H-2 Task 1 Flashcards
1) What are advantages wood has over other building materials?
- renewable resource
- strength
- unique
- lightweight
- easily cut
- easily fastened
- corrosion resistance
- holds finishes
- heat transfer
- electrical energy
- renovation
- reuse
Renewable resource:
How long will it take for trees to grow for suitable size for milling to lumber planks?
Compared to other materials used in construction, wood is?
40-100 years to mature to a sufficient size
Relatively cheap and plentiful
What is the density for wood?
What is the density for steel?
What is the density for concrete?
In kg/m cubed
Wood approximately 500-600 kg/m
Steel approximately 8000 kg/m
Concrete approximately 2400 kg/m
What is easily cut out of building materials?
What is easily fastened out of building materials?
What material has the best benifits for heat transfer?
(Out of concrete, steel, wood)
Wood is easily cut, drilled, and shaped. Steel and concrete are more difficult to cut.
Wood is easily and securely attached to other wood members.
Compared to steel or concrete, wood is a good insulator. Interior wood windows do not sweat with condensation with extreme weather conditions.
If reusing wood materials, what precautions should be taken?
Nails should be removed with care.
Finishing nails should be pulled from the backside to prevent damage to the face of stock.
Precautions are for avoiding damages to the members
What are 5 disadvantages of wood?
Comparing to steel and concrete
- swelling and shrinking
- decay
- flammable
- non-uniform
- cracks
Swelling and shrinking:
Which ways do wood swell and shrink?
What forms can wood absorb water?
Width and thickness when moisture content in the atmosphere changes.
Wood readily absorbs water in liquid and vapour forms because of its cellular structure.
Some species can absorb 2 or 3 times their own weight in water.
Flammable:
How can wooden structures be made fire resistant?
What beams will lose its support under heat/fire first?
(Wood or metal)
Can be made fire resistant by using other materials over wood, such as plaster or gypsum board.
Metal beams will lose their strength under heat way before wood beams lose theirs.
i joists lose their strength very quickly under fire
3 parts to a tree?
Trees are divided into 2 classes, what are they?
Root, trunk, and crown.
- hardwood, comes from decicuous trees, which have broad leaves.
- softwood, are from coniferous trees (cone bearing) which have narrow leaves called needles
What are the 2 main functions of a trunk?
What are the 8 types of wood structure in the trunk?
- Provide structural support for the crown
- Transport food and moisture from the roots to the crown.
1) outer bark. 5) heartwood
2) inner bark. 6) pith
3) cambium layer. 7) rays
4) sapwood. 8) annual growth rings
Outer bark:
What is the bark’s thickness range from?
What does the bark protect from the tree?
How is the outer bark formed?
- little as a fraction of a mm to as much as 300 mm
- from pests, disease, and damage
- by the inner bark changing to outer bark.
Outer bark is composed of dead cells and becomes brittle and dry with time.
Inner bark:
Performs 2 important functions, what are they?
- provides material to add to the outer bark
- contains special tube like cells that carry sugars and proteins manufactured in the leaves down to mix with the water and nutrients coming up from the roots
Where is cambium layer located?
Located between inner bark and the sapwood.
Its in this region that the cells making up the bulk of the tree are formed.
These cells are used by the tree to create new sapwood and new inner bark
Sapwood:
Where is it located?
What is its function?
What colour does it have?
Between the heartwood and cambium layer
Is to carry sap, water, and nutrients from the roots to the leaves and cones
Its the light coloured wood
Heartwood:
What is the main function of heartwood?
What portion of the tree is converted to heartwood?
How is the colour of heartwood changed?
Gives structural support to the tree, the wood becomes stronger as cell walls harden with the loss of sap
Each year a small portion of sapwood is converted to heartwood. Heartwood consists of dead cells.
Deepens as the natural tannins and resins darken.
These tannins and resins make the heartwood more durable and less susceptible to decay.
Rays:
What way do rays run in a tree?
What do rays look like?
Cells of rays are arranged horizontally rather than vertically in the tree.
Rays are long narrow structures that appear as fine lines on the surface of a cross section of a tree trunk or branch.
Moisture and drying:
Water is found in two places in wood?
Cell cavity, water in the cell cavity is called “free water”
Fibres in the cell walls, water in the fibres of the cell walls is called “bound water”
Absorbed water
What is flat grain or plain sawn?
What is edge grain or quater sawn?
Boards are cut along the tangential face and tend to cup away from the centres as they lose moisture. If they gain moisture, they cup the other way.
Edge grain lumber doesnt suffer as much distortion when exposed to changes in moisture content.
Important:
A) heartwood. E) annual growth rings
B) sapwood. F) cambium layer
C) innerbark. G) rays
D) outerbark. H) pith
Structure of a tree:
Cambrium
Sapwood
Pith
Rays
Outer bark
Heartwood
Inner bark
Annual growth rings
