PROFILE PLATE AND METHOD OF MANUFACTURING THE SAME

BACKGROUND OF THE INVENTION

[0001] The invention relates to a profile plate as claimed in the preamble of claim 1 and particularly to a pre-stressed profile plate for an intermediate floor. The present invention further relates to a method as claimed in the preamble of claim 13 of manufacturing a profile plate and particularly to a method of manufacturing a pre-stressed profile plate for an intermediate floor.

[0002] When intermediate floors of buildings or structures are manufactured, a concrete slab is cast onto a profile plate or a cellular plate. Such a profile plate tends to bend under the weight of the concreting, wherefore it must be firmly supported before the casting. According to the prior art, such bending of the profile plate under the weight of the concreting is prevented by forming the profile plate curved in such a manner that the concrete is cast onto the convex side of the plate. By pre-forming the profile plate, the plate bending caused by the concreting may thus be compensated for so that the pre-formed plate straightens because of the weight of the concreting. In this way it can be at least partly avoided that the profile plate bends to a wrong position in an undesired way. Another prior art solution for preventing the bending of the profile plate is to post-stress the profile plate by means of, for instance, strands or wires fastened thereto, whereby the profile plate tends to straighten as a result of stress.

[0003] A problem with the known arrangement described above is that the shaping of the profile plate does not sufficiently compensate for the bending caused by the weight of the concrete slab but the profile plate tends to bend under the concreting in spite of the shaping in an undesired manner. The same applies to post-stress, because the post-stress does not stress the profile plate enough to prevent the undesired bending of the profile plate under the weight of the concreting. Because of these insufficient compensation solutions, the profile plate or the intermediate floor must be supported by separate supports from underneath at least temporarily until the concreting of the intermediate floor has dried. Thus, these prior art solutions lead to either a poorer end result or a significant number of additional working stages, thus slowing down the construction process.

BRIEF DESCRIPTION OF THE INVENTION

[0004] It is thus an object of the invention to provide a profile plate and a method of manufacturing a profile plate in such a manner that the above-mentioned problems can be solved. The object of the invention is achieved by a profile plate according to the characterizing part of claim 1 , which is characterized in that the profile plate comprises a pre-stressing element, which is fastened to the profile plate in a pre-stressed state so that its pre-stressed state produces pre-stress in the profile plate. The object of the invention is further achieved by a method according to the characterizing part of claim 13, which is characterized by the method comprising the steps of: forming a profile plate; forming a pre-stressing element and producing a pre-stressed state therein; fastening the pre-stressing element in a pre-stressed state to the profile plate to produce pre-stress in the profile plate.

[0005] The preferred embodiments of the invention are disclosed in the dependent claims.

[0006] The invention is based on providing the intermediate floor with a profile plate, which is pre-stressed so that either a compression stress or tensile stress is produced therein. According to the invention, the profile plate consists of the profile plate itself and a pre-stressing element fastened thereto and fixed to the profile plate in a pre-stressed state. In this context, a pre- stressed state refers to a temperature higher or lower than that of the profile plate or a tensile or compression stress produced in the pre-stressing element. In other words, the pre-stressing element is fastened to the profile plate in a pre-stressed state, whereby the pre-stress of the pre-stressing element is transferred to the profile plate, where a pre-stress in the opposite direction is thus produced. It is further to be noted that a pre-stressed state may similarly also be produced in the profile plate, in which case the profile plate and the pre-stressing element are fastened to one another in the pre-stressed state. Due to pre-stressing, the profile plate becomes stiff and bends into an arc, whereby the stress applied by the weight of the concreting to the cellular plate may be compensated for.

[0007] The method and system of the invention provide the advantage that the profile plate may be made stiff and curved during the manufacture of the profile plate. In addition, the stiffening and bending of the profile plate

may be controlled by means of pre-stress in a rather predictable and simple way. In accordance with the invention, post-stressing of the profile plate performed afterwards need not be carried out, and no separate parts required for post-stressing, which must be fastened to the profile plate and used for producing post-stress, are required. Also, the profile plates need not be bent anymore in order to compensate for a recess caused by the concreting.

BRIEF DESCRIPTION OF THE FIGURES

[0008] The invention will now be described in greater detail in connection with the preferred embodiments and with reference to the attached drawings, in which:

Figure 1 shows an embodiment of a profile plate according to the present invention; and

Figure 2 shows a method according to the invention for pre- stressing a profile plate.

DETAILED DESCRIPTION OF THE INVENTION

[0009] With reference to Figure 1 , there is shown a principle view of an intermediate floor, wherein a concrete slab 10 is cast onto a profile plate 4. When the concrete slab 10 is cast onto the profile plate 4, the weight of the concrete slab 10 applies a load to the profile plate 4, tending to bend the profile plate concave on the side of the concrete slab 10. According to the present invention, the bending of the profile plate 4 is prevented by substantially pre- stressing the profile plate 4.

