WO2012126065A1

WO2012126065A1 - A beam and method for reinforcing concrete slabs

Info

Publication number: WO2012126065A1
Application number: PCT/AU2012/000307
Authority: WO
Inventors: Mark Allan MANNING
Original assignee: Entek Pty Ltd
Priority date: 2011-03-23
Filing date: 2012-03-23
Publication date: 2012-09-27
Also published as: EP2689075B1; AU2012231786A1; US20140298749A1; EP2689075A4; EP2689075A1; AU2012231786B2

Abstract

A beam for reinforcing a concrete slab, the beam including a channel for receiving concrete mix therein, and the beam adapted to receive at least one anchoring element such that the at least one anchoring element protrudes into the channel, wherein the at least one anchoring element is for engaging the concrete mix, such that once the concrete mix hardens, the at least one element contributes to engagement between the beam and concrete slab.

Description

A BEAM AND METHOD FOR REINFORCING CONCRETE SLABS

Field of the Invention

The present invention relates to beams for reinforcing concrete slabs, and methods of forming concrete slabs, in particular ribbed concrete slabs. Description of the Background Art

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be. taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Presently, in the field of construction, ribbed slabs are used as one of the most efficient slab designs. This is typically due to their utilisation of structural depth and reduction in concrete weight, which is generally derived from the voids which are formed between the ribbed beam elements. Permanent steel (usually cold rolled) formwork systems, which act compositely with the in-situ concrete, also offer additional efficiencies due to the designs using almost every component of the system both before and after construction.

In the past, ribbed slabs have typically been constructed using pre-cast or formed concrete beams with an in-situ slab infill between, or by using composite structural steel formwork, which is made from various cold rolled steel sheet profiles. The steel sheet profile slabs are typically only one directional in their strength characteristics.

However, the pre-cast concrete beams are typically heavy to transport, crane lift intensive due to their weight, and also pose significant safety concerns on site due to their size and weight. Conventionally formed concrete ribs are expensive and generate a lot of waste. Furthermore, structural steel formwork systems generally do not adequately harness the composite slab efficiencies of a true ribbed slab, which has its ribs spaced, according to one example, at 1500mm centres, which is far in excess of the typical 200mm to 500mm centres for standard one directional steel sheet profiles.

Thus, the present invention seeks to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements. Summary of the Present Invention

In one broad form, the present invention provides a beam for reinforcing a concrete slab, the beam including a channel for receiving concrete mix therein and the beam adapted to receive at least one anchoring element such that the at least one anchoring element protrudes into the channel, wherein the at least one anchoring element is for engaging the concrete mix, such that once the concrete mix hardens, the at least one element contributes to engagement between the beam and concrete slab.

In one form, the at least one anchoring element is received through at least one hole in the beam.

Alternatively or additionally, the at least one anchoring element is punched through the beam. In another form, the channel includes a base between two side walls, each side wall including and an inwardly directed flange portion.

In a further form, the beam has a substantially C-shaped cross sectional profile.

In one form, the at least one anchoring element protrudes from the underside of the inwardly directed flange portions, toward the base of the channel. In another form, the at least one anchoring element is at least one screw, the threaded portion of the at least one screw protruding into the channel.

In one form, the inwardly directed flange portion is substantially L-shaped.

In another form, the inwardly directed flange portion is substantially C-shaped. .

In one form, the beam is formed of two half parts. In another form, the beam is formed of light gauge steel.

In a further form, two or more of said beams are able to be fastened together.

In another broad form, the present invention provides a system for reinforcing a concrete slab including: placing formwork including at least one beam, the beam including: a channel for receiving concrete mix therein such that a rib is formed in the slab; and at least one element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens the beam is anchored to the slab.

In another broad form, the present invention provides a method for forming a concrete slab, the method including the steps of: placing formwork including at least one beam, the beam including: at least one channel for receiving concrete mix such that a rib is provided in the slab; and at least one anchoring element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens, the beam is anchored to the slab. In another form, the method further includes pouring concrete mix into the formwork and allowing the mix to harden.

In another form, placing formwork includes fastening the at least one beam to an infill sheet.

In another broad form the present invention provides a system for connecting an in-situ concrete slab to a light gauge steel beam, wherein the slab includes a ribbed section, the ribbed section being connected to the beam by one or more connectors.

In one form, the steel beam section includes top flanged portions, with the one or more shear connectors being configured to connect the flanged portions to the in-situ concrete In one form, the system further includes a metal infill sheet, the infill sheet being connected to the slab by one or more connectors.

