When constructing, for example, multi-storey buildings, it is common to use floor beams, which support and carry prefabricated joist elements, such as a concrete element, by means of bottom flanges.

However, such floor beams made of band steel or other steel elements suffer from the disadvantage that they are expensive to manufacture, since they have fixed dimensions, and thus are made in short series. Also the numerous work operations during the manufacturing process lead to a high production cost. Likewise, the cost of material is high, since the thickness of the band steel has to be large, to achieve sufficient strength. Furthermore, the floor beams of today made of steel are heavy and ungainly to handle during the construction work itself.

Lighter designs of the elements used today have a tendency to twist and buckle under stress. Also, the bottom flange usually stretches out due to the large load of a concrete element.

The floor beams may also be made of extruded light metal. Those are certainly light but are expensive to produce.

The purpose of the invention is to provide a floor beam, which has a large torsional rigidity and good strength characteristics and also is inexpensive to produce and transport.

A further object of the invention is to provide a floor beam, which in an easy way could be produced in big series and in a few dimensions. This floor beam should further, despite a relatively low weight, have a good rigidity and facilitate a good flexibility during the construction of, for example, a multi-storey building.

This is solved by a floor beam of the kind stated in the introduction, where the two ribs and the first flange constitute a profile formed in one piece with essentially U- shape, and that at least one groove formed in each rib extends in the longitudinal direction of the beam.

The floor beam further comprises, in order to increase the strength and torsional rigidity of it, one or more band-shaped strengthening elements, arranged at the first flange. The second flange also works as a support for one or more concrete elements.

Preferably, one or more grooves are provided in the first flange, in the longitudinal direction of the beam, and thereby substitute the band-shaped strengthening element mounted at the first flange.

The invention means that a floor beam has been provided, which at the same time has a light design, a large torsional rigidity and a high strength, is easy and inexpen- sive to produce and permits a flexibility at the construction of e. g. a multi-storey building.

The invention further means that a base element is provided, i. e. the profile essentially in U-form and formed in one piece, which base element makes the principal part of the floor beam. A principal part, which could be made in large series with a few dimensions and which could be added as required.

The invention will now be described more closely in the form of two embodiments with reference to the accompanying drawings, in which Fig. 1 shows a perspective view of a floor beam according to the invention, of a first embodiment, Fig. 2 shows a perspective view of a floor beam according to the invention, of a second embodiment, and Fig. 3 shows a cross-section of a profile made in one piece of essentially U-shape, according to the first embodiment.

Fig. 1 shows a floor beam 5, comprising a profile of essentially U-shape, formed in one piece, according to a first embodiment. The floor beam is in the embodiment positioned with a first flange 1 upwards. The first flange 1 constitutes the bottom of the beam 5. From the first flange 1, two outwardly inclined ribs 3 extend. The beam 5 further comprises a groove 4a in each rib 3. The beam material may, for example, be sheet metal.

Onto the first flange 1, a metal band 7 is welded, to give the floor beam a greater carrying capacity. Also other band materials may with advantage be used here. Like- wise, so-called connection pieces (not shown) may be welded to the upper side of the first flange 1 and thereby, in combination with concrete poured over the floor beam during construction, the connection pieces will give the beam 5 the desired carrying capacity.

A second flange 2 has been welded to the free edges of the ribs 3, partly to be sup- port to the concrete elements (not shown), partly for increasing the carrying capacity of the beam. It could be a metal band, band steel or some other band element. The second flange 2 will henceforth also be denoted as a band-shaped element.

The angle a between the normal of the flange 2 and the rib 3 can be between 0 and 45 degrees, preferably between 4 and 10 degrees. A certain inclination is desirable

in many cases, at which concrete easier can be transported down between the outer sides of the ribs 3 and the short sides of said concrete element (not shown). The inclination itself also implies an increased strength of the beam, since an arch vault effect is provided. The angle a can be up to 45 degrees.

However, an upper limit of the angle a is determined by the width of the second flange 2, since support surfaces 10 for the joist elements (not shown) are required.

The invention has the advantage that only the dimension of the band-shaped elements 2,7 has to be adjusted to the carrying capacity of the floor beam.

The thickness of the sheet metal of the profile with essentially U-shape is preferably between 4 and 8 mm, and the thickness of the second flange 2, which has been welded together with the edges of the ribs 3, is preferably between 10 and 20 mm and may vary depending on the load to which the floor beam will be subjected.

The height of ribs 3 may advantageously be varied in relation to the thickness of the concrete elements (not shown) and the desired carrying capacity of the beam 5. The measures, which during production of the beam may be fixed are the width of the first flange 1 and the distance from the grooves 4a to the first flange 1. The distance between the grooves 4a and the second flange 2 may advantageously vary in relation to the width of the beam material, i. e. the height of the floor beam could be deter- mined by means of the width of the sheet metal, without any change of the setting of the production device, e. g. a roll feed press, for the beam production being needed.

Preferably, the grooves 4a are made inwardly with an inclination, the convex sides of which are facing each other, in order to facilitate the transport of the concrete between the ribs and the concrete elements (not shown).

Fig. 2 shows a second embodiment according to the invention. The metal band 7 mounted according to the first embodiment in Fig. 1, has in this respect been

replaced by a groove 4b in the first flange 1, which groove 4b extends in the longitudinal direction of the beam 5.

The task of the groove 4b is to give the floor beam a larger carrying capacity and to give the qualities aimed at in the first embodiment 1. This also means a lesser material consumption during production of the floor beam. The production cost will also be reduced.

Fig. 3 shows a cross-section of a profile of essentially U-shape formed in one piece according to the first embodiment.

The profile is made with an essentially flat first flange 1. The figure shows the grooves 4a formed in the ribs 3. The grooves 4a are preferably facing inwards. Of course, the number of grooves 4a may be varied and they may also be formed in the first flange 1 of the sheet metal beam.

According to the embodiments shown, the profile has the shape of a U, but this shape can of course be varied. For example, the ribs 3 may be slightly bent and the first flange 1 may be bent inwards.

The floor beam may, of course, be placed in other positions than in traditional systems of joists, i. e. constitute support elements in walls and in inclined construc- tions.

The profile made in one piece according to the embodiments, may, for example, be made by means of a roll feed press or a folding press.