WO2022109657A1

WO2022109657A1 - Concrete structure coupler

Info

Publication number: WO2022109657A1
Application number: PCT/AU2021/051352
Authority: WO
Inventors: George Argyrou
Original assignee: Hickory Design Pty Ltd
Priority date: 2020-11-30
Filing date: 2021-11-15
Publication date: 2022-06-02
Also published as: CN116601364A; AU2021388072A1

Abstract

A coupler for coupling precast concrete structures, comprising a first connecting part having an anchor configured to be embedded in a side edge of a first precast concrete structure and a second connecting part having an anchor configured to be embedded in a side edge of a second precast concrete structure; each connecting part comprising a facing surface, wherein the facing surfaces are adapted to be mechanically joined together in a first plane to structurally couple the concrete structures.

Description

CONCRETE STRUCTURE COUPLER

Field of Invention

[0001] The present invention relates to a coupler for connecting concrete structures such as slabs and beams. Embodied in the invention is also a concrete floor formed from slabs connected using such couplers and a method of constructing such a concrete floor.

Background

[0002] Prestressing concrete is a common technique of reinforcing concrete structures such as bridges, retaining walls and building structures including floor slabs, structural walls, columns and beams. In traditional, non-prestressed concrete, load stresses are carried by the steel reinforcement cast into the concrete. In prestressed concrete structures the concrete supports the load along the entire structure by providing predetermined placed tensile members, often steel wires or tendons, to counteract the stresses on the structure when subjected to loading. Prestressing combines the high strength compressive properties of concrete with the high tensile strength of steel.

[0003] Prestressed concrete can either be pretensioned or post tensioned. Post-tensioning is usually performed on in-situ poured slabs where once the poured slabs are dry a continuous cable is extended through cast conduits in adjoining slabs and tensioned with a hydraulic jack or the like to a predetermined force. The cable ends are anchored and cemented in tension. The cables are placed at points along the concrete structure that are higher or lower in height depending whether those points are intended to support a load in tension, or be supported by a column or other support, and hence subjected to compression.

[0004] With pretensioning the wires or cables are first positioned and stressed along a casting bed before concrete is poured on the bed to create the concrete structure. With the cables tensioned and anchored at their ends concrete is poured onto the bed and around the cables.

As the concrete dries and hardens it grips the steel cables along their length and transfers tension to exert a compressive force in the concrete thereby producing a precast structure that is already prestressed and can be transported to site. Where the pretensioned precast structures are floor slabs, the floor slabs can be arranged on site on temporary supports while a concrete topping is cast to form a monolithic tying structure on top of the floor slabs. [0005] Since in prestressed concrete structures loads are supported throughout the entire structure, they are more resistant to shock and vibration than traditionally reinforced (non- stressed) concrete structures. This allows longer and thinner structures to be formed to support equivalent loads making prestressed structures suitable for longer spans and cantilevers at a more economical cost than the equivalent traditional concrete structure.

[0006] The present invention has been developed with the objective of improving prestressed concrete building methods and optimizing benefits achieved with prestressed concrete building methods, but the invention is not necessarily limited to prestressed concrete structures.

Summary of the Invention

[0007] In accordance with the invention there is provided a coupler for coupling precast concrete structures, comprising a first connecting part embedded in a side edge of a first precast concrete structure and a second connecting part embedded in a side edge of a second precast concrete structure; each connecting part comprising a facing surface, wherein the facing surfaces are adapted to be mechanically joined together to structurally couple the concrete structures.

[0008] By ‘structurally’ couple it is intended to mean that the concrete structures are connected in a manner that provides structural integrity and strength. To this end it is anticipated that continuous load transfer can occur through the coupler between the joined structures thereby providing a continuity in reinforcement, such that the joined structure is considered to act as a single continuous supported beam or cantilever. The coupler, and its connection with the concrete, can withstand and transfer the bending and shear forces between the joined structures.

[0009] Such structural coupling is achieved by mechanically joining the coupler connecting parts through a mechanical connection using mechanical fasteners such as nuts and bolts, rivets, screws, locks and other fasteners or couplers suitable for high strength joints. In a preferred embodiment a bolt assembly is used to mechanically join together the facing surfaces of the connecting parts.

[0010] In one embodiment the concrete structure may be a slab or panel. In another embodiment the concrete structure may be a beam. The concrete structures may be coupled side edge to side edge. [0011] The facing surfaces of the connecting parts could be described as being joined in tension. Alternatively, the facing surfaces could be described as being joined in a first plane that follows along the plane of the structures being connected side to side.

