Materials - Wood

How much wood does UK use annually? What is this projected to increase to? Where is softwood imported from and what's it used for?
50 million cubic metres of wood used in UK annually, production expected to increase to over 16 million cubic metres annually by 2020. Most imported wood is softwood from Scandinavia and Baltic states. Softwood used for construction,
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Where is hardwood from and what is it used for?
Hardwood imported from Eastern Europe, Western Europe and North America, for furniture/design. Tropical wood for marine construction
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What type of wood product is found in beams?
Glulam used for beams
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Where is wood seen in civ eng?
Wood can be seen in bridges, timber framed houses, beams etc. In conjunction with steel and concrete.
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What are advantages of wood?
High compressive and tensile strength, low density, readily available and cheap, good thermal properties, durability under certain conditions, predictable fire behaviour, can be sustainable, compatible with other civ eng materials
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What are cons of wood?
properties vary in different directions, wood often contains inherent flaws, significant waste can be generated from trees, durability bad in wet conditions, attacked by certain insects, transport cost, dimensional stability
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What country exports the most wood?
Canada has highest world exports
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Why is wood a sustainable construction material?
Wood only renewable construction material, low embodied energy consumption, low in use energy consumption due to low thermal conductivity. Forest growth leads to drops in atmospheric CO2
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What is photosynthesis equation?
CO2+H2O-> CH2O + O2 (CH2O is carbohydrate - makes wood)
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What do sustainable forests do?
Sustainable forests use recognised harvesting principles and crop rotation.
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Why does timber have low energy footprint?
Timber converted to usable building material relies on far less energy than concrete and steel, concrete 5 times and steel 6 times more energy to make than timber. Wood excellent insulator and offers energy efficiency.
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What is the FSC?
Forest Stewardship Council is non-governmental, promotes responsible management of world's forests by combating illegal and unethical logging. Endorsed by Greenpeace, WWF, the Woodland Trust etc. Timber should have FSC mark
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What are properties of timber and why is European softwood industry good?
Timber is organic, non toxic and renewable, European softwood industry doesn't affect deforestation issue, Europe timber industry wants to grow more trees than those harvested. Forests act as huge carbon sinks
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What are cellulose and hemicellulose percentages in wood? Are they crystalline? What are they made from? What's function?
Cellulose - 50% %w/w, crystalline state made from glucose - function=microfibre. Hemicellulose/pectin 20%, semi-crystalline, made from xylose, galactose, mannose, function=matrix
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What are lignin and extractives percentages in wood? What are they made from and what's function?
Lignin - 25%, amorphouse, made from phenyl-propane - matrix. Extractives - 5%, monomeric state, made from terpenes and phenolics, function of toxicity.
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What is chemical structure of glucose?
Glucose monomers make up wood. Glucose has a ring structure with molecules linked by alpha or beta linkages to form polysaccharides. Cellulose has beta linkages (OH on carbon-1 above glucose ring instead of below).
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What are B 1,4 bonds?
B 1,4 bonds are the oxygen bonds between the monomers in cellulose. For cellulose, the structure 'steps up', OH at carbon-1 (right end of hexagon) is above the ring plane.
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What is structure of glucose monomers?
Hexagon with C on edges, except on O edge with no other bonds, CH2OH and OH bond for one C of 5, and OH, H bonds for other C's outside ring
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What is cellulose compared to glucose? How are microfibrils (the structure) formed?
Cellulose is a crystalline polymer of glucose. Strong cross-lining between strands forms microfibrils containing 100 cellulose molecules.
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What part of polymer structure is lignin? Does it have a structure?
Lignin is massive random polymer of phenylpropane alcohol - non biodegradable part
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What is structure of as cut wood? what do we need to do to it?
As cut wood has 85% moisture. Dried by air or kiln drying. Heartwood makes centre, then sapwood, then vascular cambium, then bark, then periderm (cork lining), then cork. Wood has growth rings and rays
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What are differences between heartwood and sapwood?
Heartwood and sapwood have different colour, durability and stability characteristics.
