AU746805B2

AU746805B2 - A structural element

Info

Publication number: AU746805B2
Application number: AU72315/00A
Authority: AU
Inventors: Wladek Gontarczyk
Original assignee: ABERGELDIE G BEAM Pty Ltd
Current assignee: ABERGELDIE G BEAM Pty Ltd
Priority date: 1999-12-15
Filing date: 2000-12-15
Publication date: 2002-05-02
Anticipated expiration: 2020-12-15
Also published as: AU7231500A

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: WLADEK GONTARCZYK Invention Title: A STRUCTURAL ELEMENT The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 A STRUCTURAL ELEMENT FIELD OF THE INVENTION The present invention relates a method for making a structural element that finds particular application in the construction industries. A most preferred application is in the construction of bridges, roadways and other support structures. However, it should be appreciated that the method and the resulting structural element have a wide variety of applications throughout the construction industry.

BACKGROUND ART Composite structural elements are known in the construction industry. One type of composite structural member includes a cast concrete portion in conjunction with a girder.

The construction of such elements involves two phases. Firstly, steel girders are placed on their ooooo S 20 bearings and then formwork is erected around the steel girder. Falsework is used to support the formwork during concrete pouring. Concrete is then cast in and over the formwork and attaches to the steel girder. In this phase, the dead load of formwork, falsework and concrete is carried by the steel girder alone and consequently the steel girder must have sufficient flexural strength to ee S"accommodate such load. This has typically involved the use a steel girder having a substantial top flange of sufficient cross-sectional area and an appropriately small 30 slenderness ratio to withstand the compressive stresses resulting from flexure due to dead load (ie. self-weight, formwork weight and weight of wet concrete). Typically steel sections having similar or identical top and bottom 40634 3 flanges have been employed, such as standard universal beams and welded beams. The first phase is completed once the concrete has sufficiently cured and a composite function has been established.

In the second phase the composite structure is then subjected to additional "superimposed" dead load (eg. such as a roadway surface, road furniture etc) and must also be capable of carrying live load in use (eg. when forming part of a bridge, it must carry "live" traffic load etc thereon).

WO 90/05818 discloses a method for making a beam integral with a concrete slab. The beam 2 has a plurality of connection parts 3 in the form of a longitudinal protruding flanges. Reinforcing 1 extends transversely with respect to the beam 2 and is supported in recesses defined in parts 3. The beam and slab are assembled in an upside down configuration, but only so as to enable the concrete to fasten the reinforcing 1 to parts 3. Thus the beam 2 needs to be sized to support not only the connection parts 3, but also the reinforcing 1, both of which can be of significant extra dead load during formation of the composite structure. By virtue of this construction, as the concrete cures, its mass is transferred via reinforcing 1 and parts 3 to the beam 2.

25 Also, from Figure 1 and the description of WO 90/05818 it appears that beam 2 is of sufficient size to support the S"concrete slab 4 from the commencement of casting. Thus a "sizeable beam of increased mass and cost must be employed in WO 90/05818.

30 It would be advantageous if at least the first phase of construction of a composite structural element could be simplified or indeed eliminated.

40634 4 SUMMARY OF THE PRESENT INVENTION The present invention provides a method for forming a composite structural element that includes a concrete portion and a girder, comprising the steps of casting the concrete portion on a substrate and attaching the girder to the concrete portion in a manner such that concrete dead load is not imposed on the girder during casting.

As an alternative definition the present invention provides a method for forming a composite structural element that includes a concrete portion and a girder, comprising the steps of casting the concrete portion and attaching the girder to the concrete portion-in a manner such that the structural element does not receive any load thereon until a composite action is established between the concrete portion and the girder.

In accordance with the present invention the first phase can be eliminated such that total load (full dead load and service (live) load) is only applied on a fully established composite section which results in a considerable improvement of efficiency of the element.

S"This method allows for the use of comparatively smaller girders as the girder is not required to support the dead load of concrete and any formwork, falsework etc.

S* Alternatively, when a girder of equivalent weight to a 25 prior art girder is used, a relatively greater service load over the same span or a greater girder span for a S"similar load can be accommodated.

As a further advantage, because the concrete portion is capable of taking compressive stresses resulting from 30 flexure of the element, there is no need for the usual provision of a top flange on the girder. Thus all that is required is that the girder be capable of attachment to the concrete portion. Further as the top flange hardly 40634 5 contributes to the strength of the composite element it is thus effectively made redundant by the construction method according to the invention.

In a first form of the invention the girder can be attached to an upper side of the concrete portion (eg. to a newly cast concrete portion). In this first form, typically the girder is located upside down, just above formwork located on ground strata, so that when concrete is poured into the formwork it becomes connected to the girder located thereabove (eg. via shear connectors described below). The resultant composite structural element then requires turning (tilting) to an in use upright position (described below).

Alternatively, in a second form, the girder can be surrounded by formwork that defines the substrate such that the girder is located under and can be attached at an underside of the concrete portion. In the second form, typically the girder is continuously supported on ground strata in an upright position, and formwork is located on the ground strata on each side of the girder along its length (described below). The formwork is typically located level with the top of the girder (eg. top flange) so that when concrete is poured onto the formwork, the S.girder becomes connected thereto (eg. via shear connectors 25 that become embedded in the concrete described below).

In either case, after curing of the concrete, a S"composite action is established between the girder and concrete portion, so that the element has a unitary configuration.

30 As stated above, the method enables a girder to be employed that, for an equivalent span and equivalent load profile, has less material than a prior art girder. For example a girder can be employed that has, in cross- 40634 6 section, a base flange, a web extending from the base flange to an end that is narrower than and opposite to the base flange, and wherein the narrower end is attached to the concrete portion. The narrower end is typically adapted for attachment to the concrete portion (eg. as defined below).

Use of the terminology "web" is not intended to limit the girder configuration, the term "web" including within its scope a stem or slender part of a girder that extends between the base flange and the end, but also including thicker portions (if required), box sections etc. The girder can also be a solid member having no "flanges" as such, and can be formed eg. from reinforced concrete.

For the first form of the invention, preferably during curing of the concrete portion the girder is supported in position by falsework which typically maintains the girder in a perpendicular orientation with respect to the concrete portion. Typically after attachment of the girder to the concrete portion and after a predetermined amount of curing of the concrete portion, the composite element is tilted about an edge of the concrete portion until it is supported on the girder.

During tilting the structural element can also be S. supported on a protective member attached to and/or 25 located along the side of the concrete portion to protect eg. any protruding bars or rods and to also protect the S" edge of the concrete portion.

S"Typically (at least for larger composite elements) one or more temporary struts or props are provided to 30 extend between the concrete portion and the girder for supporting the girder during tilting, handling and erection of the composite element (ie. after curing of the concrete portion). One end of each temporary strut is 40634 7 typically attached to the concrete portion via a bracket which is incorporated in the concrete portion prior to curing (typically soon after pouring or casting), and an opposite end of each strut is attached via a bracket to the girder at or near a base thereof. The struts are typically arranged in one or more pairs along the length of the girder such that, for a given pair, one strut is located on an opposite side of the girder to the other strut. Thus, the plurality struts combine to support the girder during its movement up to and including erection.

In the second form of the invention preferably the girder base is positioned on a substrate such that the girder extends generally up and away from the substrate and formwork is positioned on either side of the girder so as to define a platform on either side thereof.

Concrete can then be cast on the platform to form the concrete portion and to attach the narrower end of the girder to the concrete portion, without imposing a concrete dead load on the girder itself, with any concrete S 20 load that is transferred to the girder being transferred to the substrate. The girder and formwork are supported on the substrate (eg. on the ground), so that no flexural movement is affected in the girder.

Preferably the formwork is not attached to the girder 25 so that also there is no dead load of formwork on the girder. This again enables a girder having eg. a narrower attachment end to be employed.

Temporary struts and/or props can then be used to stabilise the girder under the concrete portion until a 30 predetermined amount of concrete curing has taken place, so that the composite element can then be supported on the girder base.

40634 8 With this second form, after curing, the girder can also be supported by one or more struts (as defined above) which strut(s) can be subsequently removed.

Preferably the formwork is a pair of tablets (eg.

formed from plywood or timnber framing) located on opposite sides of the girder, with each tablet having an upper surface that is flush with (or even slightly above) an upper surface of the girder during casting.

Additionally, a pair of wedges can be located under the tablets (typically wooden wedges), the removal of which enables easy removal of the tablets after the predetermined amount of curing.

Preferably the girder in cross-section has an I or Tshape and, when I-shaped, the narrower end of the I is typically a flange narrower than the base flange of the I, such that the girder is attached to the concrete portion at the narrower flange of the I, or at the end of the stem of the T. Standard or other modified I-beam configurations can also be employed. Angle girders (eg.

L-shaped in cross-section) and U-girders (eg. U-shaped in S" cross-section) can also be employed, with the end attached .i to the concrete portion typically being in each case narrower than the opposing base flange.

The adaptation of the girder for attachment to the concrete portion can include: two or more shear connectors extending from and S"integral with the girder, and which are incorporated into the concrete portion prior to its curing from a casting; or 30 two or more separate fasteners which attach the girder to the concrete portion prior to or after its curing from a casting.

40634 9 Preferably the shear connectors are pins, bolts, welded angles, small channels etc extending upwardly from a top wall or flange of the girder.

The fasteners can be separate bolts or pins which are inserted through appropriate holes at the top wall or flange of the girder and then into the concrete portion.

Typically the girder is asymmetric such that in use, when the concrete portion is supported on the girder, the centre of gravity of the girder is shifted closer to the base, thus displacing the centre of tensile forces further from the centre of compressive forces in use of the girder. Such an arrangement increases the lever arm of the composite element, which provides a greater flexural capacity. Advantageously this can be achieved with less girder material or by redistribution of material to create a more efficient section.

It is further preferred that at least one side (and typically opposing sides) of the concrete portion is adapted such that the composite element can be joined to a similar or like composite element to form an extended S" structure. In other words, multiple composite elements may be joined end to end and/or side to side, for example in bridge constructions, roadway constructions, floor constructions etc Preferably the joining adaptation is formed on opposing longitudinal sides (and optionally ends) of the concrete portion and includes: SS two or more holes formed in the portion during casting which enable the tying together of adjacent 30 concrete portions of adjacent composite elements with special precast link slabs (which are designed to provide flexural continuity of the concrete deck); or 40634 10 one or more rods or bars extending out from the concrete portion and which can be arranged adjacent to (eg. to lap with) similar or like rods or bars of an adjacent composite element. Usually the adjacent rods or bars have concrete cast therearound to provide a continuous deck (slab). Typically the- rods or bars are an extension (projection) of actual reinforcement within the concrete portion (ie. protruding out beyond the original as formed concrete portion) Typically the girder is formed from a steel or steel alloy, or from a galvanised steel etc. Alternatively the girder can itself be formed from reinforced concrete, such as precast concrete, pre-stressed or post tensioned concrete etc.

Typically the concrete portion is a concrete deck, which is usually reinforced. Alternatively the concrete portion can be provided in the form of a thin slab (plate eg. of 75 to 100mm thickness) designed as formwork for an in-situ topping slab that is cast over a plurality of abutting concrete plates of a plurality of parallel composite elements. Thus the concrete plate can replace 0 the previously employed heavy top steel flange in its role in the first phase of composite construction (ie. for dead load support).

25 In a second aspect the present invention provides an extended structure including two or more joined composite structural elements as defined above. In this regard, the 55555* composite structural elements are typically tied or *o otherwise joined to form the composite structure, 30 preferably by employing said adaptation of the concrete portion of each composite element as defined above.

40634 11 BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1, 2 and 3 show end sections of preferred composite structural elements formed in accordance with the invention, each at an intermediate stage of formation; Figures 4 and 5 show end sections of two different types of finished composite structural elements, each adapted for forming an extended structure; Figure 6 shows an end section of an extended structure formed using the composite structural element of Figure 4; Figure 7 shows an end section of an extended structure formed using the composite structural element of Figure 5, but in an intermediate stage of formation; Figures 8, 9 and 10 show, respectively, end, plan and perspective elevations of a finished extended structure; Figure 11 shows an end section of a known I-beam girder in a composite structural element (which may or may not have been formed in accordance with the method of the S* present invention) and illustrating schematically the location of the centre of gravity, centre of tension and centre of compression of the I-beam girder, and depicting S- the lever arm of internal forces for that composite arrangement; Figure 12 shows an end section of a composite structural element formed in accordance with the present invention and illustrating schematically the centre of gravity, centre of tension and centre of compression, and 40634 12 illustrating an increase of the lever arm and hence an increase in flexural capacity; Figure 13 shows in perspective and schematically, in views A, B, C, D, four different types of girder for use in a formation method in accordance with the present invention; Figures 14 to 16 show, in perspective view, the sequence of steps in the formation of a preferred composite structural element; Figures 17 to 19 show, in end view, the tilting of the composite element into an in use orientation.

Figure 20 shows a partially sectioned perspective view of the finished composite element illustrating how the girder is attached to the concrete slab; Figure 21 shows a perspective view, similar to Figure 7, illustrating how a pair of like composite elements are joined together to form an extended structure; and Figure 22 shows an end section of an extended structure for use in providing formwork for a further S 20 concrete deck, in accordance with the present invention.

MODES FOR CARRYING OUT THE INVENTION Referring firstly to Figure 1, a composite structural element in the form of a composite beam 10 includes a 25 concrete portion in the form of a concrete slab 12 and a girder 14. The girder 14 shown includes a base flange 16, a web 18 and an opposing narrower flange 20 (although a variety of girders described below can be employed) The narrow flange may simply be a flattened end of the web 30 (see Figure 13) but typically is at least wider than the end of the web.

Projecting from the narrow flange and into the slab are a pair of shear connectors in the form of fixing pins 40634 13 22. Other shear connectors employable include small angles and channels typically welded to and projecting integrally from the girder for incorporation in the concrete slab. The pins 22 can be formed integrally with the flange 20, or can be separate bolts or pins insertable through appropriate holes formed in the flange. Usually, however, integral shear connector systems are employed.

In accordance with the present invention, the concrete slab can be formed on a substrate 24 such as surrounding ground adjacent to a.site or on a plywood base etc. Preferably for economic reasons the forming (casting) advantageously takes place on ground or substrate adjacent to the construction site in which the composite beam is to be used. This is a considerable advantage over prior art composite beam systems, which typically require complex and expensive formwork for the composite slab and which hangs off the girder in-situ.

With the present invention a simple border work 25 is formed on the substrate (see Figure 15) and concrete is 20 then poured into that border work. Multiple slabs may also be formed adjacent to each other. Thus slab load is transferred to the substrate (rather than the girder) during composite beam formation.

The fixing pins are positioned into the so-poured 25 concrete (or for separate fastemers may be inserted into the concrete prior to its hardening or curing) to be moulded and captured therein. Alternatively, appropriate holes can be drilled after slab curing and the girder can then be attached (eg. by bolting, screwing etc).

30 The arrangement of Figure 1 shows how the girder is supported for tilting after curing. A pair of brackets 26 having protruding hooks 28 are positioned on opposite sides of the slab so that the hooks extend into the poured 40634 14 (uncured) concrete. Each bracket is also adapted for receiving the end of a strut 30 therein, and the brackets are angled so that each strut extends towards the base flange of the girder.

A pair of integral or separately mounted girder brackets 32 each then receive the opposing end of a respective strut, and this arrangement supports the girder so that the web is maintained generally perpendicularly to the slab during tilting. However, other angled orientations can be induced and maintained by changing strut lengths, bracket inclinations etc.

Once the slab has sufficiently cured, the struts enable the composite beam to be tilted, whilst maintaining the integrity of the slab and girder. After tilting typically the struts and brackets are removed.

Alternatively, the struts can be left permanently in place if desired (although this is aesthetically less pleasing).

Figures 17 to 19 show the inversion sequence (ie.

tilting to the position shown in Figure The tilting 20 can be effected by a crane, or by winching on a cable attached to the brackets and/or girder etc. Typically *during tilting a protective support is positioned adjacent to one of the sides 34 of the slab. The composite beam is then tilted around this support (ie. to protect the side 25 of the beam and any reinforcing projecting out from the side (described below)). Also, struts may not be required for smaller composite beams.

S* Referring now to Figure 2, an arrangement similar to Figure 1 is shown (and like reference numerals are used to 30 denote similar or like parts). In this embodiment, rather than employing projecting hooks, the brackets are attached by a pair of nut and bolt arrangements 36. The advantage of this is that, once the bracket and nut and bolt 40634 15 arrangements are removed, a pair of preformed holes 38 are left in the slab, and these can be used for the subsequent formation of an extended structure (described below) Referring now to Figure 3, an alternative method for formation of the composite beam is depicted. Like reference numerals are used to denote similar or like parts.

In this case rather than forming the slab on substrate 24, formwork 40 is positioned on either side of girder 14. The formwork includes a pair of tablets 42, typically formed from a plywood or timber framed box. A pair of wedges 44 are positioned under each tablet, and are sized such that tablet upper face 46 lies flush with (or slightly above) the upper face of the flange Also, the wedges transfer the entire weight of the slab above each tablet to the substrate 24 (eg. to the ground).

In other words, only a fraction of the weight of the slab (if any) is transferred through the girder to substrate 0 024.

20 When the slab has cured sufficiently, the wedges are 00 00 simply knocked out from under each tablet and the tablets b 0" are then removed. Again the struts are used to support the girder during movement of the composite beam, but prior to or after removing the tablets the struts 30 can 0000 25 also be removed.

0000 The construction method depicted in Figure 3 is particularly suitable for larger or longer span composite o o beams, and eliminates the need for beam tilting whilst providing continuous support for the length of the slab 894 S 30 during curing.

Referring now to Figures 4 and 6, it can be seen how holes 38 can be used to join adjacent (typically like) composite beams 10. As can be seen, a pair of reinforcing 40634 16 rods 48 are typically precast in a discrete concrete slab 52 (eg. formed in separate formwork). The rods extend between adjacent composite beams, and each rod has an internally threaded ferrule 49 attached thereto and located at its opposing ends to which is secured a respective threaded bolt 50. The bolts are inserted through the holes 38 and are attached to the ferrules 49 to fasten the slab 52 in place and thus fasten the adjacent slabs 12 together. The length of the rods and the width of the slab can be selected such that the slab sides 34 abut (and there is no spacing therebetween for an infill slab). However, the embodiment of Figure 6 in fact depicts a longer set of rods and a wider discrete slab 52, to thereby widen the resulting composite structure. In this case, an infill slab 54 is subsequently poured into the space between the opposing slab sides 34 to provide a continuous slab upper face 56.

The discrete slab 52 can run for the length of the "slab 12, or can have a nominal width (as shown in Figure I20 9) sufficient to encapsulate the rods 48 securely therein.

When the discrete slab is only as wide as that shown in Figure 9, then when forming the infill slab 54, additional *0 oooo formwork is positioned in the gap between adjacent *00"discrete slabs. Again, the discrete and infill slabs are 0000 0 25 typically reinforced.

