Slab element

Abstract

 The slab element comprises a surface plate (10), a bottom plate (12) and an insulation layer (14) between the surface plate and the bottom plate. The surface plate has gripping members (16) for gripping a concrete casting. The slab element can be used as a structural part of steel-concrete composite slabs, where the slab element during the concrete casting forms a mould surface beneath the slab and after the hardening of the concrete a fixed part of the composite slab. The insulation layer has at least one elongated tensile stress member (36), such as a wire or a bar, which increases the bending strength of the slab element. The first and/or second end of the tensile stress member can have a tightening member for producing tensile stress in the tensile stress member. With the aid of the tensile stress member a compression stress can be formed in the lower edge of the slab element, which compression stress makes the slab element curve upwards. A pre-elevation can thus be produced in the slab element before the concrete is cast, which pre-elevation can compensate for the bending caused by the concrete mass set onto the slab element.

Description

[0001] The invention relates to a slab element, which comprises a surface plate, which surface plate has gripping means for gripping a concrete casting, a bottom plate and an insulation layer between the surface plate and the bottom plate. The invention additionally relates to a composite slab and a method for manufacturing a composite slab.

[0002] The base and intermediate floors of buildings can be built as concrete-steel composite slabs, which have a composite sheet manufactured from thin plate of steel and a concrete slab cast in place on top of it. The composite sheet functions during the casting of the concrete slab as a cast mould beneath the structure. As the concrete hardens, the composite sheet grips the concrete casting with the aid of the gripping means in the composite sheet. In the completed structure the composite sheet functions as a structural part forming the lower surface of the composite slab, which part at least partly replaces reinforcement elements receiving the tensile stress of the slab.

[0003] Even though the composite slabs are construction-technically and manufacturing-technically as such working solutions, they are however associated also with disadvantages. A composite sheet manufactured from a thin steel plate does not on its own withstand very big loads, wherefore the composite sheet must be supported from below before the concrete slab is cast. The number of supports needed and the length of the distance between supports depends on the profile shape of the composite sheet, the thickness of the sheet and the thickness of the concrete slab to be set on the composite sheet. With typical composite sheet profiles and concrete slab thicknesses used in building construction, the distance between supports varies in the range of 1-2 meters. Installing the supports before the casting and removing them after the casting increases the manufacturing costs of the composite slab.

[0004] A composite slab is often used as a base floor structure also in ventilated floors, i.e. in so-called ventilated foundation structures. In ventilating floors a thermal insulation layer is set beneath the load-bearing composite slab. In order for the floor to function thermal- and moisturewise in a desired manner the thermal insulation layer must be uniform and in immediate contact with the lower surface of the slab above it. Installing the thermal insulation on the lower surface of the ventilated floor is a separate work stage, which increases the construction costs of the floor. Additionally, the installation of the thermal insulation is complicated, which increases the risk of work errors and heat losses and moisture damage caused by them.

[0005] Publications WO2008041251, FI119604, FI61066 and WO2009010994 disclose slab elements, which have a surface plate, a bottom plate and a thermal insulation layer between the surface plate and the bottom plate. These slab elements can function as a cast mould for a concrete slab and after the hardening of the concrete as a structural part of a composite slab.

[0006] An object of the invention is to provide a slab element, by which the disadvantages relating to the prior art can be eliminated.

[0007] The objects of the invention are obtained with a slab element, which is characterised by what is presented in the independent claim. Some advantageous embodiments of the invention are presented in the dependent claims.

[0008] The invention relates to a slab element, which comprises a surface plate, a bottom plate and an insulation layer between the surface plate and the bottom plate. The surface plate has gripping means for gripping a concrete casting, i.e. the surface plate is a composite sheet, which can form a structure working in cooperation with a concrete slab cast on top of it. The slab element according to the invention can thus be used as a structural part of steel-concrete composite slabs, where the slab element during the concrete casting forms a mould surface beneath the slab and after the hardening of the concrete a fixed part of the composite slab. The surface plate can have any profile shape known from composite sheets, such as a trapezoid profile. The material of the surface plate is advantageously metal, such as steel, and its thickness can be selected to be suitable according to the loadbearing requirements of the slab element. The thickness of the surface plate can for example be 0.5, 0.7, 1.0, 1.2 or 1.5 mm. The material of the bottom plate can be steel or some other suitable material. The bottom plate can have the same or a different thickness than the surface plate.

