BOM065 Materials Performance – Structure of Wood PDF

BOM065 Materials Performance – Structure of Wood Yutaka Goto Group for Sustainable Building Division of Building Technology Announcement Register for the study visit to RISE on Oct 4th (Fri)! (Find the excel doc on google). 2021-09-01 BOM065 - M3 - Timber 2 Wood and Tim...

BOM065 Materials Performance – Structure of Wood Yutaka Goto Group for Sustainable Building Division of Building Technology Announcement Register for the study visit to RISE on Oct 4th (Fri)! (Find the excel doc on google). 2021-09-01 BOM065 - M3 - Timber 2 Wood and Timber in BOM 065 Materials Performance Wood and Timber related sessions: Structure and Production Week 40, 30/09/2024 08:00-11:45 Durability + Exercise Week 40, 02/10/2024 10:00-15:00 1st Lab Timber Week 40, 02/10/2024 15:00-17:00 Performance assessment Week 41, 07/10/2021 08:00-09:45 Exercise Week 41, 07/10/2021 10:00-11:45 Consultation Week 41, 09/10/2021 10:00-11:45 2nd Lab Timber Week 41, 09/10/2021 13:00-17:00 2021-09-01 BOM065 - M3 - Timber 3 Contents Intro Micro structure of wood From micro to macro structure Wood characteristics Basic material properties of wood Wrap-up Find more in Chaper 52 of Construction Materials 2021-09-01 BOM065 - M3 - Timber 4 Intended Learning Outcomes of this Lecture You can differentiate softwood and hardwood. You can explain the micro structure of softwood. You can differentiate various parts of wood based on the different stages of tree growth on both micro and macro scale. You can define anisotropy of materials. You can calculate the density and moisture content of wood. 2021-09-01 BOM065 - M3 - Timber 5  Intro 2021-09-01 BOM065 - M3 - Timber 6 Why wood? Wood has certain advantages and disadvantages as a construction material Mechanical properties Hygrothermal properties Durability Production Environmental impact 2021-09-01 BOM065 - M3 - Timber 7 Why wood? Efficient use of renewable resources from a sustainable production management. Picture: Heidelbergcement 2021-09-01 BOM065 - M3 - Timber 8 Growth is Greater than the Harvest in Sweden * m3f = Forest cubic meters Source: Swedish Forest Industries Foundation, Riksskogstaxeringen, Skogsstyrelsen Find more: www.forestindustries.se/ 2021-09-01 BOM065 - M3 - Timber 9  Development of the Swedish Wood Supply* Refers to woodland * m3sk = Forest cubic meters Source: Swedish Forest Industries Foundation, Riksskogstaxeringen, SLU Find more: www.forestindustries.se/ 2021-09-01 BOM065 - M3 - Timber 10  Structure of Wood 2021-09-01 BOM065 - M3 - Timber 11 Wood structure Wood has a highly hirachical structure Figure source: M. Harrington, University of Canterbury 2021-09-01 BOM065 - M3 - Timber 12 Wood structure 2021-09-01 BOM065 - M3 - Timber 13 Molecule level – Cellulose as “Skeleton” 2021-09-01 BOM065 - M3 - Timber 14 Molecule level – Hemicellulose as “Matrix” Figure source: https://www.e-education.psu.edu/egee439/node/664 2021-09-01 BOM065 - M3 - Timber 15 Molecule level – Lignin as “Matrix” 2021-09-01 BOM065 - M3 - Timber 16 Wood Cell Microfibrillar orientation and percentage thickness of the cell wall layer in spruce timber (Picea abies) 2021-09-01 BOM065 - M3 - Timber 17  From micro to macro structure 2021-09-01 BOM065 - M3 - Timber 18 Annual rings in coniferous wood Picture: Jozsa & Middleton, Forintek 1994 2021-09-01 BOM065 - M3 - Timber 19 Coniferous or Deciduous tree species Coniferous wood: Deciduous wood: evolutionary older evolutionary younger «simple» structure Higher degree of specialization of different cells 2021-09-01 BOM065 - M3 - Timber 20 Growth of a tree Picture: www.swedishwood.com/ 2021-09-01 BOM065 - M3 - Timber 21 Macro structure of wood Picture: Jozsa & Middleton, Forintek 1994 