[0010] According to Figure 1 , the intermediate floor comprises a first and a second profile or composite plate 4, 6, which are fixed on top of one another by, for instance, welding or laser welding, or mechanically by screws, bolts or rivets, for example. The profile plates 4, 6 may be made of a steel plate, such as a thin plate. The profile plates 4, 6 are also shaped as desired, and they may comprise reinforcing grooves or recesses. The profile plates 4, 6 may be similar or differ from one another. According to Figure 1 , the profile plates 4, 6 are preferably fixed on top of one another so that cells 9 are formed inside a produced cellular plate 2. The profile plates 4, 6, for their part, are fastened to one another on the opposite surface parts 8 of the profile plates 4, 6 by laser welding, for instance.

[0011] In accordance with the present invention, one of the profile plates 4, 6 acts as a pre-stressing element in such a manner that it is brought

to a pre-stressed state before the profile plates 4, 6 have been fixed on top of one another. It is to be noted that, if desired, both profile plates 4, 6 may be brought to a pre-stressed state. The pre-stressed state is maintained while the profile plates 4, 6 are fastened to one another, and after they have been fastened to one another, the pre-stress or pre-stresses of the profile plate or profile plates are allowed to even out. Thus, the cellular plate 2 formed as a result of the equalisation of the profile plate 4, 6 pre-stresses bends in proportion to the sum of the pre-stresses of the profile plates 4, 6. So if the profile plates 4, 6 are pre-stressed mutually in the same way, the pre-stresses thereof intensify each other and make the cellular plate 2 bend in the same direction. On the other hand, if the profile plates 4, 6 are pre-stressed in the opposite ways, the bendings caused by the pre-stresses of the plates in the cellular plate 2 cancel each other out at least partly.

[0012] The pre-stressed state of the profile plates 4, 6 may be produced in such a manner that either a tensile stress or a compression stress is formed in the profile plate 4, 6. Pre-stress is produced in the profile plate 4, 6 preferably in the longitudinal direction of its profiles, i.e. in the longitudinal direction of the cells 9 in Figure 1. However, it is to be recalled that in certain embodiments pre-stress may also be achieved in some alternative direction. In other words, the present invention is not restricted to the direction of pre- stress.

[0013] A pre-stressed state may be produced in the profile plate 4, 6, for instance, by a mechanical treatment of the profile plates 4, 6 or a heat treatment of the profile plates 4, 6 or some other alternative manner. To the present invention, it is not essential how the pre-stressed state is produced, and thus the invention is not restricted to specific pre-stressing manners.

[0014] By utilizing heat treatment of the profile plate 4, 6, pre-stress may be produced in the cellular plate 2 and/or the profile plate 4, 6 by heating or warming one of the profile plates 4, 6 before fastening it to another profile plate 4, 6. Heating causes thermal expansion in the profile plate 4, 6, and the heat-expanded and heated profile plate 4, 6 is fastened to the other profile plate 4, 6 and allowed to cool down or is cooled, whereupon it tends to shrink. Shrinkage of the heated profile plate 4, 6 with respect to the other profile plate 4, 6 fastened thereto causes a tensile stress in the other profile plate 4, 6 of the cellular plate 2, tending to bend the cellular plate 2. Similarly, one of the profile plates 4, 6 may be cooled before fastening it to the other cellular plate 4,

6. The cooled profile plate 4, 6 is thus fastened to the other profile plate 4, 6, after which it is allowed to heat up to the same temperature as the other profile plate 4, 6 fastened thereto. The cooled profile plate 4, 6 tends to expand while the temperature rises, which leads to a compression stress in the other profile plate 4, 6 of the cellular plate 2. As described above, the cooling and heating of the profile plates 4, 6 may be used together or separately in the manufacture of a cellular plate 2 to produce a pre-stressed state. In other words, only one of the profile plates 4, 6 may be cooled/heated, or alternatively one of the profile plates may be cooled and the other heated before fastening them to one another. What is essential is that these cooled and heated plates are fastened to one another in a cooled and heated state, i.e. a pre-stressed state, whereby the equalisation of their temperatures causes a tensile stress and a compression stress in the other profile plate 4, 6, which leads to bending and stiffening of the cellular plate. In this case, one of the profile plates of the cellular plate 2 is under a tensile stress and the other under a compression stress.

