GB2042616A

GB2042616A - Reinforcement for Cast Concrete Beams

Info

Publication number: GB2042616A
Application number: GB7943612A
Authority: GB
Original assignee: GKN Mills Building Services Ltd
Current assignee: RMD Kwikform Ltd
Priority date: 1979-01-11
Filing date: 1979-12-18
Publication date: 1980-09-24

Abstract

The reinforcement comprises elongate steel reinforcing bar(s), e.g. steel, having primary bar(s) 34 and secondary reinforcing bar(s) 36, spaced, e.g. vertically, from one another and connected together, e.g. by a sinusoidal steel wire 38. The building reinforcement as used in the production of downstand beams of one-way or two-way spanning concrete floors is located adjacent moulds 10. The primary reinforcing bar(s) 34 are spaced from the support structure in such manner that the primary bar(s) 34 and the secondary bar(s) 36 are spaced from the side walls of adjacent moulds 10 and above the support structure 12 so as to be totally embedded within the concrete when it is poured over and between the moulds. Specification GB 1371786 is referred to. <IMAGE>

Description

SPECIFICATION Concrete Reinforcement This invention relates to reinforcement for concrete structures such as cast concrete beams and particularly, but not essentially, to reinforcement for concrete beams in one way or two way spanning concrete floors. Floors of this type may be constructed for example using formwork comprising generally channel shaped moulds and support structure therefore of the type described in our British Patent 1 371 786.

In use of such formwork, the moulds are positioned in side by side relation on support structure with the mouths of the channels facing downwardly and then concrete in flowable condition is poured over and around the moulds.

When the concrete is set, the moulds are removed downwardly so that a concrete floor having a plurality of recesses in its under surface corresponding to the shape of the moulds is achieved.

Concrete beam elements between adjacent recesses are provided in the floor by the concrete which flows between the moulds and onto the support structure and to strengthen these beam elements it is customary to locate reinforcement between adjacent moulds and spaced upwardly from the support structure before the concrete is poured. Thus the reinforcement which usually takes the form of elongate steel reinforcing bars is embedded within the concrete beam elements when set at positions spaced from the base and side walls of each element.

In BSI "The Structural Use of Concrete", CPi 10 Part 1 1972, there is laid down certain minimum dimensions of concrete cover to the reinforcing bars in structures of the type discussed above. These minima are laid down to afford fire resistance to the structure since, if the reinforcing bars are not effectively heat insulated by the concrete cover thereto, they may become heated to a degree at which the steel becomes plastic, leading to collapse of the structure.

However, if the concrete cover is to that level required to meet the regulations relating to fire exposure of a long duration, it then becomes necessary to provide additional or secondary reinforcing bars below the primary reinforcing bars to key the concrete cover onto the remainder of the concrete structure above the primary reinforcing bars. The secondary reinforcememt is necessary because a large depth of unreinforced concrete below the primary reinforcing bars would be liable to spalling in the event of it being exposed to high temperatures in a fire thus leading to exposure of the primary reinforcing bars with the consequent danger of total collapse of the structure.

Hitherto it has been the practice to support the primary reinforcing bars on small plastic stools standing on the support structure in the channel afforded between adjacent moulds. Similarly, if secondary reinforcing bars are required, these have also been supported on plastic stools standing on the support structure so that the secondary reinforcing bars are in spaced parallel relation with and below the primary reinforcing bars and also spaced above the base of the channel. In order for the secondary reinforcing bars to function to key the concrete cover to the remainder of the structure above the level of the primary reinforcing bars, the secondary reinforcing bars have been interconnected through a steel mesh shaped to conform to the channel section between adjacent moulds.Such mesh provides a flat base containing the elongate secondary reinforcing bars and two side walls extending above the level of the primary reinforcing bars. It will be appreciated that such arrangements result in a complex disposition of reinforcement between adjacent moulds even in a one way spanning system of the type described in British Patent 1371 786. In a two way spanning system, the disposition of the reinforcement becomes even more complex.

It is an object of the present invention to provide a new or improved reinforcement for use in the production of cast concrete beams.

In accordance with one aspect of the invention, there is provided reinforcement for use in cast concrete beams in building structure comprising one or more elongate primary reinforcing members with one or more elongate secondary reinforcing members spaced from the or each primary reinforcing member and connecting means securing said secondary reinforcing members to said primary reinforcing members.

Although the reinforcement described in the preceding paragraph is applicable to use in any cast concrete beam such reinforcement may conveniently be used in building structure of the type comprising a plurality of side by side moulds positioned on support structure and wherein concrete is poured over and between adjacent moulds onto the support structure, the reinforcement being locatable on the support structure between adjacent moulds.