2021-09-01 BOM065 - M3 - Timber 22 Macro structure of wood Sapwood: “living” (active in water conduction) Heartwood: “dead” (inactive in water conduction) Pine: Spruce: Heartwood Picture: www.swedishwood.com/ Picture: Jozsa & Middleton, Forintek 1994 2021-09-01 BOM065 - M3 - Timber 23 Macro structure of wood In softwood, juvenile wood, compared with mature wood, has lower strength lower density more compression wood thinner cell walls lower cellulose content higher lignin content lower percentage of latewood Picture: Jozsa & Middleton, Forintek 1994 2021-09-01 BOM065 - M3 - Timber 24  Wood characteristics 2021-09-01 BOM065 - M3 - Timber 25 Knots 2021-09-01 BOM065 - M3 - Timber 26 Radial cross-section in tree stem and knots a) Living knot (green knot) b) Knot from a dead branch (dead or black knot) Green knot (alive) Near to the surface the knot will become loose c) Embedded knot Dead knot 2021-09-01 BOM065 - M3 - Timber 27 Knots in a tree Picture: www.swedishwood.com/ 2021-09-01 BOM065 - M3 - Timber 28 Knots and material failure Tension failure of a spruce board caused by fibre inclination around a knot 2021-09-01 BOM065 - M3 - Timber 29  Reaction wood Softwood Hardwood Compression Tension https://www.intechopen.com/chapters/79485 wood wood 2021-09-01 BOM065 - M3 - Timber 30 Reaction wood Example of compression wood Example of tension wood source: wsl_jahrringforschung_datenbank_exzentrizitaet 2021-09-01 BOM065 - M3 - Timber 31 Reaction wood Softwood with compression wood Round cells Large angle of cellulose fibrills S2 >30° No S3 layer More lignin Hardwood with tension wood Additional layers with axial orientation of fibrills Mattheck & Kubler, 1995 2021-09-01 BOM065 - M3 - Timber 32 Effects of compression wood in sawn timber 2021-09-01 BOM065 - M3 - Timber 33  Basic material properties of timber 2021-09-01 BOM065 - M3 - Timber 34 General properties Density Moisture content 2021-09-01 BOM065 - M3 - Timber 35 Density Density 𝑚𝑚 𝑚𝑚 = Mass of wood [kg] 𝜌𝜌 = 𝑉𝑉 = Volume of wood [m3] 𝑉𝑉 Specific gravity (relative density) 𝜌𝜌𝑡𝑡 𝜌𝜌𝑡𝑡 = density of wood (timber) 𝐺𝐺 = 𝜌𝜌𝑤𝑤 𝜌𝜌𝑤𝑤 = density of water at 4°C 2021-09-01 BOM065 - M3 - Timber 36 Density Wood fibres 1500 kg/m3 Spruce and pine: 300 - 600 kg/m3 2021-09-01 BOM065 - M3 - Timber 37 Density Mean density at 12% MC : Compression wood Spruce and pine 500 – 850 kg/m3 2021-09-01 BOM065 - M3 - Timber 38 Moisture Content Definition: 𝑚𝑚𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 𝑢𝑢 or 𝜇𝜇 = moisture content, MC (%) 𝑢𝑢 = 100 ⋅ 𝑚𝑚𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 = mass of water in a sample (kg) 𝑚𝑚𝑑𝑑𝑑𝑑𝑑𝑑 𝑚𝑚𝑑𝑑𝑑𝑑𝑑𝑑 = mass of oven-dry sample (kg) (~24h in 103°C) Attention! In timber engineering, MC is always given in %. In building physics, MC is often given in kg/m3. The expression in % is often called ”moisture ratio”. 2021-09-01 BOM065 - M3 - Timber 39 Fiber saturation point (FSP) FSP- fibre saturation point (𝑢𝑢 ≈ 28% for spruce) u < FSP u ≈ FSP u > FSP 2021-09-01 BOM065 - M3 - Timber 40 Moisture Content u < FSP 2021-09-01 BOM065 - M3 - Timber 41 Moisture content Average ”green” MC of sapwood & heartwood 2021-09-01 BOM065 - M3 - Timber 42 Density definitions General 𝑚𝑚𝑢𝑢 𝜌𝜌𝑢𝑢 = 𝑉𝑉𝑢𝑢 Dry-density Conversion 𝑚𝑚𝑢𝑢=0% 𝑢𝑢 𝜌𝜌0 = 𝜌𝜌𝑢𝑢 = 𝜌𝜌0 1+ 𝑉𝑉𝑢𝑢=0% 100 For most engineering applications 𝑚𝑚𝑢𝑢=12% 𝜌𝜌12 = 𝑉𝑉𝑢𝑢=12% 2021-09-01 BOM065 - M3 - Timber 43 Wrap - Up You can differentiate softwood and hardwood. You can explain the micro structure of softwood. You can differentiate various parts of wood based on the different stages of tree growth on both micro and macro scale. You can define anisotropy of materials. You can calculate the density and moisture content of wood. Can you? 2021-09-01 BOM065 - M3 - Timber 44