[0009] The slab element additionally comprises at least one elongated tensile stress member in the insulation layer. The slab elements functioning as cast moulds for composite slabs are installed in place so that the surface plate forms the upper surface of the slab element and the bottom plate forms the lower surface. The tensile stress member or tensile stress members are in the insulation layer between the surface slab and the bottom slab. The load settling onto the slab element strives to bend the slab element to curve downward. A tensile stress is thus generated in the tensile stress element in the insulation layer, which tensile stress resists the bending and thus increases the loadbearing capacity of the slab element.

[0010] In an advantageous embodiment of the slab element according to the invention the tensile stress member is in the insulation layer in a part delimited by the neutral axis of the cross-section of the slab element and the bottom plate. The neutral axis of the cross-section means the point in the cross-section of the slab element, where no deformations occur as the slab element bends. Thus a compression stress affects in the part of the slab element above the neutral axis of the cross-section, due to which compression stress the upper surface of the slab element is compressed. Correspondingly a tensile stress affects in the part of the slab element beneath the neutral axis of the cross-section, due to which tensile stress the lower surface of the slab stretches. The tensile stress member is placed in this part of the cross-section, where the tensile stress affects when the slab element is bent. In practice this means that the tensile stress member is in the insulation layer very close to the bottom plate of the slab element.

[0011] A second advantageous embodiment of the slab element according to the invention has a first end and a second end and said tensile stress member extends from the first end to the second end. The tensile stress member thus extends over the entire length of the slab element. The first end advantageously has a first end profile and the second end has a second end profile and the tensile stress member has a first end, which is attached to the first end profile, and a second end, which is attached to the second end profile. With the aid of the end profiles the tensile stress members can be firmly anchored to the ends of the slab element. The end profiles can for example be U profiles, the web plate of which forms the end surface of the slab element.

[0012] In a third advantageous embodiment of the slab element according to the invention the first and/or second end of the tensile stress member has a tightening member for producing a tensile stress to the tensile stress member. The tensile stress affecting in the tensile stress member pulls the end profiles in the ends of the slab element toward each other, whereby a compression stress is generated in the lower edge of the slab element, which compression stress makes the slab element curve upwards. By using tightening members a desired pre-elevation can thus be produced in the slab element, which pre-elevation can compensate for the bending caused by the load set onto the slab element.

[0013] The tensile stress member can be a flexible structural part withstanding tension, such as a wire, advantageously a steel wire. The tightening member can be a tightening turnbuckle attached to the end of the wire, which can be used for shortening the length of the wire in the distance between the ends of the slab element.

[0014] The tensile stress member can also be a rigid structural part withstanding tension, such as a bar, advantageously a steel bar. Advantageously there are threads at least in one end of the bar, and the tightening member is a nut fitted onto the threads of the bar.

[0015] Still another advantageous embodiment of the slab element according to the invention has a first edge surface in the longitudinal direction of the slab element and the bottom plate has a lower edge strip extending outwards from the level of the first edge surface, which edge strip has an edge seal. When setting slab elements beside each other, one edge of the bottom plate of the first slab element settles onto the edge strip of the adjacent second slab element in an overlapping manner. The edge seal thus remains pressed between the overlapping parts, whereby the joint becomes tight.

[0016] Still another advantageous embodiment of the slab element according to the invention has a second edge surface in the longitudinal direction of the slab element and the surface plate has an upper edge strip extending outwards from the level of the second edge surface. When setting slab elements beside each other, the upper edge strip of the surface plate of the first slab element settles onto the first edge of the surface plate of the adjacent second slab element in an overlapping manner. The upper edge strip of the first slab element can be attached to the surface plate of the second slab element with a screw attachment.

[0017] In still another advantageous embodiment of the slab element according to the invention the insulation layer is made of a hard thermal insulation material, such as polyurethane, polystyrene, extruded polystyrene or hard mineral wool, which have a fairly good shear force strength. Additionally the insulation layer is fixedly attached to the surface plate and bottom plate. The surface plate, bottom plate and insulation layer of the slab element thus function as a uniform, loadbearing structural part.

