27109 Wood

C O N S T R U C T I O N M A T E R I A L ST I M B E RT I M B E R

1© 2009 Praveen Chompreda, Mahidol University

O U T L I N EO U T L I N E

• Trees • Mechanical Properties Trees– Components of Tree Trunk– Wood Cells

• Mechanical Properties – Flexural, Compressive, Tensile, and

Shear StrengthsWood Cells– Hardwood vs. Softwood

• Physical Properties

– Factors Affecting Strength

• Deteriorations & PreventionsPhysical Properties– Wood Defects– Moisture & Shrinkage

– Mechanical, Physical, Chemical, and Microorganisms deteriorationsWood Protection ProductsMoisture & Shrinkage

– Density & Specific Gravity

• Lumbering

– Wood Protection Products– Fire Protection

• Wood ProductsLumbering– Conversion of Timber– Seasoning

Wood Products– Plywood– Particle BoardSeasoning– Hard Board

2

Leonardo da Vinci timber footbridge, Norway2001, 40 m main spanSource: www.makingthemodernworld.org.uk

T R E E SComponents of Tree TrunkComponents of Tree TrunkWood CellsTree GrowthHardwood vs. Softwood

3

C O M P O N E N T S O F T R E E T R U N K C O M P O N E N T S O F T R E E T R U N K

Pith

ใจ XylemCambium

แนวแมเซลลเนอไม

Phloem

เปลอกชนใน

Bark

เปลอกไมเปลอกไม

4

T R E E T R U N K – B A R K & P H L O E MT R E E T R U N K – B A R K & P H L O E M

• Outer Bark (เปลอกไม) is a ( )protective layer consisting of dead cellsCambium

Pith

X l • Can be very thick or quite thin depending on wood species

แนวแมเซลล ใจ Xylemเนอไม

Phloem

• Phloem or Inner Bark (เปลอกชนใน) is a thin layer of living cells

Barkเปลอกไม


ชนใน) is a thin layer of living cells used for transporting sugars to other parts of the tree

เปลอกไม

• Cambium (แนวแมเซลล) is a thin l i h Phl (I layer separating the Phloem (Inner Bark) from the Xylem

5

T R E E T R U N K – X Y L E M & P I T HT R E E T R U N K – X Y L E M & P I T H

• Xylem can be further categorized y ginto Sapwood (กระพไม) and Heartwood (แกนไม)Cambium

Pith

X l • Sapwood is a lighter color layer used for transporting water and foods

แนวแมเซลล ใจ Xylemเนอไม

Phloem foods• Heartwood is the inner part of

Xylem acting as a reservoir for Barkเปลอกไม


y gwastes and is darker in color

เปลอกไม

• Pith is the soft thin-walled cells at the center of the trunk

Heartwood

6

Sapwood

W O O D C E L L SW O O D C E L L S

• Wood Cell consists of 4 major componentsWood Cell consists of 4 major components– Cellulose – Long chain of glucose molecules, supply wood strength– Hemicellulose – Shorter chain of glucose and other sugar molecules, Hemicellulose Shorter chain of glucose and other sugar molecules,

providing framework for cellulose– Lignin – Large molecule that acts as binder to cellulose and

hemicellulose chains and make them rigid– Extractives – Other chemicals presented in small amounts and

ibl f l d d d i f diff responsible for color, odor, taste, and decay resistance of different woods

Different Extractives

C d

7

Cedar Redwood

T R E E G R O W T HT R E E G R O W T H

• Trees grow both in height and diameterg g– Height growth is through elongation of trunks only at

the tip– Diameter growth is through the cambium which Diameter growth is through the cambium, which

produces Xylem towards the center of the trunk and Phloem towards the bark

• In temperate regions trees grow mostly in early • In temperate regions, trees grow mostly in early spring season– Springwood (Earlywood) has lighter color large thin-

walled cells– Summerwood (Latewood) has darker color small

thick-walled cells– The different color of springwood and summer wood

creates Annual Rings (วงป)• In tropical regions (including Thailand) trees grow • In tropical regions (including Thailand), trees grow

continuously throughout the year. Thus, the annual ring is not well-defined

8

C O M P O N E N T S O F T R E E T R U N K C O M P O N E N T S O F T R E E T R U N K

9Source: Illston and Domone (2001)

H A R D W O O D V E R S U S S O F T W O O DH A R D W O O D V E R S U S S O F T W O O D

UNITED STATES

• Hardwoods are woods from broad-leaved trees such as Oak, Poplar, Maple, Ash, Walnut, Cherry

• Softwoods are woods from coniferous trees such as Pine, Douglas Fir, Cedar

Maple, Ash, Walnut, CherryThe word Hard and Soft is not indicative of its hardness property !!!

THAILAND (มอก. 421- 2525)

ไ (H d W d) ไ ไ (S ft W d) ไ • ไมเนอแขง (Hard Wood) คอไมทมความตานทานแรงดดโคงสงสดเกน 100 MPa ในสภาพทเปนไมแหงและม

• ไมเนอออน (Soft Wood) คอไมทมความตานทานแรงดดโคงสงสดตากวา 60 MPa ในสภาพทเปนไมแหงและม

ความทนทานตามธรรมชาตเกน 6 ป• ไมใบกวาง (Hardwoods) คอไม

ประเภทใบกวางทมเมลดอยในรงไข ม

ความทนทานตามธรรมชาตไมเกน 2 ป• ไมใบแคบ (Softwoods) คอไมประเภท

ใบแคบทมเมลดอยนอกรงไข และไมมประเภทใบกวางทมเมลดอยในรงไข มใบเลยงค และมทอสงนาในเนอไม ขยายใหญเปนพเศษ

ใบแคบทมเมลดอยนอกรงไข และไมมทอสงนาในเนอไมขยายใหญเปนพเศษ

10

PC1

Slide 10

PC1 ไมสน?Praveen Chompreda, 19/11/2005


• Softwood (in the US sense), has ( ),almost uniform cell structures and most of the cells (about 90%) are li d i h l i di l aligned in the longitudinal

direction. The cells that align transversely are called rays. y y

11

Source: Illston and Domone (2001)


• Hardwood (in the US sense) has ( )nonuniform structure. It has vessels (or pores) structure for

d i Thi i f d i conduction. This is not found in softwood.