[0012] The facing surfaces of the first and second connecting parts may be joined at one, two or more connection points. Where two or more connection points are provided the spacing distance between two points is such as to sustain flexural and shear forces applied between the structures. The spacing will depend on the application of the structures and the forces they are expected to sustain. A larger spacing between the connection points will provide greater stability and better distribution of forces between the connecting parts and hence between the precast structures. Specifically, the amount of stress sustained by the coupler is a function of the quantum of load forces (bending, torsion, shear) transferred over the area through which the force is imparted onto the coupler and transferred through to the adjacent structure. In the facing surfaces, the connection points could be spaced in a vertical direction or a horizontal direction or a combination of vertical and horizontal.

[0013] The connection points are preferably mechanical fasteners, which may be applied in tension. As discussed above, in a preferred embodiment the mechanical fasteners are bolts, and preferably a high tensile bolt and nut assembly. However, the fasteners could instead be a rivet-type connection, or other mechanical unions.

[0014] The mechanical connection points are preferably a primary form of connection. A non mechanical connection can be used as a secondary form in addition to the primary form. Such non-mechanical connections could include welded joints, adhesive connections or the like.

[0015] The bolt assemblies of the preferred embodiment are bolted in tension, and so lie in the same plane as the concrete structure. The mechanical connection, which can be in the form of bolt assemblies, may be prestressed to create a clamping stress of at least 500kPa. In another embodiment the clamping stress created at the joint to clamp together the connecting parts is at least 750kPa. In one specific embodiment the nuts and bolts are prestressed to a force of 200KN to create a clamping stress at the joint between the slabs of approximately 1MPa.

[0016] In a particular embodiment, the connecting parts of the coupler include corresponding planar surfaces that are adapted to be joined together in a second plane that is perpendicular to the first plane. Where the first plane is the horizontal plane in which the concrete structures lie, the second plane will be a vertical plane. Providing a secondary joint in a perpendicular plane to the first primary joint of the facing surfaces in the horizontal plane strengthens the integrity of the connector against damaging bending, torsional and shear forces experienced during flexing of the concrete structures under load during use. For maximum connector strength, the distance between the first joint and the second joint should be as far as practically possible.

[0017] In one embodiment the first and second connecting parts could be provided with similar features in that they both have a facing surface in the form of a front face, and two rearwardly extending anchoring arms that are securely embedded in the concrete structure by being cast in. The anchoring arms are flat planar members configured with anchoring features, such as a central internal slot with serrations formed in the arms protruding into the slot and around the peripheral exterior of the arms that act to grip the concrete drying through the slot and around the arms.

[0018] The front face of each connecting part extends between, and bridges, the two anchoring arms. Fastening holes in the front faces are adapted to receive mechanical fasteners that couple the front faces flat against each other.

[0019] In a particular embodiment, the first connecting part may be provided with a seat extending forwardly of and away from the first front face in a direction opposite to the rearwardly extending anchoring arms. The seat would extend from a bottom or top of the front face. In a further embodiment the seat may also extend rearwardly of the first front face to also bridge a portion of the anchoring arms, thereby reinforcing the structural strength of the first connecting part.

[0020] The second connecting part having a front face bridging the two anchoring arms, may also have a rearward-facing ledge (from the front face) that bridges the anchoring arms of the second connecting part between a top or bottom side of the second anchoring arms, behind the second front face. The ledge lies perpendicular to the front face and is adapted to couple the seat of the first connecting part. In a preferred embodiment, the ledge extends across a bottom section of the second connecting part and in use is seated above the seat of the first connecting part. Fastening holes on the seat and ledge align so as to receive fasteners, such as nuts and bolts, for the second joint.

[0021] With the front faces of the connecting parts connected in one plane and the seat and ledge of respective connecting parts connected in a perpendicular plane, the coupler is able to transfer from one structure to the other a high amount of loading forces in the form of bending, torsion and shear forces. Where the coupler is used between post tensioned precast concrete structures the coupler effectively functions to continue the reinforcement provided by the post tensioned members from one structure to the next, as if the coupled structures were prestressed as a whole.

[0022] Advantageously, the presently described arrangement does not need a concrete topping on top of joined structures in order to structurally tie the structures together. Positioning multiple couplers at pre-calculated locations transfers forces between structures avoids the need for any concrete topping.

[0023] The anchoring arms of both the first and second connecting parts may also be provided with rod receiving apertures for receiving reinforcing bars, such as perimeter bars used to reinforce the perimeter of the concrete structures.

[0024] In accordance with another aspect of the invention there is provided a concrete floor formed from precast and post tensioned concrete slabs connected together by couplers, each coupler comprising a first connecting part cast in a side edge of a first slab and a second connecting part cast in a side edge of a second slab, each connecting part comprising a facing surface, wherein the facing surfaces are adapted to be mechanically joined together in a first plane; and the connecting parts having corresponding planar surfaces adapted to be mechanically joined together in a second plane that is perpendicular to the first plane.

[0025] In an embodiment of the invention the number of couplers used between two concrete slabs is equal, or within a variance of one coupler, to the number of tendons precast into one of the concrete slabs that terminate at the edge of that concrete slab at which the coupler is cast.

In a variance there may be fewer couplers where the couplers are cast at an edge of a slab at a location midway between where post tensioned tendons are anchored. In another variance, the couplers are placed as close to the tendon anchor points as possible. The couplers may be cast within 300mm of the tendon anchor points. The couplers may be cast at one edge of the concrete slab, at all edges, or at any number of edges in between one and all edges.

[0026] The coupler may be cast at different heights at the edge of a post tensioned concrete slab. The height at which the coupler is cast may correspond with the height of the tendon anchor point. In this embodiment the height of couplers will pick up and transfer the stress carried by the tendons from one concrete slab to a tendon in the adjacent concrete slab.

[0027] While the connecting parts of the coupler are partially embedded in the concrete slab edge through anchoring arms, the facing surfaces and planar surfaces are cast to be exposed in a coupler recess at each edge of the concrete slab. This allows the connecting parts to be joined by a mechanical fastener after placement on site. Once the mechanical fastener has been applied the coupler recess is filled with grout to fill and fix the inter-slab connection.

[0028] In accordance with the present invention there is still further provided a method of constructing a concrete floor using precast and prestressed concrete slabs, including: forming precast first and second concrete floor slabs with post tensioned reinforcement and casting at least at one side edge a first connecting part of a coupler, a second connecting part of a coupler, or both first and second connecting parts, wherein the placement of the connecting parts is designed to align corresponding connecting parts when the first and second slabs are mounted in position; relocating the concrete slabs to a building site and assembling the first floor slab in position; locating the second floor slab adjacent to the first floor slab so as to align corresponding first and second connecting parts on adjacent slabs; and mechanically connecting the facing surfaces of the first and second connecting parts in the same plane as the plane of the floor slabs to form a continuous structural concrete floor.

[0029] The method may include correctly locating the slabs to ensure facing surfaces of connecting parts are aligned, by locating a horizontal ledge on the second connecting part onto an outwardly extending seat on the first connecting part. In one embodiment, the facing surfaces are connected by mechanical fasteners, preferably bolt assemblies. Concrete slabs may be joined to one or more adjacent slabs, in one or more directions in a horizontal plane to form a wide and/or long floor span.

[0030] The facing surfaces may be clamped together before connecting them mechanically.

[0031] The method may also include inserting reinforcement rods through corresponding apertures provided in the connecting parts, and specifically in the anchoring arms, before casting the concrete slabs. Such reinforcement provides perimeter reinforcement and strength on the slabs.

[0032] A packer may be inserted between facing edges of the concrete slab to provide an interface between concrete edges and/or to fill uneven gaps therebetween. Once the adjacent slabs are connected through their couplers, access coupler recesses that provide access to fastening of the couplers are filled with grout, as are any gaps between the adjacent slabs, thereby providing a continuous surface along the continuously structural concrete floor.

Brief Description of the Figures

[0033] In order that the invention be more clearly understood and put into practical effect, reference will now be made to preferred embodiments of an assembly in accordance with the present invention. The ensuing description is given by way of non- limitative example only and is with reference to the accompanying drawings, wherein:

[0034] Figure 1 shows a building constructed using precast floor panels coupled together using a coupler in accordance with the present invention’

[0035] Figure 2 is a plan view of Figure 1;

[0036] Figure 3 is an enlarged view of Area A of Figure 2 illustrating a first embodiment of the coupler;

[0037] Figure 4 is an elevation sectional view at section C-C of Figure 2;

[0038] Figure 5 is a side sectional view at section B-B of Figure 3;

[0039] Figure 6 is an upper isometric view of a second embodiment of a coupler in accordance with the present invention;

[0040] Figure 7 is a plan view of the coupler of Figure 6;

[0041] Figure 8 is a side elevation view of the coupler of Figure 6;

[0042] Figure 9a is front isometric view of a first component of the coupler of Figure 6;

[0043] Figure 9b is a top view of the first component;

[0044] Figure 9c is a front elevational view of the first component

[0045] Figure 10a is a front isometric view of a second component of the coupler of Figure 6;

[0046] Figure 10b is a side elevational view of the second component; [0047] Figure 11 is an isometric top view similar to Figure 6 but also showing a torque and alignment tool used in connecting the coupler components embedded in a concrete structure; and

[0048] Figure 12 is a side sectional view of the coupler embedded in and connecting two concrete structures.

