The invention relates to a prefabricated steel/ concrete composite beam arranged to act together with concrete as a load-bearing composite structure for various slab assemblies and having a steel member comprising two web portions and horizontal projecting flange portions extending outside the web portions, the web portions being positioned with a mutual spacing side by side and interconnected at one edge of each web portion by means of a horizontal top portion, the web portions and the horizontal top portion being arranged to define a space which can be filled with concrete, and the steel member being formed by two interconnected symmetrical parts each having a web portion and two flange portions equal in size.

The invention concerns a beam utilizing a steel beam/concrete composite structure. Such beams are today well-known in element structures. One example of the prior art is the solution described in Finnish Patent Application 882 186. The composite structure makes the steel beam lighter, and the beam can be used over longer span lengths than what has been possible previously. The steel beam according to Finnish Patent Application 882 186 reduces the amount of welding work as the beam is made of profile sections preformed by hot rolling. However, the beam structure according to Finnish Patent Application 882 186 is complicated to produce as connecting pieces by means of which the composite structure is achieved increase the amount of welding. The handling of a plurality of small pieces as such complicates the production of the beam.

Another example of the prior art is the solution disclosed in Finnish Published Specification 85 745, which eliminates the drawbacks of the solution dis-

closed in Finnish Patent Application 882 186. A draw¬ back of Finnish Published Specification 85 745, how¬ ever, is that the structure is relatively complicated to produce and requires plenty of space, which may sometimes cause storing problems.

The object of the invention is to provide a prefabricated steel/concrete composite beam which eliminates the drawbacks of the prior art. This is achieved by means of a beam according to the invention which is characterized in that one of the flange portions is arranged to form the projecting flange portion and the other is arranged to form one half of the horizontal top portion.

An advantage of the invention is mainly that it is simple, and so the production costs will be low. A further advantage of the invention is that the number of parts to be produced is small and that the parts are very advantageous to produce. Still another advantage is that the storage of the parts requires very little space, which allows large production series with further reductions in the production costs.

In the following the invention will be described in greater detail with reference to one preferred embodiment shown in the attached drawings, in which

Figure 1 shows the symmetrical parts of a steel member in a beam according to the invention as viewed in the longitudinal direction of the parts;

Figure 2 is a perspective view of one embodiment of the steel member of the beam according to the invention; and

Figure 3 shows a finished beam utilizing a steel member shown in Figure 2.

Figures 1 to 3 show one preferred embodiment of the beam according to the invention. The figures

illustrate a prefabricated steel/concrete beam arranged to act together with concrete as a load- bearing composite structure in various slab assem¬ blies. The beam comprises a steel member having two web portions 1 and horizontal projecting flange portions 2 extending outside the web portions. The steel member is shown in Figure 2, for instance. The web portions 1 are positioned with a mutual spacing side by side and interconnected at one edge of each web portion by means of a horizontal top portion 3. The web portions 1 and the horizontal top portion 3 are arranged to define a space which may be filled with concrete 4. The web portions 1 may be positioned either in an inclined position or perpendicularly with respect to the projecting flange portions in such a manner that they incline towards each other at the upper or lower edge, or are in parallel with each other in adjacent parallel planes.

The operation of the beam described above as a composite structure is fully obvious to one skilled in the art, and therefore will not be described in greater detail herein. Finnish Published Specification 85 745, for instance, is referred to herein for more detailed information. However, when the structure of Finnish Published Specification 85 745, for instance, is used, it has been found that the structure is not the best possible in view of the production process.

To solve the problems associated with the production and storage in the best possible way, the steel member has two interconnected symmetrical parts 5 each comprising a web portion 1 and two flange portions 2a, 2b equal in size. One of the flange portions, 2a or 2b, is arranged to form the projecting flange portion 2 while the other, 2b or 2a, is arranged to form one half of the horizontal top

portion 3. The symmetrical parts 5 are shown in Figure 1. The symmetrical parts 5 may be made e.g. of a high- strength steel plate by cold-moulding.

The invention is based on the idea that the steel member may be formed by two identical parts, that is, two symmetrical parts 5, which are easy to produce and store. Concrete steels 6 may be secured to the symmetrical parts 5 in order to ensure co-opera¬ tion both with the concrete 4 inside the beam and the concrete outside the beam in a manner known per se . The concrete steels 6 may be positioned on different sides of the symmetrical parts 5 e.g. as shown in Figure 1 in a way such that the original idea of the invention, i.e. the complete symmetry and reversib- ility of the parts, is retained.

Preferably a plate-like member 8 provided with openings 7 may be arranged between the symmetrical parts 5 so as to extend into the space defined between the web portions 1 and the horizontal top portion 3. In the example shown in the figures, the plate-like member 8 is attached to the junction point between the symmetrical parts 5. The tension reinforcement of the lower surface of the beam, such as means 9 made of concrete steel, an additional plate 10, etc., may be anchored in the plate-like member 5. The openings 7 are positioned in the plate-like member with mutual spacings successively in the longitudinal direction of the beam. The plate-like member 8 improves the composite effect between the steel member and the concrete 4.

The use of the plate-like member 8 is to be preferred e.g. in a structure where there is no lower flange interconnecting the lower edges of the web portions. This kind of structure is shown in the figures. In structures comprising no lower flange, the

concrete contained in the beam tends to be squeezed out, and the structure will not operate in a desired way. A similar situation occurs e.g. when the lower flange has lost its ability to operate at high temperatures. The extrusion of concrete out of the beam takes place especially at the ends of the beam, where the force causing the phenomenon is at its greatest. The plate-like member may extend from the beam ends e.g. over a length of 1 to 1.5 m, depending on the length of the beam and the loads. It is also possible to position a plurality of, e.g. two, three, etc. plate-like members in parallel with each other at the beam ends, if this is regarded as necessary. The plate-like member may also extend over the entire length of the beam, and the beam may have a plurality of, e.g. two, three, etc., parallel plate-like members extending over its entire length.

The embodiment described above is not intended to limit the invention in any way, but the invention may be modified within the scope of the claims as desired. Accordingly, it is obvious that the beam according to the invention or its parts need not necessarily be such as shown in the figures but other solutions are possible as well. The invention is not limited in any way to a solution utilizing a plate¬ like member provided with openings, but the invention is equally applicable in a beam type where the lower edges of the web portions are interconnected with a lower flange. A beam utilizing a lower flange is described e.g. in Finnish Published Specification 85 745. The invention is applicable both in pre- stressed structures and in structures that have not been prestressed. Figure 3 shows a prestressed struc¬ ture; prestressing reinforcements are indicated by the reference numeral 11.