NZ711466A - Prefabricated bridge module and method for fabrication thereof - Google Patents

Abstract

A prefabricated bridge module is disclosed, which comprises a planar timber deck having an upperside and an underside and a support bonded to the underside of the deck. The support comprises a plurality of longitudinally extending, laterally spaced logs, wherein the logs include at least one flattened surface that is configured to connect to the underside of the deck. Significant cost and efficiency gains arise from the use of logs as bridge supports. This is due to the fact that, for a given volume of material, significantly less processing, resources and time are required to prepare logs from their natural state into a suitable structural elements in comparison with other materials (for example, wooden laminates or other engineered woods). The logs therefore provide spaced longitudinal support girders or stringers for the bridge deck, and the logs are bonded to the underside of the deck so that the logs and deck provide a substantially integral module, all stresses and strains being passed between them during use.

Description

Prefabricated bridge module and method for fabrication thereof Field of the invention The present invention generally relates to a prefabricated bridge module and method for fabrication thereof. The invention also relates to a bridge assembled from one or more of such modules, and a kit of parts including one or more of said modules.

Background of the invention The use of timber as the principal structural material for bridges is receiving renewed attention in view of the potential environmental benefits that arise. In particular, during its growth period, timber absorbs carbon dioxide out of the atmosphere. And once harvested, the carbon dioxide is stored in the timber's biomass for relatively long periods of time. Moreover, timber is a sustainable resource when grown in plantations rather than relying on old growth hardwoods. id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3"

[0003] The construction of new timber bridges is also being driven from the need to maintain and replace aging infrastructure.

The present invention is aims to provide an alternative approach to the construction of timber bridges.

Summary of the invention id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5"

[0005] According to a first aspect of the present invention, there is provided a prefabricated bridge module comprising: a planar timber deck having an upperside and an underside; and a support bonded to the underside of the deck, the support comprising a plurality of longitudinally extending, laterally spaced logs. id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6"

[0006] Modules according to the invention are prefabricated and can thus be conveniently and efficiently mass produced, ready to be utilised in a wide variety of installation environments according to the particular requirements.

This is a more cost effective solution in comparison with the previous approach of individually designing and manufacturing all of the components of a bridge for each installation.

Significant cost and efficiency gains arise from the use of logs as bridge supports. This is due to the fact that, for a given volume of material, chbm A0134129837v1 120548022 significantly less processing, resources and time are required to prepare logs from their natural state into a suitable structural elements in comparison with other materials (for example, wooden laminates or other engineered woods.

The logs therefore provide spaced longitudinal support girders or stringers for the bridge deck, and the logs are bonded to the underside of the deck so that the logs and deck provide a substantially integral module, all stresses and strains being passed between them during use. Simple fixation (eg. by bolting), or bonding in a way which does not afford this effective integration, would not provide the advantages of the present invention. id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9"

[0009] The term 'logs' thus refers to cut timbers, as opposed to engineered timber products. It will be understood that this definition embraces logs that are cut, treated, coated, or otherwise processed for use in the invention. Ideally, all of the logs of a module have substantially the same cross section. id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10"

[0010] The logs are preferably softwood logs, of a sufficiently strong species. This is important, as timber road and rail bridges have traditionally been made of hardwood materials, which is less sustainable and significantly heavier (thus increasing cost, including the cost of support pilings and footings).

Modules according to the invention can provide a fast and cost effective solution for refurbishing or constructing new timber bridges.

Modules according to the invention can provide a complete bridge superstructure system, encompassing all activities in the supply chain from design, through to supply on site.

Preferably, the logs are spaced from one another. The spacing may be such that the gap between the logs is approximately equal to the log diameter. In any event, the spacing between the log centrelines is preferably in the range 600-1300mm.

Preferably, the module is devoid of filler timber or other filler materials or filler structure in the spaces between the logs on the underside of the deck.

Preferably, the module includes a means for interacting with a connecting assembly, so as to permit a module to be connected to one or more other modules in assembling a bridge. The means may include one or more holes extending through the deck, suitable to receive one or more fasteners (such as a nut and bolt). Preferably, the means includes a plurality of holes chbm A0134129837v1 120548022 provided adjacent to a longitudinal edge of the deck. This allows fasteners to be secured to bridging elements between modules.

Preferably, the logs are substantially cylindrical. According to a preferred embodiment, the logs include at least one flattened surface.

Preferably, the flattened surface extends substantially along the entire length of the log.

The flattened surface provides increased surface area for bonding with the deck.

In one embodiment, first and second parallel flattened surfaces are provided on opposite sides of each log.

The logs are bonded to the underside of the deck by any suitable means which provides the required integrity. Preferably this is by means of a bonding agent, ideally an A-bond agent, to form a permanent bond that will not deteriorate under wet conditions, heat or cold. id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20"

[0020] Optionally, the deck is constructed from an engineered wood product. Typically, the engineered wood is plywood or laminated veneer lumber (LVL). According to preferred embodiments, the plywood is subjected to a treatment method prior to its incorporation into the module, such as a veneer treatment method. id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21"

[0021] According to a second aspect of the present invention there is provided a method for fabricating a bridge module, the method including the steps of: providing a timber deck; providing a plurality of logs; bonding the logs to a face of the deck in a longitudinally extending and laterally spaced arrangement; and tensioning the logs to the deck to assist the bonding.

According to a third aspect of the present invention there is provided a bridge assembled from a plurality of the modules according to the first aspect of the invention.

According to a fourth aspect of the present invention there is provided a kit of parts for use in assembly a modular bridge, including: two or more modules according to the first aspect of the invention; and chbm A0134129837v1 120548022 connecting means for connecting the modules together.

Brief description of the drawings The invention will now be further explained and illustrated by reference to the accompanying drawings in which: Figure 1 is a perspective view of a two lane bridge constructed by connecting together two bridge modules in accordance with an embodiment of the invention; Figure 2 is a cross-sectional view through the line A-A in Figure 1, while Figures 2A and 2B are magnified views of alternative jointing assemblies; Figure 3 is a cross-sectional view through the line B-B in Figure 1 showing an end portion of the deck; Figure 4 is a perspective view of a four lane bridge constructed by connecting together bridge four modules in accordance with an embodiment the invention; and Figure 5 is a cross-sectional view through the line C-C in Figure 4.

Detailed description of the drawings Figures 1 to 3 illustrate a bridge 10 constructed from two modules 12, 13. Modules 12, 13 are prefabricated and delivered to the site of installation. Kerbing 16 can be attached to each module 12 and 13 (in the manner described below) either during the time of manufacture or at the installation site if required. Bridge 10 can be installed to span across any terrain through the use of suitable substructures and pier structures. Bridge substructures and piers are known to those skilled in the art and will thus not be described in further detail. id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26"

[0026] Each module 12 and 13 includes an elongate planar deck 18 typically manufactured from an engineered wood product. Plywood is particularly preferred, although other engineered wood products that satisfy the structural properties required by the bridge could also be used. In the illustrated embodiment, deck 18 is formed from five continuous 27mm plywood sheets 20 (Figure 3) bonded together with a permanent resorcinol resin forming an A- bond. chbm A0134129837v1 120548022 Each sheet 20 is suitably treated by the veneer treatment preservation method in order to provide protection against termite attack and fungal decay. The veneer treatment involves treating the individual sheets of veneer with Alkaline Copper Quaternary (or similar) to Hazard class H4 (in- ground protection) prior to fabrication into plywood. The treated veneers are bonded with a permanent phenolic resin using a suitable bond (A bond, alternatively Marine A or a structural bond).

As a prefabricated module, the dimensions of deck 18 are set at the point of manufacture, rather than being customised for each individual installation. In the illustrated embodiment, deck 18 has a span length of up to 10000mm and a width of 2100mm (providing a two lane bridge 4.2m wide).

These dimensions have been found to be suitable for the construction of a single-lane, single-span bridge from a single module 12. Other types of bridges (ie. multiple-lane and/or multiple-span bridges) can be conveniently constructed by joining together a suitable number of modules as described below.

Deck 18 is optionally provided with a pre-applied asphaltic cement or a multi-layered aggregate system (commonly bitumen) wearing surface (not shown). Wearing surfaces of such composition have been found to bond well with timber decking while providing the bridge with a long-lasting covering. id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30" id="p-30"

[0030] Both leading edges 17 of deck 18, as most clearly illustrated in Figure 3 are provided with L-shaped profile pieces 23. Profile pieces 23 are secured to deck 18 by way of nuts and bolts 27, 31. Profile pieces 23 provide end abutments for impact protection and to assist in sealing of the faces of the deck edges 17 of bridge 10. Such protection is particularly important when bridge 10 is constructed along an unsealed road, due to the possibility of grader blades impacting on bridge 10 during road re-profiling operations.

Support for the bridge 10 is provided by a series of three, spaced apart girders 22 provided as support stringers on the underside of each module 12, 13. Girders 22 extend longitudinally along the underside of deck 18, typically for the entire length of the module, rather than being made up of different pieces aligned end-to-end.

Girders 22 are timber logs, preferably sourced from sustainable plantation timber grown and manufactured in accordance with applicable standards and certifications (including AS 2858, AS/NZS 2269-2012 and AS/NZS 1604-2012). Utilising wooden logs as girders enables modules 12, 13 to exploit the advantages of natural timber, such as its ability to better resist chbm A0134129837v1 120548022 fatigue failure in comparison to other materials. As natural timber logs, the girders 22 are substantially cylindrical. However, a degree of variation is acceptable.

Suitable timbers include hoop pine, klinki pine and Caribbean pine, all of which are strong plantation softwoods, with a stress grade of at least F14 as defined in AS1720.

The wood used for the deck plywood is also a softwood, and may be of the same species as the girders, with structural properties including a minimum stress grade of F14. id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35" id="p-35"

[0035] Logs are selected for use as girders by applying a visual grading regime in which the log's characteristics are assessed. Relevant characteristics include: maximum knot diameter; length; geographic source; species and diameter and ovality. Other characteristics that are assessed include an absence of rot, pipe, draw wood, pipe holes, saw scarfs, excessive sweep, spiral grain, off centre pitch and butt flare.

Selected logs are trimmed in accordance with the required dimensions of bridge module 12, 13 and preservative treated to H4 to ACQ.

Otherwise, the logs are not engineered, although they may be coated or otherwise covered to provide protection from degradation. id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37" id="p-37"

[0037] As illustrated most clearly in Figure 2, each girder 22 includes deck-facing flattened surface 24 and a ground-facing flattened surface 26, both of which extend for the entire length of the girder. Flattened surfaces 24 and 26 are mutually parallel on opposite sides of the girder 22, and may be of a similar lateral dimension. This results in girder 22 having a profile that includes both flat and curved faces on its longitudinal surface and is horizontally and vertically symmetrical. The spacing of girders 22 may be such that the gaps between successive girders is approximately equal to their diameter (ie. the centreline spacing is approximately equal to twice their diameter).

Girders 22 are bonded to the underside 21 of deck 18 during fabrication. This allows the module 12, 13 to be provided as a prefabricated unit, effectively a wholly integrated piece. One or more of the modules can be included, along with required kerbing and accessories (such as connecting components and elastomeric bearing pads for abutment-facing surfaces), in a kit of parts. The kits can be conveniently and cost-effectively assembled into a bridge at the site of installation. chbm A0134129837v1 120548022 Girders 22 are permanently bonded to the underside of the deck 18 by gluing with a suitable resorcinol phenolic resin, forming an A-bond in accordance with AS2754.1. The minimum single glueline bond rating as per clause 3.3 c) in AS/NZS2269 is 4. Bonding between deck 18 and girders 22 is to a Service Class 3 conditions according to applicable Australian standards (i.e design life of 50 years in a fully exposed external environment).

Modules 12, 13 are fabricated by positioning girders 22 on a support frame (not shown) in a parallel and spaced arrangement. The wood surfaces should be as free as possible from dust, dirt, grease and other foreign materials, and as free as possible of surface imperfections. Ideally, final surfacing of the wood faces is performed shortly prior to bonding, at most 72 hours prior to bonding, so that smooth, clean accurately fitting surfaces are provided.

The resorcinol resin (mixed with appropriate hardener) is spread on deck-facing surfaces 24 in quantities of at least 250 g/m2, preferably at least 500g/m2. This quantity allows for construction to take place in higher ambient temperatures and also allows for longer assembly times.

Deck 18 is placed onto girders 22 and tack nails (not shown) are inserted as appropriate (eg. in the corners of each one), in such a way to ensure that transverse butt joins are staggered by at least 300mm.

Type 17 screws (not shown) are driven through deck 18 and into girder 22 immediately, to apply pressure during the glue curing process. In addition, girders 22 are bolted to deck 18 using M20 bolts (not shown), to assist in providing sufficient pressure while the glue is curing. Curing can also be assisted by radio frequency radiation.

Some squeezeout or beading of bonding agent along joint edges when pressure is applied is generally a good indication of adequate spread, but it is important that the fixing pressure is not too great, otherwise there may be too much loss of bonding agent. id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45" id="p-45"

[0045] It will be understood that the use of the screws and bolts to hold together deck and girders is required for the curing of the bonding, but not required for the structural integrity of the finished module. Indeed, if desired these connection means may be removed after curing is complete.

Two modules 12 and 13 can be connected together along their respective longitudinal edges 28 and 29, eg. to form a two-lane bridge. chbm A0134129837v1 120548022 Typically, the modules 12 and 13 are connected together at the site of installation, with the connecting assembly (discussed below) being pre-attached to modules 12, 13 at the time of fabrication.

In the illustrated embodiment, the two modules 12, 13 are connected together through the use of a connecting assembly 30 that extends along the full length of longitudinal edges 28 and 29 of each deck 18.

As illustrated most clearly in Figure 2A, each jointing assembly includes an elongate flange channel 32 comprising a pair of spaced apart parallel flanges 33, 35, separated by a planar web 34. Modules 12 are connected together by positioning the web of channel 32 on the underside 21 of two laterally abutting decks 18 so that approximately half of the lateral extent of web 34 contacts each module 12, 13.

Bolts 36 and 38 are inserted through suitable holes in web 34 and drilled through modules 12 and 13 at suitable positions adjacent the lateral edges. In the illustrated embodiment, bolts 36, 38 have a pitch of M20 specification, with the holes being of a corresponding diameter.

A set of nuts 40 are secured to the end of bolts 36, 38, with washers 42 provided between the bolt-deck and bolt-web interfaces. This is repeated at approximately 1m intervals. id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51" id="p-51"

[0051] Figure 2B shows an alternative form of the jointing assembly using an upper flat strip plate 43 (200 x 15mm HDG profile) attached to the deck at suitable intervals by nuts and bolts as shown. Alternatively plate 43 may be attached to the deck by coach screws (eg. M20 x 100mm coach screws at 600mm separation). id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52" id="p-52"

[0052] Typically, all fasteners used in the bridge 10 construction are hot dip galvanised (HDG) steel.

Elongate kerbing elements 16 can be attached to a longitudinal edge of each of modules 12, 13 to provide support for steel work, such as guardrails. This is preferably done at fabrication, as the kerbing can then also become an integral part of the module through a similar resin bonding process.

It may alternatively done on site if required, the kerbing elements 16 forming part of the assembly kit for a particular bridge.

As illustrated in Figures 4 and 5, a four-lane bridge 44 can be suitably constructed by connecting together four modules 12, 13, 46 and 48 side-by-side, in the manner described above. chbm A0134129837v1 120548022 Figures 4 and 5 show an alternative form of kerbing element 50 comprising a guardrail that can be attached to the finished bridge 44. Kerbing elements 16, 50 can be attached to a module by any suitable means, eg. by bonding and/or mechanical fastening such as bolting. The means of connection between the kerbing and decking will be at least in part dependent on the material from which the kerbing is made.

Multiple span bridges are constructed by connecting modules 12 and 13 together along their leading edges using a suitable connection means.

For example, a 30m span bridge may be assembled from 6 modules, with two pier structures. The assembled bridge is bolted down to abutments (not shown) located at the site of installation. Pier and/or headstock structures are constructed as necessary in accordance with the number of bridge spans (typically one fewer pier structure being required than the number of spans, as the pier structure is provide at module connection positions). id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57" id="p-57"

[0057] It will be appreciated that the invention does away with the need to use longitudinal tensors, such as prestressed tensors, as often required in conventional timber and similar bridge structures.

Further, the invention, in using spaced support girders 22, as opposed to stringers that abut one another along their longitudinal edges, utilises significantly less material than would otherwise be the case.

Bridges constructed from modules in accordance with the invention have been found to be suitable for a wide range of load conditions, including Austroads 92 T44, and AS5100 Bridge Design Light vehicle and pedestrian. id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60" id="p-60"

[0060] The mechanical properties and structural response of a bridge module of the invention having the dimensions noted above have been assessed in testing to failure. The test results demonstrate that the bridge module exceeds ULS requirements of both T44 and S1600 loading conditions.

More specifically, the bridge module sustained a single wheel path of 397kNm, without any localised punching shear under the loading pads or deformation at the supports.

Advantages of the bridge module of the invention include:  reduction in cost due to improved material efficiency (target cost <$1000/m2); chbm A0134129837v1 120548022  reduction in site installation time, road closures and labour costs;  the ability to install bridges using an existing and standard skill base;  convenient installation with a wide variety of substructures including those made from concrete and steel;  low embodied energy and life cycle energy costs;  a lightweight solution which saves on piling and footing costs; and  carbon sequestration benefits arising from the use of wood.

The design philosophies embraced by preferred embodiments of the invention focus on delivering a superior economical solution for timber bridge construction while maximising technological advances of veneer preservation treatment, exploiting the benefits of a high strength plantation resource while maintaining sustainability credentials including manufacturing using hydro-electric generated power. For approximately the same volume of material, a bridge made in accordance with the invention provides an equivalent to an existing hardwood product, at a significantly reduced cost and environmental impact, both in terms of material and manufacturing cost and time.

The word ‘comprising’ and forms of the word ‘comprising’ as used in this description do not limit the invention claimed to exclude any variants or additions.

Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention. chbm A0134129837v1 120548022

Claims (23)

The claims defining the invention are as follows:

1. A prefabricated bridge module comprising: a planar timber deck having an upperside and an underside; and a support bonded to the underside of the deck, the support 5 comprising a plurality of longitudinally extending, laterally spaced logs.

2. A prefabricated bridge module according to claim 1, wherein the logs are substantially spaced from one another.

3. A prefabricated bridge module according to claim 2, wherein each of the logs have a substantially uniform diameter and wherein the spacing is 10 approximately equal to the diameter.

4. A prefabricated bridge module according to any preceding claim, wherein the module is devoid of filler timber or other filler materials or filler structure in the spaces between the logs on the underside of the deck.

5. A prefabricated bridge module according to any preceding claim, wherein 15 the module includes a means for interacting with a connecting assembly, so as to permit a module to be connected to one or more other modules in assembling a bridge.

6. A prefabricated bridge module according to claim 5, wherein the means includes one or more holes extending through the deck, suitable to receive 20 one or more fasteners.

7. A prefabricated bridge module according to claim 5 or claim 6, wherein the means includes a plurality of holes provided adjacent to a longitudinal edge of the deck.

8. A prefabricated bridge module according to any preceding claim, wherein 25 the logs are substantially cylindrical. chbm A0134129837v-1 120548022

9. A prefabricated bridge module according to claim 8, wherein the logs include at least one flattened surface.

10. A prefabricated bridge module according to claim 9, wherein the flattened surface or surfaces extend substantially along the entire length of the log. 5

11. A prefabricated bridge module according to claim 9 or claim 10, wherein the logs include first and second substantially parallel flattened surfaces provided on opposite sides thereof.

12. A prefabricated bridge module according to any preceding claim, wherein the logs are bonded to the underside of the deck by means of an A-bond 10 agent.

13. A prefabricated bridge module according to any preceding claim, wherein the logs are softwood logs.

14. A prefabricated bridge module according to any preceding claim, wherein the deck is constructed from an engineered wood product such as a 15 plywood, laminated veneer lumber (LVL) or cross laminated timber.

15. A prefabricated bridge module according to claim 14, wherein the plywood is subjected to a treatment method prior to its incorporation into the module, such as a veneer treatment method.

16. A method for fabricating a bridge module, the method including the steps of: 20 providing a timber deck; providing a plurality of logs; bonding the logs to a face of the deck in a longitudinally extending and laterally spaced arrangement; and tensioning the logs to the deck to assist the bonding. chbm A0134129837v-1 120548022

17. A method according to claim 16, further including the step of imparting first and second substantially parallel flattened surfaces into opposite sides of each log prior to bonding the logs to a face of the deck.

18. A method according to claim 16 or claim 17, wherein the step of bonding 5 the logs to a face of the deck is effected by use of a bonding agent.

19. A method according to any one of claims 16 to 18, wherein tensioning of the logs to the deck is applied by driving one or more fasteners through the deck and into the log.

20. A method according to any one of claims 16 to 19, further including the step 10 of applying a wearing surface to the upper side of the deck subsequent to the bonding of the logs.

21. A bridge assembled from a plurality of modules according to any one of claims 1 to 15.

22. A kit of parts for use in assembling a modular bridge, the kit including: 15 two or more modules according to any one of claims 1 to 15; and connecting means for connecting the modules together.

23. A kit of parts according to claim 22, further including kerbing and/or accessories such as connecting components and elastomeric bearing pads for abutment-facing surfaces. chbm A0134129837v-1 120548022