Wood

Question 1

Why is wood used?

Answer 1

Easy to use
Durable
High strength
Low weight
Widely available
Low cost

Question 2

What is an Endogenous tree?

Answer 2

Tree that grow inward in a longitudinal fibrous mass
Very strong, flexible and lightweight
Not used for engineering application

Question 3

What is an Exogenous tree?

Answer 3

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

Question 4

What are the main structural features of a tree?

Answer 4

Pith - center stem
Heartwood (darker) - provides structural support
Sapwood (lighter) - transports the sap
Cambium (very thin layer) - location of wood growth
Inner bark
Outer bark

Question 5

What are the 2 types of annual ring?

Answer 5

Earlywood (light ring): rapid growth
Latewood (dark ring): dense summer growth (much harder & stronger)

Question 6

What are the chemical composition of wood?

Answer 6

Cellulose (40-50% by weight)
Hemicellulose
Lignin (GLUE)
Others

Question 7

Wood is anisotropic. Explain

Answer 7

the properties change with direction
Longitudinal (Strongest and least shrinkage)
Radial (rayon)
Tangential (weakest and most shrinkage)
Direction influence strength, modulus, thermal expansion, etc.

Question 8

What is free water and bound water?

Answer 8

Free water is water within cavities
Bound water is on wall cells

Question 9

What is green moisture content?

Answer 9

Highest moisture content (30 to 200%)

Question 10

on what does the moisture content depend on?

Answer 10

Humidity and temperature of the surrounding air

Question 11

When does the equilibrium moisture content (EMC) occurs?

Answer 11

no longer gaining or loosing moisture with its env.
Note: as wood absorbs or bleed moisture, it will expand or contract

Question 12

What is Fiber saturation point?

Answer 12

cells are completely saturated with bound water BUT no free water

Question 13

What are the wood product in construction?

Answer 13

Dimensional lumber
Heavy timber
Round stock

Question 14

What is the best type of board cut?

Answer 14

Quarter-sawn

Question 15

How do they do seasoning (drying) of wood?

Answer 15

Air drying
Kiln drying
Combination

Question 16

How much thickness (min) do you need to do surfacing?

Answer 16

1/4”
Note: Nominal dimension is b4 surfacing

Question 17

What are lumber defects?

Answer 17

Knots

Question 18

What is the specific gravity of the cell walls of wood?

Answer 18

1.5 (closest to 1.5–> denser & stronger)

Question 19

Wood has low ___ diffusivity

Answer 19

Wood has low thermal diffusivity

Question 20

What happens when applying heat to wood?

Answer 20

First expands the wood from thermal expansion
Then shrinks from moisture loss
Note: 5-10 times greater across grain than parallel to it

Question 21

What is the modulus of elasticity // grain?

Answer 21

7-14MPa
Note: depends on species variation, specific gravity, moisture content, direction of grains

Question 22

_____ strength of wood is greater than _____ strength of wood.

Answer 22

Tensile strength of wood is greater than compressive strength of wood.

Question 23

Tensile strength ____ to grains is 20 x greater than _____ to grains.

Answer 23

Tensile strength // to grains is 20 x greater than perpendicular to grains.

Question 24

Wood supports higher load better on short duration or longer duration

Answer 24

Short duration
Under sustained load, wood deforms

Question 25

Vibration damping increases with ___

Answer 25

Moisture content up to FSP

Question 26

What are engineered wood?

Answer 26

Plywood, OSB, MDF

Question 27

How are floor joist made?

Answer 27

two lumber flanges with OSB board as web

Question 28

What is glulam?

Answer 28

Lumber glued together with the // grains (struc. made of lumber and adhesive)
Note: low grade wood in the middle of glulam

Question 29

What does the 48/24 mean?

Answer 29

48 is max span for roofing
24 is max span for subflooring