BACKGROUND OF THE INVENTION International Patent Application PCT/GB96/01435 (Publication No. WO 97/00360) discloses a modular filter housing for waste water treatment apparatus. The floor of the housing comprises parallel support beams with drainage trays between the beams to drain the treated water out of the apparatus. The walls of the housing are assembled from standard panels made of reinforced plastics material by pultrusion. Various sizes of housing can be made by using more or fewer standard panels and because the panels are fixed together by fixing elements which are easily accessible from outside the enclosure, the housing can be partly disassembled for maintenance or even taken down entirely and moved to a new site.

SUMMARY OF THE INVENTION An object of the present invention is to optimise the design of the structural components for building a structure of the above type for cost efficiency.

According to the invention there is provided a structural coupling for use in forming a structure comprising a first structural building component having side edge slotted coupling formations and adjacently positioned locking flanges ; a second structural building component opposite

side edges of which are each provided with elongate upright coupling flanges for co- operatively engaging the slotted coupling formations; and locking means for engaging the locking flanges to secure the first structural building component to the second structural building component to form the structural coupling.

Advantageously and preferably the first structural building component is a rigid sheet and the second structural building component is a channel section.

With these building components it is possible to assemble a support member for a structure such as a support beam wherein two rigid sheets are assembled side by side and a channel section is inserted in the slotted formations at the ends of two facing rigid sheets and locked in position.

In another preferred embodiment of the invention the first structural component is an open box beam and the second structural component is a rigid sheet, the upright flanges of the rigid sheets and the slots of the open box beam being brought into opposed engagement to form a structural arrangement such as a wall, floor or roof.

By means of the structural coupling of the invention the use of a relatively few standard component shapes to form support members having different functions within a particular structure becomes possible and consequently the production volume/run for any one member is increased and the unit cost of the resulting structure is reduced.

To this end thus the invention contemplates a structural coupling which will allow a structure to be assembled from a minimum number of structural components in the sense that the components may be used in differing support capacities to construct structural members such as either a beam, strut, wall or roof for the structure.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figs. 1,2 and 3 are cross-sectional views of structural components having complementary coupling formations to form a structural coupling in accordance with the invention; Figs. 4 and 5 are illustrations of how a support beam and a wall roof or floor section of a structure may be assembled from the components of Figs. 1,2 and 3; Fig. 6 is a perspective view of part of a trickle filter for treating waste water using the structural couplings of Figs. 4 and 5; Fig. 7 is a vertically sectioned view of part of the floor of the trickle filter of Fig. 6; Fig. 8 is a horizontal sectioned view of part of the wall of the trickle filter; and Fig. 9 is a perspective view of part of a lower corner region of the trickle filter of Fig. 6; Fig. 10 is a cross sectional view through an alternative coupling constructional using the invention, for employment as floor decking or structural wall panels of a trickle filter of other light-weight enclosure.

PREFERRED EMBODIMENTS OF THE INVENTION With reference to Figs. 1,2 and 3, three structural building components 1,2 and 3, constructed in accordance with the invention, are illustrated, each having complementary coupling formations as will be described hereinafter, enabling the components to be assembled together in differing coupling arrangements so as to form the walls, floor or roof of a light-weight structure such as a trickle filter. The components 1,2 and 3 are made of a reinforced plastics material by pultrusion.

The structural building component 1 is in the form of a sheet or panel 4 which may be of varying width and length to suit requirements having oppositely directed first and second upright flanges 5 and 6 respectively along opposite side edges thereof.

The upright flanges 5 and 6 are formed at the ends of spaced wall portions 7 and 8 of the sheet or panel 4, one wall portion 7 being raised above the plane of the sheet 4 and the other wall portion 8 being in the plane of the sheet but of shorter extent by the width of the upright flange 5.

The wall portions 7 and 8 define between them coupling slots 9 extending along each side edge of the sheet or panel 4.

The inside wall of the shorter upright flange 6 is provided with a ribbed locking flange 10 defining a shallow channel 11 with the surface 12 of the sheet 4.

The structural support component shown 2 in Fig. 2 comprises a flat elongate top wall portion 13 from which, at equal distances to either side of the central axis of the wall portion 13, depend two L-shaped side walls 14 and adjacently positioned shorter flanged walls 15 defining between them coupling slots 16 in like manner as the coupling slots 9 of the sheet or panel component 4 shown in Fig. 1.

The feet of the L-shaped side walls 14 are each provided with longitudinally extending ribbed locking flanges 17 equivalent to the locking flanges 10 of the sheet or panel building component 1.

The structural component 3 shown in Fig. 3 is comprised of a channel section 18 having side watts 19 and a base 20.

The structural components 1,2 and 3 shown in Figs. 1,2 and 3 may be coupled together using the complementary coupling formations as described to form a structural support beam 21 one end of which is shown in Fig. 4.

The support beam 21 has been assembled from two structural components 1 placed in side by side relationship but at a spacing therebetween with the shorter flanges 6 thereof facing one another.

The side walls 19 of the channel section 18 are respectively inserted in the coupling slots 9 in the adjacently facing sheet 4 components 1 with the inner wall of the base 20 of the channel section 3 resting on the shorter upright flanges 6. Because the thickness of the base 19 of the channel section 3 matches that of the upright flanges 5, the top surfaces of the flanges 5 and the base 20 of the channel section 3 are in alignment to provide a generally flat broad surface at the ends of the beam 21.

To secure the channel sections 3 to the sheet components 1, a locking plate 22 bridges the locking flanges 10 and engages a threaded bolt 23 passing through the base 20 of the channel section 18, the locking plate 22 having grooves 24 to receive the ribbed formations on the locking flanges 10.

A further possible coupling arrangement using the structural components shown in Figs. 1,2 and 3 is illustrated in Fig. 5 whereby to form a wall, floor or roof of a structure.

In this arrangement the upright flanges 5 of a pair of adjacently positioned sheet components 1 engage respectively the coupling slots between the depending walls 14 and adjacently positioned shorter flanged walls 15 of structural component 2.

The gaps left between the shorter upright flanges 6 and the outer face of the depending side walls 14 of the structural component 2 with the sheet components 1 held in alignment, are occupied by the side walls 19 of a length of channel section 18.

As with the Fig. 4 coupling arrangement, a locking plate 25 bridges the locking flanges 17 of the depending side walls 14 with a bolt 26 extending through the base 20 of the channel section 18 to engage a threaded hole 27 in the locking plate 25 thereby to secure the coupling.

A trickle filter utilising the structural coupling arrangements illustrated in Figs. 4 and 5 is shown with reference to Figs. 6,7,8 and 9.

The trickle filter, see Fig. 6, comprises water treatment media 27 housed in a rectangular enclosure formed by a floor 28 and walls 29.

The trickle filter is mounted on two parallel level support members 30. The support members 30 could be replaced by, for example, masonry footings built on concrete foundations (not shown).

The floor 28 comprises an array of equally spaced elongate support beams 21 constructed as explained with reference to Fig. 4 and shown more particularly in Fig. 7, extending horizontally and parallel to one another. Each support beam 21 straddles the two support members, 30 the beams 20 and support members 30 being at right angles to one another.

An elongate tray 31, see also Figs. 7 and 9, using the sheet structural component 1 shown in Fig. 1, is laid between each two adjacent beams 20 with the longer sides of the tray adhesively bonded (or otherwise secured) by means of the upright flanges 5 of the structural component 1 to the respective sheet components 1 forming adjacent sides of the beams 20.

Each tray 31 is arranged between the beams 30 at an inclination to the horizontal for drainage purposes.

The walls 29, see also Figs. 8 and 9, are formed using the coupling arrangement illustrated in Fig. 5, wherein the structural component 2 is used to form the stanchions 32, coupled between ones of a series of in-line sheet or panel components 1.

At intervals, two of the panel components 1 are joined by a reinforced stanchion 33 as will be described with reference to Fig. 8 to give extra strength to the wall 28. Further strengthening is provided by horizontal external ties 34 of which the ends are secured to respective ones of two adjacent main stanchions 32 or to a main stanchion 32 and an adjacent corner stanchion 35.

Each tie 34 is also fixed to some of the main stanchions 32. The main stanchions 32 and the corner stanchions 35 are fixed to and also partly supported on the top surfaces of the support beams 21 but the main stanchions 32 and corner stanchions 35 also have portions that extend alongside the support beams 21 and are fixed to them as shown.

The water treatment media 27 is provided in the form of a stack of rectangular blocks resting on the support beams 21.

The incoming waste water (not shown) is distributed over the top of the stack 27 by means not illustrated in the drawing. The media stack 27 is formed with apertures (not shown) defining tortuous paths along which the waste water can trickle slowly down through the media stack 27. The walls of the aperture define a large surface area supporting a film of bacteria in contact with the water and with air contained in the apertures. The result is an aerobic biological reaction which breaks down certain chemicals in the waste water and reduces its biological oxygen demand, i. e. helps to purify it.

The treated water emerges from the bottom of the stack 27 and collects in the trays 31. It then runs out through openings 36 in the panel components 1. Thereafter, what happens to the treated water depends on the particular application. For example, the water may be collected, say by a gutter running alongside the openings, and passed on to further treatment apparatus (not shown).

With reference to Fig. 9 located in the end of each support beam 21 is a channel shaped reinforcing and fixing bracket 36 to provide anchorage and support for the lower ends of the stanchions 32,33 and 35.

To give a smooth run off of treated water from the ends of the trays 31 a rounded plastics material component 37 is fixed just beneath the end of each tray 31 and two side mouldings 38 are fixed to the ends of the sides of the tray to deflect the treated water away from the stanchions 32,33.

With reference to Figs. 8 and 9 each reinforced stanchion 33 is assembled in the same manner as the stanchions 32 except that, to give the additional strength, an additional structural component 3 is placed in back-to-back relationship with the structural component 3 of the stanchion 33 with the flanged feet 17 of the walls 14 of a structural component 2 resting on the base 20. The assembly is coupled together using a bolt 39 extending through the components 2 and 3 to engage a clamp 40 bridging the flanges 17 of a structural component 2.

Each comer stanchion 35, see Fig. 8, comprises two stanchions one of which is of the form of a stanchion 32, the other 321 being a modified structural component 2 having a part of the wall surface 13 up to flanged wall 14 removed so that the face of that flanged wall 14 abuts the wall 13 of the structural component 2 of its mating stanchion 32.

An edge portion 41 comprising upright flanges 5 and 6 on wall portions 7 and 8 is taken from a sheet component 1 and engaged with the corner stanchion 32 to form a corner piece 42, with the upright flange 5 in a coupling slot 16 of constructural component 2 forming the corner stanchion 32.

Because for any section of the walls 29, the heads of the clamping bolts 23,26,39 are exposed outside the trickle filter enclosure, any such section can be removed for service for example as shown in Fig. 1. Furthermore, the stack 27 may be divided into sections separated by support frames and then one or more sections of the stack could be removed and renewed.

In Fig. 10 a structural coupling of the invention is shown in the form of rigid planking 43 which may be used as floor decking or structural wall panelling in the construction of an enclosure of the type shown in Fig. 1.

The structural coupling comprises flat rigid sheets 44 having rigidising pairs of opposed L- shaped ribs 45 spaced at intervals along the underside surface of the flat rigid sheets 44 to form open box structures 46.

The opposed edges 47 of the flat sheets 44 are provided with coupling slots 48.

The coupling slots 48 are formed from a short vertically depending wall portion 49 of the flat rigid sheets 44 and a vertically extending channel shaped rib 50 spaced from the short wall portion 49 by a short horizontal wall section 51 which forms the base of the coupling slots 48.

The downward vertical extent of the channel shaped ribs 50 from the short horizontal wall section 51 forming the base of each of the coupling slots 48, is equal to the vertical extent of

the ribs 45, while the upward extent of the channel shaped ribs 50 from the horizontal wall section 51 is less than that of the short vertically extending wall portions 49 by a distance equal to the thickness of the flat sheets 44.

As shown individually spaced flat rigid sheets 44 are coupled together by means of channel sections 52, the flanged side walls of which engage respectively in opposed coupling slots 48 of the flat rigid sheets 44 to rest on the upper flanged side walls of the channel shaped ribs 50 with the outer base wall surface of the channel sections 52, by virtue of shorter upward extent of the channel shaped ribs 50, lying in the plane of the upper surface of the flat rigid sheets 44.

The channel shaped coupling sections 52 are locked to the flat rigid sheets 44 by means for example of a unistrut fixing 53 which in its locked position as shown, bridges the opposed flanged side walls of the channel shaped ribs 50.