GB2534033A - Casting concrete steps or stairs - Google Patents

Abstract

The framework for casting a concrete staircase or steps in-situ has a corrugated base 1 with trapezoidal corrugations running along its length, side walls 3, and a number of risers 4 running between the side walls and across the base, the frame forms part of the finished stairs when concrete is poured in and has set. The side walls and base may be made from sheet steel between 0.5 to 3mm in thickness. The base may be formed from corrugated deck, having preferably between three and six corrugations, with a height between 2 to 10% the width of the stairs. The dividing walls may be sheet metal and have tabs which engage with slots in the side members. The underside of the base may have fire resistant board placed over it to conceal the corrugated base.

Description

CASTING CONCRETE STEPS OR STAIRS

This invention relates to casting concrete steps or stairs and in particular to an improved framework for use therein.

There are many building applications in which it is desired to provide a flight of steps or stairs. A widely used construction for such stairs is one in which the stairs are cast using concrete or the like material, into a space defined by suitable shattering or boarding. It is also known to produce complete stair or stair and landing units as an integral reinforced concrete casting. Such units are necessarily heavy and require transportation to the site where they are to be installed and then to be set in position, usually using a crane capable of lifting the substantial weight concerned.

In the case of in situ casting, a simple process which is widely used is to construct, using standard formwork, a sloping base with a series of substantially vertical plates running crosswise to the direction of inclination, each of which plates constitutes a wall defining the riser of each step when the concrete is poured and set. The sides of the intended stairway are defined by further pieces of formwork and concrete is then cast into the inclined trough so formed and allowed to set. Because of the weight of the concrete, it is customary to support the sloping base using appropriate struts and beams which, after the concrete has been poured and allowed to set and acquire its design strength, may then be removed. Since setting and curing of in situ poured concrete takes a considerable amount of time, such an approach requires the support struts and beams to be left in place during setting and curing, which require temporary support design and health and safety review, as well as being inconvenient and hampering access to the area below the stairway for some time. It is not unknown for the setting and curing process to take up to 28 days. A system of this type is disclosed in US-A-1703633.

It is also known to provide formwork for supporting the concrete while it is setting and which becomes incorporated into the final stairway, i.e. it is not removed after the concrete has set. Such constructions are generally costly and complex and consist of a set of parallel beams, for example as disclosed in US-A-4250672, US-A-2012/0167521 and GB-A-2038394.

In accordance with a first feature of the present invention, we provide a framework for use in making an in situ cast concrete set of stairs or steps which comprises a base member, side members, and a plurality of dividing walls running across the base member and between the side members to define risers in the finished stairs or steps, and wherein the base member comprises a corrugated sheet with trapezoidal cross-sectional corrugations running along the length of the sheet. The framework forms part of the finished stairs or steps. A framework according to the present invention is preferably of simple structure, and can be easily manufactured to order once the dimensions required are known. It is relatively light in weight and can be rapidly placed into position where the steps or stairs are to be located. Compared to the cost of the prior art structures made up of parallel beams, it is less expensive.

We have found that by using appropriate material for the base and side members, usually sheet steel or aluminium of thickness 0.5 to 3mm, it is possible to provide a structure which, for the conventional length of a stair run between adjacent levels in a building, e.g. from one floor level to the next, typically incorporating mid-landing areas, because of the corrugations, will not sag materially when concrete is poured into it. The sheet may be made by folding flat metal sheet to provide the desired trapezoidal corrugation, or, in the case of aluminium alloy, extruded.

According to a further feature of the present invention, there is provided a method of constructing an in situ concrete stairway which comprises providing a framework as described above, installing it in situ where desired in the building structure, for example bridging the distance between two adjacent floors or stair landing areas, pouring concrete into the top of the framework to a level at or around the top of each riser-defining member, and allowing the concrete to set and cure.

By using appropriate materials and substantial trapezoidal corrugation we have found there is no need to prop up the framework or support it in any other way than by its upper and lower ends for stairs of a specified length. The trapezoidal corrugated base member sheet may be a standard trapezoidally corrugated deck, commercially available from a variety of suppliers. So-called "composite deck" works well as it has nodules and ledges formed in it to provide additional strength and an improved key between the set concrete and the base member sheet itself.

Although it is possible to incorporate reinforcement rods or the like within the space defined by the framework, in order that the set concrete is itself reinforced rather than merely set in an external frame, for most applications this is simply not necessary when using the present invention.

For given design considerations in terms of size and load-bearing capacity, it is also possible, compared with customary in-situ cast concrete stair systems, to achieve the desired results using less concrete.