[0018] The composite slab according to the invention comprises a plane constructed of slab elements and a concrete slab cast onto the plane. The plane is formed from a group of above-described slab elements set side by side. The composite slab can for example be a ventilated base floor of a building, an intermediate floor of a building or an upper floor of a building.

[0019] In the method for manufacturing composite slabs according to the invention, a plane is formed from slab elements and a concrete slab is cast onto said plane. In the method the plane is formed by setting a group of above-described slab elements beside each other.

[0020] In an advantageous embodiment of the method according to the invention the slab elements are formed to curve upwards before the concrete slab is cast by tightening the tensile stress members in the slab elements. This pre-elevation done before the concrete casting can compensate for the bending caused by the concrete mass cast onto the slab element either completely or partly.

[0021] An advantage of the invention is that it significantly reduces the need for supports beneath the composite slab during casting, which decreases the manufacturing costs of the composite slab.

[0022] An advantage of the invention is additionally that it makes the construction of thermally insulated base and intermediate floors, such as ventilated base floors, outstandingly easier, because the installation of thermal insulation traditionally done at the work site can be done already at the element factory. Installation of the thermal insulation occurring in factory conditions decreases the risk of work errors and thus decreases the danger of development of heat losses and moisture damages.

[0023] In the following, the invention will be described in detail. In the description, reference is made to the enclosed drawings, in which

Figure 1 shows as an example a slab element according to the invention as a perspective view seen from the front, diagonally from above,

Figures 2a, 2b and 2c show as an example as a series of images the manufacturing of a composite slab according to the invention with the aid of slab elements according to the invention.

[0024] Figure 1 shows as an example a perspective view of a slab element according to the invention seen from the front, diagonally from above. The slab element has a steel surface plate 10 and a steel bottom plate 12 substantially parallel to the level defined by the surface plate. The surface plate is a composite sheet formed from thin plate of steel generally used in manufacturing concrete-steel composite slabs, which composite sheet has a so-called trapezoid cross-section. Due to the profile shape of the composite sheet, grooves in the longitudinal direction of the slab element are formed in the surface of the slab element. In the bottom of the grooves there is a nodule rib 16, which has the length of the entire groove. The nodule ribs function as gripping members, with the aid of which the composite sheet grips the concrete casting cast on top of it, whereby a so-called composite effect is generated between the composite sheet and the hardened concrete. Between the surface plate and the bottom plate there is an insulation layer 14, the material of which is polyurethane. The thickness of the insulation layer can be selected as desired. The thickness of the insulation layer is advantageously such that thermal insulation requirements set for the completed structural parts are fulfilled with the aid of the insulation layer of the slab element. The thickness of the insulation layer can for example be 12, 15, 18 or 20 cm. The slab element is meant to be installed in place in the structure so that the surface plate forms the upper surface of the element and the bottom plate its lower surface.

[0025] The slab element has two edge surfaces in the longitudinal direction of the plate, i.e. in the direction of the grooves of the surface plate 10, a first edge surface 18a and a second edge surface 18b. The edge surfaces are not covered with the plate material, i.e. the even edge of the insulation layer forms the edge surface. The first edge of the bottom plate extends outside the level defined by the first edge surface and thus forms a narrow lower edge strip 20 on the lower surface of the first edge of the slab element, which strip has the length of the entire slab element. On the surface of the lower edge strip toward the insulation layer there is an edge seal 22 of butyl material. When setting slab elements beside each other, one edge of the bottom plate of the first slab element settles onto the edge strip of the adjacent second slab element in an overlapping manner. The edge seal thus remains pressed between the overlapping parts, whereby the joint becomes tight.

[0026] The second edge of the surface plate 10 extends outside the level defined by the second edge surface 18b and thus forms an upper edge strip 24 on the upper surface of the slab element, which strip has the length of the entire slab element. When setting slab elements beside each other, the upper edge strip of the surface plate of the first slab element settles onto the first edge of the surface plate of the adjacent second slab element in an overlapping manner. The upper edge strip of the first slab element is meant to be attached to the surface plate of the second slab element overlapping with it with a screw attachment.

