Sustainability of Infrastructure and the Role of Structural Timber

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Sustainability of Infrastructure and the Role of Structural Timber by Keith Crews, Professor of Structural Engineering, University of Technology Sydney.

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Sustainability of Infrastructure and the Role of Structural Timber

  1. 1. Sustainability of Infrastructure and the Role of Structural Timber Keith Crews Professor of Structural Engineering Centre for Built Infrastructure Research University of Technology Sydney 1
  2. 2. © 2009 – Keith Crews: keith.crews@uts.edu.au This presentation may be reproduced for IEAust CPD and University Educational purposes But cannot be used for commercial purposes without the prior written permission of the author
  3. 3. Overview • Sustainability & Structures • Historical Role of Timber • Current Challenges • Techniques & Tools – Health Monitoring – Assessment and Impact – Repair and Rehabilitation • New Developments and Opportunities 3
  4. 4. Sustainability • Broadly, is the ability to maintain a certain process or state, usually with respect to biological or human systems • Human sustainability has become increasingly associated with the integration of economic, social and environmental spheres • Involves “meeting the needs of the present without compromising the ability of future generations to meet their own needs” World Commission on Environment and Development (Brundtland Commission) – Report to UNGA 1987 Commission) 4
  5. 5. Sustainability & Economics • Since Industrial Revolution most Economic systems are based on growth • Growth = Prosperity • Growth = Consume • Now being confronted: – Limits to growth – Limits to resources – Limits to consumption Source: NOAH / NASA – Limits to environment 5
  6. 6. Getting the Balance Right • Sustainabilty: improving the quality of human life while living within the carrying capacity of supporting eco-systems • More recently “Triple Bottom line” approach: – commercially viable development – enhance community wellbeing – environmental renewablity and conservation of resources • Objective of balancing these is “Sustainability” 6
  7. 7. Triple Bottom Line Philosophy Social equitable bearable sustainable Environment Economic viable Balancing the spheres of influence Adams, W.M. (2006) quot;The Future of Sustainability: Re-thinking Environment and Development in the Twenty-first Century”
  8. 8. Sustainability and Infrastructure • Economic growth understood as New = Good • Political Drivers – New projects = success – No votes in maintenance • Educational Drivers – Engineers trained to design new, not sustain existing • Decisions based on traditional economic models, rather than sustainability principles 8
  9. 9. Infrastructure Challenges • “Infrastructure Australia” an excellent initiative – Highlights problems with planning – Prioritisation and best value / national interest – Aims to improve decision making processes • However, the focus still appears to be on “new” projects, rather than how we can improve / maintain existing infrastructure • Need for a change in mind-set and new economic / decision making models if we are to develop sustainable practices 9
  10. 10. Infrastructure Challenges • Declining state of existing infrastructure is evidenced by the Australian Report Cards (IEAust & GHD) – civil infrastructure is barely adequate or poor – similar situation in US (refer Civil Engineers Aust - Feb 2009) – e.g: 1 in 4 bridges either deficient or obsolete • Private investment focuses on new projects rather than maintaining existing infrastructure • The Great Challenge of “Aging Infrastructure” Priority: “Restore and Improve Urban Infrastructure” Nat. Academy of Eng. (July 2008) 10
  11. 11. Need for a change in mind-set • OECD: sustainable infrastructure (structures) requires 3% of the asset replacem’t value be budgeted each year for maintenance (on average) OECD Road Transport Research – Bridges (1992) / OUTLOOK 2000 (1999) • Obviously this varies with age and use – new assets would require less, older ones more • Expenditure in Australia varies between less than 0.5% and 1.5% depending on the asset owner (ave. for State Governments approx 1.2%; less in LG) • Creates a cycle of obsolescence 11
  12. 12. Degradation Agents Degradation is caused by one or more of: • “Normal” wear and tear • Biological / Chemical / Environmental hazards • Increased frequency of load events (e.g. more traffic) • Increased magnitude / severity of loads – e.g. increasing axle loads from 8t to10t increases the damage potential by 145% – Extreme load events – Climate change ATSE Report “Assessment of Impact of Climate Change on Australia’s Infrastructure” (2008) 12
