Lect 10 - Wood and Composites

09/10/2011

48352/S2011/L10/RS 1

Construction Materials

Wood and Composites

Lecture 10

Dr Rijun Shrestha

09/10/2011 48352 L10 Spring Semester 2011 1

[email protected]

Contents Wood Numerical problems Break Wood (contd.) Composites

48352 L10 Spring Semester 2011 209/10/2011

09/10/2011

48352/S2011/L10/RS 2

Wood and Composites (Part 1)

Wood


Application of wood Internal / External

09/10/2011 448352 L10 Spring Semester 2011

09/10/2011

48352/S2011/L10/RS 3

Application of wood (contd.) Decorative / Structural


Application of wood (contd.) Domestic Large-Span structures


09/10/2011

48352/S2011/L10/RS 4

Application of wood (contd.) Commercial Bridges


Advantages Light weight Hi h t th t i ht ti High strength to weight ratio Aesthetic value Good insulation characteristic Environmental benefits Naturally produced material - renewable Untreated wood – completely biodegradable Less energy to produce compared to steel,

concrete, aluminium, plastics. Stores carbon


09/10/2011

48352/S2011/L10/RS 5

Wood used in different forms

Sawn Timber6

Engineered Wood Products (EWPs) Plywood Laminated Veneer Lumber (LVL) Glue Laminated Timber (Glulam) Cross Laminated Timber (CLT) Particle board

5

Oriented Strand Board (OSB), etc

1 23

4


Structure of wood - cell Plant cell – composed to three main chemicals

Cellulose Cellulose network of molecules fibrous

Lignin a gel type substance - “woody” property Bonds various cells together

Hemicellulose

48352 L10 Spring Semester 2011 10

Hemicellulose cross linking - binds cellulose into the cell

Spirally wound fibres

Straightfibres

09/10/2011

09/10/2011

48352/S2011/L10/RS 6

Structure of wood – cell structure

fib res

v e sse ls

e arly w o o d

ra y s

ra y s

ra y s

ce lls

h a rd w o o d

y

la te w o o d

so ftw o o d


Vessels only in hardwoods– distinguishing structural feature between hardwood and softwood

Hardwood – birch, maple, oak - flowering Softwood – pine, spruce, fir – non-flowering

09/10/2011

Structure of wood – cell structure

Wood cells formed between b k d dbark and wood Inner side – new cells

added to Xylem (woody tissue transporting nutrients ad water)

Outer side – new cells


added to Phloem (bark like tissue transporting food materials)

09/10/2011

09/10/2011

48352/S2011/L10/RS 7

Structure of wood Sapwood and Heartwood

H t d HeartwoodProvides structural supportCells become blocked with depositsDifficult to impregnate with preservative

SapwoodYounger outermost wood


Conducts water and stores foodMore susceptible to fungal and insect attack due to

presence of starchesEasy to impregnate with preservatives

09/10/2011

Structure of wood Earlywood and Latewood EarlywoodProduced in flush of growth “springwood”Large diameter, short length, thinner wall

fibres

Latewood


LatewoodProduced later in growing season

“summerwood”Better strength characteristics

09/10/2011

09/10/2011

48352/S2011/L10/RS 8

Mechanical properties

Different properties in three different directionsp p Orthotropic Longitudinal, Transverse, andRadial

Longitudinal


Radial

Tangential

09/10/2011

Strong parallel to grain & Stiff parallel to grain


Weak perpendicular to grain

09/10/2011

09/10/2011

48352/S2011/L10/RS 9

Mechanical properties AS 4063.1 – 2010 Modulus of Rupture Modulus of Elasticity


Mechanical properties (2) Tensile strength parallel to the grain Tensile strength perpendicular to the grain


09/10/2011

48352/S2011/L10/RS 10

Mechanical properties (3) Compressive strength parallel to the grain Compressive strength perpendicular to the

grain


Mechanical properties (4) Shear strength parallel to the grain Shear strength perpendicular to the grain


09/10/2011

48352/S2011/L10/RS 11

Mechanical properties (5)

Cleavage strength – resistance to force acting perp. to grain and tending to split a member

Impact strength – energy needed to break a specimen

Hardness – resistance against wear and marking


g

09/10/2011

Factors affecting mechanical properties

Species Position in tree Age of tree Climatic conditions Density Brittleheart Rate of growth Late wood

Temperature Load duration Defects Moisture content


Late wood

09/10/2011

09/10/2011

48352/S2011/L10/RS 12

Factors affecting mechanical properties (1)

DensityDenser species – better mechanical propertiesDenser species - hard to dryDensity within a species - affected by factors

such as growth defects



Brittleheart d th h t f th t wood near the heart of the tree - core high compressive forces during early growth stages

low impact or shock resistance


09/10/2011

48352/S2011/L10/RS 13


Rate of growthSpecies with medium rate of growth have

better strength characteristics compared to slow and fast growth material



Percentage of latewood thicker walled cells in wood formed in late

growing season denser and stronger than the ones formed in

the early growing season


09/10/2011

48352/S2011/L10/RS 14


Position in tree Timber from bottom logs are sightly denser Therefore, stronger



TemperatureHigher temperature lowers the strength

propertiesRelated to moisture content Temperature change affects the relative

humidity - affects the moisture content Generally – reversible


Generally reversible Prolonged exposure above 90 degrees C,

however, irreversible

09/10/2011

09/10/2011

48352/S2011/L10/RS 15


Duration of load Ti b d l d ti l d Timber creeps under long duration load Incremental deformation under constant

load Amount and rate of creep depends upon Moisture migrationAmbient conditions (temperature, RH)


