The invention finds particular, but not exclusive, use in the on- site casting of a floor structure.

The object of the invention is to enable the production of a thin concrete slab that is reinforced with light, slim sheet-metal beams that are cast partially in the concrete slab. A particular object of the invention is to enable the sheet-metal beams and a mould associated therewith and into which concrete shall be poured, to be constructed readily on site in a building.

The invention and exemplifying embodiments thereof are defined in the independent claim relating to the slab.

The inventive method is defined in the independent method claim.

Further developments of the invention are set forth in the dependent claims.

The invention relates to structural elements in the form of grid- reinforced, thin concrete slabs (thickness about 5 cm). These slabs are cast on at least one side on parallel and plane-paral- lel sheet-metal beams whose webs are oriented at right angles to the plane of the slab, and wherein the outer edge of each web is provided with a force absorbing flange. The actual concrete slab is then able to form the other force-absorbing flange of the sheet-metal beam, providing that effective adhesion is achieved between concrete and beam in this regard.

Because the sheet-metal beams are not fully submerged in the concrete, problems arise because the sheet-metal beams shall normally be made of steel and therefore require a rust protective coating which, in turn, results in an unsatisfactory adhesion of the beams with the concrete.

In accordance with the invention, special means have been provid- ed for ensuring good adhesion between the concrete-embedded edge- parts of the beams and the surrounding concrete. According to the invention, the concrete embedded part of the sheet-metal beam has no actual force-absorbing flange but solely includes means for transmitting the forces from the web of the beam to the grid- reinforced concrete slab.

According to another aspect of the invention, the sheet-metal beams have very low intrinsic stability, i. e. the beams are slim and pliable at least prior to being embedded in the concrete slab. Thus, in the on-site construction of a floor structure, the sheet-metal beams can be cambered, i. e. bent to an upper convexity, and be kept in this cambered state during the concrete pouring stage. The beams may be cambered either with the aid of a brace or post that stands on a supportive structure, or with the aid of a pre-tensioning device fitted to each beam prior to placing said beam in position. At this stage, the tensioning device shall be tensioned only to an extent at which a camber begins to form. Tensioning of the beams to a final camber is carried out when all form panels or mould panels have been fitted. The post and the tensioning device may both be constructed so as to maintain the beam in its intended casting position. The form bottom/form panels can therewith be fastened temporarily between the webs of the cambered beams at a level beneath the upper edges of the beams. The form bottoms build a floor that can be walked upon and the grid-reinforcement of the concrete slab can be placed on the upper edge parts of the sheet- metal beams, which thus keep the grid-reinforcement spaced from the bottom of the form, so as to enable the grid-reinforcement to be embodied in the concrete at a level corresponding to half the vertical extension/thickness of the concrete slab.

The camber functions to ensure that the mechanical strength of the beam material is utilized to the best effect, when the concrete slab with embodied beams sinks to a desired flat hori- zontal position under its own weight subsequent to cur- ing/hardening of the concrete. However, this places high demands on the attachment of the beams to the concrete, particularly with regard to the small thickness of the slab.

With this in mind, it is preferred in accordance with the inven- tion to provide in the upper edge portion of respective beams recesses that localize rods belonging to one rod group of the grid reinforcement. It is also preferred to provide tongues and/or studs that extend perpendicularly out from the embedded webs of the beams. Particularly preferred embodiments of the devices for establishing effective adhesion/anchorage of the sheet-metal beams in the concrete slab are evident from the following claims and the following exemplifying embodiments.

The mould bottoms can be removed after the concrete has hardened.

Although the aforesaid cambering technique is particularly favourable with regard to the fabrication of floor structures, it will be evident that the invention can also be applied in the absence of such cambering techniques, for instance in the fabri- cation of wall elements that comprise a grid-reinforced concrete slab having sheet-metal stiffening beams embedded therein.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which Figure 1 is a schematic vertical sectional view of an inventive floor structure; Figure 2 is a sectional view taken on the line A-A in Figure 1; Figure 3 is a schematic view taken on the line III-III in Figure 2; Figure 4 is a sectional view corresponding to A-A in Figure 1 but showing an alternative embodiment of the inventive floor struc- ture; Figure 5 is a schematic view taken on the line V-V in Figure 4; Figure 6 is a schematic sectional view taken on the line VI-VI in Figure 5; and Figure 7 illustrates schematically cambering of a beam/girder embedded in the inventive floor structure.

In accordance with the invention there is constructed a floor structure which is comprised of parallel directed and parallel positioned sheet metal beams 1 each comprising a vertically positioned web 10 having on its bottom end a flange 11. The flange 11 may conveniently extend out from only one side of the web 10. The beams 1 do not themselves have an upper flange at the upper edge of respective webs 10. A concrete slab 20 is shown cast on the upper edge portions of the beams 1. To this end, mould or mould panels 24 are mounted between mutually adjacent beams 1 at a short distance beneath their upper edges. The mould panels 24 may be fitted in position after the beams 1 have been placed at correct distances apart. As illustrated, the mould panels 24 are supported on wedges/pegs 25 which are removably fitted into associated openings through respective webs 10, so as to enable the mould panels 24 to be readily removed when the concrete has set/hardened.

