GB2250039A - Deck system for concrete flooring - Google Patents

Abstract

A concrete flooring system includes deck elements having the shape of a longitudinal arch 2 extending between and resting on the beams 1. Preferably the elements rest on the bottom flange 4 of each beam so that when concrete is applied the beam is buried. For additional strength the arched elements may include corrugations extending from one side of the arch to the other. Because of their shape the arched elements are able to support the weight of the concrete over a considerable span. <IMAGE>

Description

DECK SYSTEM The invention concerns a deck element for use in constructing floors and decks by laying one or more such elements between beams and covering it or them with concrete, to floors made using such profiles, and to a method of constructing such a floor.

Buildings such as offices are often constructed nowadays by so-called "fast track" techniques. In these methods flat metal deck sections, usually corrugated, are first placed or supported on the top flanges of beams or girders for the floor in question so as to cover the area between the beams. Concrete is then poured over the covering thus formed and allowed to set, the metal sections remaining in situ. This method has the advantage of a rapid speed of construction generally costing no more, and possibly less, than conventional techniques.

In another known system metal decking is formed by approximately square sections the length of a side of which matches the distance between adjacent beams. The square sections rest on the lower flanges of the beams and may form the ceiling for the floor below. Most of the area of the square is taken up by a spherically upwardly convex dome shape serving to reinforce the section against the weight of the concrete to be applied on top of it. The square elements are laid horizontally adjacent one another in a line along the longitudinal space between each pair of adjacent beams, opposite side edges resting for instance on the bottom flange of respective I-beams, to fill the area required; the elements may be interlocked with each other at their adjacent edges.

However, such known methods have disadvantages, as follows. First, the resistance of such constructions to heat may not meet fire safety standards and additional fire protection may have to be applied.

This increases the expense of the system, reducing its economic attractiveness. Secondly, the span between adjacent beams which can be covered by such systems is limited; in the case of the dome system the span might be only 60 cm, because whilst the upwardly presented dome shapes are strong in themselves to support downwardly applied loads, the remaining flat parts of the square sections are weaker. In fast track systems the maximum span is about 3m. Thirdly, although the square sections in the dome system are left in place in the final construction the strength of the system is not generally adequate without further measures, and so the concrete usually needs to be reinforced, for instance by reinforcing bars arranged transverse to the beams and passing through them.

It is an object of the invention to solve, or at least mitigate, the above problems.

According to one aspect of the invention there is provided a deck element to be supported between two spaced beams so as itself to support the weight of concrete applied to the element, the element having opposite edge regions and between these edge regions continuous decking adapted to span the space between the beams; wherein the element is of a generally upwardly arched shape between the opposite edge regions with the axis of the arch being generally parallel to the edge regions, and wherein the upper surface of the arch element varies in depth along the axial direction of the arch, on a scale small compared with the span of the arch, so as to stiffen the arch.

Advantageously the depth variation arises from the fact that the longitudinal cross-section of the element, at least in the central area of the arch, has a corrugated form.

The variation, in particular the corrugation, is, for ease of manufacture and consistency, preferably regular and uniform across the span from one edge to the other, its pitch being considerably smaller than the beam spacing.

The arched form of the elements brings about a considerable increase in strength by comparison with known flat elements or dome shuttering. This increase in strength means that greater spans between beams can be covered by systems embodying the invention possibly 4.5m to 7.5m - without unduly large depth-tospan ratios; with the known systems heavy-gauge material would have to be used to support the wet concrete, which would be expensive and difficult to form. Since systems in accordance with the invention require no further reinforcement - although such may of course be provided if desired - standard-section beams can be used.

Conceivably the depth variation could be achieved by other features of the arch shape than corrugation.

For instance, a plain arch could have arch ribs welded on to its upper surface at intervals along its length, or indentations spaced both axially and in the curved direction.

The corrugation of the elements, as well as stiffening the arch, has the further advantage of affording an increased surface area for bonding with concrete. Hence when concrete is applied a mechanical keying or anchorage between the sheet elements and the concrete, considerably increasing the final strength and fire resistance of the structure, whereas the prior art dome elements function essentially merely as shuttering, so that additional reinforcement is required. The strength can be further increased by providing re-entrant, e.g. dovetail corrugations for full composite action.

The elements may be made of steel sheet, glass reinforced plastics or glass-reinforced cement. The deck elements and beams can be either composite or noncomposite with the concrete; in general steel elements will bond with concrete to give an at least partly composite structural member. The elements can be manufactured as continuous 'tunnel'-shaped elongate sections or assembled from two or more axially aligned curved sections. In the latter case restraint or dovetail cross-section profiles would facilitate site or shop assembly.

In another aspect of the invention there is provided a floor system, and a method of making such a floor, including beams running generally in parallel, 'with elements as aforesaid resting on the beams so as to support the weight of concrete by virtue of their arched construction. Each element preferably rests on the bottom flange of the beams, if present, or from a suitable intermediate support on the web of the beam.

In either case the elements may be simply placed on the flange or intermediate support or may be fastened to it, by welding for instance.

