Wood Flashcards
How much timber is harvested worldwide each year?
1.6 billion cubic metres
How much timber is used in the UK annually?
Approximately 50 million m^3
What amount of timber is produced by the UK per year?
16 million m^3 per year
Where does most softwood come from?
Scandinavia and the Baltic States
What is hardwood used for?
Furniture and interior design
What are the two types of tree types?
Coniferous and deciduous
Where is hardwood imported from?
Eastern and Western Europe and North America
What are glulam beams?
Type of structural timber product composed of several layers of dimensioned lumber bonded together with durable, moisture-resistant adhesives.
What is glulam short for?
Glue laminated
What is wood compatible with?
glass and steel
What is glulam used for?
Mainly arches, curved roofs, domes
What are characteristic of glulam?
- better structural properties
- dimensional stability
- large sizes
- reduced wastage of timber resource
- less material variability
- aesthetic variety
Why are timber framed houses beneficial?
Huge savings
What type of wood scaffolding can you have?
Bamboo
What are the advantages of wood?
- Excellent combination of physical properties
- High compressive and tensile strength
- Relatively low cost
- Good durability under certain conditions
- Predictable fire behavior
- Sustainable material if harvested from a sustainable forest
What are the disadvatnges of wood?
- Certain level of variability in performance
- Properties vary in different directions → the grain
- Wood often contains inherent flaws → inhomogeneous
- Durability can be poor under partially wet conditions (in soil)
- Transport costs – forests are often not near markets
- Dimensional stability → changes dimensions with moisture
- Needs to be dried before use
What country produces large amounts of wood?
Canada, Sweden, USA
How much timber is produced by Canada from the global market?
20%
Why is energy used in producing wood?
Zero energy to use apart from transport and drying out
Is wood a high or low embodied energy consumption material?
Low
Why is wood a low embodied energy material?
Converting timber into a usable building material takes far less energy and generates far fewer greenhouse gases than any other mainstream alternatives, including aluminum, steel and concrete
How much energy do conrete and steel use compared to timber?
Concrete uses 5 times, and steel 6 times more energy to produce than timber
What is photosynthesis?
Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods.
What happens during photosynthesis?
During photosynthesis, plants convert carbon dioxide and water into glucose and oxygen, using light energy trapped by chlorophyll.
How much carbon dioxide do trees absorb?
On average a tree absorbs 1 tonne of carbon dioxide for every cubic meter of growth
What makes a sustainable forest?
Uses recognised harvesting principles and crop
rotation techniques
True or false, wood is an excellent insulator?
True
True or false, wood is energy efficient?
True
What is the FSC?
Forest Stewardship Council -> non-governmental organization
What do the FSC promote?
Dedicated to promoting responsible management of the world’s forests
What do the FSC aim to combat?
Aims to combat both illegal, unethical and environmentally damaging logging
What can timber be defined as?
Timber is an organic, non-toxic, and naturally renewable building material
What role do forests play in the carbon cycle?
Carbon sink
What is the typical composition of dry wood?
- Glucose - glucose monomers
- 70 weight percent carbohydrate = cellulose and hemicellulose
How much cellulose and hemicellulose in dry wood?
- Cellulose - 50% of weight → crystalline
- Hemicellulose and pectin - 20 % of weight → semi crystalline
What are glucose monomers made from?
H and OH bonds
What is the shape of the structure of glucose?
Ring structure
How are glucose molecules linked?
Glucose molecules are linked by α or β linkages to form polysaccharides
How are mircofibrils formed?
Strong cross linking between strands forms microfibrils containing ~100 cellulose molecules
What is lignin?
- Lignin is a massive random polymer of phenylpropane alcohol
- Nonbiodegradable part of wood
How much moisture does cut wood have?
85%
How can wood be dried?
Air dried or kiln dried
What does the visible structure of wood consist of?
- Growth rings and rays
- Bark and the cork
What type material is wood?
Heterogeneous
What are the differences between heartwood and sapwood?
- Colour (sometimes)
- Durability
- Permeability
How are heartwood and sapwood similar?
Strengthwise
What does SEM stand for?
Scanning electron microscopy
What does the mircostructure of wood look like?
- Collection of longitudinal cells
- Close-packed drinking straws → vary in size
What are the key characteristics of wood microstructure?
- multi-component
- hygroscopic
- anisotropic
- inhomogeneous
- discontinuous
- inelastic
What are some features of wood affecting strength?
- Growth rings
- Wane
- Fissure
- Knot
What is a wane?
Untrimmed bark or wood that is missing along the edge or corner.
What does green mean in terms of wood?
The wood directly after it is cut?
How much mositure in green wood?
50%
How much moisture in dry wood?
12%
What is the ultimate bending strength in douglas fir during its green and dry phase?
green - 53%
dry - 91%
How can you test bending strength on wood?
- Wood will deflect when you do a 3 point bending test
How does wood behave when bending?
Behaves like a fibre reinforced composite material with significant toughness
The loading and unloading curves do not correspond, true or false?
True
How does water affect bonding?
Water reduces the bonding between fibers and cell walls making it easier to buckle
Does wood have low or high density and tensile strength?
Low density and high tensile strength
How can wood rot?
- Dry rot and wet rot
- Fungal decay
What are some common insects that can infest wood?
- Common furniture beetle
- Deathwatch beetle
- House longhorn
- Powderpost beetles
What are some marine borers?
- Shipworm (Teredo)
- Gribble (Limnoria)
What are some structural timber composites?
- New types of wood products
- Glulam
- OSB – Oriented Strand-board
- LVL – Laminated Veneer Lumber
Why are reonsititued timbers used?
- More consistent behaviour than normal wood
- Redistribution/removal of defects
- Reduced variability
What does PRF stand for?
Phenol resorcinol formaldehyde
What are orientated strand lumber used for?
Used in timber frame wall panels
How are laminated veneers produced?
Produced by bonding together veneers peeled from a log (c. 3mm thick)
What are lengths of veneers?
26 m
What are laminated veneer lumbers used for?
Typical used for roof beams, floor beams, beams in factory built housing flanges of I-joists footbridges and bridge decking
How are successive veneers usually orientated?
Orientated in a common grain direction
How are parallel strand lumber produced?
Produced by cutting peeled veneer into long strands (up to 2400mm), applying glue, and forming structural-sized sections through a heat and pressure quasi-extrusion process.
What are the characteristics of I-Joists?
- Strong
- Stiff
- Light
- Dimensionally stable
- Cost-effective
- Easy to handle
- Quality assured
What is the fastest-growing method of house construction in the UK?
Timber frame
How many homes have timber frames now?
One in four new homes
How much CO2 is saved from timber-framed homes?
4 tonnes
Why are timber-framed homes beneficial?
- The operational cost of a house can be reduced due to the improved thermal efficiency of timber frame houses
- Lighter construction
What is timber frame wall construction?
Timber frame wall construction is a method of building that uses heavy timber framing as the structural support for the walls