• Also only 80-95% of hardwood Also, only 80-95% of hardwood cells are in the longitudinal direction.

Vessel

12



• วศวกรรมสถานแหงประเทศไทยฯ แบงไมออกเปน 5 ประเภท ตามกาลงรบแรงของไม

ไมเนอออนมากกะทอน จาปา

ไมเนอออนกราด กระเจา

ไมเนอแขงปานกลางกวาว

ไมเนอแขงกนเกรา แดง

ไมเนอแขงมากกระพเขาควาย กะทอน จาปา-

ปา จกนม ยม-หอม ยางขาว

กราด กระเจา กะบาก ตะปน-ขาว พะยอม

กวาว ตะเคยนทอง ตะเคยนหม

กนเกรา แดง ตะครอไข ตะครอหนาม

กระพเขาควาย เขลง ตนนก บนนาค

สองสลง ยางแดง สก อนทนล

ตะแบก ตาเสอ นนทร พลวง มะคาแต

เตง ประด มะคาโมง ยมหน รง

มะคาแต ยมหน รง เลยงมน หลมพอ สก-ขควาย เคยม

13

P H Y S I C A L P R O P E R T I E SWood DefectsWood DefectsMoisture & ShrinkageDensity & Specific Gravity

14

W O O D D E F E C T S W O O D D E F E C T S

• The lesser the defects, ,the more desirable is the wood

• Natural defects occur by the nature of the wood such as knot wood such as knot, irregular grain, and some types of shakes

• Artificial defects are caused by mishandling of the timber or of the timber or incorrect seasoning techniquesq

15

M O I S T U R E & S H R I N K A G EM O I S T U R E & S H R I N K A G E

– The weight and volume of wood change as the moisture condition of g gthe wood changes

– Moisture Content is calculated as:

m dW -WMC = ×100%

WdW

– Wd = weight of oven-dry wood, Wm = moist weight

W b ll ll ( ll d I b b d W ) ll – Water may be in cell walls (called Imbibed Water) or cell cavities (called Free Water)The point when cell walls is saturated and no free water is called Fiber – The point when cell walls is saturated and no free water is called Fiber Saturation Point

– Shrinkage occurs when moisture content drops below fiber saturation

16

g ppoint


17


• Moisture content in the wood changes with the ambient relative humidity until it reaches the until it reaches the equilibrium condition

• Equilibrium moisture i h i content is the moisture

content at which wood neither gains nor loses moisture to air at a given relative humidity and temperaturep

• For the same relative humidity, the equilibrium moisture content moisture content decreases as the temperature increases

18

Source: Wilcox et al. (1991)

M O I S T U R E & S H R I N K A G EM O I S T U R E & S H R I N K A G E• Another way of plotting moisture content v.s. relative humidity v.s. temperature



– Tangential Shrinkage > Radial Shrinkage > Longitudinal Shrinkage (~0)g g g g g ( )

20



• Shrinkage varies ggreatly among different species of

dwoods• Tangential

shrinkage is shrinkage is significantly greaterthan Radial shrinkage for most woods

• Different in rate of • Different in rate of shrinkage in two direction may yresult in warping and/or shake

21


22Source: Forest Products Laboratory (1990)



23

D E N S I T Y & S P E C I F I C G R A V I T Y D E N S I T Y & S P E C I F I C G R A V I T Y

• Density & Specific GravityDensity & Specific Gravity– Density is calculated as:

Oven-Dry WeightDensity =

Volume at 12% MCVolume at 12% MC

– Specific gravity is calculated as:

°Density of Wood

Specific Gravity = Density of Water at 4 C

• Density of water is 1 g/cm3. Therefore, density of wood in g/cm3 is numerically identical to its specific gravity

24

numerically identical to its specific gravity

D E N S I T Y D E N S I T Y

• Density = M/Vy• Mass (M) can be obtained by

weighing the specimen in airT = Wwater

• Volume (V) cannot be accurately computed by measuring the dimensions of the specimen

Waterdimensions of the specimen

• Obtain the volume by weighing the specimen in water

Wood Specimen

the specimen in water

Wair = Mg B = ρwVwood g

ρair water

wood

W -WV =

g

ρ

ρg

25

D E N S I T Y & S P E C I F I C G R A V I T Y D E N S I T Y & S P E C I F I C G R A V I T Y

• Density & Specific Gravity ไม Specific GravityDensity & Specific Gravity– Wood substance (cell wall

material) has specific gravity

p yแดง 1.05

ตะเคยนทอง 0.76) p g yof about 1.5 regardless of speciesD S f G f

ตะเคยนหน 0.87เตง 1 07– Density or Specific Gravity of

wood is an indication of the amount of wood substance

เตง 1.07ประด 0.83

มะคาแต 0 99amount of wood substancepresented in the piece

– Typical Range of Specific

มะคาแต 0.99มะคาโมง 0.85มะฮอกกะน 0 66Gravity of Thai Woods: 0.5-

1.2

มะฮอกกะน 0.66ยาง 0.69 1 11รง 1.11

สก 0.63

26

L U M B E R I N GConversion of TimberConversion of TimberSeasoning

27

L O G G I N GL O G G I N G• Use band saw or chain saw to cut

the tree• After the tree is felled, the

branches and leaves are removed and the logs are cut to length

• The logs are then transported to a saw mill to be cut into woodsaw mill to be cut into wood