0000 Figure 5 shows an alternative composite beam in which a pair of protruding reinforcing rods 58 have been cast in 0°09 to extend out from both slab sides 34. Typically rods 58 are an extension (protrusion) of reinforcing within each 30 slab 12, or may be separate rods. As can be seen, the *0:00 reinforcing rods on one side are offset with respect to the reinforcing rods on the other side. This enables the rods to intermesh when the composite beam is joined to an 40634 17 adjacent composite beam to define a composite structure (as shown in Figure 7).

Referring now to Figures 7 and 21, when forming the infill slab 54, an upper support frame 60 is positioned to extend between the adjacent composite beams, and a pair of hangers 62 extend down from the support frame (eg. at front and rear ends of the composite structure). These hangers support a formwork panel 64 between the adjacent slabs typically for the length thereof. As shown in Figure 21, prior to pouring of the infill slab 54 a tie beam 57 can span slabs 12 to stabilise the composite beams, prior to and during final curing of the extended structure.

Thus, infill concrete 54 can then readily be poured up to the level of the slab upper face 56 to complete the deck slab. The reinforcing rods are cast within this concrete and thus hold the adjacent composite beams together and additionally provide reinforcing to infill i :0 20 slab 54.

20 Referring now to Figures 8 to 10, where like reference numerals are used to denote similar or like parts, rather than employing rods 48, a pair of nut and e000 bolt (or bolt and ferrule) assemblies 66 can be employed .00o on opposite sides of discrete slab 52 to attach a pair of 25 composite beams together. The arrangement is, in all other respects, similar to that shown in Figure 6.

Referring now to Figures 11 and 12, the mechanical advantages of structures formed from the method of the present invention are illustrated schematically. As described above, the present invention enables the formation of composite beams having asymmetric girders (eg. with a narrow top flange). Figure 11 firstly shows a known symmetrical I-beam in a composite structural element 40634 18 (but which in any case can be formed in accordance with the present invention). As can be seen, the girder centre of gravity (CoG) is spaced midway along the web of the Ibeam. The centre of compressive stresses (CoC) is approximately in the middle of the concrete slab. The centre of tensile stresses (CoT) is located just under the centre of gravity. The size of the lever arm (ie.

distance between the CoC and CoT) is depicted.

Referring now to Figure 12, it can be seen that the centre of gravity (ie. as a result of there being a drastic reduction in the size of the top flange) is moved downwardly in the girder 14. This has the effect of moving the centre of tensile stresses further away from the centre of compressive stresses (ie. because the centre of gravity is moved downwardly) thus increasing the lever arm (as shown). This results in a greater moment capacity of the composite beam, because the lever arm for internal forces is increased. Thus a greater flexural capacity is achieved with less girder material. This is a surprising and unexpectedly advantageous result flowing directly on from the construction methods of the present invention which enable the use of such girders.

Referring now to Figure 13, where like reference oooo numerals are used to denote similar or like parts, four different girder types A, B, C and D, suitable for use in accordance with the present invention are depicted.

Figure 13A depicts an angle girder, Figure 13B depicts an inverted T-girder, Figure 13C depicts a i modified I-girder (similar to girder 14 shown in Figures 1 to 10 and 12) and Figure 13D shows a U-girder. In each case, a narrower flange or end 20 of the girder (ie. that abuts the slab 12) can be provided with an attachment 40634 19 mechanism, such as integral fixing pins, screw holes etc (not shown) Referring now to Figure 22 an extended deck structure formed from a plurality of composite (precast) beams is depicted. However, in this case each beam has a concrete slab provided in the form of a relatively thinner concrete plate 12', usually of 75 to 100mm thickness which acts as formwork for a subsequently cast concrete slab This arrangement provides continuity of the deck and is also useful in replacing prior art girders having heavy top flanges (and which flanges have previously functioned as a formwork) The arrangement of Figure 22 provides a third method for forming an extended structure and is cheap to fabricate and can also be fabricated on site. The concrete plates 12' are typically reinforced 72 (eg. with light reinforcement) and the slab 70 is usually reinforced. As a further option the reinforcing 72 can project 74 up into slab 70 to provide a unified structure.

20 This joining can also be achieved by shear connectors etc (described above). Thus the resulting structure 80 is itself a composite structure.

Typically the concrete slab 12 in each of the coo.

embodiments described above is reinforced, as is the discrete slab and infill slab (as appropriate). Typically the girder is formed from steel or steel alloys, as are the fixing pins and various nut and bolt arrangements.

However, the girder itself can also be formed from reinforced pre-cast, pre-stressed concrete or posttensioned concrete, i.e. each functioning independently as a reinforced beam.

The applicant has also observed that existing socalled "super-T" girders can themselves be replaced by a 40634 20 composite structural element formed in accordance with the present invention.

Whilst the invention has been described with reference to a number of preferred embodiments, it should be appreciated that the invention can be embodied in many other forms.

*o: 40634

Claims

2. A method for forming a composite structural element that includes a concrete portion and a girder, comprising the steps of casting the concrete portion on a substrate and attaching the girder to the concrete portion in a manner such that dead load of concrete and reinforcing is not imposed on the girder during casting.
3. A method for forming a composite structural element that includes a concrete portion and a girder, comprising the steps of casting the concrete portion and attaching the girder to the concrete portion in a manner such that the structural element does not receive any load thereon 20 until a composite action is established between the V concrete portion and the girder.
4. A method as claimed in any one of the preceding claims wherein the girder is either: attached to an upper side of the concrete portion at 25 the commencement of, during or after pouring/curing of the concrete portion; or (ii) surrounded by formwork that defines the substrate, such that the girder is located under and can be attached ooooo S•at an underside of the concrete portion at the commencement of, during or after pouring/curing of the concrete portion. A method as claimed in claim 4 wherein in the girder is located upside down, just above formwork located 40634 22 on ground strata, so that when concrete is poured into the formwork it becomes connected to the girder located thereabove.
6. A method as claimed in claim 5 wherein the composite structural element is tilted after curing to an in use upright position.
7. A method as claimed in claim 4 wherein in (ii) the girder is surrounded by formwork that defines the substrate such that the girder is located under and can be attached at an underside of the concrete portion.
8. A method as claimed in claim 7 wherein the girder is continuously supported on ground strata in an upright position, and formwork is located on the ground strata on each side of the girder along its length, at a level that is aligned with the top of the girder, so that when concrete is poured onto the formwork, the girder becomes connected thereto.
9. A method as claimed in claim 5 or claim 6 wherein, during curing of the concrete portion, the girder is supported in position by falsework which maintains the V0.- girder in a perpendicular orientation with respect to the concrete portion, and wherein after attachment of the girder to the concrete portion and after a predetermined *o amount of curing of the concrete portion, the composite 25 element is tilted about an edge of the concrete portion until it is supported on the girder. A method as claimed in claim 9 wherein, during tilting, the structural element is supported on a protective member attached to and/or located along the side of the concrete portion to protect any protruding bars or rods and/or to protect the edge of the concrete portion. 40634 23
11. A method as claimed in claim 9 or claim 10 wherein one or more temporary struts or props are provided to extend between the concrete portion and the girder for supporting the girder during tilting, handling and erection of the composite element, with one end of each temporary strut being attached to the concrete portion via a bracket which is incorporated in the concrete portion prior to curing, and an opposite end of each strut being attached via a bracket to the girder at or near a base thereof.
12. A method as claimed in claim 11 wherein the struts are arranged in one or more pairs along the length of the girder such that, for a given pair, one strut is located on an opposite side of the girder to the other strut, so that the plurality struts combine to support the girder during its movement up to and including erection.
13. A method as claimed in claim 7 or claim 8 wherein the girder base is positioned on the substrate such that the girder extends generally up and away from the substrate 20 and formwork is positioned on either side of the girder so as to define a platform on either side thereof, and concrete is then cast on the platform to form the concrete portion and to attach a narrower end of the girder to the concrete portion, without imposing a concrete dead load on S. 25 the girder itself, with any concrete load that is transferred to the girder being on-transferred to the substrate.