In principle the arch elements could rest on top of the beams as in the fast track system mentioned above, but this would significantly increase the depth of the structure and would leave the beams exposed and thus afford no fire protection. Preferably the beams are at least partially buried in the concrete when this is poured, which gives built-in fire resistance. Tests have shown that the fire resistance of this composite structure is then satisfactory without the need for additional measures.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figs. 1 to 4 show cross-sections of different embodiments of arch systems according to the invention; Fig. 5 is an elevational view showing beam spacings; Fig. 6 is a schematic longitudinal cross-sectional detail of part of an arch element with concrete applied, and Fig. 7 is a partial perspective view of an arch section resting on an I-beam.

Figs. 1 to 4 all show arch systems supported on Ibeams so that at least the top part of each beam is embedded in concrete, thus ensuring effective fire protection. In Figs. 1 to 3 the arch elements 2 all rest on the bottom flange 4 of the beams 1, while in Fig. 4 they are shallower and rest on intermediate supports (not shown) on the web of the beam.

In Figs. 1 and 2 the arches have a small radius of curvature near the point of support, so that their section rises steeply from the flange 4 and then levels off fairly rapidly, continuing at a shallow inclination towards the middle. In Fig. 1 the two sides of the arch meet in a vertex, while in the Fig. 2 embodiment the arch has a gradual curve from one side to the other in the central section.

In Figs. 3 and 4 the arch has a roughly constant curvature, which may for instance be circular, elliptical or parabolic, over the entire beam spacing.

Fig. 5 shows typical dimensions for spans and lengths of the arch element sections used in embodiments of the invention.

In the sectional close-up of Fig. 6, taken in the longitudinal direction near the top of an arch and showing the concrete layer 3, the corrugations in the arch profile 2 can be seen. Typically the pitch of these might be 15-30 cm and their height 5-6 cm.

Although in this embodiment the corrugations are trapezoidal, other configurations could of course be used, such as triangular, wave-like or dovetail. Fig.

6 also shows an additional mesh reinforcement 5 in the concrete, although for many purposes the composite action produced by the mechanical bond over the extended surface area between the concrete and the corrugated profile would be sufficient.

Fig. 7 shows an embodiment with regular, transversely uniform corrugation in the arch profile 2.

As can be seen, the pitch of the corrugations is considerably smaller than the beam spacing, while the radius of curvature of the arch shape is considerably larger than the beam spacing and might typically be 10-20m.

It can also be seen in Fig. 7 that the longitudinal edge of the arch 2 is supported vertically by the flange 4 and horizontally by the web of the beam 1, resulting in a very stable configuration.

During construction the corrugated arch elements are laid on the lower flanges of the beams as shown in Fig. 7. Ties, possibly permanent but generally of a temporary nature, are then fastened or clipped to the lower flanges on end spans of the beam members to ensure that the arch does not spread when the concrete is poured. The pouring of the concrete then takes place, covering the arch elements and the beams, providing both excellent fire protection due to the embedding of the beams in the concrete and strength due to the composite action between the arch elements and the concrete.

The arch profiles themselves may be formed by rolling on a differential roll using traditional platemaking techniques or alternatively, and most simply, crimped at the corrugations to form one or more kinks, giving the arches a generally polygonal arch crosssection composed of a series of straight segments.

Arches have been made having fourteen crimps over a 6m span; these have the appearance of a smooth arc section and have performed adequately in tests.

One of the advantages of the invention over the dome system mentioned earlier is that the arch profiles can be provided in any length, and if desired cut to size on site. It is nevertheless also possible in a method according to the invention to provide two or more arch profiles along the space between the beams.

Claims (10)

CLAIMS:

1. A deck element to be supported between two spaced beams so as itself to support the weight of concrete applied to the element, the element having opposite edge regions and between these edge regions continuous decking adapted to span the space between the beams; wherein the element is of a generally upwardly arched shape between the opposite edge regions with the axis of the arch being generally parallel to the edge regions, and wherein the upper surface of the arch element varies in depth along the axial direction of the arch, on a scale small compared with the span of the arch, so as to stiffen the arch.

2. A deck element according to claim 1, wherein the longitudinal cross-section of the element, at least in the central area of the arch, has a corrugated form, constituting the said depth variation.

3. A deck element according to claim 2, wherein the corrugations have a dovetail form.

4. A deck element according to claim 1, 2 or 3, wherein the depth variation is regular and uniform across the span from one edge to the other, its pitch being considerably smaller than the beam spacing.

5. A deck element according to any preceding claim, wherein the span of the arch is approximately 4.5-7.5m.

6. A deck element according to any preceding claim, wherein the elements are made of steel, glassreinforced plastics or glass-reinforced cement.

7. A floor system comprising at least two generally parallel beams and an arched element as claimed in any preceding claim supported between each pair of beams.

8. A floor system according to claim 7, wherein each beam has a bottom flange or intermediate support on which the corresponding side of an element is supported.

9. A floor system according to claim 8 and further including a layer of concrete enveloping the upper part of each beam.

10. A floor system substantially as described herein with reference to the accompanying drawings.