28Lumberjacks circa 1910Modern Harvester MachineSource: Wikipedia Source: Wikipedia

L O G G I N GL O G G I N G

Source: Wikipedia

Logs are cut to length before transportSource: Wikipedia

29Log transport by riverLog transport by road

Source: Wikipedia

L O G G I N GL O G G I N G

Logs waiting to be cut at sawmill

Source: WikipediaSource: Wikipedia

Source: Wikipedia

Finished product!

30

Small-scale portable sawmillSource: Wikipedia

C O N V E R S I O N O F T I M B E RC O N V E R S I O N O F T I M B E R

• There are two broad ways of cutting timber into planks

• Plainsawing – is a cut tangent to the annual rings exposing tangent surfaceg p g g f(obtaining flat-grained lumber)

• Quatersawing – is a cut in the radialdirection from the center of the log direction from the center of the log exposing radial surface (obtaining edge-grained lumber)

• Which method is to be used depends Which method is to be used depends on:

– Strength desired (radial cut plank is stronger, stiffer, and less likely to stronger, stiffer, and less likely to warp)

– Wood grain (some wood exhibit beautiful grain when cut radially)g y)

– Shape and defects of the timber– Costs (radial cut is more difficult and

generates more waste)

31

g )

Source: Forest Products Laboratory (1990)


Source: Wikipedia

• In wood such as oak, a desirable feature called “medullary ray” is exposed Source: Wilcox et al. (1991)

when cut radially

32



• Experience is needed to select the most economic way to cut the timber• Different parts of the section may be suitable for different applications

33

Different parts of the section may be suitable for different applications• Wood defect also plays an important role in the selection

C O N V E R S I O N O F T I M B E RC O N V E R S I O N O F T I M B E RSource: Wikipedia

34

Modern sawmill uses computer to calculate the most economic pattern and has laser-guided blades

S E A S O N I NG O F T I M B E RS E A S O N I NG O F T I M B E R

• The objective of seasoning (การอบผงไม) is to reduce the moisture The objective of seasoning (การอบผงไม) is to reduce the moisture inside the “green” wood to equilibrium moisture content– If unseasoned wood is used, shrinkage will occurIf unseasoned wood is used, shrinkage will occur– Natural drying of wood through evaporation can take years– Even if seasoned, wood can still shrink or swell under changes in , g

humidity – There is no need to completely eliminate the moisture inside the wood

(i.e. to oven-dry) because wood will reabsorb the ambient humidity

• Two main types– Air Seasoning– Kiln (Artificial) Seasoning

35


• Air Seasoning g– May take about 1 year for 1

inch-thick wood and much l f thi k dlonger for thicker wood

– Control the rate of drying by changing the spacing y g g p gbetween pieces of wood

Source: Wikipedia

36


37Source: Wilcox et al. (1991)


• Kiln Seasoning– Kiln is a chamber which has fans to blow heated air and jets to introduce steams– Steam is needed to control the rate of drying at the surface

• prevent the “case hardening” in which the surface is dried and shrunk while the core is still wetis still wet

• Prevent splitting from rapid drying

– Kiln seasoning is much faster than air seasoning – usually takes about 2-10

38

weeks depending on the wood species and thickness

M E C H A N I C A L P R O P E R T I E SFlexural StrengthFlexural StrengthCompressive StrengthTensile StrengthShearing StrengthOther PropertiesFactors Affecting Strength

39

Factors Affecting Strength

M E C H A N I C A L P R O P E R T I E S M E C H A N I C A L P R O P E R T I E S

• Tensile Strengthg– Parallel to grain– Perpendicular to grain

• Compressive Strength– Parallel to grain

P d l – Perpendicular to grain– Oblique to grain

• Flexural Strength (Modulus of • Flexural Strength (Modulus of Rupture)

• Shearing Strengthg g– Parallel to grain– Perpendicular to grain

40

T E N S I L E S T R E N G T HT E N S I L E S T R E N G T H

• Tensile strength parallel to grain is much larger (in the order of 50:1) than g p g g ( )tensile strength perpendicular to grain

• Example of tension parallel to grain is a truss; however, wood rarely fails by d direct tension

41

T E N S I L E S T R E N G T HT E N S I L E S T R E N G T H

• Formula for Tensile Strength:g

Tσ t

T =

A

• For the tensile strength perpendicular to grain, wood is stronger when the failure plane is in tangential surface than the radial surface – average value is usually reported

>

42

C O M P R E S S I V E S T R E N G T HC O M P R E S S I V E S T R E N G T H

• Compressive strength parallel to p g pgrain is higher (in the order of 10:1) than the compressive

h p p di l istrength perpendicular to grain

• Wood compressed perpendicular• Wood compressed perpendicularto grain never “fails” even at large deformation often used as support or bearing plate

• For compression perpendicular to grain, wood is stronger when load is applied in the tangentialis applied in the tangentialdirection than the radial -- average value is usually reported

>

43

C O M P R E S S I V E S T R E N G T HC O M P R E S S I V E S T R E N G T H

• Wood under compression parallel to grain, such as columns, is often p p g , ,limited by the buckling strength, rather than the compression strength of the wood

• Formula for compressive strength

Cσ σ≤c critical

C =

A

where is the critical stress where buckling occurs. Within the proportional limit (linear elastic behavior) this can be calculated using

σ critical

proportional limit (linear elastic behavior), this can be calculated using Euler’s formula. depends on the elastic modulus (E), length (L), and cross-sectional dimensions (r)

σ critical

πσ =2

critical 2

C E =

A (L/r)

44

A (L/r)

B E N D I N G S T R E N G T HB E N D I N G S T R E N G T H

• Wood under bending usually fails g yon compression side before the tension side (unless the grain is not parallel with the longitudinal not parallel with the longitudinal direction of the member)

• Maximum bending stress is called d l f modulus of rupture

×M c×M cMOR =

I

• This is really not the stress in the top or bottom wood fiber because the compressive stress is the compressive stress is nonlinear near the maximum strength

45

• Comp // < MOR < Tens //

B E N D I N G S T R E N G T HB E N D I N G S T R E N G T H

• Bending Failure ModesBending Failure Modes

46

S H E A R I N G S T R E N G T HS H E A R I N G S T R E N G T H

• Shear strength parallel to grain (either longitudinal or rolling shear) is much ll h h h h p p di l i ( i l h ) smaller than the shear strength perpendicular to grain (vertical shear)

• Shear failure perpendicular to grain rarely occurs as it often precedes by bending failure or compression failure at load point

47

bending failure or compression failure at load point

S H E A R I N G S T R E N G T HS H E A R I N G S T R E N G T H

• Shear Strength Formula:g

Vτ V =

A

• Shear strength parallel to grain is critical in designing bolt holes

48

O T H E R P R O P E R T I E SO T H E R P R O P E R T I E S

• Modulus of Elasticityy– Slope of the linear portion of the

compression stress-strain curve ithi th l ti within the elastic range

σΔσε

ΔΔ

E =

• Hardness Test– Measure the hardness of the

surface by pushing a metal ball on the surface to a certain depth and measure the forcemeasure the force

49

O T H E R P R O P E R T I E SO T H E R P R O P E R T I E S

• Cleavage Testg– Measure the potential that the wood can be tear along the grain

• Nail Withdrawal Test– Measure the ability of wood to hold a nail

• Impact and Toughness Test– Using a drop mass or pendulum to apply impact force to a simply-supported

beam specimen– Toughness is the work required to fail the specimen which together with the Toughness is the work required to fail the specimen which, together with the

strength, can indicates how ductile the wood is

50

F A C T O R S A F F E C T I N G S T R E N G T HF A C T O R S A F F E C T I N G S T R E N G T H

• The strength (compressive, Source: Illston and Domone (2001)g ( p ,tensile, or shear) and stiffness (modulus of elasticity) of wood is

ll ff d b h


generally affected by the followings:– The grain angle relative to loading The grain angle relative to loading

direction (therefore, wood is said to be an Anisotropic material)

51


– Knots (Defects): knots cause the ( )distortion of grain, thus reduce the strength capacity. The sizes, distributions, and locations of distributions, and locations of knots are the key factors. The strength of a real structural-size timber is lower than the strength timber is lower than the strength of small clear test specimens due to the presence of knots.


52



– Density (or Specific y ( pGravity): The higher the density, the greater the strength. The the strength. The density is affected by the species of the wood and for each wood and, for each specie, the rate of growth. The latewood i d d is stronger and denser than the earlywood due to the thicker cell walls.





– Moisture Content: The general trend is that the strength decreases as the moisture content increases. However, different strength properties are affected at various degrees.



56


– Temperature: The strength p gdecreases as the temperature increases. The effect is greater at high moisture content.high moisture content.


57


D E T E R I O R A T I O N S & P R E V E N T I O N SMechanicalMechanicalPhysicalChemicalMicroorganismsInsectsPreventions

58

PreventionsWood Protection Products

D E T E R I O R A T I O N O F W O O DD E T E R I O R A T I O N O F W O O D

• Deterioration of wood may be divided into 5 categoriesy g– Mechanical– Physicaly– Chemical– Microorganisms– Insects

• Different species of wood has different resistant to deteriorations due to different in cell structures and extractives presented. Sapwood part is less durable than the heartwood because it has no extractives durable than the heartwood because it has no extractives.

59


• Deterioration of wood may be divided into 5 categoriesy g– Mechanical– Physical

– Floors subjected to heavy equipments rolled on themy

– Chemical– Microorganisms

– Wood in desert was blown by sand– Structural member at loose joint rub against

each other hen s bjected to ibration– Insects

each other when subjected to vibration– Creep of wood under sustained load causes

loss of strength

60



– Ultraviolet exposure (especially at high elevations) - causes the breakdown of lignin, y


which holds the wood cell together– Repeated cycles of wetting and drying –

causes shrinkage failures and warping– Insects

causes shrinkage failures and warping– High heat (in the order of 200 °C) or lower

heat (at > 120 °C or so) but for a long period of time.