The invention is illustrated by way of example with reference to the 25 accompanying drawings in which: Figure 1 is a perspective view of a framework unit in accordance with the present invention, seen by an observer on a level with the lower end of the framework and Figure 2 is a side view of the same unit.

Referring to the drawings, the framework consists basically of an elongate trapezoidally corrugated baseplate 1, two vertically upstanding sidewalls 2,3, and a series of riser-defining plates 4 bridging the space between the sidewalls and the base plate. Each plate 4 is fixed to tie bars 6 which run parallel to the direction of elongation of the corrugated base plate 1. The number and length of the tie bars 6 may vary and they may be omitted altogether if the riser plates 4 are sufficiently rigid. At the top and bottom of baseplate 1 are end plates 7 welded between sidewalls 2 and 3 and to the ends of baseplate 1.

The riser plates 4 are preferably welded at their ends to the internal face of each of the sidewalls 2, 3, and at their lower edges to the tie bars 6. In order to assist assembly of the riser plates and sidewalls prior to welding, the edges of the riser plates may have slightly projecting tabs and the sidewalls have corresponding slots in them into which the tabs locate. The slots in the sidewalls are preferably produced by laser cutting.

In order to prevent the risers bowing when concrete is poured into the framework, the top and bottom of each riser plate 4 is bent over to form a rim which renders the plate 4 resistant to bending. If the riser plate has tabs as noted above, these are conveniently an extension of each of the rims, i.e. the tabs are not top and bottom corners of each riser plate.

The tie bars 6 or end plates 7 can act as lifting points or handles to enable 25 the framework to be more easily located in position where desired in the intended structure.

The number of trapezoidal corrugations in the baseplate 1 may vary, as may their size. We have found that it is preferable to have at least three corrugations, generally not more than six. The height of the corrugations may be varied to suit design requirements but is generally between 2 and 10% of the width of the stair.

The underside of the framework is corrugated, i.e. the corrugations in the base plate 1 are visible, which is not necessarily desirable but may be acceptable in certain situations, for example in cast concrete fire escape towers. However, it is straightforward to provide a planar sheet material across the entire underside of the framework, which need not necessarily be made of metal but which may be affixed to the underside by any convenient means, for example welding or gluing using an appropriate adhesive. It is preferred to affix the sheet material to the underside of the corrugated base plate 1 before the framework is placed in position and concrete cast on it. In order to avoid any undesired ingress of unset concrete into the spaces between the corrugated base plate and the sheet material, these spaces between them may be filled e.g. with a hard-setting expandable foam material after the planar sheet material is attached but before the installation 15 of the framework and the pouring of the concrete.

The planar sheet material covering the underside may be of an appropriate fire-retardant board to improve the fire-resistance of the stairway.

In practice the use of a framework as described above and as illustrated in the drawings, means that stairs between adjacent floors in a building can be quickly and simply installed as it is constructed, and although they may not be ready to bear the full design load until the concrete has set and cured, this can take place without any encroachment on the space below the stair so that access to that space is unencumbered and available for continuing the building work. After an appropriate period of time, the cast concrete treads may be finished in known fashion, for example by the application of tiling or other floorcovering material, step edges and the like.

Claims (5)

1. CLAIMS1. a framework for use in making an in situ cast concrete set of stairs or steps which comprises a base member, side members, and a plurality of dividing walls running across the base member and between the side members to define risers in the finished stairs or steps, and wherein the base member comprises a corrugated sheet with trapezoidal cross-sectional corrugations running along the length of the sheet. The framework forms part of the finished stairs or steps. A framework according to the present invention is preferably of simple structure, and can be easily manufactured to order once the dimensions required are known. It is relatively light in weight and can be rapidly placed into position where the steps or stairs are to be located. Compared to the cost of the prior art structures made up of parallel beams, it is less expensive.
2. 2. A framework according to Claim 1 wherein the base and side members are formed of sheet steel or aluminium of thickness 0.5 to 3mm.
3. 3. A framework according to Claim 1 or 2 wherein the trapezoidally corrugated sheet is corrugated deck.
4. 4. A framework according to any one of Claims 1 to 3 wherein the dividing walls are formed of sheet metal and have tabs at their edges engaged in slots in the side members.
5. 5. A method of constructing an in situ concrete stairway which comprises providing a framework according to any one of Claims 1 to 4, installing it in situ where desired in the building structure, pouring concrete into the top of the framework to a level at or around the op of each riser-defining member, and allowing the concrete to set and cure.