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Materials > Wood and Timber > Flashcards

Wood and Timber Flashcards

1
Q

How many cubic meters of tinder are harvested worldwide every year?

A

~1.6 billion m^3

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2
Q

How much timber is used in the UK each year?

A

50 million m^3

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3
Q

How much timber does the UK produce each year?

A

~16 million m^3

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4
Q

How much of the UKs timber is imported?

A

66%

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5
Q

What type of wood is used in construction, and where does it come from?

A

Softwood

From Scandinavia and the baltic states

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6
Q

What type of wood is used for furniture and interior design and where does it come from?

A

Hardwood and it comes from Eastern and Western Europe and North America

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7
Q

How is tropical wood used?

A

In marine construction and high value interiors

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8
Q

What are some advantages of wood in construction?

A
  • 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
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9
Q

What are some disadvantages of timber?

A
  • 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
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10
Q

What makes wood a sustainable construction material?

A
  • 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
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11
Q

How much CO2 does a tree absorb through photosynthesis and how much oxygen do they produce in the same period?

A

1000kg CO2

727kg O2
per m^3 growth

Therefore young trees are better for the environment than old ones

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12
Q

By using wood instead of another construction material how much CO2 is embodied?

A

2 tonnes per m^3

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13
Q

How much more energy do concrete and steel use than timber strength for strength?

A

concrete uses 5x

steel 6x

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14
Q

What organisation ensures sustainable forests?

A

The forest setwarship council (FSC)

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15
Q

What does the FSC do?

A

combat illegal and unethical logging techniques as well as environmentally damaging logging

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16
Q

How much of the wood consumed in Europe is from European forests?

A

over 90%

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17
Q

Why is the European forest industry so good?

A

It plants more trees than it harvests

European forests grow by 3,500 square miles a year

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18
Q

How much carbon is stored in European forests?

A

9.5 miillion tonnes

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19
Q

How much of the weight of wood is carbohydrate?

A

70%

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20
Q

What structure does glucose have?

A

ring

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21
Q

What are glucose molecules linked by

A

alpha or beta linkages to form polysaccharides

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22
Q

What does cellulose consist of?

A

Cellulose structures, joined by beta-1,4 bonds

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23
Q

What part of wood does lignin make up?

A

The non biodegradable part

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24
Q

What is the structure of lignn

A

A massive random polymer of phenylpropane alcohol

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25
Q

What is the moisture content of wood when it is cut?

A

up to 85%

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26
Q

How is wood dried?

A

Either by air drying or Kiln drying

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27
Q

What is the structure of wood like?

A

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

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28
Q

What are the differences between heartwood and sapwood?

A
  • colour
  • durability
  • permeability
29
Q

What is not different about heartwood and sapwood?

A

Strength

30
Q

How do you tell the difference between soft and hardwoods?

A

Softwoods come from coniferous trees, hardwoods come from deciduous trees

31
Q

What are key parts of the microstructure of wood?

A
  • Multi-component
  • hygroscopic
  • anisctropic
  • inhomogeneous
  • Discontinuous
  • inelastic
  • fibrous
  • porous
  • biodegraddable
  • renewable
32
Q

What does SEM stand for?

A

Scannign electron microscopy

33
Q

What does the microstructure of hardwood resemble?

A

close packed drinking straws

34
Q

Why is are the properties of woods different in different directions?

A

Due to inherit flaws such as knots, wanes, growth rings and fissures

35
Q

What grain direction is strong in tension?

A

Along grain

36
Q

What grain direction is strong in compression?

A

Along grain

37
Q

What grain direction is resistant to shear?

A

across strain

38
Q

How does wood perform in bend strength testing?

A

like a fibre reinforced composite material with significatn toughness

39
Q

What decay mechanisms are present in wood?

A

Fungal decay

Dry and wet rot

40
Q

What moisture content is neeeded for decay to occur in wood

A

> 25%

hence why wood is not good when in contact with soil

41
Q

What is the associated costs of insect infestation a year to the UK?

A

£900 million

42
Q

What types of insects cause damage to wwod?

A 
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

43
Q

Name some structural timber composites

A
  • Glulam
  • Orientated Strand-Board (OSB)
  • Laminated veneer Lumber (LVL)
  • Parallel strand lumber (PSL)
  • Laminated strand lumber (LSL)
  • Prefab I joists
44
Q

What are the benefits of structural timber composites?

A

They are sold as products
Their properties are known
The properties are product specific
Design information is provided by technical approval documents

45
Q

What are other names for structural wood products?

A
  • Engineered wood products
  • Engineered Lumber products
  • Structural composite lumber
46
Q

What are the benefits of glulam?

A
  • 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
47
Q

What wood species mostly makes up glulam?

A

European whitewood

48
Q

Usually how deep are the laminates in glulam?

A

45 mm

49
Q

What adhesive is used in glulam?

A

PRF phenol resorcinol formaldehyde

50
Q

Where does the higher class material go in glulam if inhomogeneous?

A

on the outside

51
Q

What is the mass of glulam?

A

500 kg m^-3

52
Q

What are some of the size/ shape benefits of glulam?

A
  • standard straight cross sections
  • Curved and / or tapered
  • manufactured up to 45 m
53
Q

Where is glulam typically used?

A

Beams and columns
Domes, curved roofs and arches
footbridges

54
Q

Where is orientated strand lumber used?

A

Timber frame wall panels

55
Q

How is laminated venner lumber made?

A

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

56
Q

What is the maximum length currently available for laminated veneer lumber?

A

26m

57
Q

Where is laminated veneer lumber typicall used?

A

roof or floor beams in factory built housing

Flanges of I joists footbridges and bridge decking

58
Q

How are parallel strand lumber sections produced?

A

Long peeled veneers (2400mm) are coated with glue and layered using a heat and pressure quasi extrusion process to form long structural sized sections

59
Q

What are the benefits of I joists?

A

Strong, stiff, straight, light, long

Dimensionally stable, cost effective, easy to handle, use less timber material, quality assured

60
Q

How many new homes are made out of timber in the UK?

A

25%

61
Q

How many new homes in scotland have a timber frame?

A

3/4

62
Q

How much shorter is the construction time with timber?

A

30%

63
Q

How many days does it take to get a timber frame house weather proof

A

less than 5

64
Q

How much more wood is used than in an equivalent masonry home?

A

5-6m^3

65
Q

How many tonnes of CO2 are saved by every timber house?

A

4

66
Q

What other benefits to timber framed houses have?

A

reduced running costs

67
Q

What are the advantages of wood as an engineering material?

A
  • 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
68
Q

What are the main disadvantage of wood in construction?

A
  • 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

Materials (13 decks)

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