Detailed Description of Embodiments

[0049] Coupler 10 illustrated in the drawings is used to couple, or connect, together two or more concrete structures. In the description that follows the concrete structures referred to are precast and post tensioned concrete slab structures/panels used in building construction to form floors, particularly in multi-storey buildings. Specifically, the slab casting process involves laying conduits in one or two (perpendicular) directions on a base bed and pouring concrete onto the bed. Once the concrete dries, tendons are inserted through the conduits, are tensioned to the required force as engineered and anchored at that force. However, while the present embodiments describe using the coupler on post tensioned precast slab it is foreseeable that the coupler could be used on pretensioned slabs with equal success. Further still, the precast concrete structures need not be post tensioned or pretensioned, or prestressed at all. They may instead rely on traditional reinforcement bar/rod means of precast concrete structures

[0050] The coupler 10 is embedded in the precast slab during the casing process. The coupler 10 comprises two components forming a pair. One component of the coupler 10 is embedded and formed with a concrete structure at the time of casting and then connected to a second component of the coupler which is embedded in another concrete structure to connect the structures together.

[0051] It is understood that the concept of the coupler 10 is not limited to connecting precast concrete floor slabs but may be used to connect other precast structures, either vertically or horizontally or at a corner vertical/horizontal joint. Such concrete structures could also include wall panels, columns, beams, balcony structures, bridging structures, and the like.

[0052] A multi-storey building 12 under construction is illustrated in Figure 1. That building is shown as being constructed from modular building units 13 comprising a fagade 15 attached to a precast concrete floor slabs 20 and using temporary support structures 14 to support the next building unit 13 above. The coupler 10 is used to permanently join side edges of adjacent floors 20 to create a structural connection. It is intended that not only will the coupler provide structural integrity and strength at the structures’ joint but will also be capable of transferring structural forces between the two structures. In a manner, the coupled structures could act as if they were one structure.

[0053] In the plan view of the building 12 of Figure 2 it can be seen that multiple couplers 10 can be used to join together adjacent floor slabs 20 where the couplers are positioned, and specifically cast into, the edges of adjacent slabs 20. As will be discussed in more detail below, each coupler comprises two complementary parts where each adjacent slab edge has cast into it one of the two parts. The enlarged view of Figure 3 illustrates the two parts of the coupler 10 embedded into adjacent floor slabs 20. The two parts are brought together and coupled in order to connect the adjacent slabs. The coupler is designed on the basis of the floor slabs acting as a cantilever whereby the coupler picks up the load at the fixed edge of the cantilever and transfers the load to the adjacent cantilever (floor slab) to continue the forces through the coupler and to the next floor slab.

[0054] Also illustrated in the embodiment of Figure 2 in ghost lines are the post tensioned tendons 22 cast into the floor slabs 20. Bi-directional tendons are shown extending perpendicularly across the planar area of the floor slabs. By their nature, post tensioned tendons terminate at the edges of the structure where the tendons’ ends are anchored. Accordingly, tendons in post tensioned structures, which have the purpose of compensating predetermined loads, cannot transfer loads across to the next adjacent panel. The effective load span of the structure is therefore limited to the actual length of the structure. With the present invention the effective load span is increased because the couplers between structures can act as mediums through which bending, torsional and shear forces are transferred from one structure to the other.

[0055] To maximise load transfer through the couplers, it is desirable that the couplers are located close to the anchor points 23 of the tendons. The tendon anchor points in adjacent structures are also aligned as shown in Figure 2. The degree of closeness of the couplers to the anchors 23 will depend on the size of the structure, tendon thickness and the nature of the construction. By way of example, in floor slabs having a size of 10m to 15m x 5m for installation in a multi-storey construction it would be suitable to locate couplers within 300mm of the tendon anchors 23.