In accordance with a further aspect of the invention, there is provided building formwork comprising a plurality of side by side moulds positioned on support structure and reinforcement located on said support structure between adjacent moulds; said reinforcement comprising one or more elongate primary reinforcing members spaced away from said support structure, one or more elongate secondary reinforcing members spaced from the or each primary reinforcing member and from the support structure and connecting means securing said secondary reinforcing members to said primary reinforcing members.

It will be understood that the support structure may comprise a plurality of elongate members arranged in a horizontal plane with the moulds positioned above such members to define a channel between each pair of adjacent moulds, each channel having side walls provided by the exterior surfaces of the adjacent moulds and a base provided by the elongate member. Thus the reinforcement in accordance with the invention is provided in each channel and is spaced upwardly from the base thereof, such spacing conveniently being provided by a plurality of stools resting on the base of the channel with the or each primary reinforcing member in each channel being mounted on the stools and the secondary reinforcing members also being spaced from the base of the channel.

The primary reinforcing members conveniently comprise steel reinforcing bars whilst the secondary reinforcing members also conveniently comprise steel reinforcing bars but which will usually be of a smaller diameter than the primary reinforcing bars. The connecting means conveniently comprises a steel convolute wire or rod to which the secondary reinforcing member is secured such as by spot welding with the convolute being bent to conform to the diameter of the primary reinforcing member so that it may be suspended therefrom with the secondary reinforcing member in spaced parallel relation with the primary reinforcing member.

For example, the convolute may be a steel wire of zig-zag configuration with the secondary reinforcing member spot welded at intervals along its length to the spaced apices of the wire.

The wire may be bent along a line parallel to the secondary reinforcing member to conform in the diameter of the primary reinforcing member and at a position spaced from the secondary reinforcing member equal to the desired spacing of the secondary reinforcing member from the primary reinforcing member. The spaced bent over apices of the wire i.e., those apices of the wire remote from the apices to which the secondary reinforcing member is secured may then be hung over the primary reinforcing member so that the assembly of wire and secondary reinforcing member is suspended therefrom. The assembly may be secured to the primary reinforcing member by ties or by spot welding.

Also in accordance with the invention there is provided a cast concrete beam including reinforcement extending longitudinally thereof as described in the preceding paragraphs.

Other features of the invention will become apparent from the following description given, herein soley by way of example with reference to the accompanying drawing which shows a part sectioned perspective view of building formwork and reinforcement in accordance with the invention as used in the production of a one-way spanning system concrete floor.

In the drawing there are illustrated two moulds 10 located on support structure 12 as may be used in the production of a one-way spanning system concrete floor. The support structure 12 comprises a plurality of elongate steel sections 14 arranged in parallel side by side relation, each section having horizontally disposed flanges 1 6 on each side thereof for receiving the edges of the moulds 10 in end to end relation along the length of each section 14. Conveniently an elongate intermediate wooden support 1 8 is provided on each flange 1 6 for receiving the edges of the moulds. The web of the section 14 provided a flat horizontally disposed base 20 between adjacent side by side moulds 10.

Each mould 10 may be of the type described in British Patent 1371786 and is conveniently made of polypropylene although if desired it may be made in any other suitable similar synthetic plastics materials.

In order that the weight of the mould be kept to a minimum the thickness of the polypropylene in the mould is kept as small as possible consistant with the mould having sufficient mechanical strength to support the concrete and operatives during use of the mould. Because of the relatively small thickness of the polypropylene mould it is relatively flexible in its transversed direction but the thickness of the polypropylene is chosen so that the mould is sufficiently rigid in its longitudinal direction in order to avoid allowable deformation of the mould in its longitudinal direction. In the case of the mould shown in the drawing the polypropylene is of the order of 5 mm in thickness and this gives the mould the required properties for the particular size thereof.

Each mould 10 comprises two spaced wall portions 22 united by a base portion 24 which merges with the wall portions in a smooth curve.

At one end of the mould there is a part of reduced external and internal cross-section compared with the major part of the mould such that the end part of one mould can be engaged within the other end of an identical mould so that the moulds can be telescoped within one another to a limited extent to enable a iong mould of a desired length to be built up. Two such moulds arranged in end to end telescope relation with one another are shown in the left hand part of the drawing.

Although not illustrated herein the mould is provided internally with a plurality of transversely extending ribs for stiffening purposes. For example the mould may of the order of 400 mm n length with internal stiffening ribs provided at 75 mm intervals. The end of each set of telescoped moulds is provided with an end closure 26 and a stiffened rim 28 extends around the lower periphery of each mould. A fuller description, of a typical mould may be found in British Patent 1371 786.

In use therefore the moulds 10 are positioned on the support structure 12 with the mould rims; 28 resting on the intermediate support members 18, the spacing between adjacent sections 14 being such that the rims 28 of the moulds 10 abut firmly onto the side wall portions of the web of each section to prevent seepage of concrete when it is poured over and between the moulds.