Figure 1 also shows a grid-reinforcement embedded in the concrete slab 20. The grid-reinforcement includes a first group of rods 31 that extend parallel with the beams 1 and a second group of rods 32 that extend perpendicularly to the rods 31. The grid- reinforcement 31,32 is located approximately at a level corresponding to half the height or thickness of the slab 20, wherewith the rods 32 may conveniently be supported by the upper edge parts of the beams 1.

It will be seen from Figure 2 that the upper edge parts of respective webs 10 have outwardly open recesses 14 that can receive rods 32. The rods 31 may be placed on top of the rods 32.

In order to provide effective adhesion/anchorage of the web 10 with respect to movement of the beam 1 in the longitudinal direction relative to the concrete, the web 10 is provided with openings 40 in the proximity of its upper edge and studs 41 are inserted through the openings 40 through a distance corresponding to half the length of a stud. The studs 41 thus project out roughly equidistantly on each side of the web 10. The recesses 14 may be formed so that one edge of the recess and its bottom are formed by a section through the web 10 such as to form a tongue 15. This tongue is bent through 90° from the plane of the web 10, so as to further enhance adhesion between the beam 1 and the concrete slab 20.

Figure 4 illustrates an alternative to the recesses 14 and the tongues 15 of the embodiment in Figures 2,3. It will be seen from Figure 8, which illustrates the upper edge part of the web 10 of a sheet-metal beam 1, that slots or cuts 18 are disposed at regular intervals along the upper edge of the web 10. These cuts 18 extend perpendicularly to the longitudinal direction of the beam 1 and extend to mutually the same depths. Also shown in Figure 8 are broken lines 19 which define a constant angle with the cut 18 on each side of the cut. The lines 19 extend from the bottom region of the cut 18 and mark the axis around which the tongues 16 illustrated in Figures 4-6 are formed by the cut 18 and the lines 19. It will be seen that the tongues on each side of a cut 18 have been rotated in mutually different directions.

Because the tongues 16 have been bent out around sloping bending lines/bending axes 19, their upper edges 17 will slope downwards when the tongues are twisted, as best evident from Figure 6, wherein the tongue edge-line defined by the centre line or cut 18 forms an undercut edge-line. When the reinforcement rods 31 are placed on top of the rods 32 in contact with the undercut edge 18, the rods 31 will also form a mechanical locking against withdrawal of the web 10 in a downward direction should the concrete slab and the beams be subjected to a powerful load that acts vertically downwards. As evident from Figures 5 and 6, the two reinforcing rods 31 which coact with the two opposing edges 18 of a beam web 10 may be mutually coupled by a spring element 50. As illustrated schematically in Figures 5 and 6, this pair of reinforcing rods 31 can be fitted very easily, particularly when the edge surfaces 17 of the tongues form an expanding wedge with respect to fitting of the rods 31 that are held together by springs 50. The pair of rods 31 may thus be centered on the line defined by the intersection of the edges 17 in Figure 6 and simply pressed downwards, therewith wedging apart the rods 31.

When the rods 31 come into contact with the edge surfaces 18, they are automatically drawn downwards and inwards to correct positions by the springs 50 and held in position until the concrete slab 20 is cast.

The beams will normally be cambered in conjunction with estab- lishing a floor structure. By cambering is meant that the beams 1 are increased elastically to an upwardly curved or convex shape and maintained in this shape until the cast concrete slab 20 has set/hardened, whereafter the beams 1 are released and can return to a straight position under the influence of the weight of the beams and the concrete slab 20.

Figure 7 illustrates the cambering principle. A flexurily rigid beam 60 is connected to two symmetrically located central points on the beam 1 by means of pressurized struts 61. The ends of the beam 1 are connected to the flexurily rigid cambering beam 60 by tie rods62. A suitable camber can be obtained by adjusting the length of the tie rod 62 and the positioning of the pressurized struts 61.

With further reference to Figure 1, it will be seen that J-shaped floor beams 1 facilitate connection of the struts 61 and tie rods 62 to the beams 1, wherein the struts 61 and tie rods 62 and the rigid beam 60 also function to stabilize the associated beam 1 so as to keep the beam straight with a vertical web under those loads that occur in conjunction with building a floor structure.

It will be understood from Figure 1 that the beams 1 are conve- niently held in tight contact with the mould panels 24, so as to prevent the leakage of concrete adjacent the beams 1 and so that the beams 1 will be spaced apart correctly.