In another form, the connectors are any one or a combination of steel screws, bolts, rivets, shear studs or the like. It will be appreciated that the broad forms of the invention may be used individually or in combination.

Brief Description of the Drawings

An example of the present invention will now be described with reference to the accompanying drawings, in which: - Figure 1 A is a schematic diagram of an example plan view of a system for connecting a slab to a beam;

Figure 1 B is a schematic diagram of an example cross-sectional view (at 1 ) of the system of Figure 1 A;

Figure 1 C is a schematic diagram of an example cross-sectional view (at 2) of the system of Figure 1 A;

Figure I D is a schematic diagram of example steel beam profiles, which can be used with Figure 1 A.

Figure 2A is a schematic diagram of another example plan view of a system for connecting a slab to a beam;

Figure 2B is a schematic diagram of an example cross-sectional view (at 1 ) of the system of Figure 2A;

Figure 2C is a schematic diagram of an example cross-sectional view (at 2) of the system of Figure 2A;

Figure 2D is a schematic diagram of example steel beam profiles, which can be used with Figure 2A.

Figure 3A is a schematic diagram of another example plan view of a system for connecting a slab to a beam;

Figure 3B is a schematic diagram of an example cross-sectional view (at 1 ) of the system of Figure 3A; Figure 3C is a schematic diagram of an example cross-sectional view (at 2) of the system of Figure 3A;

Figure 3D is a schematic diagram of example steel beam profiles, which can be used with figure 3A.

Figure 4A is a schematic diagram of another example plan view of a system for connecting a slab to a beam;

Figure 4B is a schematic diagram of an example cross-sectional view (at 1) of the system of Figure 4A;

Figure 4C is a schematic diagram of an example cross-sectional view (at 2) of the system of Figure 4A;

Figure 4D is a schematic diagram of example steel beam profiles, which can be used with Figure 4A,

Figure 5A is an example of the profile of a beam formed by two half parts;

Figure 5B is a schematic diagram of the profile one half part of figure 5A;

Figure 6 A is a schematic diagram of a beam profile which may be formed into a double beam profile by fastening two profiles together, in this instance the two profiles are fastened together by screw, rivet bolt or the like;

Figure 6B is a schematic diagram of a beam profile which may be formed into a double beam profile by fastening two profiles together, in this instance the two profiles are fastened welding;

Figure 6C is a schematic diagram of a beam profile which may be formed into a double beam profile by fastening two profiles together, in this instance the two profiles are fastened welding or crimping;

Figure 6D is a schematic diagram of a beam profile which may be formed into a double beam profile by fastening two profiles together, in this instance the two profiles are fastened welding or crimping;

Modes For Carrying Out The Invention

Figures 1 A to 1C show an example system for connecting a beam to a slab and some example beam profiles. In particular, the examples in the Figures show a concrete slab 100 connected to a light gauge steel beam section 1 15. In this particular example, the slab 100 is connected to the steel beam section by one or more shear connectors 125 and 120 (anchoring elements). The system described herein can include a ribbed slab system incorporated in a typical structural flooring application, including supporting elements.

Notably, the shear connector location is, in the examples described herein, on top inwardly directed flanges of the steel beam 1 15. This can allow for the connector 125 to act as both an infill fastener and a concrete/steel beam shear connector.

As can be seen from Figures 1 A to 1 C, the steel beam section 1 15 includes sides and flanges where the preferred shear connector 125 location is on the top flanges, with additional shear connectors 120 configured on the sides and bottom flange, in order to connect the steel beam to the concrete slab 100.

The system described herein can also include a metal infill sheet 130, where the infill sheet 130 can also be connected to the slab 100 by one or more connectors (or anchoring elements) 125.

Thus, according to one particular example, steel roofing screws can be used to secure the infill sheets to the top flange of the steel beams. These screws can also act as the shear connectors between the in-situ concrete within the beam/slab and the steel beam itself. It will be appreciated, however, that many forms of connectors such as rivets, bolts, shear studs, or the like, placed through pre-drilled or punched holes, can also be used. In the instance that the connectors (or anchoring elements) are punched through the beam, the beam may have small indentations therein (or other similar means) to encourage passage of the connectors through the beam.

