AU2015268715B2

AU2015268715B2 - Bridging method and composite girder and deck therefor

Info

Publication number: AU2015268715B2
Application number: AU2015268715A
Authority: AU
Inventors: John Armstrong
Original assignee: Bridge Design and Construct Pty Ltd
Current assignee: Bridge Design and Construct Pty Ltd
Priority date: 2014-12-14
Filing date: 2015-12-14
Publication date: 2021-04-08
Anticipated expiration: 2035-12-14
Also published as: AU2015268715A1

Abstract

Composite girder assemblies (10) are in use on a headstock (11) and piers (12) and comprises spaced webs (13) welded to top flanges (14) and bottom flanges (15). Cross bracing (16) is provided at the %, M½and % web length positions to restrain the bottom flanges from buckling sideways. Diaphragm assemblies (17) each interconnect the respective ends of the webs (13) and comprise a welded diaphragm plate (20), integral upper flange (21), integral lower flange (22) and bracing gussets (23). Full- height bracing webs (24) complete the diaphragm assembly (17). Club headed shear studs (25) are resistance welded to the top flanges (14) and upper flanges (21) and resist pull-out of a concrete deck (26). 1/9 04 C*4D 11

Description

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BRIDGING METHOD AND COMPOSITE GIRDER AND DECK THEREFOR FIELD OF THE INVENTION

This invention relates to a bridging method and composite girder and deck therefor. This invention has particular application to a rail and road bed bridging method and a girder and deck assembly for use in bridging, and for illustrative purposes the invention will be described with reference to this application. However we envisage that this invention may find use in other applications where girders and decks are used such as fixed buildings, causeways and the like.

BACKGROUND OF THE INVENTION

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the referenced prior art forms part of the common general knowledge.

Composite girder and deck assemblies utilize the principal that a steel girder tends to sag under load, with alower portion being in tension and an upper portion in compression. Securing a concrete deck to the upper portion with a plurality of embedded fixings stresses the concrete in compression, its most strain-resistant mode, reducing bend. The principal has been well used since the 1940s, particularly in the US Interstate Highway system.

In a typical historical system, two or more hot-rolled I-beams are supported in situ between headstocks to prevent sag. Shear fixings are secured to the top flange of the I-beams. o Formwork is established, concrete reinforcing strands are supported in the formwork and concrete is board to form the road bed. The I- beams may be prevented from spreading under loads by transverse stressing; this is considered mandatory for 3-beam structures. After curing the support is removed, the tendency of the I-beam to sag being resisted by the concrete road bed being compressed in the direction along the girder.

The technology to fabricate and galvanize I-beams of sufficient size has enabled fabricated structures to replace hot-rolled I-beams in many applications. Typically, galvanized I-beams are formed by welding top and bottom flanges to a web. Two or more of the beams so formed are interconnected at least at their end portions by welded or bolted diaphragms of plate to form a rectangular box with the beams. In most applications, the girder so formed is built in situ on the headstocks or adjacent then craned into position. However, the structure is too heavy to be craned with the concrete deck preformed on the steel. In order that the girder resist the construction loads without sagging, the steelwork is heavy.

Examples of variations on the general theme include Japanese Patent Publication

JP2006328862 (A), wherein a composite girder is formed by integrating a hybrid steel girder and a reinforced concrete floor slab. The hybrid steel girder is constituted by forming a compression flange 1 and the web 2 of a steel material of a relatively low strength material, and forming a tension flange 3 of a steel material of a relatively high strength material. This composite girder is formed by integrating a reinforced concrete or steel concrete composite floor slab 5 on an upper surface of the compression side flange 1.

In a further example, China Utility Model CN202530365 (U) discloses a half- through type opening box-shaped section steel-concrete composite beam in a bridge structure. The composite beam comprises an opening box-shaped beam, stud connecting pieces and a o concrete slab, wherein the opening box-shaped beam comprises two upper flange plates, two web plates, a base plate and a middle horizontal plate fixedly connected together; in the box-shaped space formed by the two web plates, the base plate and the middle horizontal plate, diaphragm plates are longitudinally spaced in the bridge; the size of the diaphragm plates is matched with the box-shaped space, and the diaphragm plates are fixedly connected with surrounding steel plates; the stud connecting pieces are welded with the upper flange plates, middle horizontal plates and the web plates above the middle horizontal plates; and bar-mat reinforcements are arranged above the plates and cast with concrete to form a concrete slab.

In a yet further variation, International Patent Publication W02014169826 describes a PCSS shear force coupled construction, comprising a steel structure (2) and an assembly-type prefabricated concrete bridge road plate. The prefabricated concrete bridge road plate comprises a concrete bridge road plate body (1) and a shear transferring structure (3) integrally cast with the concrete bridge road plate body (1) via a shear connector, and is fixed on the steel structure (2) via the shear transferring structure (3). Directly mounting the assembly-type prefabricated concrete bridge road plate on the steel structure (2) during the construction process facilitates the control of the construction process, significantly reduces the construction cycle, and exposes the coupling part of a composite beam, thus facilitating daily monitoring and maintenance, requiring less time out of service during maintenance and repair, and ensuring normal use of a bridge.

In each of the above examples the method of bridging requires that the composite structure be formed in situ since the composite girder and deck assembly is too heavy to manipulate. It has been surprisingly determined that a bridging method may include the use of composite bridging girders that may be craned.

SUMMARY OF THE INVENTION

1. In one aspect the present invention resides in a bridging method including the steps of:

forming a base structure comprising at least two spaced metal webs each generally defining a depth and length of a beam, with a tensile lower flange welded to a lower edge of each web, wherein the at least two metal webs each comprise the web of a discrete I- or inverted T-beam and the tensile lower flange of each web are spaced apart, cross bracing between said webs selected to form a 3 dimensionally braced beam, and diaphragm assemblies each interconnecting the respective ends of said webs, said base structure being supported against inherent sag on supporting means;

installing a non-stressed reinforced concrete deck to interconnect upper edges of said webs and secured thereto by shear fixings to form a composite girder and deck assembly;

crane lifting said composite girder and deck assembly from said supporting means; and

installing said composite girder and deck assembly on a bridge substructure.

In another aspect the present invention resides in a bridging method including the steps of:

forming a base structure comprising at least two spaced metal webs each generally defining a depth and length of a beam, with a tensile lower flange welded to a lower edge of each web, cross bracing between said webs selected to form a 3 dimensionally braced beam, and diaphragm assemblies each interconnecting the respective ends of said webs, said base structure being supported against inherent sag on supporting means;

installing a reinforced concrete deck to interconnect upper edges of said webs and secured thereto by shear fixings to form a composite girder and deck assembly;

installing said composite girder and deck assembly on a bridge substructure.

The method may further include leapfrogging further composite girder and deck assemblies into position by a crane sitting on alast erected span so formed. Alternatively, the method may further include a launching nose bolted to the leading end of said composite girder and deck assembly and the assembly jacked or winched out.

In a further aspect, the present invention resides broadly in a bridging method including the steps of: forming a base structure comprising at least two spaced metal webs each generally defining a depth and length of a beam, with a tensile lower flange welded to a lower edge of each web, cross bracing between said webs selected to form a 3 dimensionally braced beam, and diaphragm assemblies each interconnecting the respective ends of said webs, said base structure being supported against inherent sag on supporting means; crane lifting said base structure from said supporting means; installing said base structure on a bridge substructure; and installing a reinforced concrete deck to interconnect upper edges of said webs and secured thereto by shear fixings to form a composite girder and deck assembly in situ.

The base structure may be made substantially continuous and may be jacked or winched out over said bridge substructure, such as with alaunching nose bolted to the leading end.

In another aspect the present invention resides broadly in a composite girder including:

at least two spaced metal webs each generally defining a depth and length of a beam;

a tensile lower flange welded to a lower edge of each web;

cross bracing between said webs selected to form a 3 dimensionally braced beam;

diaphragm assemblies each interconnecting the respective ends of said webs; and

a reinforced concrete deck interconnecting upper edges of said webs and secured thereto by shear fixings.

2. In another aspect, there is disclosed a composite girder and deck assembly including:

a tensile lower flange welded to a lower edge of each web such that the tensile lower flanges are also spaced part from each other;

wherein said at least two spaced metal webs each comprise the web of a discrete I or inverted T-beam,

cross bracing between said webs selected to form a 3 dimensionally braced beam;

diaphragm assemblies each interconnecting the respective ends of said webs; and

a reinforced non-stressed concrete deck interconnecting upper edges of said webs and secured thereto by shear fixings, wherein the composite girder and deck assembly is configured to be portable for transportation to a bridge structure and to be installed on the bridge structure by crane lifting.

The metal webs may be set up in a rectilinear plan or the metal webs may be relatively skewed to form a trapezoid in plan. One or both ends may be skewed at up to 600in bridging methods and composite girders in accordance with the present invention. Existing prestressed concrete designs are limited to 300. The skew is to accommodate bridges at a skew/angle over creeks or other roads.

The metal webs may each comprise the web of a discrete I- or inverted T-beam. For example, the metal webs may be each welded to respective both top and tensile bottom flanges to form an I-beam. Alternatively, one or both of the top and bottom flanges may be integrated to form, with the webs, a U-shaped girder or a box girder respectively.

The metal webs will be most practically formed of steel plate. For example, the depth of the steel webs may be selected to be substantially in proportion to the span and live load, such as in proportion to the live load of a 15m single rail track being supported on an adjacent pair of composite girders having 16mm webs of about 900mm depth.

The two-piece 15m span in accordance with the present invention weighs 50% of the current two piece prestressed concrete beams, at 22 tonnes versus 45 tonnes. The composite girder and deck assemblies may be lifted in the middle by smaller cranes whereas prestressed must be lifted and supported at the ends during transport and erection - usually with two cranes.

The tensile lower flange may be selected from steel that is one or both of heavier gauge than the web and of higher tensile strength steel. Based on a A325 loading a 15m span having 16mm webs about 1000mm deep and a top flange 250mm wide x 20mm thick may have a bottom flange of about 500mm wide by about 32mm thick. A 20m span having 16mm webs about 1200mm deep and a top flange 250mm wide x 20mm thick may have a bottom flange of about 500mm wide by about 32mm thick. A 25m span having 16mm webs about 1500mm deep and a top flange 250mm wide x 20mm thick may have a bottom flange of about 500mm wide by about 32mm thick.

The beams do not need to be pre cambered to accommodate live load deflection.

However, the bottom flange may be welded last whereby shrinkage may induce a slight upward pre camber. Positive or negative hog is not a problem under ballasted tracks.

The web may have full height web stiffeners both sides each end over the bearings and on the inside at the bracing.

The top flanges may provide at least partial formwork for pouring the concrete deck.

The upper edges of the web may in the alternative be crenellated in order to interact with the reinforcing of the concrete deck. The use of an inverted T beam of this type may have the advantage of inducing a positive hog through welding shrinkage during welding of the lower flange, thus opposing sag under load. The absence of an upper flange reduces steel weight and avoids the potential for corrosion on the upper bearing surface of a flange.

The shear fixings may comprise shear studs resistance welded to the top flanges and included threaded or clubbed ends to resist pull-out. The shear fixings may be adapted to be integrated with the deck reinforcing. The shear fixings may comprise at least two rows of typically 22 mm diameter shear studs, the spacing of the studs varying from about 200mm at the ends to about 400mm in a centre section.

In these embodiments the shear fixings comprise the interconnections and/or compressive interactions between the web edge and reinforcing and/or concrete matrix.

The girder may be composite as in the deck is cast to make the girder or the deck may be made composite by installing recessed precast panels over the shear connectors and filling the recesses with high early strength concrete/grout. Adjacent precast panels may be placed and fixed and the transverse joints provided with wine glass keys to be filled with HES concrete or grout. All will then act as composite under live loads.

The deck may for example comprise a 40MPa concrete deck of 200mm thick minimum may have top and bottom reinforcing with transverse bars of about 16mm and longitudinal strands of about 12mm. The bar reinforcement may be supplemented with sheet reinforcing mesh fabric. The deck may include one or more kerbs poured with the deck concrete or formed up with a construction joint line. Conventional decks cannot use integral kerbs and must be poured after installation to avoid hog cracking of the kerb. The kerb may be formed with gaps at, for example, 1/4, and %length to make discontinuous and provide drainage.

The concrete deck may be formed with reinforcing hooks at the ends to permit longitudinal integration with other girder and deck assemblies. The ability to join and make both the concrete and steel continuous is a desirable feature.

The diaphragm assembly may comprise a bolted in or welded in steel diaphragm assembly. The diaphragms may be swage or huck bolted in. Alternatively the diaphragm may comprise concrete diaphragms bolted in to the beam ends. Shear connectors may be welded onto the web of the main beams or long bolts put across through the diaphragms and beam webs. A concrete diaphragm could also be reinforced concrete poured before or with the deck concrete.

In addition to the end diaphragms, there may be provided one or more intermediate diaphragms. A bolted diaphragm between the ends of the main beams may use a T section with studs along the top of the T and flanges on the ends to bolt to the beams.

The cross bracing may be provided at the1/4, ½ and % web length positions to restrain the bottom flanges from buckling sideways. The cross bracing may be welded or bolted in and preferably engage at least the bottom flange and web simultaneously. In hot dipped galvanized (HDG) constructions, there may be advantages in bolting up to avoid disruption of the galvanizing. The cross bracing may comprise steel angle or channel.

o Flush proprietary lifters such as Reid or Swift may be cast into the concrete. Notwithstanding these spans can be lifted from the middle, for ease of loading and erecting lifting points can be in the centre and both ends to facilitate using 2 cranes especially on long heavy spans.

The spans can be manufactured in a workshop, casting yard, adjacent to a bridge site, on site beside the existing or new bridge or up on the piers in final position or up beside the existing track to facilitate quick installation or on falsework.

Spans may be made continuous over bridge piers to improve load carrying by incorporating splices into the flanges and webs. If needed the concrete slab can have starters or screwed joiners at the ends and the concrete made continuous by pouring an infill joiner over the piers after the spans are erected.

o Ifmaking the spans continuous, savings in span depth and flange thicknesses can be achieved by making the end spans shorter, such as 80% of the other spans. If the spans are made continuous and the spans are preassembled on the approach to the bridge, they can be launched by fitting a temporary launching nose to reach to the first pier and then push/jack/winch out across the piers. On longer bridges the spans could be launched from both ends to save time.

In general, a composite girder and deck assembly implies that the concrete deck is poured onto the sheer fixings. It is envisaged that the deck may be formed of precast or prestressed elements that are secured to the girder assembly by shear fixing means. If the deck is made from panels and simply bolted down there can be gaps between the nominal 2500 wide along the bridge with a gap to drain surface water away. These gaps may have rubber pads in the gap over the beams or full length if needed to waterproof such as over electrified tracks. The discrete panels in assembly may be made composite by filling the fixing voids around shear studs with concrete and filling the transverse joins with grout.

Longer units may be transported with the front end attached directly onto the prime mover turntable pin and a set of wheels or dolly attached at the % point or at the back end. A standard semi-trailer weighs up to 1OT and an extendable 15T, which is all dead load. To facilitate safe transport the diaphragms may have compatible 75mm diameter turn table pin holes both ends and have, at1/4 and %length points, an adaptor bracket on the dolly pin will take the diaphragm. For overloaded travel a 2, 3 or 4 axle dolly may be positioned under the load to suit the travel permit.

The purpose built socket for the pin in the end diaphragms may be used to fix the span to a bridge headstock by having a dowel with the top similar to the turn table pin and either already cast into the headstock at one end or both ends or sitting loose in a cored hole and grouted into the headstock when all is aligned. Except in extreme flooding sites the normal spans are not restrained down by the dowel pins. However, the use of turntable type pins admits the use of turntable type pin locking devices to vertically restrain the girder to the headstock; the girder may be just unlocked to remove and replace.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the following examples and non-limiting embodiments of the invention as illustrated in the drawings and wherein:

Fig. 1 is an isometric view of girder apparatus in accordance with the present invention, in use;

Fig. 2 is a partially cutaway view of the apparatus of Fig. 1;

Fig. 3 is a longitudinal section A-A of the apparatus of Fig. 1;

Fig. 4 is a detail view of Fig. 3;

Fig. 5 is a section B-B of the apparatus of Fig. 1;

Fig. 6 is a detail view of the parallel-beam structure of the apparatus of Fig. 1;

Fig. 7 is a partially cutaway isometric view of an alternative embodiment of the present invention;

Figs. 8, 9 and 10 are detail views of upper web edges useful in the embodiment of Fig. 7;

Fig. 11 is an isometric view of the steel structure of an alternative embodiment; and

Fig. 12 is a section across a typical cambered carriageway constructed on piers and crossheads using beams in accordance with the present invention.

EXAMPLE1

A bridge having 15 m spans is formed by providing a conventional pier and headstock bridge structure adapted to receive 15m girders. Off site, a girder is formed by first forming, on a supporting structure, a base structure comprising two spaced steel 16mm webs of 1000mm depth are welded first to a top flange 250mm wide x 20mm thick and second to a bottom flange 500mm wide by 32mm thick. Fabricated cross bracing is huck bolted in position at web-and-flange locations to form a 3 dimensionally braced beam. Fabricated steel diaphragm assemblies are installed to interconnect the respective web ends of the webs. An intermediate steel diaphragm assembly is also installed.

The top flanges are preinstalled with 22mm ERC-welded club-headed steel shear studs, with two longitudinal rows on each top flange. The longitudinal spacing of the stud pairs is 200mm at the girder ends, changing progressively to 400mm in a centre section.

A reinforced concrete deck is laid to the upper flanges using formwork. Where reinforcing frames and strands are in contact with shear studs, these are welded. The reinforced concrete deck in this example is a 40MPa concrete deck of 200mm thickness and having top and bottom reinforcing with transverse bars of 16mm and longitudinal strands of 12mm.

On curing, a crane lifts the composite girder and deck assembly from the supporting means for transportation to site. On site, a crane installs the composite girder and deck assembly on the bridge substructure, in this example in adjacent pairs to form a two-girder per span, single track rail bridge. This may be a straight lift, where after the crane may migrate over the spans, leapfrogging further composite girder and deck assemblies into position. The same spans may be given a launching nose bolted to the leading end and the assembly jacked or winched out.

EXAMPLE2

A bridging method is provided substantially in accordance with Example 1, except that the base structure is installed on a bridge substructure before casting of the concrete deck; in situ.

In the figures 1 to 6 there are provided 15m composite girder assemblies 10 illustrated in use on a headstock 11 on piers 12. Each girder assembly 10 comprises a pair of 16mm steel spaced webs 13, in this example of 1000mm depth. The webs 13 are welded to respective steel top flanges 14 of 250mm width and 20mm thickness and respective steel bottom flanges 15 of 500mm width and 32mm thickness.

HDG cross bracing 16 is provided at the/4,% and% web length positions to restrain the bottom flanges from buckling sideways. The cross bracing 16 engages both the bottom flange 15 and web 13 simultaneously, and is secured to the upper portion of the web 13 by huck bolts to form a 3 dimensionally braced beam.

Diaphragm assemblies 17 each interconnect the respective ends of the webs 13. Each diaphragm assembly 17 comprises a welded in steel diaphragm plate 20, integral upper flange 21, integral lower flange 22 and bracing gussets 23. Full-height bracing webs 24 complete the diaphragm assembly 17.

Club-headed shear studs 25 are resistance welded to the top flanges 14 in three longitudinal rows. The clubbed ends resist pull-out of a concrete deck 26.

The reinforced concrete deck 26 in this embodiment comprises a 40MPa concrete deck of at least 200mm thickness minimum and having top and bottom reinforcing with transverse bars of 16mm and longitudinal strands of 12mm. The deck 26 is formed with a kerb 27 formed up with a construction joint line.

In the embodiment of Figs. 7 to 10, where like numerals describe like components with the previous embodiment, the web 13 and tensile lower flange 15 form an inverted T beam having a crenellated upper edge 30, the crenellations 31 being selected to interact with the reinforcing of a concrete deck 26 formed thereon. In this embodiment, crenellations 31 may take several forms including those of Figs 8 to 10, wherein the shear fixing function comprises the interconnections and/or compressive interactions between the crenellated web edge 31 and reinforcing and/or concrete matrix.

In Fig. 8, plasma cut crenellations 31 include both inverted "Christmas tree" protrusions 32 and bar rests 33 to support reinforcing 34 in the manner of a bar chair. Some or all of the contact points may be welded. In addition, re-entrant spaces 35 between the crenellations 31 provide a key with the concrete matrix. Additional apertures 36 may take reo or starter bars to further engage the concrete matrix.

In Fig. 9, crenellations 31 are again formed with rest portions 37 adapted to support reinforcing bar 34 as before. Further rest portions 40 are provided on the web 13 edge between crenellations 31. Re-entrant spaces 35 between the crenellations 31 provide a key with the concrete matrix.

In Fig. 10 is the simplest version whereby dovetail crenellations 31 have re- entrant spaces 35 between the crenellations 31 to provide a first key with the concrete matrix. Additional apertures 36 take reo or starter bars to further engage the concrete matrix.

In the embodiment of Fig. 11, where like numerals indicate like features of the embodiment of Figs. 1 to 6, there is provided a steel girder sub-assembly comprising a pair of 16mm steel spaced webs 13, welded to respective steel top flanges 14 and respective steel bottom flanges 15.

Steel diaphragms 17 each interconnect the respective ends of the webs 13 and are integral installed at positions 1/3 and 2/3 of the length of the webs 13. Each diaphragm 17 comprises a welded in steel diaphragm plate 20, integral upper flange 21, integral lower flange 22 and bracing gussets 23 bracing the lower flange 22 to the bottom flange 15. Bracing webs 24 located on the outer surface of the webs 13 at the diaphragm locations are welded in the space between the upper 14 and lower 15 flanges to complete stiffening in the plane of the diaphragm 17.

Club-headed shear studs 25 are resistance welded to the top flanges 14 in two longitudinal rows, and are similarly welded to the integral upper flanges 21. The clubbed ends resist pull out of a concrete deck.

In this embodiment, the ends of the beam section include respective lower step portions 28 where the webs 13 are relived to allow the lower flange 22 of the end diaphragms 17 to rest on respective crossheads. In order to maximize the bearing surface area, there is provided intermediate bearing portions 29 each welded to respective webs 13, diaphragms 17 and braces 24.

Fig. 12 illustrates a typical cambered carriageway spacing marginal paths, the assembly being constructed on piers and crossheads using modular beams 10 in accordance with the present invention, wherein the reinforced concrete decks 26 are specialized and thus different for different functional parts of the carriageway. For example, the marginal path decks 50 include an integral kerb 51 and in use are asphaltic-composition coated 52. The outer carriageway deck portions 53 are similarly kerbed at 54. The main width of the carriageway is provided by a selected (in this case, three) plain deck portions 55. The camber is provided by cambering the asphalt road surfacing mixture 56 such as Hot Mix Asphalt (HMA).

The individual beams are interconnected by joiner plates 57 bolted between respective braces 24. The joiner plates may accommodate service conduits 60 and the outer overhangs may accommodate pipes 61 or the like.

The rigidity of the assemblies in accordance with the foregoing embodiments allows them to be simply lifted during and after manufacture. The greatly reduced weight allows the assemblies to be wider and longer. The reduced weight and increased rigidity allows them to be transported. The rigidity, reduced weight and transportability makes them portable. The no need to stress or grout the present girders together makes them into an instant span. The absence of stressing or grouting and their portability makes them re locatable or readily replaced.

The rigidity allows lifting from the centre for short assemblies, or the1/4 - ¾ points for longer assemblies or both ends for the longest. All other types of spans both non-stressed, pre stressed and post stressed must be lifted at the ends necessitating pairs of lifting slings or chains equal or greater in length to the span length to ensure a safe lift with 1 crane or 2 cranes used or a lifting spreader on 1 crane.

Current regulations require the load weight to be inflated by 20% or both the crane 15 capacities to be down rated by 20% for dual crane lifts. Lifting spreaders usually weigh 10% of the load being lifted creating further inefficiencies. All other types must be stored with supports at the ends only and transported supported at the ends only necessitating longer trucks and jinkers. Due to the reduced depth, rigidity, stability, increased width and lower centre of gravity the present assemblies, both frame only and full units, are safer to transport, unload, temporarily store and final place.

The reduced weight and centre lifting point allows a smaller single crane with less height needed under the hook. The ability to be lifted by the1/4 - ¾ points also allows a smaller crane to be used. The ability to be lifted by the ends allows a 2 crane lift making unloading from a vehicle parked on a slope and positioning easier especially on grades.

12m long units 2500 wide can be double stacked on a light weight semi or jinker as the semi is only loaded at the ends. 3 units could be stacked and transported if loaded directly onto the prime mover and rear end dolly.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is set forth in the claims appended hereto.

Claims

1. A bridging method including the steps of:

forming a base structure comprising at least two spaced metal webs each generally defining a depth and length of a beam, with a tensile lower flange welded to a lower edge of each web such that lower flanges of each web are also spaced part from each other, wherein the at least two metal webs each comprise the web of a discrete I- or inverted T-beam, cross bracing between said webs selected to form a 3 dimensionally braced beam, and diaphragm assemblies each interconnecting the respective ends of said webs, said base structure being supported against inherent sag on supporting means;

installing said composite girder and deck assembly on a bridge substructure.

2. A bridging method according to claim 1, further including leapfrogging further said composite girder and deck assemblies into position by a crane sitting on a last erected span so formed.

3. A bridging method according to claim 1 or claim 2, wherein the base structure is made substantially continuous and is jacked or winched out over said bridge substructure with a launching nose bolted to a leading end thereof.

4. A bridging method according to any one of claims 1 to 3 wherein wherein the metal webs are discrete I beams, each with a top flange and the bottom flanges are welded to the webs after the top flanges are welded to the web such that shrinkage induces a slight upward pre camber.

5. A composite girder and deck assembly including:

a tensile lower flange welded to a lower edge of each web such that the tensile lower flanges are also spaced part from each other; wherein said at least two spaced metal webs each comprise the web of a discrete I- or inverted T-beam, cross bracing between said webs selected to form a 3 dimensionally braced beam; diaphragm assemblies each interconnecting the respective ends of said webs; and a reinforced non-stressed concrete deck interconnecting upper edges of said webs and secured thereto by shear fixings, wherein the composite girder and deck assembly is configured to be portable for transportation to a bridge structure and to be installed on the bridge structure by crane lifting.

6. A composite girder according to claim 5, wherein tensile lower flange is selected from steel that is one or both of heavier gauge than the than the web and or higher tensile strength steel.

7. A composite girder and deck assembly according to claim 6, wherein said metal webs are relatively skewed to form a trapezoid in plan.

8. A composite girder and deck assembly according to claim 7, wherein one or both ends of the composite girder and deck assembly are skewed at up to 600.

9. A composite girder and deck assembly according to any one of claims 6 to 8, wherein the at least two metal webs comprise discrete I beams with a top flange on each metal web.

10. A composite girder and deck assembly according to claim 6 to 8, wherein the web and tensile lower flange form an inverted T beam having a crenellated upper edge, the crenellations being selected to interact with the reinforcing of the concrete deck.

11. A composite girder and deck assembly according to claim 10, wherein the shear fixings comprise the interconnections and/or compressive interactions between the crenellated web edge and reinforcing and/or concrete matrix.

12. A composite girder and deck assembly according to any one of claims 6 to 11, wherein the concrete deck comprises recessed precast panels over said shear fixings.

13. A composite girder and deck assembly according to claim 12, wherein the deck includes one or more kerbs poured with the deck concrete or formed up with a construction joint line.

14. A composite girder and deck assembly according to claim 12 or claim 13, wherein the concrete deck is formed with reinforcing hooks at the ends to permit longitudinal integration with other girder and deck assemblies.

15. A composite girder according to any one of claims 6 to 14, wherein the diaphragm assembly comprises a bolted in or welded in steel diaphragm assembly.

16. A composite girder according to any one of claims 6 to 14 wherein the diaphragm assembly comprises concrete diaphragms bolted into the girder ends.

17. A composite girder according to claim 15 or claim 16, wherein there is provided one or more intermediate diaphragms.

18. A composite girder according to any one of claims 6 to 17, wherein the cross bracing engages at least the bottom flange and web simultaneously.

19. A composite girder according to any one of claims 6 to 18, further including a downward-depending pin at a selected location and adapted to engage and be secured to a turntable of a prime mover or dolly.

20. A composite girder according to claim 19, wherein the pin is adapted to engage a corresponding recess in a bridge structure to locate said girder in use.