TECHNICAL FIELD This invention relates to a load bearing unit and structure. In a location providing a working volume bounded by a lower boundary, say a floor, and an upper boundary, say a floor or roof, there can arise a need for an intermediate floor to be provided in the working volume. Typically an intermediate floor, often termed a mezzanine floor, enables available floor area within a given working volume to be nearly doubled without requiring major alterations to the structure.

For this purpose an intermediate floor structure can be provided in which columns are used to support beams upon which the intermediate floor is mounted. The columns are typically positioned at intervals along the beam they support.

DISCLOSURE OF INVENTION According to a first aspect of the present invention there is provided a load bearing unit in the form of a floor of contiguously juxtaposed modular units such as lengths of wood, metal or concrete the floor having an upper surface and a lower surface characterised by a membrane laid over the upper surface of the floor and bonded or other wise attached to most if not all of the upper surfaces of the units.

According to a first preferred version of the first aspect of the present invention the load bearing unit is characterised by a membrane laid over the lower surface of the floor and bonded or other wise attached to upper surfaces of the units.

According to a second preferred version of the first aspect of the present invention the load bearing unit is characterised by a membrane laid over the upper surface and bonded or other wise attached to the units and a further membrane laid over the lower surface of the floor and bonded or other wise attached to the upper surfaces of the units.

According to a second aspect of the present invention there is provided a load bearing structure including a load bearing unit according to the first aspect or any preferred version thereof wherein the load bearing unit is supported on a beam which beam is in turn supported by at least one column of non-circular cross section; the or each beam having a longitudinal axis; the end of the column supporting the beam a cross section with a major axis extending through the longest cross section of the end of the column; the column being positioned so that while supporting the beam the major axis lies at a working angle relative to the longitudinal axis of the beam which it supports.

According to a first preferred version of the second aspect of the present invention the load bearing unit is supported by at least two modules; each module comprising a beam with two supporting columns as aforesaid; the two columns in the module having their major axis lying at a working angle to relative to the longitudinal axis of the beam.

According to a second preferred version of the second aspect of the present invention the load bearing unit is supported on two or more of the beams and each beam is in turn supported by at least two or more of the columns the working angle of each column lying at a working angle relative to the longitudinal axis of the beam which it supports.

According to a third preferred version of the second aspect of the present invention the working angle of a given column differs from at least some of the working angles of the remaining columns in the structure. According to a third aspect of the present invention there is provided a load bearing assembly comprising at least two load bearing structures according to the second aspect or any preferred version thereof.

BRIEF DESCRIPTION OF THE DRAWINGS An exemplary embodiment of the invention will now be described with reference to the accompanying drawing of which: Figure 1 is a plan view of a load bearing unit; Figure IA is a section on IA-IA of Figure 1; Figure 2 is an end view of the unit of Figure 1; Figure 3A is an end view of an alternative version of a load bearing unit in a first configuration; Figure 3B is an end view of an alternative version of a load bearing unit in a second configuration; Figure 4 view is a diagrammatic plan view; Figure 5 is an elevation on section IV - IV of Figure 4; and Figure 6 is a detail of part of plan view of Figure 4.

MODE FOR CARRYING OUT THE INVENTION Figures 1 and 2 variously show a load bearing unit in the form of a floor 11 made up of a series of side abutting floor modules 12 - 17 each being of metal. In alternative versions the modules can be other materials such as wood or concrete. Figure IA shows the location of floor module 14 ends within I beams II, 12 forming the sides of the floor 11.

Having juxtaposed the modules 12 - 17 making up the floor 11 and housed them in I- beams II, 12 a first diaphragm 18 is laid on upper side HA of the floor and is secured to the upper side by a layer of adhesive to ensure that the diaphragm 18 adheres to the whole upper side HA. In this way the combination of the floor 11 and the diaphragm 18 becomes an integral unit providing for loading of the floor to be transferred over a wider area and serving to resist sagging of the floor than would be possible for a floor composed with individual modules without the diaphragm. 18. The diaphragm 18 also serves to protect the floor 11 against surface wear and contamination.

The floor 11 has an underside HB which is provided with a second diaphragm 20 attached over the whole area of underside HB which acts as a stiffening and load distributing means comparable with the first diaphragm 18. In this case the second diaphragm 20 is of a material serving as fire cladding and also incorporates a decorative ceiling for a part of the workspace beneath the floor.

Figures 3A and 3B show an alternative version of a floor 31. In this case a diaphragm 30 is not laid directly on underside 31B of floor 31 but onto undersides of a series of C- section beams, typically beams Cl, C2, whose upper sides are secured to the underside 31B of each individual floor module. The beams Cl, C2 serve to stiffen the floor 31 and provide for increased unit loading. If the diaphragm 30 was not provided then, under loading, the floor 31 would tend to sag and the beams Cl, Cl behave as shown in Figure 3B showing the lower part of each C-section beam Cl, C2 deflecting apart away from one another. By applying diaphragm 30 as shown in Figure 3A the C-section beams are retained against movement so contributing to an overall stiffening of the floor 31. The gap between the beams Cl, C2 can be used for piped or cabled services.

Figures 4 to 6 variously show a mezzanine floor structure 11 for load bearing made up of columns 12 - 15, girder beams 16, 17 and a floor 18 corresponding to that described in connection with Figures 1 and 2. The beams 16, 17 have, respectively, longitudinal axis 16A, 17A. Access to the upper side of floor 18 from a level beneath the structure 11 is by way of a staircase 20.

The floor 18 serves as a load bearing means and can be used for a variety of purposes including, but not limited to, goods or record storage, offices, operational equipment. Services are readily provided to the floor area fro example by way of the columns

Figure 5 shows end 12A of column 12 supporting beam 16. The end 12A is square in plan view and is bolted to the beam 16.

Figure 6 shows the end 12A positioned so that diagonal axis 21 of end 12A lies at a working angle A relative to longitudinal axis 16A of beam 16. In this way the column 12 is disposed in the form of a diamond beneath the beam 16 with the sides of the end 12A at an angle to the beam 16 rather than as a square with an opposite pair of sides parallel to the edges of the beam. It has been found that in this way the column 12 provides for enhanced stability of the structure 11 by comparison with existing structures. In this Figure the working angle is shown as about ninety degrees. However even a small working angle A appears to provide an improvement over the situation where the axis 21 is co-axial with longitudinal axis 16A of beam 16.

In the exemplary embodiment the beams 16, 17 are of conventional I-beam section. However the invention can accommodate beams of other cross section such a box section or C-section beams.

In the exemplary embodiment the columns 12 - 15 are square in section in each case with a diagonal of the square set at a working angle to the longitudinal axis 16A, 17A of, respectively, beams 16, 17. It has been found that by varying the working angle of a given column from the most, if not all, of the remaining working angles of the remaining columns that a substantial improvement is achieved in the stiffness of the whole structure. In addition the columns do not need to have a rectilinear section but can have, for example, an elliptical or other curved form or a profile made up of a combination of straight and curved sections.

In the exemplary embodiment the column in each case is assumed to be of uniform cross section throughout. However a column could also be used where the cross section varies along its length as long as at least the end of the column secured to its beam does conform to the requirements outlined earlier.

INDUSTRIAL APPLICABILITY Basically the present invention provides for a structure comprising a load bearing surface supported on beams by means of columns. The exemplary embodiment demonstrates the invention in relation to a structure for incorporation into an existing building. If required the invention can be embodied in a load bearing assembly or building where two or more of the structures of the type described can be incorporated to function either as a separate entity or in combination with other structural elements. Thus a sequence of such structures could be formed into an assembly whether linked vertically or laterally relative to one another or including a combination of vertical and horizontal structures.