GB2484531A - Concrete floor panel with ribs - Google Patents

Abstract

A concrete floor panel 100 for use in constructing modular buildings for example multi-storey car parks, the panel comprising a substantially flat upper surface and, depending from a lower surface, a plurality of supporting ribs 110 running along substantially the entire length of the panel, said ribs having a central portion 130 not formed of concrete and said ribs comprising a plurality of cables 140 for pre- stressing the concrete. The central portion of the ribs 130 may be a void, for example a hollow, or may contain polystyrene, plywood or a plastics material. A method of manufacturing the panel is also claimed, which includes forming a mould defining a plurality of supporting ribs, disposing within the rib portion of the mould void formers, placing a plurality of cables in the vicinity of the void formers and filling the mould with wet concrete.

Description

Improvements in and relating to Concrete Floor Panels This invention is concerned with modular concrete floor panels for use in the construction of a variety of different buildings. They find particular, but not exclusive, use in the construction of multi-storey car parks or parking garages, although they may be used in a wide variety of constructions projects.

In recent times, multi-storey buildings have been constructed using a variety of techniques which rely upon utilising components which are constructed off-site, and which are then transported to the site and assembled in situ by use of appropriate machinery such as gantry cranes, together with labour. The use of pre-constructed components generally allows for a more efficient building process, requiring fewer personnel on-site and a more controlled standard off basic build quality.

However, certain limitations in existing components tend to place an unwelcome constraint on the design and construction of buildings and it is an aim of embodiments of the present invention to address these shortcomings and others not mentioned specifically herein.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 shows a cross-sectional view of a prior art double-tee floor unit; Figure 2 shows a cross-sectional view of a first embodiment of the invention; Figure 3 shows a partial cross-section through a rib of an embodiment of the present invention; Figure 4 shows a partial cross-section through a rib of an embodiment of the present invention, showing the strand pattern of the pre-stressing cables; and Figure 5 shows a partial cross-section through a rib of another embodiment of the present invention, showing the strand pattern of the pre-stressing cables.

Figure 1 shows a prior art precast concrete floor panel, known as a double-tee unit. As can be seen from Figure 1, the unit 1 is so named due to its cross sectional appearance resembling two upper case letter "T"s side by side. In a typical multi-storey car park construction, three such units are arranged side by side to give a total bay width of 7.2 metres, each unit having a width of 2.4 metres. The height of the unit is 715mm. The height is largely dictated by the rib 10 and this height is required in order to give sufficient structural strength and rigidity to the unit and is an important part of the overall design. However, this height of 715mm has a number of drawbacks. In particular, the building design typically stipulates a floor to ceiling clearance height and this must be from the floor surface to the underside of each rib 10, meaning that there is a significant portion of ceiling space which is effectively unusable i.e. the part 20 located between the ribs. The rib or vertical portion 10 of the "T" also creates an aesthetically unappealing part of building design and creates problems of shadowing when light fittings are installed in the valleys 20 between the vertical portions 10 of the "T"s.

The so called double-tee units I are typically constructed from pre-stressed concrete and are provided on their upper surface with an unfinished, i.e. rough, surface 30. This surface is not suitable for a finished building and so once the construction is basically complete, the exposed surface requires a further screed topping to provide a suitably smooth and finished surface for traffic to drive upon. This typically adds a further 75mm to the surface of the floor.

Presently, the double-tee unit 1 is a basic accepted building block for many construction projects, in spite of the shortcomings as set out herein and others associated with it.

Embodiments of the present invention provide many advantages over the prior art double-tee unit described previously.