Figure IB also shows that in-situ concrete 135 can be used with the system described herein. Furthermore, slab reinforcements 140 can also be used, and the system can include a zone 142 for post-tensioning ducts and/or additional reinforcement, as required. Figure 1C shows that flashing 145, or void fillers, or formwork, can be used between steel beam sections 1 15, as required. Notably, Figure 1C shows the conventional formwork system at 150, and Figure 1A also shows that propping 155 can occur as required, where the number and spacing of the propping lines can vary.

As can be seen in Figure I B, a typical 'C section purlin has been used as the beam 1 15. However, it will be appreciated that the gauge, size and profile may vary. Different example beam profiles are shown in Figure 1 D (and for other examples described below, in Figures 2D, 3D and 4D).

Figures 2A to 4D show variations of the example system described herein.

In particular, Figure 2C shows a variation including a steel support beam 210 and shear studs 200, used as required. Figure 3C shows the steel support beam 210 including support angles 310, as required. Figure 4C shows the use of a wall support 410.

Notably, in this particular example, the slab 100 is a concrete slab, and the shear connectors 125 and 120 can be steel screw bolts, rivets, shear studs or the like. These features are further described below.

The beam may also be formed of more than one part. For example, two beams may be fastened together to provide a desired profile (or "double beam" profile). Figure 5A shows the profile of a steel beam formed by two identical half parts 500, 501. A plate 503 is screw fastened to corresponding flanges 504, 505 of the two half parts 500, 501 fastening them together. It will be appreciated that the parts may be fastened together by other means and that the joined parts need not be identical. Figure 5B shows the profile of one half part 500 from figure 5A. The advantage of using a double beam profile is that it allows an increase the overall depth and width of the section, which would otherwise not be possible using commonly available steel coil widths. It will be appreciated that the two half parts may be fastened together by other means, such as, for example, welding, crimping or using screws rivets, bolts or the like (See figures 6A-6D). It will further be appreciated that the presently described system and method can utilise the inherent strength of the steel formwork at all stages of the design life of the floor, from before the pour of the in-situ concrete slab to the end of the design life of the structure. Thus, the system and method described herein can use the steel of the beams (ribs) both as formwork, but also as an integral part of the reinforcement of the composite concrete ribbed slab. Long term the steel shell of the rib acts as part (or all) of the bottom longitudinal and the vertical shear reinforcement. Transverse reinforcement may be required, and this can be achieved via reinforcement placed within the in-situ concrete. Some of the features of the beams and methods described herein are further described below.

Full composite action

The slab ribs can gain full composite action due to the designed connection of the metal infill to the steel beam section and in-situ concrete. The connection also includes the detailing of any additional shear connectors, as required by the design. Thus, according to one particular example, the ribbed slab composite action means that all of the steel beam section can be included in the design calculations. This includes steel for shear, bending, deflections and in some cases (depending on the profile) fire reinforcement.

Furthermore, it will be appreciated that additional reinforcement such as stressing wires/tendons, bar, mesh or fibre reinforcement, and the like, may be added to the system, as required by the design.

Increased Construction Capacity & Deflections

The steel beams can gain lateral restraint from the fixed metal infill sheets and this restraint can allow the system to span greater un-propped distances during construction (under wet concrete). The continuity of the steel beams over supports (long term or temporary) is also taken into account when calculating the systems construction capacities and deflections.

Accordingly, commercially available structural steel formwork can be used between the steel beams, such that the structural steel formwork does not require propping and can span easily with a relatively thin slab required. The steel beams (ribs) in this example, are deeper than the structural steel formwork and (usually) thicker, so they have a greater spanning capability during construction, which can reduce propping distances compared to standard structural steel formwork. Notably, the spanning capability can be increased by the fact that the average concrete depth over the net system is less than that of a standard structural steel formwork system.

Light Gauge Steel Beams

As discussed herein, the light gauge steel beams connect to the in-situ concrete slab and metal infill sheet via the shear connectors, or anchoring elements.

The steel beams can be standard commercially available steel "C" Purlins, or custom made steel sections, as required. Notably, the use of custom made sections can improve the characteristics of the system, but are not a necessary requirement.

The beams, according to one example, are formed from (but not limited to) thin gauge galvanized steel. Furthermore, they can be used to support the wet concrete slab over during the concrete pour, and to act compositely with the slab long term.

It will be appreciated that by using a readily commercially available section, the steel beams can be cost effective. Furthermore, they are generally light and easy to handle.

Additionally, the steel beams can keep the thickness of the slab over the infill sheets to a minimum, making the slab lighter/ Being deeper than the infill sheeting, they are able to, in one example, span further too. It will be appreciated that this can reduce the amount of temporary propping required during construction.

