WOOD part 1[1]

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Building Technology 1

WOOD

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WOOD

Fibrous substance which composes the trunkand branches of a tree that lies between thepitch and the bark.

defined as the lignified water conducting,strengthening and storage tissues of branches,

stem and roots of trees.

wood is known as xylem.

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PARTS OF WOOD

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PARTS OF WOOD

heartwood Hard dark-colored wood

layer made of deadsapwood; it encircles

the pith and supportsthe trunk and branches.

pith

Central part of the

trunk, composed of softtissue that containsnutrients essential forsapling growth.

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PARTS OF WOOD

bark Trees external protective

layer; its texture and color

vary depending on the

species.Phloem

Tissue located immediately

below the bark, whose main

function is to transport sap

transformed by

photosynthesis from the

leaves throughout the rest of

the tree.

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PARTS OF WOODcambium

Growth tissue that

simultaneously produces the

external phloem and the

internal sapwood, therebyenabling the tree to increase in

diameter.

sapwood

Relatively new layer of woodthat is generally pale in color; it

transports raw sap, composed

of water and nutrient minerals,

from the roots to the leaves.

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PARTS OF WOODannual ring

Each of the concentric circles

representing the layer of

wood produced in one year;

the age of the tree can bedetermined by the number of

rings.

wood ray

Conduit connecting the pith to

the core and circulating

nutrients horizontally within

the trunk.

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Properties of Wood as a Building

Material

Strong material

Durable

Light in weight

Ease of working and fastening

With artistic and natural beauty

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Advantages of Wood as Building

Material

In proportion to weight, wood is stronger than

other materials.

Wood is easily worked out with tools and

fabricated into many shapes, sizes and design.

Wood is excellent non-conductor of heat. It is

warm in winter and cool in summer.

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Material

It is abundant in many shapes, color, sizes, and

as renewable resources.

The use of timber connectors in wide trusses

and spans generally permit the use of small

wood members.

In terms of value, wood does not deteriorate if

properly handled and protected.

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Material

It is not readily affected by changing styles.

It has prompt resale value.

Neither heat nor cold or climate changes

would seriously affect the physical propertiesof wood.

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Physical Properties of Wood

1. Strength- ability of wood in resisting stress andstrain.

Strength of different wood varies in the following

manner: Resistant to compression

Stiffness or ability to resist bending stress

Strength in tension or ability to resist lengthwisestress

Shearing strength or ability of the fibers to resistrupture along or across the grain

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2. Knots and other defects in wood- affects thestrength more particularly the size, character andlocation of the knots or defects.

3. Weight-heavy woods are generally stronger thanlighter wood.

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4. Hardness-expressed as resistance to indentationor to the saw or axe across the grain.

-generally dependent on the weight of the wood,

structural elements and degree of seasoning.

5. Cleavability-resistance of wood to split along thegrains

6.Flexibility-the moisture content of the woodinfluences the flexibility to a considerable degree.

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7. Toughness-refers to the combined strength,shock resistance and pliability or flexibility of the

wood.

8. Durability-ability to resist decay ; length of its lifeunder a given condition; resistance of the woodto the influence of mechanical wear.

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Classification of Wood

Mode of Growth:

Exogenous- outward growing trees mostpreferred for lumbering

Indigenous- inside growing trees; lesspreferred for lumbering because the center

core of the log is soft and brittle in character.

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Density- mass & volume of the wood

1. Softwood- known as conifers or evergreen

1.1 Conifers: Tree that usually retains its

needle- or scalelike leaves all winter long; itbears cones, hence its name, and produces a

sticky sap known as resin.

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1.2 Evergreen- having foliage that remains

green and functional throughout the year

or through more than one growing season

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Softwood

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Softwood

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2. Hardwood-generally deciduous with broad

leaves

Deciduous- shredding leaves annually or at

the end of a growing season.

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Hardwood

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Hardwood

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Hardwood

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Leaves:

Needle shape

Broad shape

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Shade or color of wood:

White Red

Yellow

Brown

Orange

Black, etc.

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Grain:

Straight grain

Cross grain

Fine grain

Coarse grain

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Grain

When you cut a board across the grain

(perpendicular to the grain direction and the

growth rings), you reveal end grain.

Cut wood parallel to the grain direction and

tangent to the growth rings, and youll

seeplain grain(also called tangentialor flat

grain).

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Grain

Cut it parallel to the grain direction but

through the radius of the growth rings to

see quarter grain (also referred to

as radialgrain).

Both flat grain and quarter grain are

sometimes called long grain.

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Grain

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Nature of the Surface when sawed:

Plain

Grained

Figured or marked

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Figured

Wood grain isnt always straight and even. The

longitudinal and ray cells sometimes grow in

unusual patterns, many of which are strikinglybeautiful. These are known asfigured grain.

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Figured A few wood species, such

as white oak, haveespecially prominent rays.When quartersawn, these

produce silver grain.

Crotch figure, such as thiswalnut crotch, is cut from

the part of a tree wherethe trunk divides intosmaller limbs andbranches.

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Figured

Curly grainoccurs whenthe longitudinal cells growin waves. This occurs inmany species but isespecially striking inmaple.

Birds eyeslike those inthis maple are caused by

small dimples in the layersof cells. These are thoughtto be caused by a fungusthat affects the growth ofthe longitudinal cells.

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Figured

Larger dimples resultin quilted figure, like thequilting in this soft maple.This, too, is the result of afungus

The longitudinal cells ofcertain species, such asmahogany, sometimes

spiral around the trunk,reversing direction everyfew growth rings. Thiscreates ribbon figure.

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Figured

Sometimes a tree produces a large growth on theside of the trunk or a branch. The cells seem toswirl around each other inside these growths.When sliced, these produce a burl figuresuch asthis elm burl.

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Texture & Pattern

TEXTURE AND PATTERN

The size, type, and arrangement of the wood

cells differ with the species, and this also

affects the appearance of the grain.The texture of the wood is determined by the

relative size of the longitudinal cells. Wood

species with large cells are said to havea coarse texture, while those with smaller

cells have afine texture.

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Texture & Pattern

The pores in ring-porous hardwoods such as

red oak create a strong grain pattern

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Texture & Pattern

The pores in ring-diffuse hardwoods like

mahogany are more evenly distributed and the

grain pattern is less distinct

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Texture & Pattern

Softwoods such as yellow pine have no pores. The

grain pattern is due to the color difference between

the springwood and the summerwood.

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Changing Shape

Because of the difference intangential and radial movement,

boards change shape as they

expand and contract. The way

in which they change depends

on how they are cut from thetree.

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Changing Shape

The difference in tangential and radialmovement has other important

consequences. Depending on how its cut

from the tree, a board may change shape as it

dries:

If the annual rings run side to side in square

stock, the stock will shrink to a rectangle.

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Changing Shape

If the rings run diagonally from corner to

corner, the stock will become diamond-

shaped.

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Changing Shape

Round stock becomes oval as the tangential

diameter shrinks more than the radial

diameter.

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Changing Shape

Plain-sawn lumber tends to cup in the

opposite direction of the growth rings because

the outside face (the face farthest from the

pith) shrinks a little faster than the inside face.

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Changing Shape

In quartersawn lumber, both faces shrink

equally and the board remains flat.

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Preparation of Wood

1. Logging- harvesting of the tree crops

consisting a sequence of operations such as:

Cutting of the tree

Skidding- when logs are moved to an assembly

area loaded to transport equipment then

carried out of the forest to the sawmill.

Bucking- process of sawing into smaller pieces

after the removal of branches.

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Preparation of Wood

Skidded-when the log is dragged and carrieddown to an assembly area.

Yarded-when logs are delivered through the

cable or a helium filled balloon. Lumbering-operation performed in preparing

wood for commercial purposes. It involveslogging which is the process of felling trees,hauling and delivery to the sawmill.

Sawing

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Methods of log sawing employed

1. Plain or Bastard sawing- by cutting the logs

entirely though the diameter with a parallel

chord tangential to the annual rings.

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2. Quarter or rift sawing- categorized into four

methods of sawing:

Radial method

Tangential method

Quarter tangential

Combined radial &tangential

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Live saw(This is sometimes called sawing through andthrough.) Live sawing produces much wider boards

than other methods, and these boards show mostly

mixed grain flat grain near the center of the face

and quarter grain near the edges.

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Definition of Terms

Surfaced or dressed lumber- is a planed

lumber having at least one smooth side.

S2s & s4s- planed or dressed lumber of which

the number connotes the smooth sides. S2s

means smooth on two sides & s4s on four

sides.

Slab- kind of rough lumber cut tangent to theannual rings of wood running the full length of

the log containing at least one flat surface.

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Definition of Terms

Timber- is a piece of lumber five inches or

larger in its smallest dimension.

Plank- is a wide piece of lumber from 2 to 5

inches thick.

Board-is a piece of lumber less than 1 thick

and at least 4 inches wide.

Flitch- is a thick piece of lumber.

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Definition of Terms

Fine grain- when annual rings are small, the

grain marking which separates the adjacent

rings is said to be fine grain. When large, it is

called Coarse-grained.