  13. 13. Infrastructure Degradation Degradation increases with failure to: • Detail / construct for durability • Resource adequately • Correctly identify damage • Understand its impact • Intervene effectively – Maintenance – Repairs Source: Aboura et al – UTS / RTA (2008) • Strengthen / optimise 13
  14. 14. Infrastructure Degradation Degradation increases with failure to: • Detail / construct for durability • Resource adequately • Correctly identify damage • Understand its impact • Intervene effectively – Maintenance – Repairs Source: Aboura et al – UTS / RTA (2008) • Strengthen / optimise 14
  15. 15. Sustaining Infrastructure • The issue of aging infrastructure applies to all structural materials • The reality is that we cant afford to replace every structure • Engineers have a responsibility to maintain the operational effectiveness and safety of infrastructure • Both a challenge and an opportunity! • Illustrate - specific focus on timber 15
  16. 16. Background: Timber Structures in Australia • Historic applications • Current applications • Development of “tools” that enable sustainable practices – damage detection – risk assessment – strategic maintenance – repair & rehabilitation 16
  17. 17. Timber has been an essential and integral part of rural Australia’s buildings and infrastructure since early European settlement
  18. 18. Structures such as these have been “out of sight, out of mind” Yet, despite the fact they are often not well maintained Many are still performing well After 150+ years!
  19. 19. Similarly with bridges – an essential, but under valued part of our rural infrastructure
  20. 20. Multi-storey timber warehouses were common in the 1800’s - many have been recycled into offices
  21. 21. However, lack of understanding about detailing, maintenance and durability issues can lead to performance problems
  22. 22. Resulting in the need for expensive repairs!
  23. 23. Case Study: Sustaining Timber Bridges • A main focus of R&D at UTS since 1990 • Collaborative with RTA, Industry, Local and Federal Governments • Approx $5m of R&D projects • Development of new technologies: – risk ID / assessment – repair & rehabilitation 23
  24. 24. Timber Bridges - Context • Approx 40,000+ bridges in Australia • Approx. 27,000 are aging timber bridges – most are girder / corbel (spans 8-10m) – some truss bridges (spanning up to 36m) • Essential part of our transport infrastructure – mainly in rural areas / Local Government – most 70+ years old – designed for 14 to 18t – now carrying 44t plus! • Asset value in excess of $25B • An important part of our history with social & cultural significance 24
  25. 25. Timber Bridges - Drivers • Need for bridges with European expansion • 1861 decree to use local materials • Lack of steel and RC • Availability of HQ hardwoods • 400 truss bridges built between 1860 & 1936 • 1000’s of girder bridges 25
  26. 26. The “stress” of Timber Bridges • For many Engineers (particularly in LG), looking after all types of bridges is a major problem • The bridges are often “over stressed” from excessive loads combined with deterioration • Engineers looking after them are “over stressed” in trying managing these aging bridges • Compounded by general lack of confidence / expertise in timber 26
  27. 27. Engineering Challenges • Level of expertise for assessing and / or repairing bridges varies enormously – In many councils is virtually non existent • Consequently, developing and maintaining an effective BMS is often seen as “too hard” • Resources are often inadequate – Funds limited for replacement or rehabilitation – Need for sustainable practices – they have to last! • Results in “band-aid” management practices that react to emergencies • Bridge maintenance / repairs are not strategic 27
  28. 28. Proactive Bridge Management - Developing Sustainable Practices Understanding the condition of the asset involves: • Developing effective assessment systems for quantifying safe capacity / acceptable performance • Identifying where the greatest needs / risks are located • Using this information to develop and maintain an “information system” or BMS • Essential for sustainable management of infrastructure 28
  29. 29. Addressing the “guess work” in strength assessment of bridges…. One of the biggest problems has to do with the assumptions we make and conclusions we draw when we assess / model the bridge structure…… 29
  30. 30. Uncertainties & Assumptions • Reliable assessment requires accurate information about: – Integrity of member sections (decay / corrosion / spalling) – Load history and damage – Structural interactions – Material properties (variability and aging effects) • Errors can be significant! • Overly conservative decisions can be costly! 30