An elongate channel is thus provided between each pair of adjacent side by side moulds having a base 20 provided by the web of a section 14 and side walls 22 provided by the opposed side walls of adjacent moulds. When concrete is poured over and between the moulds a beam 30 is thus cast between adjacent moulds and a plane floor proper 32 is cast above the base portions 24 of the moulds.

In order to strengthen each beam 30 reinforcement is provided between adjacent moulds before the concrete is poured. As illustrated a pair of parallel side by side steel primary reinforcing bars 34 are positioned within the channel and are spaced upwardly from the base 20 and inwardly from the side walls 24. The upward spacing from the base 20 is effected by a plurality of plastic stools, not illustrated, upon which each primary reinforcing bar 34 rests; the plastic stools subsequently becoming embedded into the concrete beam 30 when cast.

To provide secondary reinforcement for the purposes explained heretofor a pair of parallel side by side steel secondary reinforcing bars 36 are also positioned within the channel spaced vertically downwardly from the primary reinforcing bars 34 but upwardly from the base 20 and inwardly from the side walls 24.

Each secondary reinforcing bars 36 is located relative to a respective primary reinforcing bar 34 by a steel wire convolute 38 formed from a zigzag or sinusoidal length of wire to the lower apices of which is spot welded the secondary reinforcing bar 36. The upper apices of the wire 38 are bent over a radius corresponding substantially to the diameter of the primary reinforcing bar 34 so that the secondary reinforcing bar 36 may be suspended from the primary bar 34 in spaced parallel relation therewith. The assembly of secondary reinforcing bar 36 and wire 38 may conveniently be tied or spot welded to its respective primary reinforcing bar 34 to retain the secondary bar 36 in its desired vertically downwardly space relation with the primary bar 34 during pouring of the concrete.

It will be appreciated that any convenient number of primary and secondary reinforcing bars may be provided within each cast beam 30 dependent upon the physical requirement of the cast structure.

Although the embodiment described herein has been with reference to a spanning concrete floor it should be appreciated that the reinforcement of the present invention is applicable to any cast concrete beam structure and is not limited to use in the above described formwork and mould arrangements. Thus the reinforcement may be utilised in concrete beams cast by alternative methods such as for example in the production of concrete beams which are precast in the factory before being used on site in building structures.

Claims

1. Reinforcement for use in cast concrete beams in building structure comprising one or more elongate primary reinforcing members with one or more elongate secondary reinforcing members spaced from the or each primary reinforcing member and connecting means securing said secondary reinforcing members to said primary reinforcing members.

2. Reinforcement as claimed in claim 1 wherein the primary and secondary reinforcing members each comprise an elongate steel bar.

3. Reinforcement as claimed in either one of claims 1 or 2 wherein a said secondary reinforcing member is connected to a said primary reinforcing member by a convolute member to maintain said secondary reinforcing member in spaced parallel relation with said primary reinforcing member.

4. Reinforcement as claimed in claim 3 wherein the convolute member comprises a steel wire or rod of sinusoidal configuration having a said secondary reinforcing member secured thereto at or adjacent the spaced apices of the wire along its length, the apices of the wire remote from said secondary reinforcing member being connected to said primary reinforcing member.

5. Reinforcement as claimed in claim 4 wherein the apices of the wire remote from the secondary reinforcing member are bent over in such manner that the wire and the secondary reinforcing member secured thereto are suspendable from said primary reinforcing member.

6. Reinforcement as claimed in any one of the preceding claims as used in building structure of the type comprising a plurality of side by side moulds positioned on support structure and wherein concrete is poured over and between adjacent moulds onto the support structure, the reinforcement being locatable on the support structure between adjacent moulds.

7. A cast concrete beam including reinforcement as claimed in any one of the preceding claims.

8. Building formwork comprising a plurality of side by side moulds positioned on support structure and reinforcement located on said support structure between adjacent moulds; said reinforcement comprising one or more elongate primary reinforcing members spaced away from said support structure, one or more elongate secondary reinforcing members spaced from the or each primary reinforcing member and from the support structure and connecting means securing said secondary reinforcing members to said primary reinforcing members.

9. Building formwork as claimed in claim 6 wherein the reinforcement is as claimed in any one of claims 2 to 5.

10. Building reinforcement as claimed in either one of claims 6 or 7 wherein the support structure comprises a plurality of elongate members arranged in a horizontal plane with the moulds positioned along said members to define a channel between each pair of adjacent moulds, each channel having side walls provided by the exterior surfaces of the adjacent moulds and a base provided by the elongate member, the reinforcement being located within said channel.

11. Building formwork as claimed in claim 8 wherein the or each said primary reinforcing member in each said channel is supported by spacers located on the base of the channel in such manner that the or each secondary reinforcing member is also spaced from the base of the channel.

12. Building formwork constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

1 3. Reinforcement for use in building structure constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawing.