Timber Flashcards
Timber in construction is used for 2 things which are;
1) Structural use
2) Non structural use
Examples of structural use for timber in construction are; (4)
Frames
Joists
Trusses
Bridge
Examples of non structural use of timber in construction; (3)
Window frames
Doors
Furniture
There are 2 main types of timber which are;
1) Softwood
2) Hardwood
The properties of softwood are; (3)
1) Grown quicker / easier therefore more economical
2) Low density
3) Easily worked with
The properties of hardwood are; (4)
1) Harder than softwood
2) Stronger than softwood
3) Durable
4) Higher resistance to insect attacked and rot
Advantages of timber are; (8)
1) Wide range of timbers with various densities, strengths, colours, grain patterns etc.
2) Easy to work with
3) Resistant to mild chemicals
4) Readily available (if managed correctly)
5) Insulates against electricity and heat
6) Sustainable and environmentally friendly (if managed correctly)
7) Can be relatively cheap compared to other materials
8) Strong
Disadvantages of timber are; (5)
1) Combustable material
2) Susceptible to insect attack
3) Hygroscopic material - absorbs and expels moisture - shrinks and swells with humidity and moisture content changes
4) Strength not the same in all directions
5) Cannot be manufactured to a particular spec like concrete?
Some reasons for selecting timber as a material in construction are; (3)
1) Availability - easy to access large quantities
2) Easy to handle - lighter than other materials, can be cut into smaller sections and re-assembled
3) Durability - if well preserved
Hardwoods come from trunks of trees which have ________ leaves
Broad
Softwoods come from trunks of trees which have ________ leaves
Needle
Examples of hardwood trees are; (4)
1) Ash
2) Oak
3) Teak
4) Iroko
Examples of softwood trees are; (4)
1) Pine
2) Fir
3) Larch
4) Spruce
Differences between hardwood and softwood are; (6)
1) Cost - hardwood is more expensive
2) Time to grow - hardwoods take longer - softwoods quicker and easier
3) Density - hardwoods are denser
4) Strength - hardwoods are stronger
5) Durability - hardwoods are more durable
6) Sustainability - softwoods are more economical
3 parts to structure of tree are;
1) Root
2) Trunk
3) Crown
The root of the tree; (2)
1) Absorbs mini raps and water from soil
2) Acts as anchor to resist wind loads
Trunk and branches of a tree; (3)
1) Transports minerals and water from root to crown
2) Provides strength / height
3) Provides timber products
Crown of a tree; (3)
1) Provides cover
2) Absorbs light and rain water
3) Allows photosynthesis to take place
Hardwoods come from _______ leaved trees, most of which are ___________
Chudley (2011)
Broad
Deciduous (meaning = shedding its leaves annually)
Hardwoods are generally used for; (2)
1) Furniture
2) Fixtures
Softwoods are from __________ trees with _______ shaped or ________ like leaves
Coniferous
Needle
Scale
Softwood is commonly used for; (2)
1) Construction elements
2) Framing
The 4 stages of the manufacturing process associated with timber are; (4)
Sawing
Seasoning
Chemical Treatment
Packing
Seasoning is the process of;
Intentionally reducing the moisture content of timber
The purpose of seasoning is; (3)
1) Reduce moisture content
2) Prevent from fungal attack
3) Make the timber stronger and easier to use, transport, glue, paint and preserve
The two types of timber seasoning are; (2)
1) Air seasoning
2) Kiln seasoning
Air seasoning is the process of;
Stacking the timber in the open air for drying naturally
Air seasoned stacks of timber are stacked in the following manner (6 points)
1) Separated with horizontal spacers to allow full circulation flow of air around stack
2) Stacked and a safe and stable manner
3) Ends of boards are sealed to prevent too rapid drying out via end grain
4) Stacks are raised well clear of ground(free of rising damp, vegetation etc.)
5) With overhead cover to protect from direct sunlight and driving weather
6) In UK further seasoning done inside in heated and ventilated buildings (as can only reduce moisture to about 16-17% naturally)
Kiln seasoning is the process of
Artificially drying timber in a controlled environment
An advantage to air seasoning is;
Cheaper than kiln drying as no energy used, less labour time
3 factors to kiln drying are;
1) Air circulation by fans
2) Heat provided by piped steam
3) Humidity control provided by steam jets
Timber is chemically treated to;
Prevent beetle or fungal attack
Two methods of chemical treatment of timber are; (2)
1) Pressure impregnation
2) double vacuum (Vac-Vac) treatment with organic solvent solution
Timber should be packed in stacks so as to prevent
Damage
Plywood is a series of;
Thin timber layers laminated together
Plywood is manufactured by; (5)
1) Softening log via water or steam
2) Rotated against a full length knife to peel veneer or ply of constant thickness
3) Ply cut to size
4) Coated with adhesive
5) Laminated together with adjacent grain directions at right angles to give uniform strength
Plywood is used in the construction industry because of its (3)
1) strength
2) versatility
3) visual properties
Plywood is commonly used in construction as; (3)
1) Sheeting material in timber frame construction
2) Form work for in-situ concrete (low grade)
3) Web section of timber beams / columns
In terms of sustainability some timber advantages are; (5)
1) Lighter than concrete therefore transportation could have less adverse environmental effect
2) All of harvested timber can be used from dimensioned lumber to sawn dust in particle boards
3) Timber products can be re-used
4) Forest systems are manageable - as forests are cleared they can be re-planted
5) In general timber has low embodied energy content, little or no waste or hazardous by products.