61Damage due to UV Rays



– Wood is quite resistant to acids but can be destroyed by alkalis due to the dissolution of y


lignin and hemicellulose– Contacts with alkaline vapors in petroleum or

chemical plants– Insects

chemical plants– In some woods, iron in rusting fasteners can

cause iron-catalyzed hydrolysis that destroy wood

62



– Fungi• Mold y


• Stain• Soft Rot Fungi

– Insects • Decay Fungi– Bacteria

63

M I C R O O R G A N I S M D A M A G E SM I C R O O R G A N I S M D A M A G E S

Source: Wikipedia Source: Wikipedia

Soft Rot (Alligator Skin Pattern & Soft)Mold Fungi

64

White Rot from Decay FungiBrown Rot from Decay Fungi (Cubic cracks)

Source: Wikipedia

Source: Wikipedia



– Termite– Beetlesy


– Wood borers– Etc…

– Insects

Source: UNEP (2000)

Source: UNEP (2000)

65Source: UNEP (2000)

T E R M I T E ST E R M I T E S

• There are more than 2600 species of termite but they can be broadly p y yclassified into 4 main types:– Dampwood Termite – Drywood Termite– Subterranean Termite

Arboreal/ Mound Builders Termite– Arboreal/ Mound Builders Termite

• Protection strategies and extermination vary among types

Ki

Source: UNEP (2000)

KingWorkers

QueenSoldier

66


• Dampwood Termite

Source: UNEP (2000)Source: UNEP (2000)

• Dampwood Termite– Most of the species like very damp wood – Their colony is often small and the damage is usually slow (decay fungi may be y g y ( y g y

more of a problem in the same environmental condition)

67


Source: UNEP (2000) Source: UNEP (2000)

• Drywood Termite– Most species attack dry wood and can live in a low moisture environment

Diffi lt t d t t it li i id th d– Difficult to detect as it lives inside the wood– Sign of drywood termite is its fecal pellets near their nest

68


Source: Wikipedia

• Subterranean Termite– Live in soil underground or in moist condition, sometimes live in a tree

Th t l t th i f d th h t l i d h lt t b – They travel to their food source through tunnels in wood or shelter tubes (which made up of soil, bits of wood, and their fecal material)

69


• Arboreal/ Mound Builders Termites

Source: Wikipedia Source: Wikipedia

– Usually build their nest on trees, fences, under roof etc…– Reach the building through aboveground tunnel

70

P R E V E N T I O N S O F D E T E R I O R A T I O NP R E V E N T I O N S O F D E T E R I O R A T I O N

• Key to the prevention of wood deteriorations:y p

W A T E R W A T E R W A T E R ! ! !W A T E R W A T E R W A T E R ! ! !

• Microorganisms, especially fungi, need water to live• Subterranean termite and many insects like moist conditiony• Moisture causes shrinkage and swelling• Water dilutes wood cell structure in the present of some p

chemicals (such as alkali)• Water washes away wood protection agents

71They call all happen at the same time!

P R E V E N T I O N S O F D E T E R I O R A T I O NP R E V E N T I O N S O F D E T E R I O R A T I O N

• Wood structure should be designed such that water will not accumulate ganywhere (termite, fungi, & moisture from soil)

• Avoid direct ground contact with wooden parts (termite & moisture from soil)soil)

• Foundation and attic should be dry and well ventilated ((insects and microorganisms)

• Select the right kind of wood for the job (durability)• Apply wood protection and/or finishing chemicals (insects and

microorganisms)microorganisms)• Building should be designed such that inspection can be done easily• Provide physical barrier and/or screens between building and surrounding Provide physical barrier and/or screens between building and surrounding

area (insects especially termite)

72

W O O D P R E S E R V A T I V E SW O O D P R E S E R V A T I V E S

• Wood preservatives provide protections from Insects/ Microorganismsp p p g

• Ways to apply wood preservatives • Typesy pp y p– At lumber manufacturing plants

• Pressurizing

• Oilborne Preservative• Water Soluble Preservative

L h bl T• Dip, Hot/Cold Soaking– At construction sites

• Dip

• Leechable Type• Fixed Type

• Dip• Brush, Spray

73


Pressure Chamber

74

W O O D P R E S E R V A T I V E S W O O D P R E S E R V A T I V E S

• Oilborne PreservativesOilborne Preservatives– Utilizes oil to carry preservatives into the wood– Examples:Examples:

• Coal-Tar Creosote/ Petroleum Creosote– Heavy black-brown liquid produced by condensing vapors y q p y g p

from heated carbon-rich sources, such as coal or wood. It is sometimes mixed with tar oils and petroleum oils.

– Advantages: Very effective, Very toxic to insects & fungi, not water-soluble, good absorption to wood, inexpensiveDisadvantages: Strong odor flammable impart a dark – Disadvantages: Strong odor, flammable, impart a dark color to the wood, wood is unpaintable, may cause irritation when contacted with skin. Long-term exposure g pmay lead to skin cancer

– Mostly used for railroad ties, bridge timbers, piling, and l l

75

utility poles


Source: Wikipedia

Source: Wikipedia

Creosote Treated Wood

76

Source: Wikipedia


• Pentachlorophenol (C6HCl5O)p ( 6 5 )– White organic solid with needle-like crystals and a phenolic

odor– Advantages: Toxic to insects & fungi, not water-soluble– Disadvantages: Environmental damage issues – if only low level

d h d is contaminated in the water sources, it may cause damages to liver or kidney, cancer, damage to nervous system; strong odor; flammable; impart a dark color to the wood; wood is flammable; impart a dark color to the wood; wood is unpaintable; may cause irritation when contacted with skin

– Mostly used for railroad ties, bridge timbers, piling, and utility poles

• Copper Naphthenate– Advantages: Moderately effective

D d C d l h

77

– Disadvantages: Can induce corrosion in metals such as fasteners and hinges


• Water-Soluble “Leachable” PreservativesWater Soluble Leachable Preservatives– Dissolved in water but also can be washed away so

they are not suitable for exterior applicationsy f pp– Examples:

• Zinc Chloride, Sodium Fluoride– Advantages: Inexpensive, help paint attach

to wood better, odorless, not flammable, h dl d ( hi Zinc Chloride

Source: Wikipedia

easy to handle and transport (white powder to be dissolved in hot water)

Zinc Chloride

B• Borates– Naturally occurring minerals that exist in small amounts in rock,

soil water and all living things soil, water and all living things. – Advantages: Effective fungicide/ insecticide, low toxic to human, low

environmental impact, odorless, colorless, non corrosive to metals

78

p


• Water Soluble “Fixed” PreservativesWater Soluble Fixed Preservatives– Dissolved in water but fixed on wood once applied– Examples:Examples:

• Copper Chrome Arsenate (CCA) – most popular• Ammoniacal Copper Arsenite (ACA)pp ( )• Ammoniacal Copper Zinc Arsenite (ACZA)• Acid Copper Chromate (ACC)pp ( )• Copper Chrome Boron (CCB)• Fluor Chrome Arsenate Phenol (FCAP)• Copper Azole

– Advantages: Will not be leached out by water, does not change color of wood at low levels, odorless, wood can be painted

– Disadvantages: Effectiveness varies among wood species, should not be used where it is in contact with food or water

79

where it is in contact with food or water


• Many of the wood preservatives has environmental and health issuesy p

– European Union ban the non-commercial use of creosote in 2003– Pentachlorophenol general public purchase in the USA was restricted in 1980s– CCA use in USA is currently restricted by Environmental Protection Agency

(EPA) to only certified applicator No residential wood treated with CCA was (EPA) to only certified applicator. No residential wood treated with CCA was sold since 2003.

80

W O O D F I N I S H E SW O O D F I N I S H E S

• Wood finishes provide protection from the environmentp p

– Water-repellent preservative is a non-film-forming liquid consisting of p p g q gwax/resin in solvents and sometimes with fungicide

– Stain is a non-film-forming liquid consisting of wax in solvents, some pigments, and usually with preservatives. Pigments not only dye the wood color but also help preventing photodegradation of wood cellswood color but also help preventing photodegradation of wood cells.

– Penetrating Oil is a non-film-forming finish often used in furniture to Penetrating Oil is a non-film-forming finish often used in furniture to protect wood from staining and hot dishes

81


Furniture with Penetrating Oil Finish

82Various Colors of Wood Stain


– Film-forming clear finishes (Lacquer, Varnishes, Shellac, Polyurethane)g ( q , , , y )form a thin film on the surface which repel water. They are not suitable for exterior finish because light can pass through and damage wood as

ll h fi i hi i lf hi h ll h fil l ffwell as the finishing itself, which eventually causes the film to peel-off.

Paint (Oil based or Water based (latex) paint) contains color pigments – Paint (Oil-based or Water-based (latex) paint) contains color pigments, binder (hold the pigment and provide glossy finish), and solvent. It provides film finish and also prevent photodegradation of wood. Oil-p p p gbased paints can penetrate wood better than the water-based types and may be used as a primer

• They may be used in combination with each other

83

F I R E P R O T E C T I O N O F W O O DBurning of WoodBurning of WoodFire Retardants

84

B U R N I N G O F W O O D B U R N I N G O F W O O D

• There are 3 processes involved when wood is exposed to elevated p ptemperature1. Drying of Wood

Th t i id th d (i iti d ll ll ) b il t 100 °C • The water inside the wood (in cavities and cell walls) boils up at 100 °C and releasing steam

• This process consumes a lot of heat energy and helps delay the next step• No loss of mass in wood – wood reabsorbs moisture when cooled

2. Thermal Degradation (Pyrolysis)• Occurs at the temperature over 70 °C and ends at about 480 °C • Occurs at the temperature over 70 C and ends at about 480 C • No oxygen is needed in the process• There is a loss in mass and strength – wood constituents decompose to

gases (such as carbon monoxide, formic acid, acetic acid, and methanol) and charcoal

• Charcoal produced resists further burning (charcoal has only 30-50% of p g ( ythermal conductivity of normal wood)

• Slow pyrolysis occurs at low temperature, Rapid pyrolysis occurs at much higher temperature (150-250 °C)

85

g p ( )• Strength loss of wood is much slower than steel or aluminum

B U R N I N G O F W O O DB U R N I N G O F W O O D

90

100

900

1000

60

70

80

ngth

600

700

800

(C)

AluminumSteelW d

40

50

% In

itial

Stre

n

400

500

Tem

pera

ture

(WoodTemperature

10

20

30

%

100

200

300

T

0

10

0 5 10 15 20 25 30 35 40

Time (Minutes)

0

100

( )

86

B U R N I N G O F W O O DB U R N I N G O F W O O D

3. Ignitiong• Pyrolysis product reacts with oxygen (exothermic reaction) and progress to

combustion and burning of fire. Fire becomes self-supporting.• Ignition occurs only under favorable conditions:

– Gases from pyrolysis must be combustible– Gases and oxygen must be in appropriate concentrationyg pp p– Must have sufficient heat

• Large section of wood burns slowly because oxygen cannot reach the inside• Spontaneous Ignition (no pilot fire) occurs over 430 °C but may occurs over

long period of slow pyrolysis at low temperature• Induced Ignition occurs by pilot fire raise the temperature at contact point Induced Ignition occurs by pilot fire raise the temperature at contact point

to ignition level• Combustibility of wood depends on the species of wood

– Flammable extractives that may present– Density (affect thermal diffusivity)

• Spreading of fire is a series of ignition (one area is acting as a pilot fire for the

87

Spreading of fire is a series of ignition (one area is acting as a pilot fire for the adjacent area)

I M P R O V I N G F I R E C H A R A C T E R I S T I C SI M P R O V I N G F I R E C H A R A C T E R I S T I C S

• Retarding pyrolysis (prevent strength loss)g py y (p g )– Minimize heat of combustion– Insulate wood from heat of fire– Promoting charcoal formation