Figure 2 shows a cross-section through a floor panel 100 according to an embodiment of the present invention. As can be seen, the floor panel 100 comprises three substantially vertical ribs 110 descending from the lower surface of the floor panel, rather than the two in the prior art. It can also be seen that the depth of the floor panel is significantly smaller than the prior art and the individual ribs are a little wider. The overall depth is of the order of 400mm, compared to 715mm in the prior art. As can be appreciated, this shallower floor panel 100 contributes to a reduction in the overall building height whilst maintaining specified floor to ceiling heights for a particular project. This reduction in building height offers significant savings in the cost of the structure itself but also has consequential benefits in reduced costs of cladding, services and various other aspects of the build.

It will be noted that a construction using floor panels according to an embodiment of the present invention requires significantly fewer individual floor panels than a similar construction using the prior art double-tee unit 1. This, again, has significant advantages in terms of a more speedy construction, and a cheaper one, since fewer crane lifts are required in order to position the individual panels into position. Since the units are constructed off-site and then transported to the construction site, fewer journeys will be required to transport the floor units to the construction site and this has a cost saving and a consequentiai environmental benefit.

The use of fewer floor panels also results in a reduction in the overall number of construction joints, reducing costs again and also reducing possibilities for errors or construction problems.

In order to manufacture a floor unit 100 according to an embodiment of the present invention, it is desirable to minimise, where possible, the weight of the unit so that it continues to meet stringent building regulations regarding strength and load-bearing ability, but is also able to be constructed and transported with no significant problems.

In order to address the weight issue, the rib elements 110, which run along the entire length of the floor unit, utilise a polystyrene void former 130 which is positioned in a central portion of the rib elements 110. The void former 130 is a trapezoidally-shaped polystyrene element which sits within the construction mould such that the central portion of each individual rib 110 is formed not from concrete but from polystyrene. Alternatively, other lightweight void formers could be used instead of polystyrene. Examples of these include plywood or plastics materials, which can be used to define a physical void within the structure.

The use of voids within concrete structures is known, but the inventor in the present application is unaware of any prior art where voids are formed within supporting ribs, since the prevailing prejudice in the industry is that such a structure would not possess sufficient mechanical strength to conform to building specifications.

Figure 2 shows a flooring element having three separate reinforcing ribs, which are substantially equispaced but, as will be appreciated, embodiments of the invention may have more or fewer ribs, positioned as required by the particular application. The particular example shown in Figure 2 is l6metres long and 3.6metres wide. This is significantly larger than a typical prior art double T unit, which offers the benefits set out previously.

The ribs run along substantially the entire length of the panel. However, they may be configured such that there is a relatively short length at each end of the panel with no rib, with this area being provided to sit atop a beam or column for supporting the entire panel.

Figure 3 shows a partial cross-section through one of the supporting ribs 110 of the embodiment shown in Figure 2. This view shows the shape, relative size and location of the void 130 formed in the concrete of the rib 110. The polystyrene-filled void is essentially trapezoidally shaped, having an upper edge of 158mm, a lower edge of 86mm and a height of 205mm. Also marked on Figure 3 are three dimensions: A, B and C. A is the thickness of the upper surface of the panel, also known as the biscuit. B is the thickness of the lower planar section of the rib 130. C is the overall height or depth of the panel from the exposed upper surface to the base of the rib.

The panel described has a span (or length) of 16m, and a width of 3.6m. In order to provide a specified load bearing capacity of 2.SKNm2 which is suitable for use in a car park deck supporting cars and other light vehicles, then A, B and C can be, respectively, 95mm, 100mm and 400mm.

In a further embodiment, having a much greater load-bearing capacity of 12.5KNm2, which can be used as decking for a structure able to support articulated trucks, buses, coaches and the like, the span is still 16m, the width is 1.875m and A, B and C are, respectively, 115mm, 160mm and 825mm. A different strand pattern is required in this embodiment, due to the greater forces which will be experienced. A suitable strand pattern is shown in Figure 5. This shows a greater concentration of pre-stress cables provided in the lower region of the rib, to provide greater strength in this region.

To construct the floor panel 100, wet casting techniques are used. Wet concrete is poured into a suitable mould, and a polystyrene void former 130 is already located in each rib of the mould, positioned so as to form a central void as shown in Figure 3.