Further still, the steel beams can also enable the metal infill to maximize its spanning capability by shortening the effective span of the infill. They act with the in-situ concrete and the shear connectors to form a composite unit utilizing the above-described materials.

The infill used can include any type of formwork, and in one particular example is a commercially available structural steel formwork (subject to detailed design), which can be used to span the slab between steel beams during the concrete pour, and long term. Thus, the infill used can be cost effective, light, and easy to handle. According to one particular example, the infill is able to connect to the steel beams via the shear connectors. Thus, the infill being connected (via the shear connectors) to the beams, helps to restrain the top of the beams during the pouring of the in-situ concrete slab.

Notably, it will be appreciated that the beams can be lined next to each other such that there are only shear connectors in the top flanges of each beam, and the system acts as a composite ribbed slab, and infill is not required.

It will further be appreciated that the presently described system may be implemented without the infill component.

Shear Connectors The shear connectors keep the metal infill, steel beams, and the in-situ concrete slab connected. It will be appreciated that this can provide stability for a deck as a working platform. The connectors can also restrain the top of the steel beam from buckling during the concrete pour, and connect the in-situ concrete to the beams in the hardened concrete state. Thus, they can be large steel screws and may be placed anywhere on the top flanges of the steel beam.

According to one example, the shear connectors can be implemented as screws which act as both infill sheet fasteners and composite action shear connectors. It will be appreciated that the screw connectors may be substituted with bolts, rivets, shear studs or the like located in pre-drilled, or pre-punched holes. Additional screws, bolts, rivets, shear studs or the like may be installed as required by the design.

Thus, the shear connectors can connect the infill to the steel beams. During the concrete pour, the shear connectors can enhance the buckling resistance of the top of the open beam. Additionally, it will be appreciated that in the long term, the connectors can connect the in- situ concrete slab to the steel beams providing composite action between the concrete and steel.

As described, according to another particular example, the shear connectors can be typically commercially available steel screws. They may also take the form of commercially available bolts, rivets, shear studs, or the like. Thus, they can be implemented in a cost effective way, can be easy to attach and require very little specialized equipment.

Accordingly, the shear connectors can be used to bring the system all together, enabling the metal infill, steel beams and in-situ concrete to act together as a unit during the various design stages of a structure.

It will be appreciated that other anchoring elements may also be used.

Flashing

In one example, folded steel flashing can be used to close the space between the metal infill and a supporting surface. Flashing can. also provide sound and fire separation by setting down the slab over load bearing and non load bearing walls (refer to the Figures) for further system details.

Thus, the flashing can close off gaps at end supports to control the flow of the in-situ concrete slab during the concrete pour. The flashing can, in one example, keep the concrete from pouring out the ends of the deck during a concrete pour. Notably, commercially available flashing, void fillers, formwork or variants thereof, can be used. Furthermore, flashing is typically light weight, commercially available, easy to handle, and cost effective.

Notably, any commercially available sheet metal may be used for the flashing. It will be appreciated that void fillers or formwork may also be used in place of steel flashing. It will further be appreciated that the presently described system may be implemented without the flashing component.

System Installation procedure

According to particular examples, the system described herein can be either partially assembled off site or fully assembled on-site. For the first case (partial off-site assembly) the light gauge steel beams arrive on-site already connected to the metal infill. These component sections are then laid out on the supporting elements at the required centres. Alternate infill sheets are then placed and fastened between the pre-assembled beam elements. Steel flashing is then installed as required to close the space between the infill sheets and the supporting structure.

For the second case (full on-site assembly), the light steel beams and metal infill arrive on- site separately. The system is installed by first placing the steel beams onto the supporting elements at the required centres. The metal infill sheets are fastened to the beam elements and, as with the first case, steel flashing is then used to close the space between the infill sheets and the supporting structure. The number, size and spacing of any shear connectors, required to achieve full composite action, will vary depending on the design. These connectors can be installed either on or off site.

Installation of Temporary Propping

If required (depending on the spans, beam size and spacing), temporary propping lines at the nominated centres can be installed prior to installation. This propping will generally consist of (but not limited to) standard propping frames and header beams.

Installation of Additional Reinforcement

Additional reinforcement, such as, for example, stressing wires/tendons, bar, mesh or fibre reinforcement, may be added to the system, as required by the design. Placement of In-situ Concrete

According to one particular example, once the system and any additional reinforcement is installed in-situ concrete is placed over the slab deck at the required design thickness and allowed to cure.

