AU2019206009A1 - Load bearing structure and sections therefore - Google Patents

Abstract

A section for a load bearing structure (10), the section comprising at least one tubular structural member joined to at least one further tubular structural member, the first tubular structural member comprising a fiber-reinforced polymer (FRP) outer tube (14) and a metallic or FRP inner tube (12) and the at least one further tubular structural member comprising a fiber-reinforced polymer outer tube and a metallic or FRP inner tube; wherein when the inner tubes (12) are joined together, the outer tubes (14) are fluidlyjoined together to define a continuous annular space (18) between the inner and outer tubes about the joint for filling with a settable filler. Figure 2 12 14 DSTA 116 Figure 2 (a) and (b) Figure 3a

Description

LOAD BEARING STRUCTURE AND SECTIONS THEREFORE

TECHNICAL FIELD [0001] The present disclosure relates to the field of construction and civil engineering and in particular, the field of bridge design and construction.

BACKGROUND [0002] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

[0003] The present disclosure places particular emphasis on a load bearing structure that is a bridge. However, it will be appreciated that the disclosed structure may have other applications that may be readily ascertained by a structural engineer and limitation is intended thereby. Exemplary applications include viaducts, causeways, culvert, walkways, pipelines and the like.

[0004] A common aim when designing a load bearing structure such as a bridge, whether pedestrian, road or rail, is to providing a design that meets or exceeds the required load bearing standards, is corrosion resistant and meets construction deadlines.

[0005] Traditional bridge construction methods are labour intensive, time consuming and require the use of heavy materials. Beams for conventional bridge construction are generally made from reinforced concrete or steel. Such beams are subject to deterioration and corrosion. Corrosion protection such as installation of anodes adds to costs. Further related costs are incurred where road closures and/or detours are required.

[0006] Fibre-reinforced polymer (FRP) composites are formed by mixing high performance fibres such as carbon fibres and glass fibres with a resin matrix. The composite material is light weight, corrosion resistant and is able to be easily moulded. FRP has been used in a number of ways in structural beams. Beams have been produced from entirely FRP, hybrid beams incorporating FRP and concrete and concrete filled FRP tubes. In practice these beams suffered a number of disadvantages such as low stiffness and poor ductility.

[0007] In order to address these disadvantages double skin tubular members (DSTM) have been proposed. The DSTM’s consist of an outer tube made of FRP and an inner tube 1

2019206009 16 Jul 2019 made from steel and the space between the tubes is filled with concrete.

[0008] DSTMs in the form of columns (DSTC) have found application in construction for use as support columns or piles. DSTMs may also be in the form of beams (DSTB.) The two tubes may be concentrically placed for use as columns or eccentrically spaced suitable for use as beams. The metal tube and FRP act as a stay in place formwork for the concrete. The inner steel tube allows connection to the inner steel tube of other members or to conventional steel members by welding.

[0009] The provision of the steel inner tube also allows relatively easy interconnection with other structural members such as for the interconnection of beams and columns or columns and floor slabs. The inner steel tube, particularly provided without a filler, may allow steel to be run from an interconnecting beam or floor slab into the steel tube and welded against stiffeners fitted to the inner steel tube. This is typical for existing columns utilizing steel tubes.

[0010] It should also be noted that the inner tube may be appropriately modified and/or provided with shear connectors to ensure composite action with the filler material if desired.

SUMMARY [0011] The present inventors have appreciated that there are still improvements or modifications to be made to the use of double skin tubular member technology in construction of load bearing structures or the desire to provide construction engineers with a useful or commercial choice.

[0012] According to a first aspect, there is disclosed a section for a load bearing structure, the section comprising at least one first tubular structural member joined to at least one further tubular structural member, the first tubular structural member comprising a fibre- reinforced polymer outer tube and an inner tube and the at least one further tubular structural member comprising a fibre- reinforced polymer outer tube and a metallic inner tube; wherein the inner tubes are joined together, the outer tubes are fluidly joined together to define a continuous annular space between the inner and outer tubes about the joint for filling with a settable filler.

[0013] It will be appreciated that by joining both the inner and outer tubes and that introducing a settable filler allows the filler to flow continuously in the annular space around the joint. Thus, it may be possible to provide a joint that may have more favourable structural properties rather than by merely welding to together the inner metallic tubes of 2

2019206009 16 Jul 2019 the two parts.

[0014] Suitably two or more sections are joined together and the filler is introduced after the sections have been joined together so as to provide an integrated structure.

[0015] The inner tubular member may made from any suitable material having the desired physical properties. The inner tube may be metallic or also formed from FRP or any other suitable composite material. The metallic members are suitably steel as this is a common construction material. Other metals or composites may be used that have similar physical properties to steel. The inner tube may be strengthened with fibre composites or additional reinforcing steel or plate steel.

[0016] Thus there is further disclosed a method of constructing a load bearing structure or a section thereof, the method comprising joining together two or more tubular metallic members to form a tubular metallic segment, placing at least one FRP tube around each tubular metallic member in the segment, joining the FRP tubes together to define a continuous annular space between the two or more metallic members and FRP tubes and filling the annular space with a filler.

[0017] Suitable types of reinforced fibre polymers are known in the construction arts and are readily available. Glass fibre reinforced polymers are a preferred type.

[0018] In the present specification and claims, the terms tube or tubular are understood to not to be limited to having a circular cross section but includes any desired cross section including square and rectangular.

[0019] In the present specification the term bridge will be understood to broadly apply to any structure that allows passage thereover (deck truss) or thereunder (through truss).

[0020] The metallic tubes will generally be hollow, but there may be some applications, where the tube may be filled with a filler.

[0021 ] The filler is suitably an flowable, self compacting expoxy material and is suitably a flowable, self compacting concrete.

[0022] A suitable concrete is a high strength self-consolidating or self-compacting concrete (HSCC). Such concretes are a stable and cohesive high consistency concrete mix with enhanced filling ability properties that reduce the need for mechanical compaction. HSCC’s are used for pre-cast concrete in the construction industry. Suitably the HSCC has

2019206009 16 Jul 2019 a strength of at least 50Mpa, preferably at least 70Mpa and preferably less than 100Mpa.

[0023] It is also suitable that the HCSS concrete has good flowability. Suitably, the HSCC has a minimum slump of about 400mm (determined using a standard cone test), more suitably a minimum of about 500mm.

[0024] The concrete may also include steel, FRP, stressing cables and/or other compressive or tensile reinforcement as used in the construction arts.

[0025] As discussed in the introduction, known DSTM’s are either columns or beams. The properties have been studied and columns have a circular cross section with concentric double tubular arrangement so as accommodate load from any direction. Beams on the other hand have a rectangular cross section and the inner tubes are generally eccentric to move the steel to the zone having greater tensile stress.

[0026] There is also disclosed in the present specification a novel double skinned tubular arch member (DSTA). Suitably the DSTA is a concentric tube of circular cross section. As discussed in the detailed description the DSTA may have superior properties to a reinforced concrete (RC) arch whilst being up to about 35% lighter.

[0027] It may be appreciated that the disclosed tubular segments and methods in which one or more of the tubular members are arcuate or straight segments forming an arch, the outer FRP layers are arcuate or straight segments forming and arch, and are joined to a DSTC or DSTB have wide application.

[0028] The ability to provide a DSTA significantly extends possible applications of DSTM’s. DSTA’s may be used in any application to where an arch design is used such as bridges, viaducts and culverts, rail, vehicle and pedestrian overpasses.

[0029] Arch bridges are well known and comprise an arch with columns joined thereto for supporting or suspending beams that support a deck. Arches are conventionally formed from RC or concrete filled steel tubes.

[0030] In the disclosed DSTAs The annular layer of concrete sandwiched between the outer FRP tube and the inner metal tube arch, the inner tube arch can provide steel tension reinforcement for the section to resist bending. The inner steel tube arch can also act as propping during the construction process of placing the FRP tubes, sealing the tubes and casting the filler.

2019206009 16 Jul 2019 [0031 ] The tubular inner metallic arch may be formed in one piece or a number of arch tubes joined together.

[0032] In this case, one or more of the metal arch tubes are joined to a column metal tube to obtain a metallic segment. FPR tubes are placed around the metallic segments that are then welded together, the FPR tubes are the joined or sealed together to define a continuous annular space about the entire segments and joints that is then filled with a filler.

[0033] A DSTM beam can then be joined to the tops of the columns for an overarch construction or to the bottom of the columns for an underarch construction. The beam may be a section as disclosed herein in which a number of metallic tubular sections are joined end to end and FRP tubular sections are placed around the joined metallic sections and sealed so as to provide a continuous annular space along the length of the beam for filling with a filler.

[0034] The beam section may then be joined to the columns by welding or other joints which are composed of steel plate, steel tubes, concrete, epoxy, steel or RFP pins, and bots. The beam section may then be filled with filler.

[0035] In order to finish the construction of the load bearing bridge member, the process is repeated and the two arch sections are joined together.

[0036] The final step is to fix a deck to the beams. Suitably a light weight deck system of reinforced concrete or FRP decks will be used. FRP lightweight bridge systems are well known and are available “off the shelf”.

[0037] Such bridge deck systems are typically designed to transfer loads transversely to supports such as longitudinally running girders, cross beams and the like. In other words, traffic direction is generally transverse to the longitudinal axis of the deck.

[0038] The completed structure is a bridge module that is significantly lighter than a known RC bridge modules. RC modules require lifting into place by a fixed crane [0039] The light weight of the bridge module allows transport by road or rail to the construction site. Whilst fixed cranes may be used to lift the disclosed bridge modules into position the lighter weight means this is not necessary.

[0040] Suitably the bridge modules may be lifted into place from transport using self erecting hydraulic rams or winches. Such rams and winches are known in the construction

2019206009 16 Jul 2019 industry.

[0041] The bridge modules are typically of a size that may be transported on a truck bed or rail carriage that complies with the overall maximum dimensions and does not require obtaining special permits, escorts, pilots or the like. By way of example, the maximum dimensions for a truck according to the Queensland Department of Transport guidelines are 12.5m in length, 4.6m in height and 3.5m in width. Suitably modules may have a length of about 12m. Such a length can comfortably span two lane roadway that is typically about 6m to 7m wide.

[0042] If spans of greater than about 12m are required, two or more modules may be connected end to end.

[0043] In another aspect, the modules may be configured to as bridge sections that may be joined together. The individual sections are thus generally joined together on site. Such jointing may be by any suitable means. The ends of the steel inner tubes may be permanently joined by welding.

[0044] In an alternative arrangement, the joints are temporary joints that allows the structure to be disassembled. For example, it may be desirable to provide a temporary bridge structure to enable passage of traffic whilst a permanent bridge structure is being built or repaired.

[0045] In one aspect, there is provided a connector having a first end for being received within an end of the hollow inner tubular member of a first segment and a second end for being received within an end of the hollow inner tubular member of a second segment. The connector is suitably fixed to the respective ends, by fixation such as pins, bolts or the like.

[0046] The bridge sections are suitably dimensioned for truck transport as described above. The segments may be up to 12m. Still further, as the sections are of lighter weight than conventional concrete sections, the sections may be launched using by mobile cranes that are designed to travel on public roads and can pick up a load and carry the load to a desired locations, as opposed to fixed cranes with outriggers (often referred to in the art as ‘pick and carry’ or ‘franna’ cranes).

[0047] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0048] The reference to any prior art in this specification is not, and should not be taken 6

2019206009 16 Jul 2019 as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

BRIEF DESCRIPTION OF DRAWINGS [0049] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

[0050] Figure 1 is a photograph a prototype of one embodiment of a bridge module as disclosed herein;

[0051 ] Figure 2 is a schematic view of the bridge module as shown in Figure 1;

[0052] Figure 3a is a schematic lower perceptive view of the bridge module of Figure

1;

[0053] Figure 3b is a drawing of a front view of the bridge module of Figure 1;

[0054] Figure 4a is a schematic cross sectional view of the DSTA of the bridge module of Figure 1;

[0055] Figure 4b is a schematic cross sectional view of the DSTC of the bridge module of Figure 1;

[0056] Figure 4c is a schematic cross sectional view of the DSTB of the bridge module of Figure 1;

[0057] Figure 4b is a DSTA axial load-movement curve;

[0058] Figure 5a is a front view of the bridge module of Figure 1 showing the respective segments;

[0059] Figure 5b is a photograph of segments 2 and 6 as shown in Figure 5a;

[0060] Figure 5c is a photograph of segment 7 as shown in Figure 5a;

[0061] Figure 5d is a photograph of FRP tubes that are used to place over the beams of the module of the bridge module of Figure 1;

2019206009 16 Jul 2019 [0062] Figure 6a is a photograph of sheer studs attached to the segments;

[0063] Figure 6b is a photograph of a segment with strain gauges attached;

[0064] Figure 7a is a photograph of placing a FRP tube around a metallic column;

[0065] Figure 7c is a photograph showing completed placement of a FRP tube about segment 1 and aligning with segment 2;

[0066] Figure 7d is a photograph showing completed placement of a FRP tube about segments and segments a and 2 welded together;

[0067] Figure 8a schematically shows a DSTA-DSTC joint layup sequence;

[0068] Figure 8b schematically shows a DSTC-DSTB transverse joint layup sequence;

[0069] Figure 8c schematically shows a DSTC-DSTB joint layup sequence;

[0070] Figure 9a is a photograph showing FRP joint segments before sealing;

[0071] Figure 9b is a photograph showing connecting FRP with epoxy;

[0072] Figure 9c is a photograph showing placing pre-preg strips around the joint as shown in figure 9b;

[0073] Figure 9d is a photograph showing placement of breather an applying vacuum about the joint shown in figure 91;

[0074] Figure 9e shows placement of the heat blanket about the joint;

[0075] Figure 9f is a photograph showing the sealed joint;

[0076] Figure 10a is a photograph showing the glass fibre plastic sheet for use in the wet lay up process;

[0077] Figure 10b is a photograph showing the wet lay-up process;

[0078] Figure 10c is a photograph showing placing of a release film;

[0079] Figure 10d is a photograph showing placing a breather;

[0080] Figure 10e is a photograph showing applying a vacuum to the joint;

2019206009 16 Jul 2019 [0081 ] Figure 10f shows applying a shrink tape about the joint;

[0082] Figure 11 a is a photograph showing the arch and column segments sealed;

[0083] Figure 10b shows pouring concrete into the annuls;

[0084] Figure 11c is a photograph showing concrete poured between the FRP and steel;

[0085] Figure 12a is a photograph showing placement of FRP tubes around the steel of DSTBs;

[0086] Figure 12b is a photograph showing top DSTBs placed on DSTCs and welded;

[0087] Figure 13a is a schematic front view showing concrete pumping locations on the DSTB;

[0088] Figure 13b is a photograph showing casting of the concrete into the DSTB;

[0089] Figure 14a is a photograph showing a DSTA-DSTC joint with pre-preg;

[0090] Figure 14v is a photograph showing a DSTC-DSTB joint with wet-layup FRP;

[0091] Figure 14c is a photograph showing a DSTA-DSTA joint with pre-preg;

[0092] Figure 15a is a schematic view of a bridge comprising bridge modules of a second embodiment of the disclosure;

[0093] Figure 15b is a front view of a bridge module as shown in Figure 15a;

[0094] Figure 15c is a detail of a truss joint of the module as sown in Figure 15a;

[0095] Figure 16a is a front view of the bridge module as shown in Figure 15a;

[0096] Figure 16b is a segment view of the module through lines B in Figure 16a;

[0097] Figure 16b is a cross section view through 1 -1 of Figure 16b;

[0098] Figure 17 is a schematic view of one method of erecting a bridge structure using modules as disclosed herein;

[0099] Figure 18 is a schematic view of a road or rail overpass constructed from modules as disclosed herein;