[0056] The height location of tendons 22 in a post tensioned precast structure varies according to the design of the construction. Figure 4 illustrates by way of a cross-sectional elevation such variation of tendon height across three floor slabs 20 adjacently connected with couplers 10 (not shown). In regions where loads on a floor slab will be higher, namely midpoint between two supporting columns 16, the tendon is located closer to a lower height of the floor slab thereby compensating for bending/sagging forces at that point. In regions where the floor slab is fully supported, namely at the columns 16, the tendon is located higher in the floor slab thickness. The overall effect of the curved height profile of the tendons is to evenly distribute bending/flexing forces across the full length of the structure.

[0057] Because the couplers are adapted to transfer forces between structures, the reinforcing effect of the tendons can extend across structures, and not be confined to one structure. Accordingly, it is possible to design a building floor so that the tendon anchoring locations in adjacent slabs are matched in height and position at the slab edge. This arrangement is shown in Figure 4 where the termination point of a tendon in one floor slab is at the same height in the slab as the closest immediate tendon termination point in the adjacent floor slab. Together with a coupler, which can optionally also be located at the same corresponding height and position to the tendon anchors 23, co-linear tendons 22 can act as a single long tendon to pass bending, torsional and shear forces from one floor slab 22 to the next. The advantageous outcome is a structure with an overall greater strength. This allows a longer effective length between supports compared to traditional prestressed techniques, and therefore requires fewer supports and a possible reduction in thickness of the structure for the same slab strength.

[0058] Figures 3 and 5 illustrate a first embodiment of the coupler 10. Coupler 10 comprises two parts adapted to each be embedded into one or another adjacent structure and to then be coupled together to join the structures. The two parts are a first connecting part 30 and a second connecting part 40. The two parts have a number of physical features in common.

[0059] Figures 6 to 12 illustrate a second embodiment of the coupler 10, which only differs from the first embodiment in features that will be explained below. Again, features in common between the first embodiment of Figures 3 and 5 and the second embodiment of Figures 6 to 12 will share the same reference numbers in this description.

[0060] Figures 7, 8, 11 and 12 illustrate the second embodiment of the connecting parts coupled together. Figures 9a, 9b and 9c illustrate the first connecting part (of the second embodiment) on its own, and Figures 10a and 10b illustrate the second connecting part (of the second embodiment) on its own.

[0061] As best shown in Figures 6 to 10b, the first and second connecting parts 30, 40 of coupler 10 each have parallel anchoring arms 32, 42, respectively, extending rearwardly from a front face 33, 43, respectively. The front faces 33, 43 each define a facing surface, 31 , 41 respectively, where the facing surfaces are adapted to abut flat and join together. The anchoring arms 32, 42, are securely embedded in the concrete structure by being cast into the concrete during the casting process. In practice, the anchoring arms are embedded to protrude inwardly of a side edge of the panel structure so that the front faces are exposed outwardly of the side edge such that the facing surfaces of complementary parts 30, 40 in adjacent structures can be brought together. The connecting parts are therefore embedded in a first plane, and namely the plane in which the floor slab lies. With the facing surfaces connected, the floor slabs are joined together side edge to side edge which structurally connects the slabs horizontally in tension.

[0062] As shown in Figures 5 and 12, a coupler recess 25 is formed toward a side edge of the concrete slab to provide a pocket for exposing the front faces and allow room for fixing the faces together. After connection, the recess 25 is filled with grout or cement, etc., bonding the exposed parts of the coupler into the slab and levelling off to be level with the surface of the structure, which in the embodiments shown is a floor 24.

[0063] The anchoring arms are flat members configured with anchoring features to maximise the arms’ grip in the dried concrete. The anchoring features include an internal central slot 50 in each arm and rounded inverse serrations 51 cut out and protruding into the internal slot and on the outer perimeter of each arm. The slot 50 and serrations 51 have the effect of increasing the planar surface area of the arms against which the drying concrete can form a firm purchase for a permanent anchor.

[0064] The anchoring arms 32, 42 also include sets of rod receiving apertures 55 in each connecting part 30, 40. Rod receiving apertures are adapted to receive reinforcement rods or bars 56 through each set of apertures to better anchor the coupler’s connecting parts into the concrete structures during the casting process. The apertures 55 may be provided at various points on the anchoring arms around the central slot 50, with a particular concentration of apertures closer to the front faces 33, 43 to receive perimeter bars 56.