[0027] The slab element has two opposite ends, a first end 30a and a second end 30b. Both ends have a substantially identical U-shaped end profile 32, which has an upper flange in the direction of the surface plate and a lower flange in the direction of the bottom plate and a web plate 34 connecting the upper and lower flange. In Figure 1 the end plate in the first end is shown only partly, in order to better bring out the structure of the slab element. The end profiles are sheet metal profiles formed from thin plate of steel, the plate thickness of which can be for example 0.5, 0.7, 1.0 or 1.5 mm.

[0028] Inside the insulation layer, close to the bottom plate, there are two steel wires 36 in the longitudinal direction of the slab element, which wires extend over the entire length of the slab element, i.e. from the first end of the slab element to its second end. Figure 1 shows with a dashed line the neutral axis N of the cross-section of the slab element. When the slab element bends to curve downwards, a compression stress affects in the part above the neutral axis and a tensile stress affects in the part below the neutral axis. The steel wires are in the part of the cross-section between the neutral axis and the bottom plate, i.e. in the part to which the tensile stress is directed when the slab element bends downwards. The steel wires are attached by their second end in a fixed manner to the end profile 32 of the second end 30b. The first ends of the steel wires extend through holes in the web plate of the end profile of the first end to outside the level of the end surface. The first end of the steel wire is attached to the first end plate with a turnbuckle screw (the turnbuckle screw is not shown in the figure). The steel wires are tensile stress members, in which tensile stress is generated, when the slab element bends downward by the force of the load above it. The steel wires thus increase the bending strength and load bearing capacity of the slab element.

[0029] By tightening the turnbuckle screws, tensile stress can be produced in the steel wire already before the load is set onto the slab element. The tensile stress of the steel wire pulls the end profiles of the first and second end toward each other, whereby a compression stress causing compression is formed in the lower edge of the slab element, which compression stress makes the slab element curve upwards. This so-called pre-elevation can be used to compensate for the bending caused by the load from above, so that the slab element in a loaded situation settles in a substantially horizontal, unbent position.

[0030] The slab element is primarily meant to be used as a part of concrete-steel composite slabs, where the slab element in a casting situation functions as a cast mould for fresh concrete mass and after the hardening of the concrete as a part of the completed composite slab. The load directed onto the slab element and bending the slab element downwards is thus made up of the own weight of the fresh unhardened concrete mass and the own weight of the slab element. By tightening the turnbuckle screws, tensile stress can be produced in the steel wires, which tensile stress makes the slab element curve upwards by so much that it completely or at least partly compensates for the bending caused by the load directed onto the slab element. The pre-elevation is formed in the slab element before the concrete is cast onto the element. After the casting of the concrete the slab element thus settles in a substantially horizontal position. The pre-elevation can be done either completely or partly at the element factory or completely or partly at the work site. After the concrete has hardened, the slab element and the concrete cast above it function together as a composite structure, where mainly compression stresses are directed at the concrete cast and tensile stresses are directed at the slab element.

[0031] Figures 2a, 2b and 2c show as an example as a series of images the manufacturing of a composite slab according to the invention with the aid of slab elements according to the invention. In the method a plane 50 functioning as cast mould beneath the slab is first formed by setting beside each other a suitable number of slab elements according to the invention. The slab elements are supported at their ends on bearing support structures 200, such as the upper surface of a footing or a wall or a bearing beam (Figure 2a). The slab elements are set beside each other so that the edge surfaces of adjacent slabs are connected together with a butt joint. Adjacent slabs are attached together with the aid of the upper and lower edge strip in the above-described manner. If necessary, the tightness of the seam between the edge surfaces can be ensured by installing a sealing mass in the seam, such as polyurethane foam. Edge moulds and the parts ending up inside the concrete casting, such as pipes, conductors, additional reinforcements etc. are further installed onto the plane. These parts are not shown in the figure.

[0032] Next a pre-elevation is formed in the slabs by producing a suitable tensile stress in the steel wires functioning as tensile stress members 36, whereby the slab elements bend upwards in the middle (Figure 2b). Alternatively the tensile stress can be produced already at the element factory, whereby the slab elements curve upwards already when they are brought to the work site. The pre-elevation can be formed in the slab elements also in several steps for example so that a preliminary pre-elevation is formed at the element factory and the final pre-elevation is formed at the work site in connection with the installation of the slab elements.

[0033] Finally a layer of concrete of a desired thickness is cast onto the plane formed by the slab elements, and it is allowed to harden into a concrete slab 100. After the concrete has hardened the concrete slab 100 and the slab elements according to the invention function as a uniform steel-concrete composite slab (Figure 2c).

[0034] The slab element according to the invention is primarily designed for use in concrete-steel composite slabs, whereby it forms during the casting a cast mould beneath the concrete part and after the hardening of the concrete a fixed part of the composite slab. The composite slab can be a base, intermediate or upper floor of a building. The thermal insulation layer in the plate element can on its own form the thermal insulation layer of a completed composite slab or additional thermal insulation material can be installed in the composite slab either above or beneath the slab structure. In addition to its primary use purpose, the slab element according to the invention can also be used for other use purposes, such as for plate-like reinforcement structures of tall buildings and for temporary auxiliary structures of construction sites, such as scaffolding or bridge structures crossing ditches and excavations.

[0035] Some advantageous embodiments of the slab element, composite slab and method according to the invention have been described above. The invention is not limited to the solutions described above, but the invention can be applied in different ways within the scope of the claims.

Claims

1. A slab element, which comprises a surface plate (10), which surface plate has gripping members (16) for gripping a concrete casting, a bottom plate (12) and an insulation layer (14) between the surface plate and the bottom plate, characterised in that it additionally comprises at least one elongated tensile stress member (36) in the insulation layer.

2. The slab element according to claim 1, characterised in that said tensile stress member (36) is in the insulation layer (14) in the part delimited by the neutral axis (N) of the cross-section of the slab element and the bottom plate (12).

3. The slab element according to claim 1 or 2, characterised in that the slab element has a first end (30a) and a second end (30b) and said tensile stress member (36) extends from the first end to the second end.

4. The slab element according to claim 3, characterised in that the first end (30a) has a first end profile (32) and the second end (30b) has a second end profile (32) and the tensile stress member (36) has a first end, which is attached to the first end profile, and a second end, which is attached to the second end profile.

5. The slab element according to claim 4, characterised in that said end profiles (32) are U-profiles, which have a web plate (34) forming the end of the slab element.

6. The slab element according to any of the claims 1-5, characterised in that the first and/or second end of the tensile stress member (36) has a tightening member for producing tensile stress in the tensile stress member.

7. The slab element according to claim 6, characterised in that said tensile stress member (36) is a flexible wire, advantageously a steel wire, and said tightening member is a tightening turnbuckle attached to the end of the wire.

8. The slab element according to any of the claims 1-6, characterised in that said tensile stress member (36) is a rigid bar, advantageously a steel bar.

9. The slab element according to claim 8, characterised in that at least one end of the bar (36) has threads and the tightening member is a nut fitted onto the threads of the bar.

10. The slab element according to any of the claims 1-9, characterised in that it has a first edge surface (18a) in the longitudinal direction of the slab element and the bottom plate (12) has a lower edge strip (20) extending out from the level of the first edge surface, which strip has an edge seal (22).

11. The slab element according to any of the claims 1-10, characterised in that it has a second edge surface (18b) in the longitudinal direction of the slab element and the surface plate (10) has an upper edge strip (24) extending out from the level of the second edge surface.

12. The slab element according to any of the claims 1-11, characterised in that the insulation layer (14) is made of a hard thermal insulation material, such as polyurethane, polystyrene, extruded polystyrene or hard mineral wool and the insulation layer is attached in a fixed manner to the surface plate (10) and bottom plate (12).

13. A composite slab, which comprises a plane (50) constructed from slab elements and a concrete slab (100) cast onto the plane, characterised in that said plane is formed from a group of slab elements according to any of the claims 1-12, set beside each other.

14. A method for forming a composite slab, which method comprises forming a plane (50) from slab elements and casting a concrete slab (100) onto the plane, characterised in that said plane is formed by setting a group of slab elements according to any of the claims 1-12 beside each other.

15. The method according to claim 14, characterised in that the slab elements are formed to curve upwards before the concrete slab (100) is cast, by tightening the tensile stress members (36) in the slab elements.

Drawing