Wood and Timber Flashcards
How many cubic meters of tinder are harvested worldwide every year?
~1.6 billion m^3
How much timber is used in the UK each year?
50 million m^3
How much timber does the UK produce each year?
~16 million m^3
How much of the UKs timber is imported?
66%
What type of wood is used in construction, and where does it come from?
Softwood
From Scandinavia and the baltic states
What type of wood is used for furniture and interior design and where does it come from?
Hardwood and it comes from Eastern and Western Europe and North America
How is tropical wood used?
In marine construction and high value interiors
What are some advantages of wood in construction?
- Excellent combination of physical properties
- High compressive and tensile strength
- Readily available
- Relatively low cost
- Good thermal properties
- Good durability in some conditions
- Predictable fire behaviour
- Sustainable material if harvested right
- compatible with other engineering materials
- Aesthetically pleasing
What are some disadvantages of timber?
- Widely variable properties
- variability in performance
- properties vary in different directions
- contains inherent flaws
- significant waste from each tree
- durability can be poor under particularly wet conditions
- attacked by certain insects, bacteria, and fungi
- transport costs
- needs to be dry before use
- dimensional stability
- fire performance
What makes wood a sustainable construction material?
- It is the only renewable construction material
- Low embodied energy consumption
- Low in use energy consumption due to low thermal conductivity
- High embodied carbon due to photosynthesis
How much CO2 does a tree absorb through photosynthesis and how much oxygen do they produce in the same period?
1000kg CO2
727kg O2
per m^3 growth
Therefore young trees are better for the environment than old ones
By using wood instead of another construction material how much CO2 is embodied?
2 tonnes per m^3
How much more energy do concrete and steel use than timber strength for strength?
concrete uses 5x
steel 6x
What organisation ensures sustainable forests?
The forest setwarship council (FSC)
What does the FSC do?
combat illegal and unethical logging techniques as well as environmentally damaging logging
How much of the wood consumed in Europe is from European forests?
over 90%
Why is the European forest industry so good?
It plants more trees than it harvests
European forests grow by 3,500 square miles a year
How much carbon is stored in European forests?
9.5 miillion tonnes
How much of the weight of wood is carbohydrate?
70%
What structure does glucose have?
ring
What are glucose molecules linked by
alpha or beta linkages to form polysaccharides
What does cellulose consist of?
Cellulose structures, joined by beta-1,4 bonds
What part of wood does lignin make up?
The non biodegradable part
What is the structure of lignn
A massive random polymer of phenylpropane alcohol
What is the moisture content of wood when it is cut?
up to 85%
How is wood dried?
Either by air drying or Kiln drying
What is the structure of wood like?
On the very outside you have bark, consisting of the periderm (cork cambium and cork) and the living phloem
Then you have the sapwood
Then the heartwood
What are the differences between heartwood and sapwood?
- colour
- durability
- permeability
What is not different about heartwood and sapwood?
Strength
How do you tell the difference between soft and hardwoods?
Softwoods come from coniferous trees, hardwoods come from deciduous trees
What are key parts of the microstructure of wood?
- Multi-component
- hygroscopic
- anisctropic
- inhomogeneous
- Discontinuous
- inelastic
- fibrous
- porous
- biodegraddable
- renewable
What does SEM stand for?
Scannign electron microscopy
What does the microstructure of hardwood resemble?
close packed drinking straws
Why is are the properties of woods different in different directions?
Due to inherit flaws such as knots, wanes, growth rings and fissures
What grain direction is strong in tension?
Along grain
What grain direction is strong in compression?
Along grain
What grain direction is resistant to shear?
across strain
How does wood perform in bend strength testing?
like a fibre reinforced composite material with significatn toughness
What decay mechanisms are present in wood?
Fungal decay
Dry and wet rot
What moisture content is neeeded for decay to occur in wood
> 25%
hence why wood is not good when in contact with soil
What is the associated costs of insect infestation a year to the UK?
£900 million
What types of insects cause damage to wwod?
Not as moisture dependent: Common furniture beetle Death watch beetle House longhorn Powderhpost beetles Forest longhorn beetles Pinhole borer Wood wasps
Marine Borers:
Shipworm
Gribble
Name some structural timber composites
- Glulam
- Orientated Strand-Board (OSB)
- Laminated veneer Lumber (LVL)
- Parallel strand lumber (PSL)
- Laminated strand lumber (LSL)
- Prefab I joists
What are the benefits of structural timber composites?
They are sold as products
Their properties are known
The properties are product specific
Design information is provided by technical approval documents
What are other names for structural wood products?
- Engineered wood products
- Engineered Lumber products
- Structural composite lumber
What are the benefits of glulam?
- Better structural properties
- dimensional stability
- large sizes
- reduced wastage of timber resource
- less material variablilty
- aesthetic variety
- utilization of material unuitable for conversion to sawn timber
What wood species mostly makes up glulam?
European whitewood
Usually how deep are the laminates in glulam?
45 mm
What adhesive is used in glulam?
PRF phenol resorcinol formaldehyde
Where does the higher class material go in glulam if inhomogeneous?
on the outside
What is the mass of glulam?
500 kg m^-3
What are some of the size/ shape benefits of glulam?
- standard straight cross sections
- Curved and / or tapered
- manufactured up to 45 m
Where is glulam typically used?
Beams and columns
Domes, curved roofs and arches
footbridges
Where is orientated strand lumber used?
Timber frame wall panels
How is laminated venner lumber made?
Produced by bonding together veneers peeled from a log (~3mm thick)
These long panels are cut into structural sized sections
Veneers are orientated in common grain direction
What is the maximum length currently available for laminated veneer lumber?
26m
Where is laminated veneer lumber typicall used?
roof or floor beams in factory built housing
Flanges of I joists footbridges and bridge decking
How are parallel strand lumber sections produced?
Long peeled veneers (2400mm) are coated with glue and layered using a heat and pressure quasi extrusion process to form long structural sized sections
What are the benefits of I joists?
Strong, stiff, straight, light, long
Dimensionally stable, cost effective, easy to handle, use less timber material, quality assured
How many new homes are made out of timber in the UK?
25%
How many new homes in scotland have a timber frame?
3/4
How much shorter is the construction time with timber?
30%
How many days does it take to get a timber frame house weather proof
less than 5
How much more wood is used than in an equivalent masonry home?
5-6m^3
How many tonnes of CO2 are saved by every timber house?
4
What other benefits to timber framed houses have?
reduced running costs
What are the advantages of wood as an engineering material?
- Low energy content needed for preduction
- Low cost of production
- Wood is environmentally friendly material
- wood is renewable
- wood has very high specific strength
- wood is low density, which makes it easier to transport
- very low disposal costs
- not electrically conductive
- most are non-toxic
- low thermal conductivity
- not weakened by nails and screws
- resistant to stress concentrations
What are the main disadvantage of wood in construction?
- Large variability in properties between species
- wood is dimensonally unstable
- strength decreases when wet
- time-dependent deformation such as creep and visco-elasticity
- susceptible to termites, wood worms etc.
- cannot be used at high temperatures
- suscpetible to rot and disease
- highly anistropic
- Not particularly fire resistant
