CE 60 Final

Question 1

List examples and characteristics of Softwood .

Answer 1

Examples: Fir, spruce, pine,

Chacteristics:
Soft to the touch
Tree seeds exposed

Question 2

List examples and characteristics of Hardwood.

Answer 2

Examples: oak, maple, cherry
Characteristics:
Hard to the touch
Tree seed covered

Question 3

What structure size does annual rings fall in? Describe annual rings for summer and spring wood.

Answer 3

Annual rings (macro)

Summer wood- denser therefore darker color 

Spring wood- more porous therefore lighter color

Question 4

What structure size do Rays fall into. Where are rays?

Answer 4

Rays (macro)

from surface to center of trees (radius)

Question 5

Describe difference between heartwood and sapwood.

Answer 5

Heartwood is darker because there are more mineral deposits when tree was Smaller

Sapwood is lighter because cells cease their conductive function (water travels at the outer layers instead of the majority of the trunk as the radius of the trunk increases)

Question 6

Give all the layers in wood in macro.

Answer 6

Layers in wood 
	Dead bark (Outermost)
	Inner bark- (living)
	Cambium- very small layer
	Sapwood
	Hearthwood
	Pith-center of the stem

Question 7

Give the three directions of wood.

Answer 7

Longitudinal direction: parallel to the long axis of the stem.

Radial direction: perpendicular to both the growth rings and the long axis of the
Stem

Tangential direction: tangent to the growth rings

Question 8

What are 3 things relating wood specimen and knots?

Answer 8

Source of previous location of branch
Knots are stress concentrations
More knots reduce E modulus and strength of wood.

Question 9

What are characteristics of tracheids and rays?

Answer 9

Tracheids- parallel to the L direction

Rays- Parallel to the R direction

Question 10

Can you describe summer and spring wood in microstructure?

Answer 10

Summer wood micro- thicker cell wall smaller cell cavity called lumen
Spring wood- thinner cell wall and larger cell cavity called lumen

Question 11

Can you describe softwood and hardwood in microstructure levels?

Answer 11

Softwood micro- tracheids provide both mechanical support and conduction of water
Hardwood micro-wood fibers provide mechanical support, vessel conduct water

	Ring porous-spring vessel is smaller than summer 

	Diffuse porous-vessel sizes are similar

Question 12

What are three main parts of atomic microstructure of wood?

Answer 12

Cellulose (Microfibrils):
40-50% by weight of solid wood, linear crystalline polymer (600A from HW with amorphous region as well)

Hemicellulose
15-35% by weight of solid wood
amorphous branched polymer

Lignin
20-35% by weight of solid wood
cross-linked 3D amorphous polymer

Question 13

What is shrinkage a function of?

Answer 13

How water is held

Spring vs summer wood

Moisture content (MC = (moist weight - dry weight) / dry weight x 100)

Question 14

Where can water be held in wood? Explain each.

Answer 14

(1) bound water- Bound water is held within the cell walls by adsorption force adsorbed in the amorphous regions
(2) free water- situated in the cell cavities know as lumen

Question 15

What is fiber saturation point?

Answer 15

• moisture content at which the cell wall is saturated
• averages about 28% moisture content
• Addition or removal of water below the FSP has a pronounced effect on practically all wood properties.
• Addition or removal of water above the FSP has a almost no effect on any wood properties.

Question 16

What is shrinkage attributed to in summer wood?

Answer 16

Cells dominate since they absorb much more water in tangential

Question 17

Where is the free water and bound water?

Answer 17

The free water can be found in lumens (inside the straw where your beverage comes in) but the bound water is in the cell wall (within the plastic)

Question 18

What can shrinkage do the the rings?

Answer 18

The rings can become distorted and all wiggly but still in a circular path.

Question 19

Cell wall density vs wood density. What are differences?

Answer 19

Cell wall-density is higher than wood due to limited porosity (about 1.5g/cm^3)
Wood density-has high porosity so it actully has a lower volume since V=m/v
Density of wood is about .5g/cm^3

Question 20

What is strength of wood a function of?

Answer 20

density
Moisture content
Testing direction

Question 21

How do the strengths compare to direction?

Answer 21

longitudinal:radial:tangential directions on average are in the ratio of 20:1.5:1.

Question 22

How does moisture content affect wood (when)?

Answer 22

Once we reach the fibre saturation point, not much affect on strength. Before that, as you increase water content, the wood becomes weaker

Question 23

Green wood vs air wood and compression vs tensile. What do we expect to have higher and lower strengths?

Answer 23

Green wood is weaker for both. Air dried is stronger for both. Compressive is weaker than tensile strength.

Question 24

What is the proportional limit?

Answer 24

Point in stress strain that no longer has linear shape.

Question 25

Stiffness is a function of what?

Answer 25

Density
Moisture content
Direction
Summerwood vs springwood

Question 26

What insects cause deterioration of wood? What causes what?

Answer 26

Carpenter ants - like high moisture and softer wood

Beetles- prefer low moisture and both soft and hard wood 

Termites

Question 27

What are two other causes of deterioration in wood?

Answer 27

Timber rot- caused by fungi. Live on cellulose Can not live in 18% below moisture content

Molds- minimal strength effects Usually on sapwood

Question 28

What are three softwood lumber classifications? Briefly explain each.

Answer 28

Board lumber -thickness less than 2 in

Dimension lumber-thickness 2-4 in

Timber -thickness 5 or more