In order to further enhance the strength of the precast concrete unit 100, pre-stressing is used during the formation of the unit. A plurality of pre-tensioned steel cables are positioned in the mould before concrete is poured in such that once the concrete sets and the external tension on the steel cables is released, the pre-stressed cables serve to add considerable strength and rigidity to the floor unit 100 in a known manner.

Figure 4 shows the location of the pre-stressing cables 140, which are used to surround the void 130. A total of nine cables are provided: two are positioned near the upper edge in the vicinity of each upper corner; three are positioned equispaced near the lower edge; and a further four are positioned in pairs in the vicinity of the lower half of the void 130. Of course, different arrangements of strand pattern will be apparent to the skilled person and these can be adjusted to provide the desired mechanical strength.

In the strand pattern shown in Figure 4, the load on each of the nine strands is 118KM.

Each strand has a diameter of 12.5m For a typical unit 100, which measures approximately 16 metres (length) x 3.6 metres (width) x 400mm (depth), a weight saving of approximately 3000Kg can be achieved by use of voids within the ribs. This makes the unit more practicable, especially during manufacture, transport to the site and assembly. This sort of weight saving has further advantageous effect in the design and construction of the building. For instance, the weight saving can ease the requirements for foundations and other supports. The saving in concrete also offers a cost saving over a unit constructed entirely from concrete.

Compared to a similarly sized and specified building, constructed using prior art double tee units, a saving of 10% in the amount of concrete required can be achieved by use of embodiments of the present invention. This has corresponding savings in terms of costs, environmental impact, transport and assembly time on-site.

The valleys 120 between the ribs 110 are shallower than in the prior art unit 1, meaning that lighting can be fitted here more readily and with less shadowing than is the case in the

prior art.

The upper surface of the unit 100, which is exposed in use, is prepared to be regular, smooth and does not require any further layers of screed or other finish. The gaps between adjacent units merely require grouting, and then the floor surface is ready for traffic. This lack of a need to finish the surface saves time, money and does not restrict the specified floor-ceiling clearance.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disciosed.

Claims (11)

1. CLAIMS1. A concrete floor panel for use in constructing modular buildings, comprising a substantially flat upper surface in use and, depending from a lower surface, a plurality of supporting ribs running along substantially the entire length of the panel, said ribs having a central portion not formed of concrete and said ribs comprising a plurality of cables for pre-stressing the concrete.
2. 2. The concrete floor panel of claim I comprising three ribs, substantially equispaced.
3. 3. The concrete floor panel of claim 1 or claim 2 wherein the central portion of said ribs is formed from a void former comprising a material other than concrete.
4. 4. The concrete floor panel of claim 3 wherein the material is one or more of polystyrene, plywood or a plastics material.
5. 5. The concrete floor panel of any preceding claim wherein each rib tapers from a relatively wide end adjacent the lower surface to a relative narrow end.
6. 6. The concrete floor panel of any preceding claim wherein the plurality of cables are distributed substantially uniformly within the concrete portion of each rib.
7. 7. The concrete floor panel of any preceding claim wherein the thickness of the biscuit is in the range: 95-115mm.
8. 8. The concrete floor panel of any preceding claim wherein the thickness of a lower substantially planar portion of each rib is in the range: 100-160mm.
9. 9. The concrete floor panel of any preceding claim wherein the overall depth of the panel is in the range: 400-825mm.
10. 10. A method of manufacturing a concrete floor panel for use in constructing modular buildings, comprising the steps of: forming a mould, defining a plurality of supporting ribs; disposing within the mound a plurality of void formers, located within the areas defining the ribs; providing a plurality of pre-stressing cables in the vicinity of the void formers; and filling the mould with wet concrete.
11. 11. The concrete floor panel as hereinbefore described having particular reference to Figures 2-5 of the accompanying drawings.