Floor element and its manufacturing method

Abstract

 The invention relates to a floor element (1), comprising a structural concrete hollow core slab (2) having a structure substantially rectangular in top plan view. The width is a standard dimension and the length is tuned to a distance to be spanned between two spaced supports. The hollow core slab (2) is provided with at least one internal channel (5) which extends substantially in the longitudinal direction of the slab and is free from sound absorbing material. The hollow core slab is further provided at the underside (4) with perforations (8) which open into the at least one internal channel (5).

Description

[0001] The invention relates to a floor element, comprising a structural concrete hollow core slab having a structure substantially rectangular in top plan view, wherein the width is a standard dimension and the length is tuned to a distance to be spanned between spaced supports, the hollow core slab being provided with at least one internal channel which extends substantially in the longitudinal direction of the slab.

[0002] Such floor elements are generally known and are mainly used in office buildings but also in serial built housing and project-based commercial and industrial building. Floor elements are a particularly effective product that is highly successful owing to the combination of an effective production technique, a high degree of flexibility in uses and efficient logistics for the purpose of rapid building.

[0003] Despite the fact that a structural element is concerned, the prefab structural concrete hollow core slab floor elements have a taut exterior and, at the underside, which, upon completion of a building, is most often also the visible side, a closed surface. The floor elements are provided with relatively large internal channels which extend in the longitudinal direction of the slab. These channels are primarily used for reducing weight. Viewed in vertical direction, the channels are located virtually in the middle in the floor element, where the stress caused by loading of the floor elements is zero or practically zero.

[0004] The closed surface at the underside causes room acoustics with an annoyingly long echo. Traditionally, this annoying room acoustics is prevented through the use of lowered acoustic ceilings. However, the use of lowered ceilings also has an insulating effect so that concrete activation, including the introduction of heating and cooling elements in the channels, has only a limited effect on the temperature in the room below the lowered ceiling.

[0005] The object of the invention is to obtain a floor element according to the opening paragraph, whereby, while maintaining the advantages, at least one of the drawbacks is counteracted. In particular, the object of the invention is to obtain a floor element according to the opening paragraph, wherein concrete core activation is useful for conditioning a room located below the element, while the occurrence of annoying acoustic effects is substantially prevented in the room located below the element. To that end, the internal channel is free from sound absorbing material, and the hollow core slab is provided at the underside with perforations which open into the at least one internal channel.

[0006] Surprisingly, the use of perforations that form passages between the at least one internal channel and the room below the floor element provides an echo barring effect which renders the use of lowered acoustic ceilings or sound absorbing material in or below the floor element superfluous. Due to the absence of lowered ceilings, concrete core activation can be successfully used, while still, an acoustically pleasant room below the floor element can be involved.

[0007] It is noted that the Swiss patent publication CH 689 674 describes a floor element which is provided with perforations at the top. It is further noted that the US patent publication US 3 275 101 describes a floor element with internal channels in which acoustic absorbing material is provided. It is further noted that the European patent publication EP 1 350 609 describes a mold with upward reaching projections which, upon hardening of a concrete hollow core slab, reach into the concrete mixture.

[0008] According to one aspect of the invention, thus, a basis for agreeable room acoustics can be created which can optionally be improved further by adding sound absorbing floor finishing and sound absorbing walls.

[0009] Further, through the use of a floor element according to the invention in combination with concrete core activation, optionally combined with heat recovery units, heat pumps and/or heat and cold storage by means of closed and open systems, also called geothermics, a positive contribution can be made to durable energy concepts with a low CO2 emission.

[0010] Another important advantage can be obtained in the so-called phase shift in climate control of buildings. This means that the building has sufficient critical mass to store heat in and to remove it again in the evening. In this manner, the increasing cooling load in buildings is limited and hence also the amount of CO2 emission.

[0011] By the use of the floor element according to the invention, furthermore, in an elegant manner, a trend in architecture can be followed whereby bearing elements in buildings and constructions are not hidden from view by covering elements and the like, but are kept as visible as possible.

[0012] The invention further relates to a method for manufacturing a floor element.

[0013] Further advantageous embodiments of the invention are represented in the subclaims.