  31. 31. Strength Assessment Methods Various methods, in 4 basic tiers: 1. Visual inspection 2. Desk top analysis 3. Load Testing 4. Health monitoring and damage detection • Each of these has its place • Generally speaking, the higher the tier, the more cost that is involved • But, with the benefit that the reliability of the information gained, improves 31
  32. 32. Inspection & Assessment • Most modern asset management systems involve visual inspection • Visual systems tend to qualify condition • Some information can be gathered to quantify effects of damage - if visible / measurable • Assumptions must be made about member and material properties, in order to estimate safety using “desk top” modelling • Testing of select elements and load testing can confirm some of these assumptions • But - significant damage is often undetected! 32
  33. 33. How safe is safe? 33
  34. 34. Potential Tools for Facilitating Sustainable Practices
  35. 35. New Technologies for Damage Detection • Significant R&D on NDE technologies for determining the location and extent of “damage” • Emerging Technologies (most promising): – Dynamic / Modal Analysis – Radiography and GPR – Stress Wave • Impact • Sonic • Ultrasonic – Acoustic Emission • Potential for a “quantum leap” in assessing the condition of existing structures 35
  36. 36. Dynamic / Modal Analysis • New method developed by UTS in partnership with IPWEA / RTA • Provide good “global” indication of safe response of superstructure • Quick to perform and cost effective • Provides accurate information about global behaviour of beam structures (timber, conc & steel) 36
  37. 37. Dynamic / Modal Analysis • Next generation identifies location and size of damage (voids / loss of member integrity) • Development of neural networks that enable the system to “learn” • Linked with probabilistic strength models derived from testing 37
  38. 38. Ground Penetrating Radar • Uses electromagnetic waves to generate an image of internal features • Ideal for investigating objects with low conductivity such as masonry, concrete and timber 38 Source: W.Muller – QDMR (2008)
  39. 39. Ground Penetrating Radar • Recent developments can create 3D images • Can be used effectively with other NDE (e.g. thermal imaging) 39 Source: L. Binda – TU Milano (2008)
  40. 40. Ultrasonic Tomography • Ultrasonic pulse velocity (UPV) used to create 2D and 3D images of internal voiding • Data is analyzed in terms of propagation velocities and arrival of the transmitted ultrasonic pulse Source: De La Haza et al - SFR (2008) 40
  41. 41. Acoustic Emission • AE signals can identify micro-cracking mechanisms in reinforced concrete • Applied to corrosion-induced cracks due to expansion of corrosion products • Potentially effective for identifying / quantifying damage accumulation Estimate of crack depth Image of water filled crack 41 Source: Ohtsu et al - SFR (2008)
  42. 42. Engineering Challenges • Translating R&D into practice • Key Forums – SFR Edinburgh – RILEM TC215 • Training Engineers to interpret • What is the effect of damage on structural performance? • Is it still safe? • What needs to be done? Client: How do I fix it? 42
  43. 43. Repair & Rehabilitation of Timber Bridges • Many councils and road authorities are now finding it difficult to secure large section, durable hardwoods • This has lead to a number of alternatives to “adhoc” replacement being developed and trialled for future use • Designed for durability and high performance to sustain timber bridges 43
  44. 44. Challenges with Heritage Structures • Heritage Legislation means that many old bridges must be kept operational • Tension between maintaining hist. integrity (size of members) and safety for current loads • Significant R&D projects, consulting and training • Development of new structural systems, design & detailing methods 44
  45. 45. Concrete / Timber Systems 45
  46. 46. Engineered Wood Products • Bridge-Wood decking systems • Alternative Girder products – LVL – Glue Laminated Timber • Stress Laminated Timber – Plate decks – Cellular decks 46
  47. 47. Bridgewood 47
  48. 48. EWP girder systems 48
  49. 49. SLT Systems 49
  50. 50. SLT Systems 50
  51. 51. SLT Systems 51
  52. 52. Hybrid Design Methods 52
  53. 53. Modern “best practice” detailing “Best practice” detailing methods combined with careful use of new products can lead to significant improvements in durability and long term performance of timber bridges – without the need to replace existing structures. 53
  54. 54. Durable Design Detailing 54
  55. 55. Durable Design Detailing continued • 8 yr old footbridge • Detailed for durability • Excellent – condition 1 • Minimal maintenance required 55
  56. 56. Potential of Timber in Structures • Does timber have a role in infrastructure? • Why? – renewable & sustainable – we can grow more • Overview existing uses • Introduce new timber based technologies and potential applications in Australia 56
  57. 57. Normal “current” uses ALL LOADS CARRIED BY TIMBER!
