Innovation in Engineered Wood Product Bridge Components

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1 Innovation in Engineered Wood Product Bridge Components Peter Robinson Business Development Manager Boral Plywood, Queensland, Australia Abstract Over the past 2 years Boral Plywood has embarked on an extensive research and development program in collaboration with Roads and Transport Directorate - Institute of Public Works Engineering Australia (IPWEA) NSW Division, Australian Rail Track Corporation (ARTC) and University of Technology Sydney under the guidance of Professor Keith Crews to develop an Engineered Wood Product (EWP) alternative to the traditional hardwood sections used in the construction of timber road and rail bridges. The design philosophies embraced include sustainable resource, lowest life cycle energy cost, and utilization of developments in gluing and treating technology, minimise on-site installation labour, design life of 50+ years and must be commercially viable. This research has resulted in a suite of bridge components ranging from individual component girders and transoms to a pre-fabricated modular bridge system. Re-building a 12m span 4.2m wide timber bridge would traditionally require replacement girders and Bridgewood decking panels plus considerable amount of on-site labour to install together with extensive road closures. Under the Bridgewood modular system the bridge is delivered to site as a pre-fabricated bridge span in two sections 12m x 2.1m. Advantages from the modular system are:- Reduction in site installation labour costs. Reduction in road closure time. Elimination of the transverse cracking and resultant degradation of the asphaltic cement (AC) deck wearing surface. Can be used with concrete supporting members. Low embodied energy and life cycle energy costs. Light weight solution which saves piling/footings costs. Pilot program commenced in September 2008 with girders installed in rail bridges in New Zealand by Ontrack and modular bridges installed by Kyogle Council. Page 1

2 Introduction The issue of the condition and maintenance options for aging timber bridges is well documented (IPWEA Road Asset Benchmarking Project (7)) as well as the declining availability and quality of suitable traditional hardwood timbers (IPWEA Road Asset Benchmarking Project (7)) not to mention a shortage of funding. A variety of replacement component alternatives options in differing materials have been or are in the process of being developed. However, developments addressed in this paper are focussed on an engineered wood product solution with an emphasis on reducing the installed cost, maintaining existing labour skill set and probably the most important having the lowest carbon footprint. In particular this paper starts with the evolution of Engineered Wood Products (EWP) in timber bridges, then progresses to discuss recent developments of EWP bridge component members and finally EWP modular bridges for both rail and road applications. Boral Plywood has a long established history of designing and commercially manufacturing plywood decking for highway road bridges utilising sustainable managed softwood plantations located in South East Queensland with full chain of custody certification to Australian Forestry Standard AS 4707:2006. The two species predominantly used in the manufacture of Bridgewood are Slash Pine and Hoop Pine which have distinct strength advantages over the more common Radiata Pine softwood plantations. Advances in processing and preservation technologies have firstly allowed the resource to be segmented by stiffness with the high strength resource used in this application, and secondly CoreTreat preservation technology allows 100% treatment which underpins a 50 year design life. development of a suite of timber bridge components and solutions for both rail and road applications. This paper details the development and testing evolution of a plywood bridge decking product developed in the 1980 s to a suite of bridge components including kit modular bridges and rail transom decks. Background - Review of Bridgewood Decking Product Performance Bridgewood decking has been available now for over 20 years with the product s longevity proving itself over this time. Recently, Boral Plywood conducted a review of Bridgewood decking comparing the condition and performance of decks over 15 years old to recent installations. Specifically, each bridge was checked for evidence of:- Structural failure. Bond degradation. Dimensional stability. Termite attack. Fungal attack (rotting). The results of this review is best demonstrated by the following series of photos below which show bridges of similar conditions with Renyolds Creek Bridge being installed in 1990, Elaman Creek Bridge (1993) compared to a recent installation, Mill Bridge (2008). None of the bridges inspected showed any evidence of structural failure in the Bridgewood decking, bond degradation, dimensional issues, insect and fungal attack. The conclusion draw from this review is that 20 year old Bridgewood decks have not deteriorated and continue to perform in accordance with their original design. The availability of good quality hardwood has deteriorated to the point where the task of procuring other timber bridge components has become difficult to say the least. Boral Plywood has recognised this problem and has applied considerable resources to the Page 2

3 Figure 1: Renyolds Creek Bridge (1990) Figure 2: Deck wearing surface Figure 3: Elaman Creek (1993) Maleny Kenilworth Rd However two bridges installed just after the product was launched did not perform to expectations. This initial adverse reaction to the product was caused by an inadequate substructure which caused the panels to over deflect and flog which led to a premature degradation of the deck wearing surface. Figure 4: Mill Bridge Maleny Kenilworth Rd (2008) Preservative treatment - Plywood, which are both fundamental to its design. Adherence to these standards is controlled and monitored by ISO 9001 Quality System with third party auditing. Bridgewood Design Design Principles and Objectives A key part of Bridgewood s success has been the consistency of the delivered product which is distinctly different to the traditional hardwood. As an Engineered Wood Product (EWP), Bridgewood is manufactured to a tight set of design parameters including two key Australian standards AS/NZS 2269 Plywood Structural, and AS/NZS The design objective was for a flexible suite of EWP s to suit road and rail applications including girders, transoms and modules that are structurally and geometrically compatible with existing bridge components all in addition to the traditional Bridgewood decking. Page 3

4 Key design principles used within this project include:- Designed in accordance with AS5100 (6) with the design life being 50 years. Utilization of a sustainable resource. Equivalence to existing hardwood members. Environmental responsibility. Incorporation of design features which facilitate full scale commercial production. Development of a standard set of transom, girders and modules which can be mass produced and readily available as opposed to individually designed and manufactured beams. This provides a cost effective solution for both road and rail infrastructure issues. Minimise the amount of retraining necessary to handle and install the product by retaining the skills and tools required to continue to work with wood based products. Leverage off 20 years experience in manufacture of plywood bridge decking substituting hardwood planks in highway road bridges. Resource selection Variability of plantation softwood is less than sawn hardwood and is further reduced by using veneer stiffness sorting techniques. The common misconception about the strength characteristics of softwood plantations is that they are inherently weaker than Australian Eucalypts. This is the case for the majority but as can be seen from the histogram of Modulus of elasticity below, there is a percentage in our resource which has stiffness of F22 and above. It is this wood which will be utilized in the transoms and girders. F grade yield % <F7 F7 F8 F11 F14 F17 F22 F27 F34 Table 1: Stiffness yield for typical resource used Page 4

5 Sustainability All of the girders and transoms produced for this project are manufactured from timber sourced from pine plantations, a resource that is renewable and sustainable. As timber absorbs carbon dioxide during its growth phase and stores the carbon in the finished product, it assists in the greenhouse gas problem that we are all faced with. The process of making plywood has relatively low Embodied Energy. Embodied Energy is the amount of energy required to manufacture a product in our case deconstructing a tree and turning it into a flat panel. Table 2 below is a comparison of energy required to produce key building materials together with a comparison of the amount of carbon released to the atmosphere. It should be noted that timber based building products are the only products that have a net storage of carbon from the atmosphere method, often referred to as 100% penetration (CoreTreat) due to the complete penetration is recognised as the most effective treatment process and the key basis for the ability to provide a 50 year design life. Figure 5: CoreTreat treatment schematic Building Material Comparison Fossil Fuel Energy Used (MJ/m3) Carbon released (kg/m3) Carbon Stored (kg/m3) Timber including EWP s Figure 6: CoreTreat treatment with uniform treatment throughout the cross section Steel Concrete Aluminium Table 2: Energy required and carbon released comparison Preservation treatment Traditional preservation treatment occurs after the product is produced, which in the case of softwood EWP s results in an envelope treatment with the centre of the product containing little or no preservative treatment. Veneer impregnation on the other hand, is where each individual veneer is treated prior to assembly of the plywood. This Figure 7: Envelope treatment showing untreated core veneers Page 5

