Module 7: Timber

1. softwood

2. hardwood

2 major classifications of wood

false; not necessarily

true or false: hardwood is harder, stronger, and more durable than softwood

dead bark

protective layer of which covers the trunk of a tree

living bark

a layer of which is found inside dead bark

longitudinal

living bark is composed of _________, _________ cells that conduct nutrients downward from leaves to roots and other living parts of tree

cambium

very thin layer within living bark

cambium

creates new bark cells toward outside of the trunk and new wood cells toward the inside

sapwood

thick layer of lviing wood cells inside cambium

heartwood

result of dead sapwood

heartwood is darker than sapwood

How is heartwood easily distinguished from sapwood?

false; no longer participates in life processes, only structure

true or false: heartwood participates in life processes of tree and structural strength

pith

small zone of weak wood cells at the very center of the trunk surrounded by heartwood that were first year’s growth

grain of wood

direction of long axes of cells in tree

faster: moist, cool

stronger: warm, dry

compare growth speed and wood strength of tree grown under moist, cool conditions vs warm, dry conditions?

exogenous trees

trees that grow diametrically by adding new cells in a layer between existing wood and bark

book-matched

result of resawing thick lumber into thinner boards, opening two halves like a book, and gluing them together along the edge to create a panel with mirrored grain pattern

cathedral grain

V-shaped grain pattern running along length of the board

check

separation of wood fibers running with the grain that do not go through whole cross-section; result of tension and stress caused by wood movement during drying

dimensional stability

ability of section of wood to resist changes in volume at fluctuating moisture levels

expansion, contraction

low dimensional stability produces _______ in humid environments and ________ in dry ones

figure

patterns on wood surface by growth rings, rays, knots, and irregular grains

descriptors include interlocked, curly, tiger, wavy, and fiddleback

grain

size, alignment, and appearance of wood fibers in a piece of lumber

heartwood

harder, nonliving innermost layers of a tree

generally darker, denser, more durable, less permeable than surrounding sapwood

moisture content

percentage that represents a wood board’s ratio of water weight to the weight of oven-dried wood

stud

lumber used for load bearing and stud walls

2” x 4” and 2” x 6”

dimensions of lumber used for load bearing and stud walls

warp

bowing, cupping, and twisting distortion in lumber that occurs after it has been planed, usually during drying process

• sapwood

• heartwood

• cambium

• phloem

• outer bark

label from top

green lumber has greater moisture content

dry lumber vs green lumber

19%

dry lumber has moisture content less than ______; similarly, green lumber has moisture content more than _____

1. cutting

   1. rift cut

   2. slash cut

2. seasoning

   1. air drying

   2. kiln drying

3. shrinkage

   1. volumetric

   2. longitudinal

   3. radial

   4. tangential

physical characteristics of wood

cutting

usually done when flow of sap is minimal and destructive fungi is least active

fall, winter; dry season

when is destructive fungi least active?

rift cut (quarter-sawing)

cut parallel to the axis of the tree and radially across the annual rings; causes wood

slash cut

cut tangential to the annual rings

seasoning

process done to reduce uptake and retention of moisture

air drying

reduces moisture in wood by up to 15%

kiln drying

removes moisture by subjecting wood to elevated temperatures at 68—82 C

hardwood

usually dried gradually as they warp easily

true

true or false: moisture affects physical properties of wood such as size and strength

true; 2.5x

true or false: dried wood is stronger than green wood; by how much?

combined moisture

moisture incorporated into the cell walls

shrinkage

starts at evaporation of combined moisture

heavy-celled wood; larger combined moisture

what shrinks more, heavy-celled wood or thin-walled wood? why?

1. volumetric

2. tangential

3. radial

4. longitudinal

rank types of shrinkage by size of their range

1. shakes

2. checks

3. knots

4. pitch pockets

5. bark pockets

6. waynes

7. compression wood

defects in lumber

shakes

longitudinal cracks following growth rings and develop prior to cutting lumber; due to wind heavily blowing through trees

checks

longitudinal splits across growth rings resulting from uneven drying

knots

formed at the base of branches where they extend into wood and can significantly affect bending strength of wood

loose knots

knots formed when branches die

spike knots

knots formed when cut is made longitudinal to branch

pitch pocket

accumulation of resins in openings between annual rings

bark pocket

formed when bark is wholly or partially encased in wood

waynes

areas where lumber has been cut too closely at edge of log and there is bark on boards

compression wood

formed on lower side of branches or leanign tree trunks; such woods have highly varying properties and are not suited for structural use

old growth stud

stud that is more dimensionally stable; slow growth, more rings per inch

farmed wood stud

stud from wood that grows bigger faster due to more aggressive watering, fertilizing, and exposure to sunlight, resulting in less dense wood

laminated veneer lumber (LVL)

made of thin sheets of wood sandwiched and glued together, much like plywood, resulting in heavy and dense wood members that resist warping and shrinkage and are designed to carry significant loads

Microllam (Weyerhauser)

proprietary name of LVL

board feet

by which most lumber is measured and sold

144 cubic inches

board feet Imperial equivalent

(thickness x face width x length) / 144

board feet calculation

high

relative to its compressive strength, wood has _____ elastic modulus

false

true or false: the yield point of wood can be generalized

tension; 3x

what is wood better in, tension or compression; by how much

parallel

is wood stronger when loaded by compression parallel or perpendicular to the grain?

1. grain orientation

2. moisture content

3. weight

4. rate of growth

factors affecting wood strength

true

true or false: denser wood is stronger

26,200 x SG^1.25

modulus of rupture for air-dry timber

18,500 x SG^1.25

modulus of rupture for green timber

higher

the greater number of annual rings per unit length, the _______ the strength

stress grades

lumber groups with ideally similar structural properties

lumber stress grading

process by which lumber is sorted into stress grades

1. fungi

2. insects

3. marine organisms

4. bacteria

organisms that degrade wood

fungi

feed on cell structure or contents of woody plants; moisture content above fiber saturation point is required for its growth; attacks produce stains and/or decay damage

beetles and termites

most common wood-attacking insects

true

true or false: annual damage attributed to termites exceeds losses due to fires

close to the ground, poorly ventilated, wet

conditions for termites to enter wood more likely

salt or brackish waters

where shipworms, phloads, Limnoria, and Sphaeroma (marine organisms that deal damage to wood) come from

bacteria

organisms that cause wet wood or black heartwood in living trees and general degradation of lumber; growth is sometimes fostered by prolonged storage in contact with soils; produces softening of outer wood layers which results in excessive shrinkage when re-dried; attackc does not pose significant problem to common structural wood species

1. petroleum-based solutions

2. waterborne preservatives

wood preservation kinds

petroleum-based solutions

very effective wood preservation method but environmentally sensitive; used where high degree of environmental exposure exists and human contact is not a concern

waterborne preservatives

cleaner wood preservation kind and can be painted; removed by leaching when exposed to moist conditions over long periods of time; environmentally senstivie

quality of veneer on both front and back sides of panel

how is plywood quality graded

1. N

2. A

3. B

4. C Plugged

5. C

6. D

veneer grades