GB2306526A

GB2306526A - Floor decking

Info

Publication number: GB2306526A
Application number: GB9522456A
Authority: GB
Inventors: Keith Kendal
Original assignee: RICHARD LEES STEEL DECKING Ltd
Current assignee: RICHARD LEES STEEL DECKING Ltd
Priority date: 1995-11-02
Filing date: 1995-11-02
Publication date: 1997-05-07
Anticipated expiration: 2015-11-02
Also published as: MY112344A; GB2306526B; GB9522456D0

Abstract

A profiled decking sheet (10) for use in concrete flooring. The sheet includes embossments or corrugations (15), produced by embossing the sheet (10), which enhance the strength of the sheet (10) at regions thereof which are subjected to the highest levels of stress. Also a method for the production of such profiled decking sheets.

Description

FLOOR DECKING This invention relates to floor decking. In particular, but not exclusively, it relates to sheeting used in floor decking and methods for manufacturing such sheeting.

In the construction of many buildings, typically commercial and industrial buildings, the floor of each storey is formed of so-called "composite floor decking". Such composite floor decking is constructed by pouring fluid concrete onto a profiled sheet or decking profile of galvanised steel, which provides an initial soffit shutter to the concrete. On drying, the concrete mechanically grips the sheet via friction and interlock to form a structurally-efficient, loadcarrying floor slab.

The profiled steel sheet relies on its inherent strength and stiffness in providing the initial shuttering function, whereas, when the concrete has hardened, the sheet contributes to the overall composite properties of the floor and contributes to the necessary tensile reinforcement of the concrete slab.

It is when the profiled metal sheet has to support the weight of the wet concrete that it is subjected to the severest structural stress levels and strength demands. Consequently, the structural properties of the profiled sheet can determine the permissible span of the final floor decking, or the spacing of any temporary propping of the floor decking.

It follows that it is desirable to have a profiled sheet with the maximum possible strength. Thus, investigations have been made into improving the strength of profiled sheets by optimising the shape of the profiles and including strategically-located stiffeners. When making these investigations, problems specific to the function of the profiled sheet in composite floor decking must be considered. For example, the trough volume of the profile must be kept relatively small, otherwise more concrete will be required to fill these troughs and the resulting floor slab will be less economic. Many of the profile configurations resulting from these investigations (known as "super-stiffened configurations") suffer from the disadvantage that they require more metal to produce the profile configuration.

Typical composite floor decking profiles are rollformed from galvanised steel of 0.8 to 1.2 mm nominal thickness, currently complying with BS EN 10147:1992 using strength grades designated Fe E 250 G to Fe E 350 G with a Z275 galvanised coating mass. This material has a guaranteed yield strength of 250 to 350 N/mm2 and can be satisfactorily processed on conventional rollforming lines.

In order to improve the strength of a profiled sheet, steel with a higher strength grade and/or thickness could be used. However, an increase in these properties may mean that the steel could not be processed on conventional roll-forming lines.

Furthermore, steel with a higher strength grade and/or thickness costs more and means that the floor decking becomes less economic.

The cross-sectional properties of a decking profile are a function of the cross-sectional geometric shape and, in particular, the behaviour of the parts of the profile that are subjected to compressive and tensile stresses. The performance of these parts is related to the breadth to thickness ratio and the plate edge conditions. If these parts could be made to sustain induced stress levels approaching the yield strength of the material without buckling prematurely, then the structural properties of the profile would be improved. However, in known decking profiles, the compressive plates can never achieve full yield, due to instability and premature buckling and consequently are, in effect, inefficient in the use of material.

According to a first aspect of the present invention, there is provided a sheet for use in floor decking, which sheet, in use, acts to retain a hardenable material when the hardenable material is in an unhardened state and to reinforce the floor decking when the hardenable material is in a hardened state, the sheet having a substantially uniform thickness and having one or more deformations out of the plane of the sheet, at least a part of the or each deformation having corrugations.

In one embodiment, the part of the sheet having corrugations has respective upper and lower surfaces the cross sections of which are in the form of a substantially sinusoidal wave. In this embodiment, the ratio of the wave-height of said wave to the wavelength of said wave is preferably in the range 1:5 to 1:10, more preferably in the range 1:8 to 1:9, and most preferably 1:8.33.

The thickness of the sheet may be at most about five times, preferably about twice, the wave-height of said wave. Moreover, the or each deformation may be trapezoidal in section.

According to a second aspect of the present invention, there is provided floor decking comprising a sheet according to the first aspect of the invention and a hardenable material.

Preferably, the sheet is of metal and the hardenable material is concrete.

According to a third aspect of the present invention, there is provided a method of manufacturing a sheet for use in floor decking, comprising: providing at least a part of the sheet with corrugations; and deforming at least the part of the sheet having corrugations out of the plane of the sheet.

The steps of providing corrugations and deforming the sheet may be performed simultaneously. The corrugations may be provided by embossing the sheet.

Preferably, the corrugations are provided and the sheet is deformed by one or more pairs of shaped, mating rollers.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1 is a perspective cut-away view of typical prior art floor decking; Figures 2a and 2b are schematic end views of mating rolls used in the manufacture of the profile of Figure 1; Figure 3 is a schematic sectional view of the profile of Figure 1 illustrating the compression and tension stresses borne by the profile when under load; Figure 4 is a schematic end view of a floor decking profile in accordance with the present invention; Figure 5 is a partial perspective view of the profile of Figure 4; Figure 6 is an enlarged end view of a part of the profile of Figure 4; Figures 7a-d illustrate stages in the manufacture of the profile of Figure 4.

Referring to Figure 1, prior art floor decking 1 typically comprises concrete 2, which may be reinforced with a steel mesh 3 or the like, and a profiled metal sheet 4. Sheet 4 is typically of thin gauge, hot dipped galvanised steel strip which has been cold rolled so that it has a pattern of deformations or "profiles" 5 which enhance its strength. Sheet 4 may also include protrusions 6 from its surface, the function of which will be described below.

The floor decking is constructed by pouring fluid concrete onto sheet 4, which provides an initial soffit shutter to the concrete. On drying, concrete 2 mechanically grips the sheet 4 via friction, deformations 5 and protrusions 6 to form a structurally-efficient, load-carrying floor slab.

Referring to Figure 2a, sheet 4 can be manufactured by passing a web 7 of galvanised steel between one or more sets of mating rolls each comprising top roll 8a and bottom roll 8b both of which are driven. Alternatively, as shown in Figure 2a, the sheet can be formed by a disc-forming line, in which the web 7 is passed between upper and lower discs 9a,b, neither of which are driven. The roll-forming folds and displaces the metal at various locations to create the basic desired profile shape, and in doing so the metal is manipulated at the fold points. Once these fold points are established, gradual folding takes place, typically in 15 to 25 separate operations. The fold points undergo a strain hardening or cold-working which locally enhances the properties of the metal.

However, this working is uncontrolled and causes a decrease in the thickness of the metal at the fold points. Also, the metal is not worked, and hence enhanced, in areas remote from these fold points.

The manner in which composite floor decking profile 4 bears the load of concrete is complex but can most easily be described as an array of stress levels that are induced into various "plates" of the profile.

This is shown diagrammatically in Figure 3, in which T represents tension stresses and C represents compression stresses. To a large extent, the structural properties of the profile depend on the stress levels that can be borne by the various plates of the profile, particularly those plates which bear compressive stresses. If these plates can be made to sustain induced stress levels approaching the yield strength of the metal without buckling or deforming prematurely, then the structural properties of the profile would be at a maximum.

However, in conventional composite floor decking profiles such as that illustrated in Figure 1, the plates, and particularly those that are compressed, never achieve full yield because of instability and premature buckling. Consequently, these plates are, in effect, an inefficient use of metal. As mentioned previously, for a given profile shape, a higher strength and stiffness can be achieved by increasing the strength grade and/or thickness of the metal.

However, in addition to the problems that this may cause with conventional roll-forming plant, it may not be consistently effective because the stress distributions through the profile are not constant and uniform.

Referring now to Figure 4, a sheet 10 in accordance with the present invention includes a series of deformations or profiles 11 out of the plane 12 of the sheet 10, each of which includes a "V"-shaped portion 13 extending towards the plane 12. In the illustrated embodiment, deformations 11 have a trapezoidal shape, the non-parallel sides of the trapezoid diverging towards plane 12. In an alternative embodiment, sheet 10 has trapezoidal deformations in which the non-parallel sides of the trapezoid converge towards plane 12: such a profile is known as a "re-entrant" profile. Sheet 10 also includes protrusions 14 (see Figure 5), which act as shear keys for concrete poured onto sheet 10 in the construction of a composite floor deck.

In the regions around the intersections of the surfaces of sheet 10 which are parallel to plane 12 and the surfaces of sheet 10 which are transverse to plane 12, sheet 10 includes corrugations or embossments 15.

As seen from Figure 3, it is these regions that are subjected to the highest stresses when the profile is loaded.

Referring now to Figure 6, it will be seen that corrugations 15 are substantially sinusoidal in cross section and that sheet 10 has a substantially uniform initial thickness, ti. The effect of the corrugations 15 is locally to increase the effective thickness, tet and thus the strength of sheet 10. In the illustrated embodiment, the ratio of the wave-height, e, to the wavelength, P, is in the range 1:8 to 1:9, preferably 1:8.33. The ratio of the initial thickness, ti, of the sheet 10 to the wave-height e, is about 2:1, preferably 1.67:1. Te is approximately 30% greater than Ti. The minimum extent of the "bank" of the embossments is preferably not less than about 10 (10 x p).

Sheet 10 is typically of hot dipped, galvanised steel and, in one example, has a thickness in the range 0.8 to 1.2 mm. The galvanised layers are 0.02 mm thick and the steel is 0.76 to 1.16 mm thick.

A profiled sheet with strategically-located embossed corrugations which have a uniform thickness may have a strength which is up to 30% greater than a sheet without such corrugations. This enables steel with a lower strength grade and a lower thickness to be used in a composite floor deck, thus resulting in significant cost savings. Alternatively, such an embossed profiled sheet could be formed from steel of conventional strength and thickness and cost savings could be made by virtue of the increased span that the additional strength of the sheets allows.

Sheet 10 is manufactured using a modified rollforming technique, in which embossments 15 are formed by a set of mating, single-pass, powered rolls provided with respective mating projections and recesses such that the metal is embossed in certain areas with corrugations 15 which locally increase the strength of the steel. These rolls manipulate the metal by stretching, folding and extruding in such a way that the thickness of the finished worked area is substantially uniform. The worked areas undergo a strain hardening, or cold working, which enhances the strength of the metal. Thus, in addition to the strength enhancements provided by increasing the effective thickness, tel , of the metal sheet, the areas which are embossed also undergo a controlled strain hardening.

In a roll-forming line, the process of embossment may be carried out after the shape of the profile has been formed, but before length cutting. In discforming lines, embossment may be carried out on the strip of metal before it is profiled. Referring to Figure 7, it can be seen that the respective sets of discs gradually deform the web into a profiled shape.

Protrusions 14 which, as mentioned above, act as shear keys to concrete, may also be formed by embossing.

In the conventional manner of roll-forming profiled sheets, the metal is only manipulated in the areas where it is folded to form the profiles. In these areas, the thickness of the metal is thinned, and thus weakened, by the folding. Remote from these fold points, the metal is not worked or stretched and therefore its strength is not enhanced in any way.

However, in the present invention, the process of embossing sheet 10 hardens the metal and increases its effective thickness, te, in areas which are to be subjected to the greatest stress.

Claims

CLAIMS:

1. A sheet for use in floor decking, which sheet, in use, acts to retain a hardenable material when the hardenable material is in an unhardened state and to reinforce the floor decking when the hardenable material is in a hardened state, the sheet having a substantially uniform thickness and having one or more deformations out of the plane of the sheet, at least a part of the or each deformation having corrugations.

2. A sheet as claimed in claim 1, wherein the part of the sheet having corrugations has respective upper and lower surfaces the cross sections of which are in the form of a substantially sinusoidal wave.

3. A sheet as claimed in claim 2, wherein the ratio of the wave-height of said wave to the wavelength of said wave is in the range 1:5 to 1:10.

4. A sheet as claimed in claim 3, wherein the ratio of the wave-height of said wave to the wavelength of said wave is in the range 1:8 to 1:9.

5. A sheet as claimed in claim 4, wherein the ratio of the wave-height of said wave to the wavelength of said =ve is 1:8.33.

6. A sheet as claimed in any one of claims 2 to 5, wherein the thickness of said sheet is at most about five times the wave-height of said wave.

7. A sheet as claimed in claim 6, wherein the thickness of said sheet is about twice the wave-height of said wave.

8. A sheet as claimed in any preceding claim, wherein the or each deformation is trapezoidal in section.

9. A sheet for use in floor decking substantially as hereinbefore described with reference to and as shown in Figures 4-7 of the accompanying drawings.

10. Floor decking comprising a sheet as claimed in any preceding claim and a hardenable material.

11. Floor decking as claimed in claim 10, wherein the sheet is of metal and the hardenable material is concrete.

12. A method of manufacturing a sheet for use in floor decking, comprising: providing at least a part of the sheet with corrugations; and deforming at least a part of the sheet out of the plane of the sheet.

13. A method as claimed in claim 12, wherein the step of providing corrugations is performed before the step of deforming the sheet.

14. A method as claimed in claim 12, wherein the step of providing corrugations is performed after the step of deforming the sheet.

15. A method as claimed in claim 12, 13 or 14, wherein the corrugations are provided by embossing said sheet.

16. A method as claimed in any one of claims 12 to 15, wherein the corrugations are provided by one or more pairs of shaped, mating rollers.