14. A method as claimed in claim 13 wherein the girder and formwork are supported on the substrate so that no flexural movement is affected in the girder. A method as claimed in claim 13 or claim 14 wherein the formwork is not attached to the girder so that there is no dead load of formwork on the girder. 40634 24
16. A method as claimed in any one of claims 13 to wherein temporary struts and/or props are used to stabilise the girder under the concrete portion until a predetermined amount of concrete curing has taken place, so that the composite element can then be supported on the girder base.
17. A method as claimed in claim 16 wherein, after curing, the girder is supported by the one or more struts or props which strut(s) or prop(s) can be subsequently removed.
18. A method as claimed in any one of claims 13 to 17 wherein the formwork is a pair of tablets located on opposite sides of the girder, with each tablet having an upper surface that is flush with (or slightly above) an upper surface of the girder during casting.
19. A method as claimed in claim 18 wherein a pair of wedges are located under the tablets, the removal of which enables easy removal of the tablets after the OVeee: predetermined amount of curing. 20 20. A method as claimed in any one of the preceding claims wherein the girder has, in cross-section, a base flange, a web extending from the base flange to an end that is narrower than and opposite to the base flange, and •co* wherein the narrower end is attached to the concrete 25 portion.
21. A method as claimed in claim 20 wherein the girder in cross-section has an I or T-shape and, when I-shaped, the :narrower end of the I is typically a flange narrower than the base flange of the I, such that the girder is attached to the concrete portion at the narrower flange of the I, or is attached to the concrete portion at the end of the stem of the T. 40634 25
22. A method as claimed in any one of the preceding claims wherein the girder is adapted for attachment to the concrete portion by the inclusion of: two or more shear connectors extending from and integral with the girder, and which are incorporated into the concrete portion prior to its curing from a casting; or two or more separate fasteners which attach the girder to the concrete portion prior to or after its curing from a casting.
23. A method as claimed in claim 22 wherein the shear connectors are pins, bolts, welded angles or small channels extending upwardly from a top wall or flange of the girder.
24. A method as claimed in claim 22 wherein the fasteners are separate bolts or pins which are inserted through appropriate holes at the top wall or flange of the girder and then into the concrete portion.
25. A method as claimed in any one of the preceding 20 claims wherein the girder is asymmetric such that in use, a. when the concrete portion is supported on the girder, the centre of gravity of the girder is shifted closer to the base, thus displacing the centre of tensile forces further from the centre of compressive forces in use of the 25 girder.
26. A method as claimed in any one of the preceding claims wherein similar or like composite structural elements are joined together to define an extended structure, after the formation of each composite element.
27. A method as claimed in claim 26 wherein at least one side of the concrete portion is adapted such that the composite element can be joined to an adjacent adapted 40634 26 side of a similar or like composite element to form the extended structure.
28. A method as claimed in claim 27 wherein the joining adaptation is formed on opposing longitudinal sides (and optionally ends) of the concrete portion and includes: two or more holes formed in the portion during casting which enables the tying together of adjacent concrete portions of adjacent composite elements with special precast link slabs; or one or more rods or bars extending out from the concrete portion and which can be arranged adjacent to similar or like rods or bars of an adjacent composite element.
29. A method as claimed in claim 28 wherein the adjacent rods or bars have concrete cast therearound to provide a continuous slab. A method as claimed in claim 28 or claim 29 wherein the rods or bars are a projection of actual reinforcement S eCo within the concrete portion, protruding out beyond the original as-formed concrete portion.
31. A method for making a composite structural element substantially as herein described with reference to the accompanying drawings.
32. An extended structure including two or more joined composite structural elements as produced by the method of any one of the preceding claims.
33. A composite structural element as produced by the S method of any one of claims 1 to 31. Dated this 15th day of December 2000 WLADEK GONTARCZYK By his Patent Attorneys GRIFFITH HACK 40634