The acoustic properties in a building are often described as footstep sound, airflow sound and structural sound. Footstep sound is defined as sound which occurs in adjacent enclosures as a result of footsteps on flooring structures, in stairways etc. Airflow sound is defined as the sound emitted from the sound source into the ambient atmosphere by the air. Finally, structural sound is defined as sound which is propagated via the structure of a building.

In order to avoid irritation, it is desirable to restrict the sonic transfer between different spaces or enclosures in a building as far as is practically possible. The present invention specifically relates to footstep sound insulation, i. e. to reduce, on dynamic loading, the transfer of sound between two storeys and/or apartments. The term dy- namic loading relates to that type of loading which occurs as a result of footsteps on a floor.

In addition to the bearing wooden beams, a traditional flooring struc- ture consists further of a floor and a ceiling. In the actual flooring structure and between floor, ceiling and flooring structure, respec- tively, there are normally various types of insulating material. There may also be provided battens for supporting any possible insulation between the beams and false ceiling panels. At their ends, the bearing wooden beams are secured in the structure of the building.

The principle of today's homogenous flooring structures entails that the individual wooden beams are united via steel bands, nails or glue.

Traditional light flooring structures are normally interconnected by the intermediary of various types of panels on the upper and lower sides. This implies that the flooring structure oscillates as an equivalent, orthotropic, homogeneous plate in the event of a dynamic

loading such as a footstep. This in turn implies that the entire sur- face of the flooring structure emits sound out towards adjacent areas.

In prior art flooring structures, there is a large number of different strata or layers. In the present invention, the same or improved sound insulation will be obtained with a fewer number of layers. This affords obvious advantages both as regards material costs and material consump- tion.

If a homogenous flooring structure is employed, it is moreover possible to use it as a"floor"during building work.

One object of the present invention is to reduce the footstep sound, i. e. to reduce the drawbacks inherent in traditional flooring struc- tures as described above in the event of dynamic loading. Naturally, the flooring structure must satisfy the usual requirements as regards mechanical strength, structural sound insulation and airflow sound in- sulation, fire safety etc.

The footstep sound damping effect is obtained according to the present invention in that the flooring structure only reacts locally to a dy- namic loading, which entails that the flooring structure only emits sound immediately adjacent the applied dynamic loading.

In a flooring structure according to the present invention, the bearing wooden beams are not dynamically interconnected.

The present invention will now be described in greater detail hereinbe- low, with reference to the accompanying Drawings. In the accompanying Drawings: Fig. 1 shows the principle of a homogeneous wooden flooring structure with steel band according to prior art technology; Fig. 2 is a cross section of a traditional light wooden flooring structure according to prior art technology;

Fig. 3 shows the principle of a homogeneous wooden flooring structure according to the present invention; Fig. 4 shows the principle of a semi-homogeneous wooden flooring structure according to the present invention; Fig. 5 is a perspective view of a grooved beam which may be employed in the present invention ; and Fig. 6 is a schematic cross section of an alternative flooring struc- ture according to the present invention.

The figures show substantially only the beams, the floor structure, in- cluded in the flooring, but a person skilled in the art will readily perceive that the flooring structure also includes floor, ceiling and various insulating layers.

Today, basically only two types of wooden flooring structures are em- ployed, namely a homogeneous wooden flooring structure as in Fig. 1, or a so-called light wooden flooring structure as in Fig. 2.

The homogeneous wooden flooring structure according to Fig. 1 has a number of closely adjacent wooden beams 1 which are united together, for example, by means of two steel bands intimated at reference numeral 2 in Fig. 2. This is a relatively rigid construction. When such a rigid construction is subjected to a dynamic loading 3, such as a footstep, it oscillates as an orthotropic, homogeneous plate. This entails that the whole surface of the flooring structure emits sound to adjacent ar- eas, as intimated by the sketched sound waves 4.

In the normal construction of a light wooden flooring structure as in- timated in Fig. 2, the beams 1 are interconnected with the aid of floor panels 5 and ceiling panels 6. Also, in such a flooring structure, the individual beams co-operate via the panels so that footstep sound 4 is transferred from its entire surface towards adjacent areas.

In a homogeneous flooring structure according to the present invention as illustrated in Fig. 3, the individual beams 1 are not dynamically joined together. The ends of the beams are secured in the structure of the building. The present invention is based on the feature that the bearing beams 1 of the flooring structure do not co-operate dynamically with one another in any significant manner.

In all embodiments, according to the present invention, the beams 1 are not interconnected with each other apart from at certain discrete points, for example bearing supports at the ends of the beams.

Compared with prior art light flooring structures, the beams 1 in the flooring structure according to the present invention lie considerably closer to one another. A suitable rule of thumb in such instance has proved to be that the distance between the beams 1 should be less than the height of an individual beam 1.

When a dynamic loading 3 is applied on a flooring structure according to the present invention, only the beam or beams 1 which lie directly beneath the point of impact of the loading will be affected. The trans- fer of movement to adjacent beams is minimized. In such instance, the footstep sound 4 is only transferred via these directly affected beams.

The flooring structure may be said to react locally in that it only emits sound immediately adjacent the applied dynamic loading 3.

As intimated in Fig. 4, the local reaction principle according to the present invention also applies to semi-homogeneous flooring structures without interconnected beams 1. In such instance, the beams 1 lie a distance from each other and insulation 7 has been placed between the beams 1. This insulation 7 must have low shearing rigidity. If the in- sulation has too high shearing rigidity, there is a risk that the vi- brations are transferred between the beams 1. An example of suitable insulation material is mineral wool of low shearing rigidity. Also in this case, the flooring structure reacts only locally to a dynamic loading 3.

In one alternative embodiment of the present invention, the local reac- tion to a dynamic loading is attained in that the flooring beams in the flooring structure under consideration are provided with grooves which reduce torsional rigidity and compression rigidity at the anchorage point to the floor and/or ceiling panels. The same effect is achieved with separate, grooved studs in accordance with the foregoing which are mounted on the upper and/or lower side of the flooring structure.

In this embodiment, use is made either of beams 8 or studs 10 which have been provided with grooves 9. In such instance, the grooves 9 are made in a manner illustrated in Swedish patent No. 510 722. The grooves 9 in beams 8 or studs 10, respectively, are fully open in one direction and have through-going defined apertures 11 in the other direction.

Each cross section displays at least one part without any material, i. e. at least one of the grooves 9 has no residual material in that cross section.

When grooved beams according to Fig. 5 are employed, the floor may rest direct on the beams. In the embodiment according to Fig. 6, grooved studs 10 are placed between the beams 1,8 and the floor panels 5. In this latter embodiment, both beams 1,8 with and without grooves may be employed.

As a ceiling, it may be of interest to employ wood wool panels. Wood wool panels absorb sound efficiently and transmit little sound compared with, for example, a plaster board.

The form of the flooring structure may be varied in many different ways without deviating from the inventive concept as herein disclosed. How- ever, it is always important to ensure that, when one or more adjacent beams 1 are subjected to a dynamic loading, the transfer of the loading movement of the beam/beams to other beams in the flooring structure is minimized.

While the present invention shows and is described in connection with wooden flooring structures, a person skilled in the art will perceive that the same principle may be employed for flooring structures of other materials, such as, for example, concrete and steel.