[0015] The pre-stressed state, i.e. tensile stress or compression stress, may alternatively be produced mechanically by drawing or compressing the profile plates 4, 6 in order to produce a tensile and/or compression stress in the profile plates 4, 6. The mechanical tensile or compression stress may also be achieved indirectly by securing to the profile plate 4, 6 a pre-stressed piece, which transfers its tensile stress to the profile plate 4, 6. Figure 2 shows one of such indirect ways of producing pre-stress in the profile plate. According to Figure 2, a metal wire or strand 12 is fastened to a profile plate 14 by laser welding, for example. Before the fastening, the metal wire 12 is pre-stressed by drawing it mechanically to a tensile-stressed state. After this, the metal wire 12 is fastened in the pre-stressed state to the profile plate 14 by laser welding. The pre-stress of the metal wire is transferred to the profile plate 14 in such a manner that, when the metal wire 12 tries to return to its original state, a compression stress is produced on the side of the metal wire 12 in the profile plate 14, as the metal wire 12 tries to contract the profile plate 14. Accordingly, on the other side of the profile plate 14, i.e. on the side opposite to the metal wire 12, a tensile stress is produced, in which case the profile plate 14 tends to bend in such a manner that the concave side of the profile plate 14 is the side of the metal wire 12. Similarly, a metal bar pre-stressed by compression and subjected to compression stress may be fastened to the profile plate 14. When such a bar under compression stress is fastened to the profile plate 14, the

profile plate tries to return to an unstressed state, whereupon it produces a tensile stress on that side of the profile plate 14 to which the bar is fastened. Similarly to the above, a compression stress is thus produced on the other side of the profile plate 14. The tensile and compression stresses on the opposite sides of the profile plate tend to bend the profile plate. The cellular plate 2 according to the present invention is provided by further fastening such a mechanically pre-stressed profile plate to another non-prestressed profile plate, or by fastening two such mechanically pre-stressed profile plates to each other, in which case the pre-stresses of the profile plates tend to bend the produced cellular plate 2. It is to be noted that when two pre-stressed profile plates are fastened to each other, the profile plates may be fastened so that they tend to bend in the same direction, in which case the pre-stresses thereof intensify one another, or they may be fastened in such a manner that they tend to bend in different directions, in which case the pre-stresses thereof cancel each other out at least partly.

[0016] The metal wire or strand 12 is preferably flexible in order to allow the bending of the profile plate 4, 6 and/or the cellular plate 2. In addition, the profile plate may be pre-stressed according to the above by fastening to the profile plate a heated or cooled wire, which, when the temperature becomes even, applies a tensile or compression stress to the profile plate according to the above.

[0017] According to the present invention, a pre-stress is produced in the cellular plate 2 consisting of two profile plates 4, 6 fixed on top of one another. In the solution of Figure 1 , the cellular plate 2 is pre-stressed in such a manner that it bends convex on the side of the concrete slab 10 in order to compensate for the bending caused by the weight of the concrete slab. The pre-stressing of the cellular plate 2 also strengthens the cellular plate 2 so that fewer intermediate supports are needed during the casting and the distance between them may be increased.

[0018] According to the above, the pre-stressing of the cellular plate 2 may be achieved in such a manner that a tensile stress is produced in the upper cellular plate 4 and a compression stress is produced in the other profile plate 6, in which case the cellular plate tends to bend convex on the side of the concrete slab 10. This may be achieved so that the first, upper profile plate 4 is pre-stressed in order to produce a tensile stress therein and the second, lower profile plate is non-prestressed. Alternatively, the first, upper profile plate 4 is

non-prestressed and the second, lower profile plate 6 is pre-stressed in order to produce a compression stress therein. Both profile plates 4, 6 may further be pre-stressed in such a manner that the upper profile plate 4 is under a tensile stress and the lower profile plate 6 under a compression stress.

[0019] According to the above, the pre-stressing of the cellular plate 2 may be achieved by fastening the profile plates to one another in a state, i.e. a pre-stressed state, in which they have different temperatures. The first, upper profile plate 4, for example, is hereby cooled to a lower temperature than the second, lower profile plate 6. Or vice versa, the second, lower profile plate 6 is heated to a higher temperature than the first, upper profile plate 4. As the temperatures of the profile plates 4, 6 even out, the length of the profile plates 4, 6 fastened to each other tends to equalize, and a pre-stress is produced in the cellular plate 2, which means that a compression stress is produced in the profile plate 6 fastened at a higher temperature and a tensile stress is produced in the profile plate 4 fastened at a lower temperature, and the cellular plate 2 tends to bend.

[0020] The above-described pre-stressing of the cellular plate 2 may similarly also be applied to an individual profile plate in an intermediate floor. It is also to be noted that the pre-stressing element may also be, for instance, a composite plate, another profile plate, a straight plate, metal wire or cord, a bar or a flat bar, which is fastened to the profile plate in a pre-stressed state. Furthermore, one or more said pre-stressing elements may be fastened to one single profile plate.

[0021] It is further to be noted that in pre-stressing of the profile plates 4, 6 it is also possible to utilize combinations of heating/cooling and mechanical drawing/compressing in order to achieve a greater pre-stress.

[0022] It is obvious to a person skilled in the art that as technology advance, the basic idea of the invention may be implemented in various ways. The invention and the embodiments thereof are thus not restricted to the above examples but may vary within the scope of the claims.