GB2162231A - Beam formwork - Google Patents

Abstract

Formwork for use in casting a reinforced concrete beam in the construction of a reinforced concrete floor, including a pair of mutually similar elongate side formwork members 1, 2 for defining the sides of the beam, each of said members being substantially Z-shaped in transverse cross-section and comprising (a) a central web 3 for defining the side of the beam, (b) an outwardly extending top flange 4 for suspending the said member from, for example, adjacent table formwork in use, and (c) an inwardly extending bottom flange 6 for supporting further formwork for defining the bottom of the beam, and engaging means 7 at the bottom of each of said side members for positive releasable engagement, in use, with joists 8 extending transversely of the said side members and spaced longitudinally thereof, to hold the said side members,against outward displacement during casting. <IMAGE>

Description

SPECIFICATION Beam formwork This invention relates to the construction of reinforced concrete floors, and in particular to formwork for use in the in situ casting of beams therein.

The conventional manner of forming such floor beams is to use timber or metal formwork consisting of a beam base and two beam sides. Normally the beam sides are strutted or secured by form-ties to resist the concrete pressure. Such an operation, which involves the in situ assembly of all beam formwork including props, struts and form-ties to the precise dimensions required for each successive floor of a building, followed by its complete disassembly when the floor has become self-supporting, is both time-consuming and labour-intensive. The repeated assembly and disassembly of the beam formwork structure also results in high wear and tear of material. Therefore the conventional method is expensive.

According to the present invention there is provided formwork for use in casting a reinforced concrete beam in the construction of a reinforced concrete floor, including a pair of mutually similar elongate side formwork members for defining the sides of the beam, each of said members being substantially Z-shaped in transverse cross-section and comprising (a) a central web for defining the side of the beam, (b) an outwardly extending top flange for suspending the said member from, for example, adjacent table formwork in use, and (c) an inwardly extending bottom flange for supporting further formwork for defining the bottom of the beam, and engaging means at the bottom of each of said side members for positive releasable engagement, in use, with joists extending transversely of the said side members and spaced longitudinally thereof, to hold the said side members against outward displacement during casting.

Such an arrangement has numerous advantages over conventional apparatus, chief among which are that the Z-section configuration of the said side formwork members, and their positive engageability with the said joists, provides integral stiffening and support for the formwork members and thereby eliminates the need for form-ties, struts, props and nails to hold them in position during casting.

In one form of the invention the said engaging means of each said side member comprises a downwardly extending flange portion along the bottom of said member, for engagement in slots in the said joists.

In another form the said engaging means of each said side member comprises a series of downwardly extending pegs spaced along the bottom of said member, for engagement in holes in the said joists.

In yet another alternative the said engaging means of each said side member comprises a se ries of holes spaced along the bottom of said member, for receiving upstanding pegs on the said joists.

Formwork as provided in accordance with the invention need not include the said joists as these are of relatively simple construction and may be provided separately by the user. Preferably, how ever, they are provided as part of a formwork assembly according to the invention.

The said side formwork members are preferably made of mild steel not more than 3 mm thick, to save weight and reduce costs.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic view in end elevation of a formwork assembly according to the invention with the parts disengaged from each other; Figure 2 is a plan view of a joist forming part of the assembly of Figure 1; Figure 3 is a view in side elevation of what is shown in Figure 1; Figure 4 is an end view of part of the formwork for a reinforced concrete floor, incorporating the assembly of Figure 1; Figure 5 is a perspective view of an alternative embodiment; and Figure 6 is a perspective view of another alternative.

Referring first to Figures 1 to 3, formwork for use in casting a reinforced concrete beam in the construction of a reinforced concrete floor comprises a pair of mutually identical elongate side formwork members 1 and 2, each substantially Z-shaped in transverse cross-section and each comprising a central web 3, an outwardly extending top flange 4 including a dependent and inwardly returned terminal portion 5, and an inwardly extending bottom flange 6 including a downwardly extending terminal flange portion 7. The formwork assembly further comprises a plurality of joists 8 each formed with a series of slots 9 in the top surface to receive the terminal flange portions 7 of the side members 1 and 2.