6 Bridgewood Girder The Bridgewood girder consists of a series of CoreTreat treated LVL units orientated on edge which are scarf jointed with secondary lamination to provide the necessary bridge component section sizes and length requirements. All bonds are A bonds and of a phenolic type complying with AS (8) which are of a permanent nature. 295mm Figure 9: 6 Completed girders ready for shipment 305mm Figure 8: Cross section of 305mmx295mm Bridgewood girder Bridgewood Transom The Bridgewood transom consists of a series of CoreTreat treated EWP units orientated on flat with secondary lamination to provide the necessary bridge component section sizes and length requirements. All bonds are A bonds and of a phenolic type complying with AS (8) which are of a permanent nature. Design Component Existing Hardwood Bridgewood Girder Stress Grade F22 F22 Member size 300x300mm 300mmx300mm Ultimate Moment Capacity Φ Ms knm knm Ultimate Static Shear Capacity ΦV 195kN 201kN Bending Stiffness 16000MPa 16000Mpa Table 3: Bridgewood girder design comparison to hardwood Page 6

7 Bridgewood Modules The third section of the development involves changing from delivering individual bridge components to site namely, decking and girders to delivering a pre-fabricated modular bridge spans. For example, in re-building a 12m span 4.2m wide single lane timber bridge would traditionally require replacement girders (say 4) and 10 Bridgewood decking panels 4.2m x 1.2 x 166mm plus considerable amount of on-site labour to install together with extensive road closures. Under the Bridgewood enhanced modular system, two pre-fabricated bridge sections 12m x 2.1m are delivered to site. Each module comprises 3 Bridgewood Girders with Bridgewood Deck and kerbings bonded to the Girders. Results for both transoms and girders demonstrate the equivalence to existing materials, with Table 4 below comparing the bending moment capacity of F22 hardwood members to the equivalent Bridgewood transom and girder. In the case of the Girders the Bridgewood 305x295mm girder is compared to a 375mm diameter unseasoned hardwood girder. One of the most pleasing outcomes has been the consistency of the results and load carrying capacity after failure in both transoms and girders. The Bridgewood girder below failed at 30 tonne but was able to be reloaded to 24 tonne after the initial failure. Advantages from the modular system are:- Reduction in site installation labour. Reduction in road closure time. Minimization of cracking and resultant degradation of the asphaltic cement (AC) deck wearing surface. Can be used with concrete supporting members. Low embodied energy and life cycle energy costs. Light weight solution which saves piling/footings costs. Figure 11: Girder Static test setup Bridgewood System Testing The girders, transoms and modules were extensively tested at the University of Technology Sydney (UTS) and included:- Non-destructive static testing to confirm linear elastic behaviour. Cyclic T44 load testing at a frequency of 1Hz. Non-destructive static testing to determine if there is any stiffness change due to fatigue. Destructive testing to determine ultimate load capacity testing at failure. Figure 12 Girder destructive test Page 7

8 Description Nominal d x b Actual BM capacity d x b Z (mm 3 x10 3 ) f' b phi 1 (knm) Bridgewood Transom 204x x F22 hardwood unseasoned Transom 200x x Bridgewood Girder 305x x F22 hardwood unseasoned Girder 375 dia 375 dia Note (1): Capacity reduction factors from AS ; Table 4:Transom and Girder result summary Likewise the transom shown above ultimate failure was at 26.5 tonne however the transom after this failure was still able to carry 19 tonne. This load carrying capability after failure is different to say a concrete or steel member that when it fails it has no or limited further load carry capability. In addition to the flexural testing above it was necessary to also demonstrate the performance of the connection between the LVL transoms (and compare to Hardwood F22) and the pandrol plate fixing the rail to the transom. These tests included:- AS would reduce F22 to 0.65 The results of testing connections between the steel rail pandrol plate and the Bridgewood transom product are that the Boral Bridgewood transoms exhibit the similar characteristics to those of the currently accepted F22 hardwood transoms and existing fastener systems can be used. Static horizontal testing simulating nosing loads on the pandrol plate. Cyclic testing at ULS load for 10 3 cycles. Cyclic testing at SLS load for 10 6 Cycles. In order to ensure the correct interaction of the vertical (gravity) with the horizontal (nosing or centrifugal) loads a number of pilot tests were required. Figure 13: Transom test setup Page 8