In fire conditions the _________ wood initially ignites and burns rapidly. The burned wood becomes _________________
1) Surface
2) Surface char
Surface char; (3)
1) Stops passage of oxygen into the core wood
2) Prevents burning because of the lack of combustible gases
3) insulates the core wood and protects it from ignition and burning
Due to surface char timber members have _________________ to fire and can _____________ and ____________ for reuse
1) good resistance
2) survive
3) be repaired
Laminated Veneer Lumber (LVL) is made from…
Multiple layers of thin timber sheets assembled with adhesives in their longitudinal direction (gluing and pressing)
Advantages of LVL are (3)
1) Very Deep
2) Very Strong in bending
3) Very Straight
Glued Laminated Timber (Glulam) is made from…
Many small pieces of timbers to form a deep and long member, assembled with adhesives on their contact surfaces (gluing and pressing)
A disadvantage of LVLs is
Laterally unstable
Advantages of glulam timbers are (3)
1) Deeper and longer
2) Very strong in bending
3) Can be curved or tapered
A disadvantage of glulam members are
Gluing
3 examples of structural members using timber and their composition are;
1) I Beam - Timer LVL flange, plywood web
2) Box beam - Timber LVL flange, plywood web
3) Timber/steel beam - Timber LVL flange, steel web
The solid timber strength classes are defined in BS
EN 338:2003 (Structural timber. Strength classes.)
Strength grading asseses the _________ and _________ of pieces of timber intended for structural use
Strength and stiffness
The structural use of timber is defined in BS
5268-2
Design of timber structures is defined in BS
EN 1995-1-1:2004 Eurocode 5
The visual grading of hardwood and softwood is defined in BS and BS
1) 5767:1997
2) 4978:1996
Strength grading can be carried out by (2)
1) Visual - a slow skilled process
2) A grading machine
During visual grading the timber is inspected for (7)
1) Distortions
2) Growth ring size
3) Slope of grain
4) Natural defects
5) Knots
6) Waneyedge
7) Fissures
The 2 type of grading machines are
1) contact
2) bending
Grading mark has 7 pieces of information - 3 on top and 4 on bottom. From left to right top to bottom these are;
1) Accredited certification authority
2) Grader or company licence number
3) Timber type / species
4) Standard reference
5) Condition marker (e.g. kiln dried)
6) Grade (e.g. GS general structure, SS Special structure)
7) BS strength class (e.g. C14, C24)
The trunk of trees show a darker coloured area in the centre; this is the ____________. Around this is a ring of ________________
1) Heartwood
2) Sapwood
An increase in moisture content of timber; (3)
Decreases strength, stiffness and durability
Durability classes in relation to fungal decay of heartwood are defined in BS
EN 350-1
The 5 classes in relation to fungal decay of heartwood are
Class 1 - Very durable +25yrs Class 2 - durable 15-25 yrs Class 3 - moderately durable 10-15 years Class 4 - slightly durable 5-10 yrs Class 5 - not durable <5 yrs
Timber may be degraded by (6)
1) fungal attack
2) wood borers
3) weathering
4) mechanical wear
5) fire
6) chemical attack
The BS standard detailing the 4 levels of treatability of timber is BS __________. The four categories are;
EN 350-2
1) Easy
2) Moderately Easy
3) Difficult
4) Extremely difficult
Fungal attacks can be by; (2)
1) Wet rot
2) Dry rot
Preservation of timber recommendations is defined in BS
8417:2003
Dry rot (serpula llacrymans) life cycle is (5)
1) Red rust spores come into contact with timber, germination occurs
2) White strands colonise on timber (hyphae)
3) cotton wool like patches appear (mycelium)
4) Fruiting bodies emerge as fungi matures (sporophore)
5) Evolves and transports to other areas (rizomorphs)
Dry rot is deactivated at temperatures of above ______ and below _______
40deg C
0deg C
Dry rot is deactivated at a moisture content o below
22%
Timber should have a moisture content of below _____ to be “healthy”
15%
Remedial action for dry rot is (3 parts)
1) Cut out infected area 600mm either side of last trace
2) Splice repair and insertion of new Vac Vac preserve treated timber to BS 4072
3) Treat affected areas with fungicide by brushing, spraying, pastes etc as per BS 5268 part 5 (for structural timbers) and BS 5589 for more general
Alternative treatments for dry rot are (3)
1) Heat treatment
2) Borite rods
3) Rot hounds
Two types of pressure impregnation process (2)
1) Low pressure <5bar
2) High pressure >5bar
High pressure impregnation process stages (2)
1) timber closed into steel pressure vessel
2) preservative forced into the wood cells under hydraulic pressure between 5 & 14 bar for between 1 to 6 hours
Common insect species that attacks wood is
Common furniture beetle / woodworm (anobium punctatum)
Anobium punctatum lifecycle; (4)
1) female lays eggs in rough crevasses or former boreholes
2) larvae hatch and bore into the wood (using it as food and shelter) - biggest part of life cycle
3) after a few years matures to pupa (chrysalis) stage
4) matures again to adult stage where it emerges from wood to reproduce
Woodworm can be recognised from (2)
1) boreholes in wood
2) powdery deposits (frass) on wood surface