Figure 4 shows the above described assembly in use in conjunction with a table formwork system for casting a floor 10 incorporating a beam 11, the table formwork system being similar to that described in my published Specification No. 2125475 to which reference may be made. The joists 8 of the beam formwork assembly rest on angle bars 12 secured to uprights 13 of the table formwork, and the top terminal flange portions 5 of the beam formwork side members 1 rest on, and are thereby suspended from, the ends of joists 14 of the table formwork. Engagement of the bottom terminal flange portions 7 of the formwork members 1 in the slots 9 in the joists 8 positively prevents outward displacement of the formwork members 1 away from each other during casting. Selection of the pair of slots 9 to receive the flange portions 7 enables the lateral thickness of the beam to be varied.The bottom or soffit formwork for the beam is defined by sheets 15, e.g. of plywood, resting on the bottom flanges 6 of the formwork members 1.

In the alternative construction shown in Figure 5 the bottom terminal flange portions 7 of the side formwork members 1 are replaced by engaging means in the form of rows of pegs 16 secured in the flanges 6 and engageable in holes 17 in the joists 8. A series of such holes may if desired be provided in each joist, for the same purpose as the series of slots 9 in the first embodiment. In the further alternative shown in Figure 6 the arrangement of figure 5 is simply reversed to provide engaging means in the form of pegs 18 in the joists and holes 19 in the angle bars 20 backing onto the bottom flanges of the side formwork members. The holes 19 could be formed directly in the flanges 6 if desired.

The side formwork members 1 are formed from 3 mm mild steel sheet by a pressing operation.

The joists 8 may he of any suitable material but are preferably of metal.

In use, three o- f ,Us~ days after concreting, de- pending on the tyne of concrete used, the beams 11 of the floor slab may be back-propped by adjustable steel props. When this has been done, the table formwork units are lowered a few inches by means of their screw jacks, the joists 8 removed, and the side formwork members 1 taken down and hooked to the sides of the table formwork units, which are now jacked down onto the floor for flying to the next floor. The plywood sheets 15 forming the base of the beam may be released together with the adjustable steel props when the floor slab becomes fully self-supporting. Thus this system allows the table formwork units to be released and re-used much earlier than hitherto, thus reducing the cost of the formwork equipment.

It is to be clearly understood that there are no particular features of the foregoing specification, or of any claims appended hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in the fiiing or prosecution of any divisional application based thereon.

Claims (8)

1. Formwork for use in casting a reinforced concrete beam in the construction of a reinforced concrete floor, including a pair of mutually similar elongate side formwork members for defining the sides of the beam, each of said members being substantially Z-shaped in transverse cross-section and comprising (a) a central web for defining the side of the beam, (b) an outwardly extending top flange for suspending the said member from, for example, adjacent table formwork in use, and (c) an inwardly extending bottom flange for supporting further formwork for defining the bottom of the beam, and engaging means at the bottom of each of said side members for positive releasable engagement, in use, with joists extending transversely of the said side members and spaced longitudinally thereof, to hold the said side members against outward displacement during casting.

2. Formwork as claimed in claim 1, wherein the said engaging means of each said side member comprises a downwardly extending flange portion along the bottom of said member, for engagement in slots in the said joists.

3. Formwork as claimed in claim 1, wherein the said engaging means of each said side member comprises a series of downwardly extending pegs spaced along the bottom of said member, for engagement in holes in the said joists.

4. Formwork as claimed in claim 1, wherein the said engaging means of each said side member comprises a series of holes spaced along the bottom of said member, for receiving upstanding pegs on the said joists.

5. Formwork as claimed in any preceding claim, further comprising the said joists.

6. Formwork as claimed in claim 5, wherein each of the said joists is formed or provided with a series of engagement means, complementary to the engaging means of the said side members, spaced lengthwise of the joist to permit different lateral spacings of the side members when engaged with the joists and thereby the casting of beams of different thicknesses.

7. Formwork as claimed in any preceding claim, wherein the said side members are made from mild steel plate of less than 3 mm thickness.

8. Formwork as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawings.