section can be used for the chord elements, reducing the amount of material and providing a lighter weight of structure.

According to a second aspect of the present invention there is provided support structure suitable for use alongside a highway, and comprising: a plurality of substantially vertical chord members anchored at one end to a ground base, wherein

each chord member includes at least one substantially straight keyway; and a plurality of panels, wherein each panel has a length and comprises a pair of opposing edge members extending substantially the length of the panel, each edge member having a substantially uniform cross-section at least a portion of which is housed within the keyway of an associated chord member; wherein the panels include a first panel extending vertically from the ground base to a first height, and a second panel disposed above the first panel, and wherein the first height is selected to provide a break between the edge members of the first and second panels within the keyways of the chord members such that the chord members bend at the location of the break in the event of a vehicle impact.

It is an advantage that the support structure can be assembled on site without the need for welding, from simple components (chord members and panels), and that the break between the first (bottom) panel and the panel above can be selected to occur at an optimum height to ensure that the structure bends under a vehicle impact. This means that the structure can be designed as an HE structure (according to EN 12767) or at least an LE structure.

Preferably, a cap is provided at the top of each vertically disposed chord member. The cap may be secured to the chord member by suitable fastening means. It is an advantage that the cap, secured to the chord member prevents the edge members of the panel elements from rising up the keyways as a result of an impact. This helps to ensure that the chord members bend under the impact.

In embodiments of the invention the chord members and the panels may be formed of the same material, for example aluminium. Other suitable structural materials such as steel or other alloys or composite materials may also be used.

Embodiments of the invention may also make use of chord members having a different material specification to the panels. The chord members may be formed of an alloy having a certain specified material composition, while the panels have a different composition. Alternatively, the chord members may be heat treated at one set of treatment conditions so as to be provided with a first material property, while

the panels are heat treated at a second set of conditions so as to be provided with a second, different material property. The heat treatment conditions may include tempering at specified temperatures. Where the chord members and/or the panels are formed by extrusion, the heat treatment is preferably carried out as part of, or immediately after the extrusion process.

It is an advantage that the chord members and the panels can be provided with different material properties, so that each component can be designed for optimal performance of a certain structural function. For example, the chord members may be formed of a material having properties that enable the structure to withstand a certain wind loading, while the panels have a different material property that provides for optimal energy absorption under an impact.

The invention will now be described by way of an example with reference to the accompanying drawings, as follows.

Figure 1 is perspective view of part of a support structure of a known type.

Figure 2 is a cross-section through a pair of chord elements and a panel element forming a module of a structural support system according to the invention.

Figure 3 is an elevation of the module of Figure 2.

Figure 4a and 4b illustrate conditions of the panel element of Figure 2 before and after an expansion operation.

Figures 5a and 5b are cross-sections through the panel element in the two conditions shown in Figures 4a and 4b respectively.

Figures 6a, and 6b illustrate a vertical section of structural support before and after a vehicle impact.

Referring to Figure 1, a known open frame type of structural support system 10 includes a box-frame arrangement having longitudinal tubular members 12 interconnected by a lattice of bars 14, in a zigzag pattern. The bars 14 are joined to the tubular members 12 welding at the nodal positions (such as 15a, 15b in Figure 1). Typically such structures, when used, for example, as gantries to support road signs or the like, will be prefabricated in lengths of box-frame section. As shown in Figure 1, box-frame sections 16 and 18 would each be prefabricated and transported in that form to the construction site, where the sections would be erected and welded together at the corner 20. As discussed above, this welded construction has numerous disadvantages.

Referring to Figure 2, a cross section through module that makes up the structural support system in accordance with an embodiment of the present invention, includes a pair of chord members 22, 24. The chord members 22,.24 have a uniform cross- section (as shown), which is generally of a square form, with rounded corners. The chord member 22 has four key-ways 26a - 26d, disposed orthogonally with respect to each other opening onto each of the four sides of the square section. The chord member 24 has an identical cross-section with four keyways 28a - 28d.

A panel element 30 extends between the chord members 22, 24. The panel element 30 has edge members 32, 34 that extend along opposite edges of the length of the panel element 30. The edge members 32, 34 each has a cross-section shaped to fit into the keyways, 26a - 26d, 28a - 28d, of the chord members 22, 24. As shown in Figure 2, the edge member 32 has been inserted into the keyway 26a of chord member 22, and the edge member 34 has been inserted into the keyway 28c of chord member 24. The panel element 30 extends between the edge members 32, 34 and has a form that will be discussed in more detail below.