9 Figure 14: Static nosing test comparing Bridgewood transom sample no. 8 with a typical hardwood transom. Module tests involved non destructive static tests, cyclic testing using T44 loading pattern, and destructive testing to determine the ultimate load at failure. The aim being to:- Determine the stiffness under normal loading conditions. Measure any residual deflection due to the cyclic testing. Determine that the ultimate serviceability loads are in the linear elastic range, and the linear elastic limit. Determine the ultimate bending moment capacity. Fig 16: Module Destructive test setup The static tests before and after the cyclic tests indicated an average EI of the module of 82.5 x and the conclusion from the cyclic loading being that the cyclic loading has negligible effect. The test setups are shown below for both the static and cyclic test (figure 15) and a different configuration for the destructive test (figure 16) due to the high loads anticipated. Figure 17: Actuator load versus displacement at 1 x 10 6 cycles. Fig 15: Module Static and Cyclic test setup The module exhibited considerable composite behaviour throughout the testing. Based on the characteristic bending capacity of the individual girders in the module, the predicted capacity for the destructive test was 750kNm which when compared to the actual achieved during the destructive test of just over 1400 knm confirms the composite behaviour. Page 9

10 Specific testing of the Bridgewood deck was undertaken to determine the shear performance mid span under a derailment situation as shown in figure 20. Figure 18: Load versus deflection chart for the destructive test of the module. The modular bridge pilot program started with installing a 12m single lane bridge with Kyogle Council NSW. The Bridgewood modules were able to re-utilize existing concrete abutments due to the light weight structure, with installation taking only 5 days. Figure 20: Derailment load test using a half train wheel assembly. The conclusion from this testing is that the Bridgewood rail deck has more than enough capacity to withstand the shearing effect resulting from a train wheel derailment. Conclusion Figure 19: Completed modules being installed. Rail Transom Decks Rather than replace individual transoms on a rail bridge with EWP transoms a Rail Transom deck has been developed where a continuous Bridgewood deck replaces the transoms. The advantages are:- Provides a waterproof membrane protecting the supporting structure. Ability to withstand derailment loads. Over the past 2 years Boral Plywood has embarked on an extensive research and development program to develop an Engineered Wood Product (EWP) alternative to the traditional hardwood sections used in the construction of timber road and rail bridges. The design philosophies embraced include sustainable resource, lowest life cycle energy cost, utilization of developments in gluing and treating technology, minimise on-site installation labour, design life of 50+ years and must be commercially viable. Products developed include individual replacement girders, rail transoms and kit or modular bridges. Extensive testing of these products has demonstrated structural performance equivalent or superior to existing products. The Bridgewood module s capacity far exceeds the ultimate (ULS) load requirement for a T44 load pattern with no permanent damage as a consequence of this load. Page 10

11 AS/NZS , Standard Australia, 2008 Acknowledgements The author would like to acknowledge the support and valuable input into the project of the following people and organisations. In particular Professor Keith Crews (University of Technology Sydney), Mick Savage (Roads and Transport Directorate, NSW Division, Institute of Public Works Engineers Australia), Peter Prasad (Australian Rail Track Corporation), John Greenfield (Ontrack), Frank Winter (Kyogle Council) and Russell Burke (Eurobodalla Shire Council). References 1. STANDARDS AUSTRALIA., Specification for preservative treatment Part 3: Plywood AS/NZS , Standard Australia, STANDARDS AUSTRALIA., Plywood-Structural AS/NZS 2269, Standard Australia, AUSTROADS, Australian Bridge Design Code, Austroads STANDARDS AUSTRALIA., Timber structures Part 1:Design methods AS , Standard Australia, STANDARDS AUSTRALIA., Bridge design-scope and general principles AS , Standard Australia, STANDARDS AUSTRALIA., Bridge design-design loads AS , Standard Australia, IPWEA(NSW) Roads & Transport Directorate, "Road Asset Benchmarking Project - Timber Bridge Management", September STANDARDS AUSTRALIA., Adhesives for timber and timber products Adhesives for manufacture of plywood and laminated veneer lumber (LVL): Page 11