[0065] Front faces 33, 43 of the connecting parts in effect bridge between the anchoring arms 32, 42 of each part. The front faces and anchoring arms could be formed separately and joined together by welding, etc., but preferably the connecting parts are formed from a single metal sheet stamped and folded to create a “U” shape with two anchoring arms extending from a central front face. [0066] Fastening openings 52 or slots in the front faces are adapted to receive mechanical fasteners for coupling together the connecting parts. The mechanical fasteners illustrated in the described embodiment are a nut and bolt assembly 53, whereby the strength rating of the nuts and bolts is selected to withstand stresses, strains and deflections resulting from the transfer of bending, torsional and/or shear forces expected through the structures. It is however understood that it is quite within the broad concept of the coupler to use other mechanical connections including screws, rivets, locks or otherwise mechanically fix together the front faces rather than using nuts and bolts. Furthermore, secondary non-mechanical connections can be used to supplement or assist the primary mechanical connection. Such non-mechanical connections include welds and adhesive fixings.

[0067] The coupler may be made from any number of known materials that exhibit sufficient strength and withstand tensile forces between adjacent slabs. In a preferred embodiment the components of the coupler is made of metal, but it is also foreseeable that other materials such as carbon fibre and composite materials could also function well. Examples of suitable materials from which the coupler components may be formed include low carbon steel (hot or cold rolled), high strength low alloy steel, stainless steel, cast iron or die cast aluminium.

[0068] A packing plate 54 is illustrated in the drawings between the front faces 33, 43, which can optionally be used for better engagement of the two connecting parts and to accommodate tolerances between the adjacent precast floors. Gaps between the front faces can be packed using one or more packing plates 54. Packing plate 54 is typically made of the same material as the coupler. Similarly, when bringing together entire concrete side edges of adjacent floor slabs packers (not shown) can be used to pack gaps between the slabs before the edge joins and coupler recesses 25 are filled with grout.

[0069] In the embodiments shown the facing surfaces 31 , 41 are joined at two connection points through two vertically aligned and spaced nuts and bolts 53. Having multiple fasteners improves the coupler’s ability to sustain exchanges of forces and moments between the structures, and also improves the strength of the coupler and its ability to transfer load forces between structures.

[0070] In designing coupler 10 to effectively withstand expected loads consideration should be given to the resulting stresses, strains and deflections at the coupler. In stress analysis the following equation applies for the amount of stress at the joint : s = P/A (1) where s = stress

P = total clamping force of the couplers across the joint A = area through which force is applied, namely joint face of precast slab

[0071] In the above equation an increase in the total combined clamping force of the couplers across the area of the joint will increase the amount of stress the joint can sustain before it begins to fail. By calculating the expected loading on a building slab the stress required to be sustained at a joint can be calculated. From there the number of couplers required for the joint can be determined.

[0072] The coupler design provides for high clamping forces across the joint. Contributing to the high forces are the well anchored arms against the moment applied to develop the full tensile capacity of the fasteners 53. Also, the greater the distance between the vertical fasteners between the connecting parts, the bigger the moment that can be sustained by the coupler.

[0073] By way of example, in a common 200mm thick precast concrete slab having a width of 3.7m, the fasteners are tightened to produce a clamping force of 200KN in each fastener. Using four couplers spaced along the width at the joint face, approximately 1MPa clamping stress can be achieved at the joint. The spacing of the couplers is approximately 1m apart. Obviously, more couplers spaced closer will provide a higher total clamping force which will result in higher stress capacity of the joint. However, it is noted that lower clamping stresses may be sufficient where a joint is at the point of contraflexure in the post tensioned panel. It is at the engineer’s discretion to calculate how many couplers are required for a given joint and what stresses need to be applied. In some instances it may be suitable to apply a clamping stress of 500kPa, while in others clamping stresses of at least 750kPa may be sufficient to connect the coupler parts.

[0074] The structural effect of the coupler is that the clamping stress will increase the friction and P/A axial precompression stresses at the joint, which in turn increases the shear capacity and the bending moment capacity of the slab at the joint.

[0075] The above description of the coupler 10 refers to both the first embodiment as illustrated in Figures 3 and 5 and the second embodiment illustrated in Figures 6 to 12. The second embodiment differs from the first in that it can also be joined together in a second plane that is perpendicular to the first plane. [0076] In the embodiments described where the concrete structure is a floor comprising panels/slabs joined edge to edge and the first plane lies in the same horizontal plane as the floor slabs, the second plane is the vertical plane. Coupling the connecting parts in a second and perpendicular plane has the effect of increasing the coupler’s resistance to bending, shear forces, moments and provides better transfer of loads. Connecting in two planes increases the moment strength at the coupler. For maximum connector strength, the distance between the first joint in the horizontal plane and the second joint in the vertical plane should be distanced as far apart as practically possible. In providing for a second connection in a perpendicular direction to the first connection, both the connecting parts 30, 40 are provided with additional features, as will now be discussed.

[0077] Figures 9a to 9c illustrate the first connecting part 30 with its front face 33 from which anchoring arms 32 extend rearwardly. In addition, a seat 35 extends in a cantilever fashion forwardly of, and away from, the front face 33. In the embodiment shown the seat is a rectangular planar piece welded across a bottom edge of the front face and extending a little rearwardly of the front face to also span across, and be attached to, a bottom edge of a front portion of the anchoring arms 32, which contributes to strengthening the cantilever aspect of the seat 35. In another embodiment not shown, the seat 35 extends much further rearwardly of the front face and almost as far as the end of the anchoring arms 32, which improves the torsional strength of the first connecting part 30. A forward part of the seat is also provided with bolt holes 36 for receiving fastening bolts 37. The front face 33 and the forward part of the planar seat are oriented perpendicularly to each other.

[0078] The seat 35 is adapted to receive and support a ledge 45 on the second connecting part. Figures 10a and 10b illustrate the second connecting part 40 having a ledge 45 that extends rearwardly from the front face 43 of the second connecting part and bridges between a front portion of the anchoring arms 42. In effect, the ledge is a planar rectangular piece that is bound on three sides by being welded to a bottom edge of the front face 43 and to adjacent bottom edges of the anchoring arms 42 behind the front face 43. Again, the ledge 45 lies perpendicular to front face 43. The ledge 45 also includes bolt holes 46 that are adapted to line up with bolt holes 36 in seat 35 to receive fastening bolts 37 for fastening the ledge to the seat to create the second joint.

[0079] As implied above, when coupling the first and second connecting parts 30, 40, ledge 45 is configured to align with and sit on top of seat 35. Figure 7 illustrates the assembled connecting parts in plan view and Figure 8 illustrates the assembled parts in side view. As shown, the horizontal and vertical joints comprise two nut and bolt assemblies each. The perpendicularly arranged joint connections provide a superior joint suitable for sustaining the flexural forces along the length of the coupler 10, as well as shear forces and moments between the concrete structures.

[0080] In one way, the coupler could be described and assessed as if it is acting as a fixed end in a loaded cantilever beam. The size of the coupler 10, its gauge thickness, the number of fasteners used and the distance between fasteners including the distance between perpendicularly oriented fasteners can be modified and calculated according to the intended application for the coupler in a particular concrete structure. The coupler should be able to withstand the expected stresses in the structure but also to function as a means of transferring forces between structures, as if the structures were formed as a single structure.

[0081] In assembling precast panels on site the panels, which are preferably prestressed, are designed to be assembled with one component of the coupler cast in at an edge of the panel and the other corresponding component cast in at the edge of the next panel. Care should be taken to avoid designing adjoining structures with the same coupler component cast into the joining structure edges. In practice, the same coupler component may be chosen to be cast in several positions along one edge of a panel, while the other complementary component in the pair could be cast into a second edge of the same panel. Or all edges that are to be joined in a panel could be cast with the same coupler. The building/structure designer will determine the most appropriate arrangement of the coupler pairs.

[0082] In the second embodiment of the coupler, at least, the process of aligning a craned precast panel into position adjacent another panel is simplified through use of the horizontal alignment means on the coupler (for the vertically restraining joint). Specifically, the seat 35 of the first component 30 acts as a guide and support for the ledge 45 of the second component 40. Once the ledge 45 is correctly positioned on the seat 35 nuts and bolts 37 are assembled by accessing through coupler recess 25 to loosely fasten together the ledge and seat. With at least half of the length of the anchoring arms 32, 42 cast into the concrete slab 20, the remain front portion of the arms 32, 42 and the front faces 33, 43 are exposed and accessible in coupler recess 25.

[0083] The horizontally restraining joint can then be completed and the vertically restraining joint adjusted and tightened. A torque and alignment tool 60 is shown mounted alongside the coupler components on the adjacent slabs 20 and across the gap 27 between the slabs. The function of tool 60 is to align and apply a vice-like closing force on the coupler components that will move them toward each other thereby closing the gap 27. Use of this tool is optional.

Packing plate 54, if used, is positioned between the front faces, and the tool 60 tightened further before and nuts and bolts 53 can be inserted and tensioned. This process is repeated along the length of the slab edge for all couplers 10 along that edge. Once all coupler components have been connected the coupler recesses are filled with grout, or other suitable filler, to permanently fix the couplers and finish off the structure’s surface.

[0084] The present coupler and its use particularly with building construction provides significant advantageous over known building techniques. Referring to one specific use, the coupler allows use of precast post tensioned concrete panels or beams that can be used in a completely different manner than previously known. There is no need for a concrete topping layer over a precast slab assembly to tie the slabs together. The couplers function as mechanical connections between the slabs providing excellent joints that can withstand and transfer all forces between the slabs, namely bending, shear and torsional forces.

[0085] Furthermore, on-site construction time is reduced because the couplers are cast in with the precast concrete slab in a factory setting, which saves time on site that would have otherwise been spent pouring a topping layer and waiting for it to dry. Longer unsupported spans using less material is another benefit of the coupler because rather than acting as discrete individual panels or beams, the coupler joins multiple panels or beams so that forces can transfer between them as if the multiple panels or beams were a single unit.

[0086] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0087] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, namely, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0088] It is to be understood that the aforegoing description refers merely to preferred embodiments of invention, and that variations and modifications will be possible thereto without departing from the spirit and scope of the invention, the ambit of which is to be determined from the following claims.

Claims

CLAIMS:

1. A coupler for coupling precast concrete structures, comprising a first connecting part having an anchor configured to be embedded in a side edge of a first precast concrete structure and a second connecting part having an anchor configured to be embedded in a side edge of a second precast concrete structure; each connecting part comprising a facing surface, wherein the facing surfaces are adapted to be mechanically joined together in a first plane to structurally couple the concrete structures.

2. The coupler claimed in claim 1 , wherein in each connecting part, the anchor extends rearwardly of the facing surfaces.

3. The coupler claimed in claim 1 or 2, wherein the anchor of each connecting part comprises two anchoring arms extending rearwardly of the facing surface, which bridges the two anchoring arms.

4. The coupler claimed in any one of the preceding claims, wherein the connecting parts further comprise corresponding planar surfaces adapted to be mechanically joined together in a second plane, the planar surfaces being perpendicular to the facing surfaces, and the second plane being perpendicular to the first plane.

5. The coupler claimed in claim 4, wherein the planar surface of the first connecting part is a seat extending forwardly and perpendicularly from an edge of the first connecting part’s front face.

6. The coupler claimed in claim 5, wherein the seat also extends rearwardly of the front face bridging across the anchoring arms.

7. The coupler claimed in any one of claims 4 to 6, wherein the planar surface of the second connecting part is a ledge extending rearwardly of the facing surface and bridging across the second connecting part’s anchoring arms.

8. The coupler claimed in any of the preceding claims wherein corresponding facing surfaces and/or corresponding planar surfaces are each mechanically joined at one or two connection points .

9. The coupler claimed in claim 8, wherein the connection points are mechanical fasteners.

10. The coupler claimed in claim 8 or 9, wherein the connection points are fastened to create a clamping stress of at least 500kPa.

11. A concrete floor formed from precast and post tensioned concrete slabs connected together by one or more couplers as claimed in any one of the preceding claims.

12. A method of constructing a concrete floor using precast and prestressed concrete slabs, including: forming precast first and second concrete floor slabs with post tensioned reinforcement and casting at least at one side edge an anchor of a first connecting part of a coupler, an anchor of a second connecting part of a coupler, or anchors of both first and second connecting parts, wherein the placement of the connecting parts is designed to align corresponding connecting parts when the first and second slabs are mounted in an adjacent position; relocating the concrete slabs to a building site and assembling the first floor slab in position; locating the second floor slab adjacent to the first floor slab so as to align corresponding facing surfaces of the first and second connecting parts on adjacent slabs; and mechanically connecting the facing surfaces of the first and second connecting parts in the same plane as the plane of the floor slabs to form a continuous structural concrete floor.

13. The method claimed in claim 12, including casting the first and second connecting parts into adjacent floor slabs at a similar height to an anchor point of a post tensioned tendon located at one or both of the side edges of the floor slabs.

14. The method claimed in claim 13, including casting the first and second connecting parts into adjacent floor slabs at a position along the side edges of the floor slabs that is in between anchor points of post tensioned tendons.

15. The method claimed in claim 13, including casting the first and second connecting parts into adjacent floor slabs at a position along the side edges of the floor slabs that is as close as possible to anchor points of post tensioned tendons.

16. The method of any one of claims 12 to 15, including mechanically connecting corresponding planar surfaces of the first and second connecting parts in a plane perpendicular to the plane of the floor slabs.