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CIVI 321 > Wood > Flashcards

Wood Flashcards

1
Q

Why is wood used in construction?

A
  • Easy to use
  • Durable
  • High Strength
  • Low weight
  • Widely Available
  • Low Cost
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2
Q

In what is wood widely used?

A
  • Building Frames
  • Bridges
  • Utility Poles
  • Floors
  • Roofs
  • Trusses
  • Piles
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3
Q

Classification of Trees?

A
  • Endogenous
  • Exogenous
  • Decidious
  • Coniferous
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4
Q

Describe Endogenous trees.

A

Trees that grow inwards in a longitudinal fibrous mass

  • Very strongm flexible and lightweight
  • Not generally used for engineering applications
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5
Q

Describe Exogenous trees.

A

Fibers grow from the center outward by adding concentric layers (annual rings) which gives more predictable engineering properties.

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6
Q

Describe Decidious trees and give an example.

A
  • Broad Leaf
  • Hardwood
  • Expensive slow growing
  • Example: Ash, Oak, Maple.
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7
Q

Describe Coniferous trees and give an example.

A
  • Cone Bearing
  • Softwood
  • Example: Fir, Pine and Spruce
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8
Q

List the main Structural Features of tree stem.

A
  • Pith, which is the center stem
  • Heartwood, which is darker and provides structural support
  • Sapwood, which is lighter and transports the sap (Vascular tissue)
  • Cambium, which is a very thin layer and is the location of the wood growth
  • Inner Bark
  • Outer Bark
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9
Q

What are each annual rings of exogenous tree composed of?

A
  • Earlywood, which is a light ring that has a rapid spring growth of hollow thinwalled cells.
  • Latewood, which is a dark ring that has a dense summer growth of thickwalled cells which are much harder and stronger.
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10
Q

What is the Chemical Composition of wood?

A
  • Cellulose, which is 40-50% by weight.
  • Hemicellulose, which is 15-20% of softwood and 20-30% of hardwood.
  • Lignin, which serves as glue. It is 23-33% of softwood and 16-25% of hardwood.
  • Others, which include Extractives (5-30% by weight), Ash-forming (mineralsm 0.1-3% by weight).
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11
Q

What does wood being anisotropic mean?

A

Properties change with direction

  • Longitudinal, which is parallel to the long axis (grain) and is the strongest and least in shrinkage.
  • Radial, which is perpendicular to the growth rings.
  • Tangential, which is tangent to the growth rings and the weakest and with the most shrinkage.
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12
Q

Which properties does direction influence?

A
  • Strength
  • Modulus
  • Thermal Expansion
  • Conductivity
  • Shrinkage
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13
Q

Descibe what bound water is.

A

Water held by surface attraction.

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14
Q

Describe what free water is.

A

Water or water vapour inside the cell cavities.

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15
Q

What is the formula for Moisture content?

A

(Weight of water/Weight of wood) x 100

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16
Q

Moisture Content of wood is directly related to?

A

Humidity and temperature of the surrounding air.

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17
Q

What depends on moisture content?

A

Shrinkage, strength and weight.

18
Q

Explain the Equilibrium Moisture Content.

A

Occurs when the wood has reached a water content equilibrium with its environment and is no longer gaining or losing moisture.

19
Q

Explain the Fiber Saturation Point.

A

Moisture content when cells are completely saturated with bound water but no free water inside cell cavities.

20
Q

What is the range in % of the FSP?

A

21-32%

21
Q

What happens when it goes above the FSP?

A

Changes affect only wet weight.

22
Q

What happens when it goes below the FSP?

A

Small changes strongly affect all physical and mechanical properties.

23
Q

Where is the largest shrinkage?

A

Tangential Direction.

24
Q

Where is the smallest shrinkage?

A

Longitudinal Direction.

25
Q

What happens to the shrinkage above FSP?

A

Zero Shrinkage regardless of direction.

26
Q

What are the step to produce wood?

A
  1. Harvesting
  2. Sawing
  3. Seasoning (drying)
  4. Surfacing (Planing) (Optional)
  5. Grading
  6. Preservative Treating (Optional)
27
Q

Describe Dimensional Lumber and its use.

A
  • 2” to 5” thick.

- Used for light framing such as studs, joists, beams, rafters, trusses, decking.

28
Q

Describe Heavy Timber and its use.

A
  • 4x6, 6x6, 8x8 and larger
  • Usually rough sawn (actual sizes)
  • Used for heavy framing, railroad ties and landscaping.
29
Q

What are the different type of sawing?

A
  • Live (Plain) Sawing, which is the most rapid and economic
  • Quarter Sawing, which has the maximum amount of prime (vertical) cuts.
  • Combination of the two, which is the most typical one.
30
Q

What are the three types of board cut?

A
  • Flat-sawn (grain is less than 45 degree from flat side), which is the worst quality, has the most problems and defects.
  • Rift-sawn (45-80degree)
  • Quarter-sawn (vertical- or edge-sawn) (80-90), which is the best quality, least shrinkage problems.
31
Q

What the methods of seasoning?

A
  • Air drying, which is the cheapest and slowest.
  • Kiln Drying, which is the fastest and most expensive
  • Usually a combination.
32
Q

What does uneven shrinkage in different directions during seasoning causes?

A
  • Warping
  • Checks
  • shakes
33
Q

How can you control the uneven shrinkage?

A

With the different types of cuts (vertical is the best)

34
Q

What is meant by surfacing?

A
  • Surfacing takes 1/4” (or more) from each side.
35
Q

What is meant by S4S?

A

Surfaced 4 sides = Dressed

36
Q

What are some agencies that grade lumber?

A
  • BC Lumber Manufactureres Association
  • West Coast Lumber Inspection Bureau
  • Western Wood Products Association
  • Eastern Spruce Grading Commitee
37
Q

What is lumber graded on?

A
  • Visual (appearance) Grading
  • Stress (structural) Grading (Strength and durability)
  • Imperfections (number of defects: knots, checks)
38
Q

What causes lumber defects?

A
  • Natural Wood growth
  • Seasoning too fast
  • Wood Diseases
  • Animal Parasites
  • Faulty Processing
39
Q

What are the lumber defects?

A
  • Knots: branch base that degrades mechanical properties
  • Bow: curve along the face of a board that usually runs from end to end.
  • Blue stain: A bluish grey discoloration on the woods surface. This feature is most common in woods like Holly, Pine and Sycamore.
  • Checks or Splits: Breaks at the end of a board that run along the grain.
40
Q

Explain Engineered wood product

A

Made by bonding together wood strands, veneers, lumber or other form of wood fibers to produce large units.

41
Q

Why are Glulam preferred?

A
  • Ease of Manufacturing Large Members from standard commercial lumber
  • Can vary the cross section along the length
  • Special architectural designs
  • Can use lower wood grade in less stressed areas
  • Minimizes shrinkage defects

CIVI 321 (7 decks)

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