• Reduce flame spread or surface flammabilityM d l b bl d d– Minimize or dilute combustible gas produced

– Blanket surface with non-combustible gas to prevent reaction with oxygen

• Prevent afterglow of charcoal• Prevent afterglow of charcoal– Blanket surface with non-combustible gas

• Reduce formation of smokeReduce formation of smoke– Most people are killed by smoke inhalation, not the heat of fire– However, most of the smoke are produced from building contents that burn before

the wood structure

88

F I R E R E T A R D A N T SF I R E R E T A R D A N T S

• Currently, there is no perfect fire retardant for woody, p– Poor retention capacity– Costs– Many reduce only flame spread but do not reduce pyrolysis– Many attract moisture into the wood (raise the equilibrium MC)

C i f t l– Corrosion of metals

• Examples are: – Ammonium phosphateAmmonium phosphate– Ammonium sulfate– Ammonium chloride– Borax (sodium tetraborate) – Zinc chloride

• Fire retardants are usually pressure-treated at the manufacturing plant with wood preservatives

89

W O O D P R O D U C T SPlywoodPlywoodParticle BoardHard Board

90

W O O D P R O D U C T SW O O D P R O D U C T S

• Besides lumber, following products are also derived from Besides lumber, following products are also derived from wood:– PlywoodPlywood– Particle Board– Hardboard– Paper– Resin Products (turpentine, tannins, volatile oils, dyes)( p y )– Sugar– Plastic– Etc…

91

P L Y W O O DP L Y W O O D

• Plywood is a crossbanded assembly y yof wood (veneer) layers joined with adhesive

• Crossbanding = arrangement of wood fiber in alternating direction

• Layers may have different thicknesses, or of different speciesthicknesses, or of different species

• More layers are needed to achieve thick plywood

• The number of layers is usually the same on each side of the core( l ) Th f h (center layer). Therefore, there are odd number of layers

92Source: Wilcox et al. (1991)

P L Y W O O DP L Y W O O D

• PropertiesProperties– Tensile strength of plywood is between that of solid wood in the

transverse direction (small) and longitudinal direction (large)( ) g ( g )– Shrinkage of plywood is between that of solid wood in the fiber

direction (very small) and solid wood across the grain (high shrinkage)– Warping may occur due to different moisture condition of face and

back or due to differences in species, thickness, and natural variability on both sideson both sides

– There are interior and exterior grades, depending on the adhesive used

93

P A R T I C L E B O A R DP A R T I C L E B O A R D

• Particle Board is obtained by ybonding fragments of wood with glue (binder/ resin) and compressing under pressure to compressing under pressure to form a sheet (Extruded or Mat-Form)Th hi h h h • The higher the pressure, the stronger the board (particle board may have 20-30% greater in density than wood it made up of)

• Glue only coats fractions of the particle surfaceparticle surface

• Particle board may have layers containing different particle size,

h l d ll or have particle size gradually changes from the middle to the surface (the core will have cheap

94

( pcoarse particles)


P A R T I C L E B O A R DP A R T I C L E B O A R D

• Mat-Formed Particle Board swell/shrink in plane slightly more than plywood p g y p ybut less than lumber in tangential/radial directions

• Mat-Formed Particle Board swell in thickness much more than timber and plywood. This is because the particles that were compressed during the manufacturing try to “spring back” moisture protection is important, especially around the edgesespecially around the edges

• Extruded Particle Board swell very little in thickness but much more in plane considerable warping may occurp p g y

• Particle board often used as a core with veneered surface such as cabinets, countertops

95

H A R D B O A R DH A R D B O A R D

• Hardboard is made up of wood ppulp (lower-grade than those used for paper making) compressed

d hunder heat• No glue is used. The heat and

pressure activates lignin inside the pressure activates lignin inside the pulp to act as a binder

• Examples of applications: p ppperforated board (for ventilation or sound absorbing), interior siding panels picture frame siding panels, picture frame backing

96

S T A N D A R D S F O R T I M B E R P R O D U C T SS T A N D A R D S F O R T I M B E R P R O D U C T S

• มอก 421-2530 ไมแปรรป: ขอกาหนดทวไป– กาหนดประเภท ขนาด การแปรรป การแบงชนคณภาพไม สาหรบไมทไดจากการแปรรปดวยเครองจกร

ไ ป ป ไป• มอก 424-2530 ไมแปรรปสาหรบงานกอสรางทวไป– สาหรบไมทตองนาไปใชในการรบแรงอดหรอแรงดง เชนทาคาน เสา จนทน แป

มอก 178 2538 แผนไมอด• มอก 178-2538 แผนไมอด– กาหนดประเภท ขนาด ชนคณภาพไม สวนประกอบ การผลต และคณสมบตทตองการ สาหรบไมอดททาจากแผนไมบางตงแต 3 ชนขนไป

97

S T A N D A R D F O R S A W N T I M B E RS T A N D A R D F O R S A W N T I M B E R

• มอก 421-2530– ไมทใชแปรรปแบงเปน 2 ชนด คอไมสก และไมกระยาเลย (ไมอนๆนอกจากไมสก)– ความหนามาตรฐาน 12 16 19 22 25 32 38 44 50 63 75 88 100 113 125 138

150 200 มลลเมตร– ความกวางมาตรฐาน 25 38 50 63 75 88 100 113 125 150 175 200 225 250

275 300 350 400 มลลเมตร275 300 350 400 มลลเมตร– ความยาวมาตรฐาน ไมสก เรมท 0.30 เมตร และเพมชวงละ 0.15 เมตร