[0014] The invention will be further elucidated on the basis of exemplary embodiments which are represented in the drawing. In the drawing:

Figure 1 shows a schematic perspective bottom view of a floor element according to the invention;

Figure 2a shows a schematic bottom view of the floor element of Fig. 1;

Figure 2b shows a schematic bottom view of a second embodiment of a floor element according to the invention;

Fig. 2c shows a schematic bottom view of a third embodiment of a floor element according to the invention;

Figure 2d shows a schematic bottom view of a fourth embodiment of a floor element according to the invention; and

Figure 3 shows a schematic side view and a schematic rear view of a hopper carriage.

[0015] The Figures are only schematic representations of preferred embodiments of the invention. In the Figures, identical or corresponding parts are indicated with the same reference numerals.

[0016] Figure 1 shows a schematic perspective bottom view of a floor element according to the invention. The floor element 1 comprises a structural concrete hollow core slab 2 having a structure substantially rectangular in top plan view. The width of the floor element 1 is a standard dimension, for instance 1200 mm. The length of the floor element 1 is tuned to a distance to be spanned between two spaced supports of a building to be built (not represented in the figure), for instance 5 meters. The hollow core slab 2 is provided with internal channels 5. The internal channels 5 extend substantially in the longitudinal direction L of the slab 2 and are free from sound absorbing material. Although the channels 5 in Figure 1 are represented to be substantially ovoid, the channels 5 can also have a different cross section, such as, for instance, substantially square or circular. The channels can be uniform, i.e. have approximately the same dimensions and geometry. However, the dimensions and/or the geometry of the internal channels can also be mutually different. For instance, the width of the channels may also be selected to be alternately relatively large and relatively small so that there is a row of alternating channels in the slab. It is noted in this context that a channel with a substantially square cross section is understood to be a channel whose corners can be somewhat rounded.

[0017] At the underside, the hollow core slab 2 is provided with perforations 8 which open into the internal channels 5. Preferably, the floor element 1 further comprises pre-stressed steel cables 6a, 6b. The steel cables 6a, 6b extend, in the slab 2, substantially in the longitudinal direction L of the slab 2. Because especially in the bottom layer of the floor element 1 utilized in a building tensile stresses are involved which have to be absorbed by the steel cables 6a, 6b, the steel cables 6a 6b are mainly located in the bottom layer of the hollow core slab 2. It is also possible to provide steel cables 7 which are located closer to the top 3 of the floor element 1, usually above a cable 6a, 6b provided in the bottom layer of the hollow core slab 2. In practice, the steel cables 7 provided closer to the top of the floor element are hardly pre-stressed, if at all. The amount and the position of the cables 6a, 6b, 7 depend on, inter alia, the specified load and span.

[0018] Preferably, the perforations 8 are located between the pre-stressed steel cables 6a, 6b in the bottom layer of the hollow core slab 2.

[0019] Figure 2a shows a schematic bottom view of the floor element 1 of Figure 1. Viewed from the bottom side of the hollow core slab 2, the perforations 8 have a circular profile.

[0020] Figure 2b shows a schematic bottom view of a second embodiment of a floor element 1 according to the invention. In the second embodiment, the perforations 8, viewed from the underside of the hollow core slab 2, have a triangular profile. The perforations can also have other polygon-shaped profiles which are, for instance, regular or concave.

[0021] Fig. 2c shows a schematic bottom view of a third embodiment of a floor element 1 according to the invention. In the third embodiment, the perforations 8, viewed from the underside of the hollow core slab 2, have an elliptic profile.

[0022] Figure 2d shows a schematic bottom view of a fourth embodiment of a floor element 1 according to the invention. In the fourth embodiment, the perforations 8 also have an elliptic profile, just as in the third embodiment. However, the elliptic shaped perforations 8 are rotated one quarter turn compared to the elliptic perforations of Figure 2c and, in the fourth embodiment, are transverse to the longitudinal direction of the channels 5 and therefore also transverse to the longitudinal direction of the slab 2. Viewed from the underside of the hollow core slab, the perforations 8 can also have a profile different from polygonal, circular or elliptic. A hollow core slab can further have perforations 8 of different shapes. Also, identically or not identically shaped perforations can have different orientations, for instance such as the triangular perforations in Figure 2b, which have different orientations. Preferably, the total surface of the perforations 8 together forms 20% to 50% of the surface area of the underside 4 of the hollow core slab 2, but this can also be more or less.

