Wood Flashcards
How much of UK wood is imported
66%. It produces only around 16 million m^3 but uses 50 million m^3 annually
What is softwood used for and where is it primarily sourced
construction, from Scandanavia
What is hardwood used for and where is it primarily sourced
Furniture and interior design from eastern and western Europe as well as North America
What is tropical wood used for
Marine construction + high value interiors
Advantages of wood
high compressive and tensile strength, readily available, lightweight, relatively cheap, good thermal insulator, aesthetic, can be sustainable
Disadvantages of wood
variability in performance, planes of weakness, can rot, contains inherent flaws, significant waste produced, requires transporting as wood is not often grown near the places it is used, can burn. (but predictable)
why is wood the most sustainable material
Harvested from trees that can be regrown and suck carbon dioxide out of the air. Also is low in embodied energy and can be burnt for more energy, releasing only the amount of co2 it absorbed.
Why are European Forests Growing despite the increase in the wood industry
More trees are being planted than they are harvested. The total European forest land grows at a rate of 3500 square miles annually
What is the composition of dry wood by percentage and give their function
cellulose 50% microfibre, hemicellulose and pectin 20% matrix, lignin 25% matrix, extractives 5% toxicity
why type of linkages form between cellulose
beta 1,4 bonds between glucose monomer (recall glucose has 6 carbons from the carbon attached to an oxygen and OH group going clockwise) and a lot of H bonds between the strands of cellulose
Why is lignin not biodegradable
It is formed from phenyl propane which has a strong and unreactive carbon chain
What must be done to wood before it can be used
Dried from 80% water content to about 20% by air or kiln drying
Microstructure of wood
hygroscopic (absorbs moisture), discontinuous, anisotropic, inelastic, fibrous, porous, biodegradable,
longitudinal cells, similar to a bunch of closely packed straws
What is the structure of wood
heartwood in the inside and sapwood on the outside. These vary in durability, permeability and colour sometimes but not strength
What are some flaws that affect the strength of wood
fissure, knot, wane, growth rings
Establish the strength along and across grain for tension, compression and shear
along grain - strong in tension and compression but weak in shear
across grain -weak in tension and compression but strong in shear
How can we tell wood is not a brittle material
The crack propagates in a different direction
Why is the loading and unloading curve of wood not the same
Wood behaves non elastically after a while and becomes viscoelastic due to the amorphous nature of lignin
what is the benefit of using structural wood composites
Reduced variability in strength (but not necessarily increased strength) and increased dimensional stability, allows formation of shapes that are not normally possible with normal cut wood
What are some examples of structural timber products
glulam, laminated veneer lumber and parallel strand lumber
What is the biggest advantage of timber frame house building
It has a faster construction time
What is the biggest advantage of timber frame house building
It has a faster construction time