ไมกระยาเลย เรมท 0.30 เมตร และเพมชวงละ 0.30 เมตร– เรยกขนาดตาม ความหนา x ความกวาง x ความยาว– การแปรรปไมจะมการเลอยเผอขนาดทงความหนาและความกวาง ตงแต 1.5 มลลเมตรสาหรบไมสกและไมกระยาเลยขนาดเลก ถง 15 มลลเมตรสาหรบไม มลลเมตรสาหรบไมสกและไมกระยาเลยขนาดเลก ถง 15 มลลเมตรสาหรบไมกระยาเลยขนาดใหญ

98

S T A N D A R D F O R S T R U C T U R A L T I M B E RS T A N D A R D F O R S T R U C T U R A L T I M B E R

• มอก 424-2530 แบงไมออกเปน 3 ชนคณภาพ– ชน 80 คอไมทมความตานทานแรงอดและแรงดงไมนอยกวารอยละ 80 ของไมชนดเดยวกนทปราศจากตาหน และมขนาดของตาหนตางๆไมเกนขนาดทกาหนดไวในคณลกษณะทตองการในมาตรฐาน (เชนไมท

80เกนขนาดทกาหนดไวในคณลกษณะทตองการในมาตรฐาน (เชนไมทรบแรงดง ตองมตาไมเกน 1/8 ของความกวางหรอความหนาทมตา เปนตน)– ชน 67 คอไมทมความตานทานแรงอดและแรงดงไมนอยกวารอยละ 67 ของไมชนดเดยวกนทปราศจากตาหน และมขนาดของตาหนตางๆไมเกนขนาดทกาหนดไวในคณลกษณะทตองการในมาตรฐาน

67เกนขนาดทกาหนดไวในคณลกษณะทตองการในมาตรฐาน

– ชน 50 คอไมทมความตานทานแรงอดและแรงดงไมนอยกวารอยละ 50 ของไมชนดเดยวกนทปราศจากตาหน และมขนาดของตาหนตางๆไม ไ ใ ใ 50เกนขนาดทกาหนดไวในคณลกษณะทตองการในมาตรฐาน

50

99

S T A N D A R D F O R P L Y W O O DS T A N D A R D F O R P L Y W O O D

• มอก 178-2538 แบงไมอดออกเปน 3 ประเภท– ภายนอก - ใชกาวททนทานตอลมฟาอากาศ– ภายใน - ใชกาวททนพอสมควร

– ชวคราว – ใชกาวทมความทนทานจากด เหมาะกบงานชวคราว

• แบงชนคณภาพไดเปน 4 ชน โดยแตละชนจะกาหนดขนาดใหญทสดของตาหนทจะมได ตาหนทจะมได– ชนคณภาพ 1 (เกรด I) เหมาะสาหรบงานทตองการแสดงผวหนาไม – ชนคณภาพ 2 (เกรด II) เหมาะสาหรบงานทควรทาสทบผวหนาไม ชนคณภาพ 2 (เกรด II) เหมาะสาหรบงานทควรทาสทบผวหนาไม– ชนคณภาพ 3 (เกรด III) เหมาะสาหรบงานทตองทาสทบผวหนาไม หรอทๆ ไมอาจเหนผวหนาได – ชนคณภาพ 3 (เกรด III) เหมาะสาหรบงานทผวหนาไมไมมความสาคญ

• ความหนา 2 3 4 6 10 12 15 และ 20 มลลเมตร

100

R E F E R E N C E SR E F E R E N C E S

• ASTM (1994), Standard Methods of Testing Small Clear Specimens of Timber, D 143 94 W C h h k PA143-94, West Conshohocken, PA

• ASTM (1994), Standard Test Methods for Specific Gravity of Wood and Wood-Based Materials, D 2395-94, West Conshohocken, PAF P d L b (1990) W d E i i H db k 2nd Edi i • Forest Products Laboratory (1990), Wood Engineering Handbook, 2nd Edition, Prentice-Hall, New Jersey.

• Microsoft Corporation (1999), Encarta Encyclopedia, Richmond, WA.S i h R C A d C K (1989) M i l f C i 4th Edi i M G• Smith, R. C., Andres, C. K. (1989), Materials for Construction, 4th Edition, McGraw-Hill, New York, 401 pp.

• Watson, D. A. (1986), Construction Materials and Processes, 3rd Edition, McGraw-Hill, New York 486 ppNew York, 486 pp.

• Wilcox, W. W., Botsai, E. E., Kubler, H. (1991), Wood as a Building Material: A Guide for Designers and Builders, John Wiley & Sons, New York, 215 pp.

• UNEP FAO Global IPM Facility Expert Group (2000) Finding Alternatives to • UNEP, FAO, Global IPM Facility Expert Group (2000), Finding Alternatives to Persistent Organic Pollutants (POPs) for Termite Management, http://www.chem. unep.ch/pops/termites/termite_fulldocument.pdf, 47 pp.

• http://www wikipedia orghttp://www.wikipedia.org• http://www.ccaresearch.org

101

R E C A PR E C A P

• Trees (components of tree, wood cells, growth of wood, hardwood & ( p , , g ,softwood)

• Physical characteristic (defects, moisture & shrinkage, density & specific gravity)

• Timbering (conversion of timber, seasoning)M h l P (b d h l h • Mechanical Properties (bending strength, tensile strength, compressive strength, shear strength)

• Deterioration of wood (fungi termites etc)• Deterioration of wood (fungi, termites, etc)• Wood protections• Other wood products (plywood particle board hardboard)Other wood products (plywood, particle board, hardboard)

102

Documents

27109 Wood