In its hardened state, the in-situ concrete interacts with the shear connectors, so as to facilitate the transfer of internal shear forces between the concrete, shear connectors and the light gauge steel beams. This transfer of shear forces enables the slab to act as a fully composite concrete/light gauged steel ribbed slab system,

Further Examples According to one particular example, the system and method described herein can maximise the composite actions between the steel beams and the in-situ concrete above and within the beam element. This composite action can be achieved through the longitudinal shear connection detail of the steel beams to the in-situ concrete and the metal infill sheeting. The connection detail between the metal infill sheets and the steel beams is also utilised during construction, which can also maximise the system's un-propped span length.

Thus, in one particular example, the slab system can include commercially available structural steel formwork (metal infill sheets) spanning between the steel beam sections, which in themselves also act as an integral part of the formwork system. A reinforced in-situ concrete slab is poured over the deck, and can act compositely with all elements of the formwork system. The composite action can be achieved principally via the connection of the metal infill sheets to the steel beams via steel screws, plus any additional connectors between the beam and the in-situ slab as required by the design. It will be appreciated that the screw connectors may be substituted with bolts, rivets, shear studs or the like.

It will be appreciated that many modifications will be apparent to those skilled in the art ^' without departing from the scope of the present invention.

In the context of this specification, the word "comprising" means "including principally but not necessarily solely" or "having" or "including", and not "consisting only of. Variations of the word "comprising", such as "comprise" and "comprises" have correspondingly varied meanings.

Claims

The claims defining the invention are as follows:

1. A beam for reinforcing a concrete slab, the beam including a channel for receiving concrete mix therein, and the beam adapted to receive at least one anchoring element such that the at least one anchoring element protrudes into the channel, wherein the at least one anchoring element is for engaging the concrete mix, such that once the concrete mix hardens, the at least one element contributes to engagement between the beam and concrete slab.

2. A beam as claimed in claim 1 , wherein the at least one anchoring element is received through at least one hole in the beam.

3. A beam as claimed in claim 1 , wherein the at least an anchoring element is punched through the beam.

4. A beam as claimed in claim 1 , wherein the channel includes a base between two side walls, each side wall including and an inwardly directed flange portion.

5. A beam as claimed in an one of the preceding claims, wherein the beam has a substantially C-shaped cross sectional profile.

6. A beam as claimed in any one of the preceding claims, wherein the at least one anchoring element protrudes from the underside of the inwardly directed flange portions, toward the base of the channel.

7. A beam as claimed in any one of the preceding claims, wherein the at least one anchoring element is at least one screw, the threaded portion of the at least one screw protruding into the channel.

8. A beam as claimed in any one of the preceding claims, wherein the inwardly directed flange portion is substantially L-shaped.

9. A beam as claimed in any one of the preceding claims, wherein the inwardly directed flange portion is substantially C-shaped.

10. A beam as claimed in any one of the preceding claims, wherein the beam is formed of two half parts.

1 1. A beam as claimed in any one of the preceding claims, wherein the beam is formed of light gauge steel.

12. A system for reinforcing a concrete slab including: placing formwork including at least one beam, the beam including: a channel for receiving concrete mix therein such that a rib is formed in the^' slab; and at least one element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens, the beam is anchored to the slab.

13. A method for forming a concrete slab, the method including the steps of: placing formwork including at least one beam, the beam including: at least one channel for receiving concrete mix such that a rib is provided in the slab; and, at least one anchoring element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens, the beam is anchored to the slab.

14. A method as claimed in claim 13, further including pouring concrete mix into the formwork and allowing the mix to harden.

15. A method as claimed in claim 13 or 14 wherein placing formwork includes fastening the at least one beam to an infill sheet.

16. A system for connecting an in-situ concrete slab to a light gauge steel beam, wherein the slab includes a ribbed section, the ribbed section being connected to the beam by one or more connectors.

17. The system of point 16, wherein the steel beam section includes top flanged portions, with the one or more shear connectors being configured to connect the flanged portions to the in-situ concrete

18. The system of any one of claims 16 or 17, wherein the system further includes a metal infill sheet, the infill sheet being connected to the slab by one or more connectors.

19. The system of any one of claims 17 to 18 wherein the connectors are any one or a combination of steel screws, bolts, rivets, shear studs or the like.

20. A beam as claimed in any one of claims 1 to 1 1 , wherein two or more of said beams are able to be fastened together.