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What trees do heartwood and softwood come from?
Softwood - coniferous trees. Hardwood - deciduous trees (less volumptuous)
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What is microstructure of wood? (seen through electron microscopy)
Wood is anisotropic, inhomogeneous, discontinuous, inelastic, fibrous, porous, etc
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What type of packing does hardwood and softwood show?
Hardwood has a closed packed drinking straws SEM appearance while softwood has a softer less packed appearance. Hardwoods from oak, ash, beech mahogany trees
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What sort of things show heterogeneity in wood?
Wood has growth rings, fissures (cuts), wanes (where wood separates like opening curtains), and knots which affect strength. Different properties across and along grain
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How does strength vary according to grain of wood?
Along grain wood has greater tensile (40x)and compressive strength(3-10x), lower shear compared to across grain. (along grain is where the lines are parallel to the sides of wood)
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How does wood behave in bend strength testing? Why does loading and unloading not align?
Bend strength testing - wood behaves like a fibre reinforced composite with toughness. Wood shows viscoelasticity as there is deflection after unloading due to viscous deformation with time, due to amorphous lignin.
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How does wood behave in compressive testing as water content increased?
In compressive strength testing compressive strength drops rapidly with water content as water reduces bonding between fibres and cell walls easier to buckle.
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What threatens wood durability?
Fungal decay causes dry and wet rot. Both need moisture contents >25%, Wood not good in contact with soil. Insects like furniture beetles and marine borers like shipworm bio-deteriorate wood. Causes £900 mil in damage costs to UK pa
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What are types of structural timber composites? Why are they better than wood?
Structural timber composites : glulam, OSB (oriented strand-board, LVL - laminated veneer lumber, PSL - parallel strand lumber, LSL - Laminated strand lumber. I-joists. Remove defects and reduce variability
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How are structural timber composite supplied? what are other names?
Supplied as products, with durability, treatment, fire behaviour product specific. Also known as engineered wood/lumber products or structural composite lumber. Combine best aspects of wood with other materials
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Why is glulam good?
Glulam has dimensional stability, can be in large sizes, reduces waste of timber, has less variability, and aesthetic variety. Utilises materials unsuitable for conversion to sawn timber. Planks of wood glued together to form larger sections.
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What is makeup of glulam? (planks of wood glued to make larger sections)
Glulam commonly 45mm deep laminates with PRF adhesive and can be homogeneous wood species or mixed. PRF is phenol resorcinol formaldehyde.
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How can glulam be shaped, what are typical uses, and what are sizes for beams and portals?
Can be curved or tapered and manufactured to large lengths. Used for beams, domes/curved roofs, can have 1-30m length for beams and 10-50m length for portals
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What are OSL used in and what is laminated veneer lumber?
Oriented strand lumber used in timber frame wall panels. Laminated veneer lumber bonded veneers peeled from log, long panels cut to structural sections, normal grain direction oriented and up to 26m
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What is LVL used in and how is parallel strand lumber made?
LVL used commonly in roof beams, floor beams, flanges of I-joists in footbridges etc. Parallel strand lumber produced by cutting peeled veneers into long strands, coating with glue, and using heat and pressure quasi-extrusion process to form sections
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What are I-Joist advantages?
I joists are strong, stiff, dimensionally stable, cheap, straight, light, use less timber, can be made long
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How common is timber frame housing and what are advantages?
Timber frames in 1/4 new homes. Has 30% shorter and more predictable construction time than bricks, reduced disruption to communities, a timber frame house can be weather tight in less than 5 days.
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Why is timber good for environment when framing houses?
Every timber frame house saves 4 tonnes of CO2, and operational house costs reduced. Benefits from off-site construction.
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Card 2


Where is hardwood from and what is it used for?


Hardwood imported from Eastern Europe, Western Europe and North America, for furniture/design. Tropical wood for marine construction

Card 3


What type of wood product is found in beams?


Preview of the front of card 3

Card 4


Where is wood seen in civ eng?


Preview of the front of card 4

Card 5


What are advantages of wood?


Preview of the front of card 5
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