2019206009 16 Jul 2019 [00100] Figure 19 is a schematic view showing a first step in launching of a modular bridge according to another aspect of the disclosure;

[00101] Figure 20 is a schematic view showing the second step in launching of the modular bridge;

[00102] Figure 21 is a schematic view showing the next step in launching of the modular bridge;

[00103] Figure 22 is a schematic view showing the next step in launching of the modular bridge;

[00104] Figure 23 is a schematic view showing the next step in launching of the modular bridge;

[00105] Figure 24 is a schematic view showing the next step in launching of the modular bridge;

[00106] Figure 25 is a schematic view showing the next step in launching of the modular bridge;

[00107] Figure 26 is a schematic view showing an alternative method to carrying out the step shown in Figure 24;

[00108] Figure 27 is a schematic view showing an alternative method to carrying out the step shown in Figure 25;

[00109] Figure 28 is a schematic view of the completed modular bridge as launched by the methods as shown in Figures 19 to 27;

[00110] Figure 29 is a schematic view of a completed modular bridge according to another aspect of the disclosure and

DETAILED DESCRIPTION [00111] In the present specification and claims, the word ‘comprising’ and its derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers.

[00112] Reference throughout this specification to One embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the 10

2019206009 16 Jul 2019 embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[00113] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

[00114] Figure 1 is a photograph of a bridge module 10 as disclosed herein. The module is constructed of DST beams (DSTBs), DST columns (DSTCs) and DST arches (DSTAs). These hybrid double-skin tubular members (DSTMs) have an inner steel tube 12, an outer fibre reinforced polymer (FRP) tube 14, a concrete layer between the two tubes 16 and a hollow core 18.

[00115] Figures 2a and 2b schematically shows the cross sections of the DSTA and DSTB. There is a hollow steel inner tube, an outer Glass Fibre reinforced polymer tube and a concrete annulus therebetween. It can be seen that both tubes of the DSTB are square in cross section and the inner tube of the DSTB is eccentric towards the tension zone of the section. The cross section of the DSTA tube is circular and the inner tube is concentric.

DESIGN METHODOLOGY [00116] A span of 12 to 12.5m was selected for the DSTA bridge, considering the need for easy transportation. A bottom perspective view of the DSTA bridge module 10 is given in Figure 3a. The bridge 10 has a first side 20 and a second side 22 that are connected through transverse DSTMs 24 [00117] The height of the DSTA bridge to the top surface of the DSTBs was taken to be 2.5m, or the maximum height able to be transported by road. The width of the bridge was so selected that the centre line distance between the two adjacent DSTB top chords is equal to the standard railway track gauge for rail bridges, and up to 3.5m wide for road bridges. The design actions were determined according to AS5100.2 (2004). The ultimate loading applied to the DSTA test module 10 was based on the 300LA railway traffic load (AS5100.2

2019206009 16 Jul 2019

2004) and is summarised in Figure 3b.

[00118] The design procedure proposed by Yu and Teng (2011) for the design of circular DSTCs under static loading, which was also adopted by the relevant Chinese national standard (GB 50608-2010), was used to carry out the design of the DSTA bridge. In the procedure, the stress-strain behaviour for the glass FRP (FRP) tube and ultimate condition (rupture failure) are obtained using a combination of material test data and theoretical analysis. A variable confinement model (GB 50608-2010) was adopted for modelling the stress-strain behaviour of confined concrete to account for the effect of strain gradient on confinement effectiveness. In this variable confinement model, the design-oriented stressstrain model proposed by Lam and Teng (2003) was adopted for the confined concrete under concentric compression, forming the upper bound of the model, while a modified unconfined concrete model with a long plateau is adopted for the confined concrete subjected to pure bending forming the lower bound of the model. The DSTA, DSTC and DSTB cross-sections used in the DSTA bridge 10 are given in Figures 4a, b and c respectively, while a typical axial load-moment interaction curves for a DSTA section generated using Yu and Teng’s (2011) procedure is given in Figure 4d.

[00119] Design actions for the DSTMs were evaluated through linear and non-linear analysis. In these models, the DSTAs and DSTBs were modelled as continuous members. The critical axle load configuration was determined by applying moving loads in the linear analysis. The critical load configurations were then modelled in a nonlinear analysis developed in OpenSees (McKenna et al., 2000) which considers geometric and material nonlinearity.

CONSTRUCTION [00120] Construction of the DSTA bridge can broadly be divided into three phases:

(a) fabrication of steel core by welding straight sections together and fabricating straight FRP segments, (b) assembling FRP segments around steel core and joining the FRP segments, either (c) constructing joints by welding the steel segments together, completing the FRP wrapping around the welded steel joints and concrete casting of the annulus between the steel and FRP, (both joints and segments cast concurrently)

2019206009 16 Jul 2019 (d) attaching the beam to the arch and columns by welding the steel, completing the FRP wrapping around the welded steel joint, (e) concrete casting of the annulus between the steel and FRP of the beam and joints.

or (f) concrete casting of the annulus between the steel and FRP segments, joining the complete steel, concrete, FRP segments, using steel, concrete, epoxy joints, wrapping the joints in FRP, concrete casting of the annulus between the steel and FRP around the joints.

(a) Fabrication of steel and FRP segments [00121] Each module 10 was divided into 14 segments (Figure 5a). Segments 1-7 each consists of an arch segment 30 and a column segment 32, while segments 8-14 each consists of a beam segment 34. Hot rolled grade 250 steel sections were welded into segments, (Figures 5b show segment 2 and 6 & 5c shows segment 7. The FRP tubes were filament-wound (with 8 layers of FRP, having fibre angles of 15 degrees to the tube axis) in a factory, to standard lengths (Figure 5d shows the FRP tubes with a circular cross section 36 for the columns and the PFR tubes 38 with a rectangular cross section used for the beams). The steel segments and the FRP tubes were cut to size. Shear studs 40 were welded to the tubes 12 (Figure 6a). These shear studs 40 provide optimum composite action between the steel tube 12 and the concrete annulus 16. In addition, strain gauges 42 were also attached to the steel surface 12 on pre-determined positions (Figure 6b).

(b) Assembly of FRP segments around steel of arch or columns and welding [00122] Once the steel segments 12 were fabricated and the shear studs 40 were welded, the FRP segments 36, 38 were placed around the steel segments 12 (Figures 7a7c), and then adjacent steel segments were welded together (Figure 7d). To ensure all segments were levelled and to restrain against movement, a reference I-beam was welded to the column steel tubes protruding above the FRP to form a top chord, allowing the connected segments to be aligned and lifted. Once lifted into position and attached to the strong floor, the two sides (Figure 3a) of the DSTA bridge where connected to form the bridge through transverse DSTMs.

(c) Sealing of FRP tubes and concrete casting of arch and columns [00123] Two different techniques were used in fabricating the FRP-FRP joints. All

2019206009 16 Jul 2019

DSTA-DSTC joints and all DSTA-DSTA joints were made using pre-impregnated FRP (prepreg), and DSTC-DSTB-transverse and DSTC-DSTB joints were made using the wet-layup process.

[00124] The wet-layup process does not require heating for curing, but is more difficult to apply than pre-pregs and may not lead to the same quality as pre-pregs.

[00125] In order to design the manufacturing of joints, a simple linear elastic finite element analysis was carried out to determine the stress trajectories of the FRP-FRP joint regions. Based on the stress trajectories, FRP fibre orientations were determined. The final FRP fibre orientations and the numbers of layers used in each joint type are given in Figures 8a to 8c that show the connection of column to arch, column to beam and beam to column respectively. The Figures show rectangular resin strips 50, U jacket 52, cross strips 54, circumferential strips 56, curvature strips 58 and perimeter strips 60.

[00126] Before proceeding with the pre-preg or wet-layup procedures, adjacent FRP tubes were first attached together with epoxy resin 62 (Figures 9a & 9b) to ensure no air voids were present at the joints. For both the pre-preg and the wet-layup processes, the surface preparation undertaken immediately before bonding involved abrasion and wiping with acetone to remove any surface contaminants and produce a chemically active surface. Pre-pregs were manufactured by impregnating fibres with epoxy and then storing at low temperature to prevent the epoxy from curing.

[00127] To join adjacent FRP tubes by pre-preg, a pre-preg laminate 64 was first cut into a number of strips and placed onto the joint (Figure 9c). A release film and a breather were placed, and a vacuum was applied (Figure 9d). To apply heat for the curing process, a simple heat box was used 66 (Figure 9e) or heat blankets 68 were used. Each joint was heated to 900C, and the heat was maintained for 4 hours for pre-preg adhesive curing to provide a sealed joint as shown in Figure 9f.

[00128] For the wet lay-up process, a fabric sheet was cut in to strips 70 of required dimensions, laid on a flat surface (Figure 10a) and saturated with epoxy. The fabric strips 70 with epoxy were then wrapped around the joint 72 (Figure 10b). Rollers were used to squeeze out any excessive epoxy. A release film (Figure 10c) and a breather (Figure 10d) were placed, and a vacuum (Figure 10e) was applied. For joints of less complexity (e.g. DSTB-DSTB joints), a shrink tape (Figure 10f) was used instead of a vacuum.

[00129] Once all arch and column FRP tubes were connected (Figure 11b) and fully

2019206009 16 Jul 2019 cured, concrete was cast into the annulus between the steel and the FRP Self-compacting concrete with a characteristic strength of 80MPa was used. In order to ensure good flowability of concrete, concrete with a minimum slump of 500mm (determined using a standard cone test) was used. Three plain concrete cylinders (110 mm x 200 mm) were tested for each batch to determine the concrete properties following ASTM C39/C39M (2011). The average elastic modulus and compressive strain at peak stress of the concrete cylinder tests are 45 GPa and 0.0021, respectively. Concrete pouring started from the two outer most columns of each DSTA, and worked towards the mid-span.

(d) Assembly of FRP segments around steel of beam segments and welding [00130] After the casting of concrete into DSTAs and DSTCs, the concrete was left to cure for 7 days. Then the I-beam I acting as the top chord was removed and replaced with a steel RHS surrounded by FRP (Figure 12b). Welding of the steel was then carried out. The gap provided between the bottom of the steel beam and the top of the FRP of the DSTCs (i.e. 50mm) was found to be sufficient for carrying out welding. In order to prevent any heat damage on the FRP tubes during welding, the FRP tubes were covered using insulation materials.

(e) Sealing of FRP tubes and concrete casting of beams.

[00131] The FRP tubes were sealed together using epoxy, and surface preparation was undertaken immediately before bonding to remove any surface contaminants and produce a chemically active surface. FRP strips were then placed in a manner similar to that explained in the previous section and was cured under vacuum for 12 hours. Once all the joints were made, concrete casting was carried out. The concrete properties were controlled to be the same as those of the concrete used previously for DSTAs and DSTCs. Concrete casting was done using a pressure pump, from the top of DSTB sections starting from one end as shown in Figure 13a at spaced pumping locations 80, 82, 84, 86 . The concrete advancing front is schematically shown. 10mm diameter weep holes were made (@ 1m spacing) at the top of the FRP tube to allow air to escape during concrete casting. Figure 13b is a photograph of the process.

(f) Joining completed segments.

[00132] An alternative to steps (c), (d) and (e) above is to concrete cast the annulus between the steel core tube and FRP outer tube before the jointing. The completed segments are then jointed with a combination of some or all of steel tube, plate steel, steel

2019206009 16 Jul 2019 or FRP pins, bolts, expoxy and high strength concrete. At this stage the joint is load bearing but does not have its ultimate capacity. The joint is then wrapped in FRP and the annulus between the joint and FRP is concrete cast to provide the ultimate capacity.

CONSTRUCTION QUALITY

FRP Joints [00133] Visual inspections were carried out to determine the quality of the bonded joints. Typical pre-preg joints are shown in Figures 14a and 14c, while a typical wet-layup joint is shown in Figure 14b. Wet-layup joints showed some wrinkles (Figure 14b), but much fewer wrinkles were seen on DSTA-DSTC joints made using pre-pregs (Figure 14a). No wrinkles were observed in DSTA-DSTA joints made using pre-pregs (Figure 14c). In the wet-layup process, while care was taken to ensure the layup of FRP strips without wrinkles, due to the complicated nature of the DSTC-DSTB joints, wrinkles resulted once vacuum was applied due to movement of the excess epoxy and strips..

[00134] During the loading test of the DSTA bridge, no signs of damage were observed in any of the joints and a significant effect from the wrinkles on the structural performance of the DSTA bridge was not detected.

Concrete Casting [00135] Video cameras were used inside the DSTAs between the FRP tube and the steel tube to observe the concrete flow during concrete casting. These observations showed a good flow around the corners of the joints, and no visible air pockets were observed. Visual inspections from outside the semi-transparent FRP tubes also identified no signs of air pockets.

ALTERNATIVES [00136] Figure 15 shows another embodiment of the disclosed bridge module 10. In this embodiment four additional truss members DSTTs are provided 90. In step (b) above, FRP segments will be placed around the steel truss tubulars which are then welded to the arch adjacent a column. As shown in figure 15c, there is a DSTA-DSTT-DSTC joint.

[00137] Figure 15a shows schematically a number of bridge modules installed side to side with a lightweight FRP deck 92 and lateral bracing 94.

[00138] In step (c) above the DSTA-DSTT-DSTC joint is sealed and concrete casting as 16

2019206009 16 Jul 2019 described above.

[00139] Figure 16a is a schematic front view of the module 10 of figure 15. Figure 16b is a section through B-B of Figure 16a and shows how the respective arch-column; archtruss, beam-column, beam truss steel member are welded together. This Figures also show how the concrete 16 surrounds the joints 17 in a continuous manner.

[00140] The modules as disclosed herein are considerably lighter than conventional RC construction because of the hollow core. Further construction is considerably quicker as the steel tube and FRGP outer tube act as the formwork. Because of the reduced weight, modules can readily be transported by road or rail. Modular construction significantly reduces on site construction time, labour costs and traffic/rail disruption.

[00141] A particular application for the disclosed modules is for pedestrian, rail or road overpasses. As traffic congestion is continually increasing, providing such overpasses to reduce congestion and improve pedestrian safety is highly desirable. For example, conventional RC construction may take months to years. On the other hand, the disclosed modules may be installed in days or even hours.

[00142] Figure 17 is a schematic showing how modules 10 as disclosed herein may be used to construct for example a rail over road overpass. First, the footings and piers 1, where required, are constructed, suitably at an off peak time that may occupy one lane at a time. Installation requires road closure. However, this time is minimal and could be as little as three days. Thus the road closure may occur over a holiday period such as Easter or Christmas.

[00143] The modules 10 are delivered to the site by road transport 2. The approach modules may be positioned directly on footings from the transport. In order to install a module on an extended pier, the module is driven into position by the transport. Mobile hydraulic column lifts lift the module off the transport and onto the pier. The transport is then driven away. Pre-installed bridge rail is erected. The overpass is then open for traffic in as little as 72 hours.

[00144] Figure 18 is a schematic view of a completed bridge 111.

[00145] Figures 19 to 27 show construction of a bridge using bridge sections as disclosed herein. A bridge formed from multiple bridge sections may have a span greater than 12m. The bridge has a single arch span rather than multiple individual spans as shown above in Figures 17 and 18. Such bridges may thus be used to span waterways, roads and 17

2019206009 16 Jul 2019 railways or the like without blocking any part of the space beneath the bridge structure.

[00146] The first step is to install an abutment 100 on each side of the waterway, roadway or railway as is known in the bridge construction arts for installing an arch bridge. (The forces on the arch are transferred to the abutments).

[00147] In the example in the Figures, the abutment 100 is 2.5m high. For convenience, construction is shown from one side only. It will be appreciated that each constructed step is repeated on the other side, as is known in incremental arch bridge construction.

[00148] Figure 19 shows the first section 102 being delivered by truck 104. The section 102 has two units 106, 108, each part being 6m in length. The first unit 106 is similar to the one side of the above described bridge module and may constructed as described above that includes welding the inner tubular steel members together and/or connecting segments with joints after each segments steel, FRP annulus has concrete cast..

[00149] Thus the unit 106 has a double skin tubular arch (DSTA) section 106a, double skin tubular columns (DSTC) 106b and a double skin tubular beam (DSTB) 106c.

[00150] The second unit 108, has parallel beams with cross bars for receiving a deck in a manner also as described above.

[00151] As shown in Figure 19, the units 106, 108 are linked together around a hinge or pivot 109.

[00152] The section 102 is placed on the abutment 100 from the truck. The units 106, 108 may launched using rams pivoting on the abutment 100 (not shown). Alternatively the units 106, 108 may be launched using a mobile crane 103 as shown in Figure 20. The mobile crane 103 is of the “pick and carry” type in that it can pick up a load and carry the load to a desired location and launch the load. This may be compared to fixed cranes. The size and weight of the respective units permits use of “pick and carry” cranes. This offers significant versatility and cost reduction during launching.

[00153] A deadman anchor 110 or temporary props 112 support the section 102 during the installation. The second unit 108 is then moved into place by the mobile crane 103 to the position shown in Figure 21. The units 106, 108 are joined together using a joint that will be described below.

[00154] A second bridge section 120 is then installed onto the first bridge section 102

2019206009 16 Jul 2019 using the crane 103. The second bridge section is 12m in length and comprises an upper arch comprising DSTA sections joined together and DSTC sections joined together as described above.

[00155] The columns 120 are fixed to the beam 102 using the joint shown in figures 30 and 31.

[00156] In the next step two 6m arch section units 122, 124 units are installed by a pick and carry crane. Each are section has an arch DSTA section, 122a, 144a columns DSTC 122c, 124c and beams DSTB 122b, 124b joined together.

[00157] Launching may be done in one of two ways as shown in Figures 22 to 24 or Figures 26 and 27.

[00158] In the first method, the units 122, 124 are pivotally/hinged linked together and placed on the top of arch section 120 for launching. The two units 122, 124 are pushed along the top of the second bridge section 120 by the crane 103, as shown or by hydraulic rams (not shown). The first unit 122 is pivoted into position by rams 126 and installed by joining with mechanical joints between the inner steel tubes. The second unit 124 is similarly installed with rams 107 fixed to the end of installed unit 22.

[00159] In the second method of launching units 122, 124 are installed using the crane 103 that is able to drive along the deck 130 of the partially installed bridge. Installation using the crane 103 in this manner may be compared to the use of large fixed overhead cranes that are used to install conventional RC bridge sections.

[00160] The identical launch and installation procedures are carried out on the opposite side until the bridge 140 is completed as shown in Figure 28. The span of the complete bridge 140 is 48m.

[00161] An alternative modular bridge 142 is shown in Figure 29 that has a span of 24m. This bridge is installed using two 12m sections 102 that are joined in the centre of the span.

[00162] Figure 30 is an elevation view of a jointed section 200 as used in the installation of the modular bridges 140, 142 as discussed above. Figure 31 is an end elevation of the jointed section 200.

[00163] Figures 30 and 31 show double skin tubular members 210 having an inner steel tube 212 with a hollow inner annulus 214, an outer RFP skin 216 and concrete 218 between

2019206009 16 Jul 2019 the steel tube 212 and FRP skin 216.

[00164] The inner steel tube 212 is stiffened with steel plate 216 so as to distribute and spread the load of the joint.

[00165] The jointed section 200 comprises a joint member 220 is made from 10mm steel plate. 40mm diameter pins 222 pass through the steel plate of the joint member connecting to the inner steel tube 212 and the concrete 218.

[00166] In this way, the bridge sections may be readily installed without requiring welding. This allows for temporary installation that may be desired for example during construction of repair of a permanent bridge. Alternatively, the section may of course be welded if so desired.

[00167] It will be appreciated that the disclosed bridges may be launched using trucks and cranes that may be used on public roads. This may be compared with the use of overhead cranes that are typically used to lift bridge modules into position.

[00168] The ability to load the sections onto conventional transport can reduce costs and is also significantly more convenient and cost effective for installing bridges in remote locations.

[00169] In some applications, additional strength may be required. In this case, the inner voids of the steel tubes may be filled with concrete after installation.

[00170] It will be appreciated that various changes and modifications may be made to the invention as disclosed and claimed in the present specification without departing from the spirit and scope thereof.

2019206009 16 Jul 2019

CITATION LIST [00171] ASTM C39/C39M. (2011). “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens”, (ASTM C39/C39M), ASTM International, USA.

[00172] AS5100.2. (2004). “Bridge design Part 2: Design loads” (AS5100.2), Standards Australia, NSW, Australia.

[00173] de Waal, L., Jiang, S., Hislop-Lynch, S.R., Fernando, D., Ahn, S., Teng, J.G., Rodman, P. and Burnton, P. (2019). “Novel bridge systems for durable, low-cost and rapid construction”, Winning entry of the WIBE Prize for World Innovation in Bridge Engineering, expected to be published in March 2019.

[00174] GB 50010 (2003). “Code for Design of Concrete Structures” (GB 50010 2003), National Standard of the People’s Republic of China, China: China Architecture and Building Press.

[00175] Higginson, K. (2014). “72-Hour bridge project: A feasibility study”, Bachelor of Engineering Project Report, School of Civil Engineering, University of Queensland, Australia.

[00176] Lam, L., and Teng, J.G. (2003). “Design-orientated stress-strain model for FRPconfined concrete”, Constr. Build. Mater., 17(6-7), 471-489.

[00177] McKenna, F., Fenves, G.L., and Scott, Μ. H. (2000). Open system for earthquake engineering simulation” (OpenSees), California, University of California Berkeley.

[00178] National Heavy Vehicle Regulator. (2016). “National heavy vehicle mass and dimension limits”, Retrieved from https://www.nhvr.gov.au/files/201607-0116-mass-anddimension-limits.pdf.

[00179] Teng, J.G., Yu, T., Wong, Y.L. and Dong, S.L. (2007). “Hybrid FRP-concretesteel tubular columns: concept and behaviour”, Construction and Building Materials, 21 (4), 846-854 [00180] Terex. (2014). “Mac 25-4: 25 Tonne Lifting Capacity Pick & Carry Crane Datasheet Metric”, Retrieved form http://eewaste.com.au/wp-content/uploads/FrannaCrane-full-specs.pdf.

2019206009 16 Jul 2019 [00181] Wong, Y.L., Yu, T., Teng, J.G. and Dong, S.L. (2008). “Behaviour of FRPconfined concrete in annular section columns”, Composites: Part B-Engineering, 39 (3), 451-466.

[00182] Yu, T., Wong, Y.L., Teng, J.G., Dong, S.L. and Lam, S.S. (2006). “Flexural behaviour of hybrid FRP-concrete-steel double skin tubular members”, Journal of Composites for Construction, ASCE, 10 (5), 443-452.

[00183] Yu, T. (2007). “Structural behavior of hybrid FRP-concrete-steel double-skin tubular columns” (Doctoral dissertation). The Hong Kong Polytechnic University, Hong Kong.

[00184] Yu, T., Wong, Y.L. and Teng, J.G. (2010a). “Behaviour of hybrid FRP-concretesteel double-skin tubular columns subjected to eccentric compression”, Advances in Structural Engineering, 13 (5), 961-974 [00185] Yu, T. and Teng, J.G. (2011). “Design of concrete-filled FRP tubular columns: provisions in the Chinese technical code for infrastructure applications of FRP composites”, Journal of Composites for Construction, ASCE, 15 (3), 451-461

Claims (18)

1. A section for a load bearing structure, the section comprising at least one tubular structural member joined to at least one further tubular structural member, the first tubular structural member comprising a fiber-reinforced polymer (FRP) outer tube and a metallic or FRP inner tube and the at least one further tubular structural member comprising a fiber-reinforced polymer outer tube and a metallic or FRP inner tube; wherein the inner tubes are joined together, the outer tubes are fluidly joined together to define a continuous annular space between the inner and outer tubes about the joint for filling with a settable filler.

2. The section of claim 1, comprising at least two tubular structural members joined end to end to form an arch section.

3. The section of claim 2, wherein the at least two structural tubular members are circular or rectangular in cross section.

4. The section of claim 2 or claim 3, further comprising at least one further structural member joined to the arcuate section such that in the formed load bearing structure, the at least one further structural member projects vertically away from the arcuate section so as to provide a column (compression or tension) support for the load bearing structure.

5. The section of any one of claims 1 to 4, wherein the inner tubes are steel tubes or FRP tubes.

6. The section of claim 5, wherein the inner steel or FPB tubes are joined by welding or pre-preg or wet layup.

7. The section of claim 5, wherein the inner steel tubes are mechanically joined.

8. A method of constructing a section for a load bearing structure, the method comprising joining together two or more tubular metallic or FRP members to form a tubular metallic or FRP segment, placing at least one FRP tube around each tubular metallic or FRP inner member in the segment, joining the FRP tubes together to define a continuous annular space between the two or more inner tubular metallic or FRP members and FRP tubes and filling the annular space with a settable filler.

9. The method of claim 8, comprising joining at least two tubular structural members end

2019206009 16 Jul 2019 to end to form an arch section.

10. The method of claim 9, wherein the at least two structural tubular members of the arch section are circular or rectangular in cross section.

11. The method of any one of claims 8 to 10, further comprising joining at least one further structural member to the arcuate section such that in the formed load bearing structure, the at least one further structural member projects vertically away from the arcuate section so as to provide a column (compression or tension) support for the load bearing structure.

12. The method of any one of claims 8 to 11, wherein the inner tubes are steel or FRP tubes.

13. The method of claim 12, wherein the inner steel tubes are joined by welding or prepreg or wet layup.

14. A section of a load bearing structure constructed by the method of any one of claims 8 to 12.

15. A load bearing structure comprising at least one section constructed by the method of any one of claims 9 to 13.

16. The load bearing structure of claim 14, wherein the structure is a transportable bridge.

17. A method of launching the load bearing structure of claim 15 in an elevated on site position, comprising installing elevated piers on site, delivering the module to the site by transport and position the module into position by the transport, lifting the module using mobile hydraulic column lifts onto the pier or hydraulic rams and driving away the transport.

18. A method of onsite launching a load bearing structure across a space comprising transporting two or more sections of claim 14 to a site, launching the modules across the space and joining adjacent modules together using a mobile crane or hydraulic rams.