[0023] The hollow core slab floor elements are provided with hollow openings in the cross section of the floor element, the channels 5. These channels can be made with a specific extrusion technique, as described in the following.

[0024] This manufacturing technique enables manufacture of elements having indeed standard widths, for instance 1200 mm, but with a large diversity in heights and channels. The result of this technique is that the underside of the floor elements, the visible side, always has a taut and closed surface and that the top is rough. The tables on which the hollow core slab floor elements are manufactured, are usually configured with a steel plate. On these plates, a thin layer of water can be provided to ensure the floor element will not adhere.

[0025] The prefab structural concrete hollow core slab floor elements are successful because of applied production technique, flexibility and logistics owing to the smart constructional properties.

[0026] From the viewpoint of construction, the hollow core slab floor elements are standard width floor slabs mounted on two supports. With the architectural construction, the floor element rests on two supports so that the underside is oriented downward. In the building process, the elements are laid directly next to each other and are connected by a bonding concrete layer that is poured over them. This concrete layer provides a fixed connection so that together, the elements form a complete floor area. Generally, a uniformly distributed load rests on this floor area. As an element resting on two supports is involved here, there is compressive stress in the top layer and tensile stress in the bottom layer of the element. The channels are almost always located between these two layers. But as concrete can absorb hardly any tensile stress, if at all, additional steel is added in the bottom layer - steel is eminently capable of absorbing tensile stresses - in the form of so-called strands. Strands are composite steel wires which are pre-stressed according to the expected load on the floor elements. By pre-stressing these strands tensile stresses are readily absorbed and a floor element is formed that almost wholly absorbs compressive stress, and this is what concrete does very well. Thus, every fibre of the hollow core slab floor element is optimally used. As a rule, the pre-stressed strands are in the bottom layer of the floor element and preferably between the channels. The concrete which is under the channels provides virtually no constructional contribution, it is "idle". If a taut and closed surface were not desired, this concrete could be omitted. Accordingly, the provision of the perforations hardly, if at all, affects the constructional properties of the floor element.

[0027] According to one aspect of the invention, perforations are formed at the underside of the prefab structural concrete hollow core slab floor elements. The perforations are positioned there where the concrete is "idle". Through the provision of these perforations, so-called Helmholtz resonators are formed. These provide sound absorption in the underlying space. The perforations can be configured in different shapes and sizes and with a percentage of openness which is preferably between 20% and 50%.

[0028] Preferably, the perforations are arranged in a regular pattern. In principle, however, the perforations can also be provided in a seemingly unordered fashion. The perforations can further be designed such that the profile and/or the size of the perforations is mutually different. For instance, two types of perforations can be provided, for instance relatively large and relatively small ones, or perforations with a first type of contour and perforations with a second contour. By varying the profile and/or the size of the perforations a specific damping property can be realized which meets preset damping requirements over a relatively wide part of the sound spectrum.

[0029] Fig. 3 shows a schematic side view and a schematic rear view of a so-called kubelwagen (hereinafter: hopper carriage) 10. Figure 3 further shows a portion of a concrete casting track 23 on which, in top plan view, a substantially rectangular structural concrete hollow core slab 2 is manufactured. A portion of the hollow core slab 2 is in a stage where the concrete is hardening. The concrete casting track 23 comprises a slab-shaped mold 24. It is possible that a plurality of slab-shaped molds 24 are placed one behind the other and/or next to each other for together forming a large slab-shaped composite mold 24, which is also called table 24. The slab-shaped mold 24 comprises upward reaching elements 22 preferably tapering towards the top, which extend as far as the elements (not shown) which form the channels 5.

[0030] Preferably, the mold 24 is manufactured from steel or a plastic such as polyurethane. Further, the upward reaching elements 22 are preferably integrally formed. The mold 24 is preferably manufactured with a pressing technique, a casting process or an injection molding process, but other production techniques are also possible.

[0031] The width of the table 24 is preferably a standard dimension, for instance approximately 1200 mm. As will be clear to the skilled person, the length of the table 24 depends on the length of the concrete casting track, often several tens of meters long. The concrete casting track 23 further comprises guides 20 for guidance of the wheeled hopper carriage 10. Thus, the guides 20 can form rails for bearing the wheels 16a,b of the hopper carriage 10.