Straight grained- when the direction of the

wood fibers are nearly parallel with the sides

and edges of the board.

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Definition of Terms

Lumber- is the term applied to wood after it wassawed or sliced into boards, planks, sticks, etc. forcommercial purposes.

Strips. Lumber less than 2 thick and less than 8wide.

Board Lumber. Pieces less than 2 thick and atleast 8 wide.

Dimension Lumber. Pieces more than 2 and lessthan 5 in any dimension.

Timbers. Pieces 5 or more on the smallest

dimension

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Definition of Terms

Rough lumber- is the term applied to newly

sawed lumber.

Silviculture- is the process of growing timber

crops of a better and more valuable species as

rapidly as possible through scientific forestry.

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Defects in Wood

1. Abnormal growth Heart shakesare radial cracks originating at the

heart of the logs.

Wind shakes or Cup shakes- cracks or breaksacross the annual rings of timber during itsgrowth caused by excessive bending of the treedue to wind.

Star shakes- composed of several heart shakes

radiating from the center of the log in a star-likemanner.

Knots- usually occur at the starting point of alimb or branch of the wood.

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Defects in Wood

Dry-rot-is the presence of moisture in

seasoned wood caused by fungi.

Wet rot-usually takes place sometime in the

growth of trees caused by water saturation.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Bow

A curve along the face of a board that usually

runs from end to end. Usually resulting from

imporper storage.

Defects in Wood

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Defects in Wood

(Man Made Defects)Check

A crack in the wood structure of a piece,

usually running lengthwise. Checks are usually

restricted to the end of a board and do not

penetrate as far as the opposite side of

a piece of sawn timber. This is easily overcome

by removing the endpieces of the board.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Crook

Warping along the edge from one end to the

other. This is most common in wood that was

cut from the centre of the tree near the pith.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Cup

Warping along the face of a board across the

width of the board. This defect is most

common of plain-sawn lumber.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Shake

Separation of grain between the growth rings, often

extending along the board's face and sometimes

below its surface.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Split

A longitudinal separation of the fibers which

extends to the opposite face of a piece of

sawn timber.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Twist

Warping in lumber where the ends twist in

opposite directions. Probably the worst of the

defects. This board is unworkable unless it iscut into smaller pieces and flattened with a

jointer.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Wane

The presence of bark or absence of wood on

corners of a piece of lumber.

Defects in Wood

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Defects in Wood

(Man Made Defects)

Machine Burn Discoloration of the wood due to overheating caused

by friction, and either scorching the wood or the

resins within it. Machine burn is caused by stopping

or not feeding the wood across the blades at the

correct rate of speed. Although species like cherry,

pine, or walnut are more susceptible than others,

machine burn can almost always be prevented by

using sharp blades and correct

feed rates.

Defects in Wood

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Defects in Wood

(Natural Defects)

Worm hole- This is caused by

insects boring through the wood.

Defects in Wood

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Defects in Wood

(Natural Defects)Blue Stain

A discoloration that penetrates the wood fibre. It

can be any colour other than the natural colour of

the piece in which it is found. It is classed as light,medium or heavy and is generally blue or brown.

Defects in Wood

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Defects in Wood

(Natural Defects)

Spalt

Typically found in dead trees, spalting is any form of

wood discoloration caused by fungi. There are three

types of spalting that are typically incorporated intowoodworking as design elements, pigmentation (or

sapstain), white rot, and zone lines.

Defects in Wood

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Defects in Wood

(Natural Defects)Pitch

An accumulation of resinous material on the surface

or in pockets below the surface of wood. Also called

gum or sap.

Defects in Wood

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Defects in Wood

(Knot)

Dead or Loose

Knot having annual rings not intergrown with

those of the surrounding wood.

This is caused by a dead branch that was notfully integrated into the tree before it was cut

down.

Defects in Wood

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Defects in Wood

(Knot)

Tight Knot- a knot held firmly in

place by growth or position

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Seasoning of wood

Seasoning- drying of wood

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Methods of Seasoning Wood

1. Natural or air seasoning-one of the best

methods of seasoning lumber although the

period involved is relatively longer than the

artificial seasoning method. Air drying

Sun drying

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Methods of Seasoning Wood

2. Artificial seasoning-quick drying of wood

Kiln drying

Forced air or pressure drying

Vapor drying

Radio frequency dielectric drying

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AIR DRYING

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KILN DRYINGSEASONING

RADIO

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RADIO

FREQUENCY

DIELECTRIC

DRYING

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VAPORDRYING

M h d f T i L b

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Methods of Treating Lumber

Tantalizing

Permanizing

Wolmanizing

Bolidine salt

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WOOD part 1[1]

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