Figure 3 shows an elevation of a cross-section through the centre-line C-C of the assembly shown in cross-section in Figure 2. The chord members 22, 24 are drawn with fainter lines, while the panel element 30 is shown with bolder lines. AS can be seen from both Figures 2 and 3, the panel element 30 includes tubular portions 36, 38, which are linked by a web portion 39 in the centre of the panel element 30. The

tubular portions 36, 38 are linked at each corner of the panel to the edge members 32, 34 by further web portions 41a-41d. In the expanded condition shown in Figure 3, the panel element 30 includes open regions 40a-40d.

Figures 4a-5b show the panel 30 in an unexpanded and an expanded form. In the unexpanded form (Figure 4a in elevation and Figure 5a in cross-section) the panel is cut from a length of extruded aluminium section having the cross-section shown in Figure 5a. Before being expanded longitudinal cuts 42, 43, 44, 45 are made along part of the length of each of the web portions 39, 41. The edge members 32, 34 are then pulled apart opening up the open regions 40a-40d and bending the tubular portions 36, 38 into the form shown in Figure 4b. It will be appreciated that the distance by which the edge members 32, 34 of the panel 30 are pulled apart may be varied to suit the required dimensions of the structural support.

Referring again to Figure 2, further panel elements, similar to panel element 30 can be provided with edge members inserted into other keyways 26b-26d, 28a,b,d, to build up a box-section structural support element. Moreover, the chord members 22, 24 can be cut from a length of extruded section so as to extend the full length of the required height or span of the support structure. As many panel elements as required to extend the length/breadth of the support structure can be connected to the chord members by slotting their edge members into the appropriate keyways.

Figure 6a shows a vertical support structure 50 made up of a box-section of chord members 52, 54, and panel elements 56a-c extending upwards from a ground base 58. Each face of the box-section, between a pair of chord members 52, 54 includes three panel elements 56a, 56b, 56c. At the top of the structure 50 caps 60a, 60b cover the ends of the chord members, and particularly the ends of the keyways. The caps 60a, 60b are secured on the ends of the chord members using a suitable fastener.

The lowest panel element 56a has a height that has been pre-selected to correspond with a most likely height of an impact from a vehicle crashing into the structure (as can be seen with the vehicle 62 in Figure 6b). The presence of the edge members of the panel elements 56a, 56b, 56c within the key-ways of the chord members (as

00621 shown in Figure 2) increases the rigidity of the chord members 52, 54. However, the break between the edge members of the lowest panel 56a and the next panel 56b provides points 59 of lower rigidity at this height. This means that the chord members 52, 54 will bend preferentially at these points 59 when impacted by a vehicle 62, as depicted in Figure 6b. The bending of the chord members 52, 54 absorbs a high proportion of the energy of the impacting vehicle 62. The caps 60a, 60b secured to the top of the structure 50 prevent the panel elements 56a, 56b, 56c from rising up under the impact. A structure of this type may therefore be expected to meet the requirements of an HE structure, or at least an LE structure.

Where roadside structures are installed at locations such as at the top or bottom of an embankment, the point of impact may change. In such cases, it is necessary for the structure to meet the same HE or LE requirements as it would if it were located at the same level as the roadway. In these circumstances, it is possible for the height of the lowest panel 56a to be reduced or increased as necessary to correspond to the most likely height of a vehicle impact.

Known open frame support structures similar to the type shown in Figure 1 may, of necessity, be designed as a compromise between conflicting performance demands. For example, the structure may be required to withstand a certain wind loading, which will require the structure to have a certain stiffness. In that case the material used will be selected to meet the wind loading demands. Because the structure is made up as a single construction (e.g. with welded connections) any specification of the material properties, such as by heat treatment, will apply to the entire structure. In the modular construction of the present invention the chord members can have a different material specification to the panels. For example, the chord members may be formed of an alloy having a certain specified material composition, while the panels have a different composition. Alternatively, the chord members may be heat treated at one set of treatment conditions (e.g. tempered at a specified temperature) so as to acquire a stiffness that is suitable for the design wind loading; the panels may be heat treated at a second set of conditions (e.g. tempered at a different temperature) so as to acquire a second, different stiffness that allows the panels to absorb more energy in an impact. Where the chord members and/or the panels are formed by extrusion (for example

extruded aluminium or other suitable metal/alloy), the heat treatment is preferably carried out as part of, or immediately after the extrusion process.