[0032] The hopper carriage 10 comprises different parts 11, 13-15, among which a storage hopper 11, wheels 16a, 16b, and channel forming elements (not represented) designed as vibrating tubes. The vibrating tubes may have a length of approximately 1 meter. The storage hopper 11 is filled with a concrete mixture 12. As will be clear to the skilled person, the hopper carriage 10 may also be configured differently with, for instance, a suspended hopper carriage or slideable hopper carriage.

[0033] After provision of the mold 24, steel cables 6a, 6b, 7 are tightened above the table. Then, the hopper carriage 10 is moved forward over the guides 20, while the hopper carriage pours the concrete mixture 12 onto the mold 24. The upward reaching elements 22 of the mold extend as far as the channel forming elements. The concrete mixture 12 forms around the vibrating tubes and the steel cables 6a, 6b, 7. As the hopper carriage 10 continues to move forward, it pulls the vibrating tubes from the previously formed portion of the hollow core slab 2. Owing to the correct viscosity of the concrete mixture, the portion of the hollow core slab 2 just formed retains its shape while the poured concrete mixture 12' has not yet hardened. As the upward reaching elements 22 are in line with the channel forming elements of the hopper carriage 10, perforations are formed in the underside 4 of the hollow core slab 2, which open into the internal channels 5. As will be known to the skilled person, the underside of the hollow core slab which is formed by the mold 24 can be manufactured to be taut. As the form of the upward reaching elements 22 tapers somewhat toward the top, a hollow core slab 2 can be removed from the mold 24 relatively easily after it has sufficiently hardened.

[0034] The perforations are thus provided integrally in the production process. The standard steel plates with flat tops which are provided on the production table are replaced according to one aspect of the invention by steel plates which are provided with counter-forms for the desired perforations, the upward reaching elements 22.

[0035] As a possible explanation for the empirically determined acoustic properties, the following is noted.

[0036] A Helmholtz resonator comprises a volume of air which is in communication with the outside air through a narrow neck. The air volume behind the neck acts as a spring for the mass of air in the neck. Together, this forms a mass-spring system with a fixed resonance frequency. At and around this resonance frequency, sound is amplified by the Helmholtz resonator. In order to prevent amplification of sound and to render the Helmholtz resonator sound-absorbent, friction must be introduced by, for instance, an acoustic fibrous fabric behind the opening of the neck and/or sound absorption in the air volume. The Helmholtz resonator enables easier amplification or absorption of low pitches than other conventional systems because there is physically less space needed.

[0037] Another application of the Helmholtz resonator takes place in perforated panel absorption where the perforations, the holes, act as Helmholtz resonators. In contrast to the "pure" Helmholtz resonator, with a panel absorber, a broadband sound absorption is envisaged by means of a perforated bending slack plate on a cavity, filled with sound absorption. Here, a plate is considered to be acoustically bending slack when it has a high border frequency from ca 2 kHz.

[0038] The perforated panel absorbers are frequently used in architectural acoustics. Various suppliers in the construction market supply standard products of perforated plaster boards, wooden boards and steel plates. Here, the bandwidth of the sound absorption depends on the amount of sound absorption in the cavity. The frequency range and the bandwidth over which the perforated panel absorber absorbs sound depend on the mass and stiffness of the plate and the cavity depth.

[0039] In comparison with the above-mentioned principles it can be concluded that the structure with the channels 5 and perforations 8 is not built up from "pure" Helmholtz resonators, neither can it be qualified as a panel absorber because the hollow core slab must be considered to be a bending stiff slab owing to the low cutoff frequency. It appears non-trivial to assess the acoustic performance of the floor element according to the invention on the basis of theoretical models. Approximate expectations can indeed be formulated.