  58. 58. Recent developments • Changes in available resource – Reduced supplies of native hardwood – Increased availability of plantation timbers such as radiata pine – Smaller logs / quicker growing • Development of new products; – Engineered Wood Products 60
  59. 59. Importance of collaborative R&D for design innovation
  60. 60. Source: B Hutchings - TimberBuilt P/L (2008)
  61. 61. Source: B Hutchings - TimberBuilt P/L (2008)
  62. 62. Source: B Hutchings - TimberBuilt P/L (2008)
  63. 63. New Building Applications - Local & O/S developments • Current R&D in Australia / NZ • Composite Flooring systems • Cross laminated timber (CLT) • Prefabricated Floor, Wall & Roof systems • Multi-storey Buildings – commercial – residential • Modern Bridges in Europe 72
  64. 64. Current R&D – Aust & NZ • Number of projects focusing on developing new “engineered” timber products for non-residential markets • FWPA projects – New structural systems (e.g. CLT) • STIC: 3 Main Programs – Roof Systems – Floor Systems – Wall and Framing Systems • Collaborative Partnerships: Research Providers & Industry 73
  65. 65. Timber Framing Systems Internal or external Rocking motion dissipation devices • Recent work at UC • Use of column & θ imp Unbonded post- beam frames for tensioned tendon U multi-storey buildings • Post tensioned LVL frames that are “self healing” • Particular application in seismic regions 74
  66. 66. New floor systems • Current focus on non residential building forms • New composite floor systems • Prefabricated using CAD/CAM • High performance – 8 to 10 m spans – 3 to 8 storeys • Use with existing structural forms 75
  67. 67. Cross Laminated Timber (CLT) • Ability to utilise lower quality, fast grown plantation softwoods • Prefabrication under factory conditions • Floors, walls & roofs • Quick to construct • Significant uptake & development in EU 78
  68. 68. Prefabricated Building Systems • Factory Fabrication – Excellent QA / QC • Use of CAD / CAM / CNC • Modular structural system – material combinations • Efficient Erection • “Green building” strong driver in terms of carbon store, process and operating energies 81
  69. 69. Multi-Storey Timber Buildings • Multi-storey timber framing for buildings in North America and Europe well established, for 4 to 6 storey • 9 storey residential built from “cross laminated” panels in London • 4 - 6 storey commercial using glulam frames and TCC floors in Europe • Excellent Fire & Acoustic Performance 83
  70. 70. First Storey RC, then Timber
  71. 71. 8 storey timber building in Växjö, Sweden
  72. 72. 9 storey CLT building in London
  73. 73. Examples of Excellence – Timber Bridges
  74. 74. Use with steel and concrete
  75. 75. Conclusions: Sustainable Infrastructure • Significant challenges facing Civil and Structural Engineers • Urgent need to educate existing & future PE’s: – Triple Bottom Line “sustainability” principles – Design of new structures incorporating “renewable” mat’s – Assessment, protection / enhancement of existing • Need for us to provide leadership in the community – Understanding and communicating the need for change – Lobbying for appropriate resources – Using our skills & new technologies to create and implement sustainable practices 92
  76. 76. Conclusions: Timber as a modern material Viable timber structures are created by: • Designing for “whole of life” value & worth • Understanding sustainability processes • Detailing / const. for durability • Creative use of new products • Designers developing understanding and confidence in timber & hybrid systems 93
  77. 77. Conclusions: Timber as a modern material • Structural timber is a truly sustainable and remarkable engineering material • Yet there is a lot of fear, based on ignorance, about using it • With professional skills timber structures can be designed or rehabilitated for: – high performance – stringent environmentally sustainable design criteria – and can be both durable and aesthetically pleasing structures 94
  78. 78. Timber has important role to play in contributing to the Economic, Environmental and Social aspects of Australia’s Infrastructure being truly Sustainable. The creative leadership and skills of Professional Engineers is critical for this to occur. thank you for your attention

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