Lesson 9 - Timber

Question 1

comes from a deciduous tree which loses its leaves annually

Answer 1

Hardwood

Question 2

tend to be slower growing, and are therefore usually more dense.

Answer 2

Hardwood

Question 3

an angiosperm, a plant that produces seeds with
some sort of covering such as a shell or a fruit. Angiosperms usually form flowers to reproduce. Birds and insects attracted to
the flowers carry the pollen to other trees and when fertilized
the trees form fruits or nuts and seeds. It includes
eucalyptus, yakal, apitong

Answer 3

Hardwood

Question 4

comes from a conifer, which usually remains evergreen.

Answer 4

Softwood

Question 5

known as a gymnosperm. Gymnosperms reproduce by forming cones which emit pollen to be spread by the wind to other trees. Pollinated trees form naked seeds which are dropped to the ground or borne on the wind so that new trees can grow elsewhere. Some examples of it includes
pine, agoho

Answer 5

Softwood

Question 6

do tend to be less dense than deciduous trees, and
therefore easier to cut, while most hardwoods tend to be more
dense, and therefore sturdier. In practical terms, this denseness
also means that the wood will split if you pound a nail into it. Thus
you need to drill screw or bolt holes to fasten hardwood together.
But structural lumber is soft and light, accepts nails easily without
splitting and thus is great for general construction.

Answer 6

Evergreens

Question 7

wood that has been recently cut and therefore has not had an
opportunity to season (dry) by evaporation of the internal
moisture. It is considered to have 100% moisture
content relative to air-dried

Answer 7

Green wood

Question 8

Natural Characteristics Affecting Mechanical Properties of Wood

Answer 8

1. Knots
2. Reaction Woods
3. Juvenile Wood
4. Pitch Pocket
5. Bird Peck
6. Wane
7. Warp
8. Check
9. Shake
10. Split
11. Stain
12. Spalt
13. Dry Rot
14. Wormholes

Question 9

that portion of a branch that has become incorporated in the bole
of a tree.

Answer 9

Knots

Question 10

abnormal woody tissue is frequently associated with leaning boles
and crooked limbs of both conifers and hardwoods.

Answer 10

Reaction woods

Question 11

the wood produced near the pith of the tree, it has considerably different physical and anatomical properties than that of mature wood

Answer 11

Juvenile wood

Question 12

a well-defined opening that contains free resin. The pocket
extends parallel to the annual rings; it is almost flat on the pith
side and curved on the bark side. Accumulation of resinous
material (gum or sap)

Answer 12

Pitch pocket

Question 13

damage caused by woodpeckers, most of the time small holes
around the wood.

Answer 13

Bird peck

Question 14

the presence of bark or absence of wood on the corner of along
the length of a lumber

Answer 14

Wane

Question 15

distortion in wood due to shrinkage and swelling( eg. Twist, cup,
bow, kink and crook/spring)

Answer 15

Warp

Question 16

A crack in the wood structure of a piece, usually running
lengthwise, usually restricted to the end of a board and do not
penetrate as far as the opposite side of a piece of sawn timber.

Answer 16

Check

Question 17

separation of grain between the growth rings, often extending
along the boards face and sometimes below its surface

Answer 17

Shake

Question 18

longitudinal separation of the fibers which extends to the opposite
face of the lumber

Answer 18

Split

Question 19

discoloration that penetrates the wood fiber, can be any color
other than the natural color of wood (blue or brown)

Answer 19

Stain

Question 20

any form of discoloration caused by fungi (found in dead trees)

Answer 20

Spalt

Question 21

fungus breaks down wood fibers and renders the wood weak and
brittle

Answer 21

Dry rot

Question 22

small holes caused by insects (beetles)

Answer 22

Wormholes

Question 23

Strength of wood

Answer 23

1. Tensile strength
2. Compression strength
3. Flexural strength
4. Elastic properties

Question 24

// to the grain is much higher (~3x) than compressive strength

Answer 24

Tensile strength

Question 25

Limiting factor for tension members is compression or shear at the
point of concentration

Answer 25

Tensile strength

Question 26

perpendicular to the grain is ~(1/3) of the strength // to the grain

Answer 26

Tensile strength

Question 27

// to the grain is 3~4x than compressive strength when load is perpendicular to the grain

Answer 27

Compression strength

Question 28

Failure when load is perpendicular to the grain: crushing of wood fiber

Answer 28

Compression strength

Question 29

Failure when load is // to the grain: bending or buckling of wood fibers

Answer 29

Compression strength

Question 30

critical factors are:
• comp strength // to the grain
• shear strength // to the grain

Answer 30

Flexural strength

Question 31

shear strength is very low but if wood is free of defect, initial failure will be compressive

Answer 31

Flexural strength

Question 32

shear strength is very low but if wood is free of defect, initial failure will be compressive

Answer 32

Flexural strength

Question 33

Factors affecting Strength of Wood

Answer 33

1. direction of wood fibers
2. moisture
3. weight
4. Rate of growth

Question 34

(strength depends heavily of the direction of load with respect to the grain)

Answer 34

Direction of wood fibres

Question 35

(drying beyond the FSP (Fiber saturation point), leads to increase in strength)

Answer 35

Moisture

Question 36

(denser wood is stronger)

Answer 36

Weight

Question 37

• for air-dry timber
• for green timber

Respectively

Answer 37

• modulus of rupture = 26,200 x (specific gravity)1.25
• modulus of rupture = 18,500 x (specific gravity) 1.25

Question 38

greater number of annual rings per unit length gives higher strength

Answer 38

Rate of growth