[0040] For instance, expectations are that a high degree of perforation provides the best performance for the middle and high pitch sound absorption, which is desired for a good audibility in a room. Further, the perforation has a positive effect on the sound scattering of high pitches, which is positive for spatial perception and for preventing or limiting disturbing reflections. Additionally, it appears that generally, with a larger opening of the perforation, a Helmholtz resonator becomes less effective, but that the effectiveness of the sound absorption in the middle and high frequency increases. The smaller the perforation, or the lower the degree of perforation, the lower the resonance frequency of the Helmholtz resonator. Further, the sound insulation decreases through the perforation, more specifically: the expectations are that the air sound insulation index I_lu,lab decreases by approximately 1 to 3 dB, depending on the perforation. It is expected that also the contact sound insulation index decreases by approximately 3 to 5 dB, depending on the perforation and the mass. As stated hereinabove, the final acoustic performance can be determined by means of test measurements.

[0041] Owing to the perforations in the channels, these can act as chimneys in case of fire. Preferably, therefore, the channels are closed off by means of a standard fire resistant or fire retardant provision at both ends of the hollow core slab floor elements. Also, the reduced mass due to the reduced concrete volume should be taken into account.

[0042] Through the application of some minor adaptations, the floor element according to the invention can be integrally included in the production process of the prefab structural reinforced concrete hollow core slab floors. The product thus formed can make a striking acoustic contribution without interfering with the important advantages in production technique, flexibility and logistics. Expectations are also that the floor element according to the invention will make a positive contribution to climate control of the space.

[0043] The invention is not limited to the exemplary embodiments described here. Many variants are possible.

[0044] For instance, the floor element can be used not only in newly built houses, but also for renovation purposes in existing buildings. In addition, the floor element can be used as noise barrier, for instance, next to high-traffic thoroughfares. The floor element can then be placed in a tilted orientation, i.e., with the underside directed sideways.

[0045] Such variants will be clear to the skilled person and are deemed to fall within the scope of the invention as set forth in the following claims.

Claims

1. A floor element, comprising a structural concrete hollow core slab having a structure substantially rectangular in top plan view, wherein the width is a standard dimension and the length is tuned to a distance to be spanned between spaced supports, the hollow core slab being provided with at least one internal channel which extends substantially in longitudinal direction of the slab and is free from sound absorbing material, and wherein the hollow core slab is provided at the underside with perforations which open into the at least one internal channel.

2. A floor element according to claim 1, wherein the hollow core slab is provided with a plurality of internal channels which extend substantially in the longitudinal direction of the slab.

3. A floor element according to claim 1 or 2, further comprising a plurality of pre-stressed steel cables which, in the slab, extend substantially in the longitudinal direction of the slab.

4. A floor element according to claim 3, wherein the pre-stressed steel cables are located near the underside of the hollow core slab.

5. A floor element according to claim 2, 3 and/or 4, wherein the dimensions and/or the geometry of the internal channels are mutually different.

6. A floor element according to any one of the preceding claims, wherein the total surface of perforations forms between approximately 20% and 50% of the surface area at the underside of the hollow core slab.

7. A floor element according to any one of the preceding claims, wherein the perforations are arranged in a regular pattern.

8. A floor element according to any one of the preceding claims, wherein the profile and/or the size of the perforations are mutually different.

9. A floor element according to any one of the preceding claims, wherein the perforations, viewed from the underside of the hollow core slab, have a polygonal, circular or elliptic profile.

10. A floor element according to any one of the preceding claims, wherein the perforations are located between the pre-stressed steel cables.

11. An architectural construction, comprising a floor element according to any one of the preceding claims, and two supports on which the floor element rests, such that the underside of the hollow core slab is oriented downwards.

12. A method for manufacturing a floor element, comprising a structural concrete hollow core slab having a structure substantially rectangular in top plan view, wherein the width is a standard dimension and the length is tuned to a distance to be spanned between two spaced supports, the method comprising the steps of providing a slab-shaped mold and, with the aid of a hopper carriage, pouring a concrete mixture on the mold, the hopper carriage being provided with channel forming elements and wherein the slab-shaped mold comprises upward reaching elements which extend as far as the channel forming elements.

13. A method according to claim 12, wherein the upward reaching elements taper upwards.

14. A method according to any one of the preceding claims 12 or 13, wherein the floor element is used for renovation purposes, or, in tilted orientation, as noise barrier.

15. A method according to any one of the preceding claims 12-14, comprising placing the floor element on two support elements such that the underside of the hollow core slab is oriented downwards.

Drawing