Member size Creep deformation in green timber is more

significant than seasoned timber under constant humidity

09/10/2011


Defects K t Knots Grain distortion Decay Insect attack

Discussed later


09/10/2011

48352/S2011/L10/RS 16

Moisture Content

in wood water ofWeight CM E d %

Strength normally increases as wood dries Modulus of rupture and compressive

strength parallel to grain - increase by 70-100% at 12% m c

woodof dry weightoven . CM Expressed as %


100% at 12% m.c. However, M.C has reverse effect on impact

resistance. Checks, splits and honeycombing

09/10/2011

Moisture in Wood Cells100% Growing

tree

Unseasoned timber

free water

25% bound waterPartially

removed bound waterSeasoned

timber15%

fibre saturationPartially seasoned

timber


09/10/2011

48352/S2011/L10/RS 17

Moisture content and Shrinkage Moisture in two forms

Bound water cell walls Bound water – cell walls Free water – cell cavities

Fibre saturation point Level of moisture content when the cell walls are fully

saturated and there is not moisture in the cell cavities Varies between 21 and 32% 30% for engineering calculations


g g Shrinkage/swelling below FSP

09/10/2011

Shrinkage and Swelling Change in moisture content beyond FSP has no effect

on shrinkage and swellingon shrinkage and swelling Only when the moisture content is below FSP, wood

shrinks/swells with change in moisture content Different rates in longitudinal, radial and tangential

direction

67

89

g ra

te %

Tangential


01

234

56

0 5 10 15 20 25 30

Moisture Content %

Shr

inka

ge/s

wel

ling

Longitudinal

Radial

Tangential

09/10/2011

09/10/2011

48352/S2011/L10/RS 18

Numerical ProblemA wood sample weighing 412.5g was weighed and then oven dried at 103C till a constant weight was reached If the moisture at 103C till a constant weight was reached. If the moisture content was calculated to be 22.75%, find the weight of the oven dried sample.Answer 336.05 g


Numerical ProblemA 300 mm wide radiata pine plank is cut out such that the width is

in the tangential direction of the annual rings Calculate the in the tangential direction of the annual rings. Calculate the width of the plank if the moisture content changes from 35% to 15%.

The tangential shrinkage/swelling rate for radiata pine is known to be 9% when its moisture content is varied from fibre saturation point to oven dried state. The fibre saturation point for radiate pine is 27%.


(Answer = 288 mm)

09/10/2011

09/10/2011

48352/S2011/L10/RS 19

Production Sawing Seasoning Surfacing Grading Preservative treatment


Production (1) Sawing Different types of saws can be used Circular Frame Band


09/10/2011

48352/S2011/L10/RS 20

Production (2) Seasoning-process to remove water from

dwood Kiln drying Air drying Other – Chemical, microwave


Reason for drying Dimensional stability in service condition Strength Drying facilitates preservative treatment Prevention from decaying and insects Reduced weight – easier transportation


09/10/2011

48352/S2011/L10/RS 21

Production (3) Surfacing To achieve plain wood surface Better results when done after seasoning


Production (4) Grading Visual stress grading Machine stress grading Proof grading


09/10/2011

48352/S2011/L10/RS 22

Production (5) Preservative treatment Water-borne preservatives Light organic solvent-borne preservatives Oil-borne preservatives


Defects in wood (1) Knots – remnants of branches captured by

i t kgrowing trunk


09/10/2011

48352/S2011/L10/RS 23

Defects in wood (2) Grain distortion

Construction Materials Lecture 12 4509/10/2011 4548352 L10 Spring Semester 2011

Defects in wood (3) Shakes, Checks and splits


09/10/2011

48352/S2011/L10/RS 24

Defects in wood (4) Bark pocket


Defects in wood (5) WarpBowSpring/CrookCup Twist


09/10/2011

48352/S2011/L10/RS 25

Other defects (6) Wane/want – missing pieces from cross-section Reaction wood Pitch/resin pocket

Construction Materials Lecture 12 49

Resin pocket Reaction wood


Defects in wood (7) Organisms that degrade wood

Fungal growth Fungal growth Oxygen Temperature Food Moisture

Insects – beetles, termites, borers Bacteria

Prolonged contact with soil


Prolonged contact with soil Marine organisms

Marine boring organisms

09/10/2011

09/10/2011

48352/S2011/L10/RS 26

Wood and Composites (Part 2)

Composites


What are Composites? Two or more materials combined Property is a function of constituents Superior properties compared to constituentsStiffnessStrengthDensityCorrosion resistance


Corrosion resistance Fatigue life Insulation and thermal resistance

09/10/2011

09/10/2011

48352/S2011/L10/RS 27

Composites Constituent materials have different properties Alloys – not compositesSimilar properties for constituents

Examples – Fibre Reinforced Polymers (FRP)ConcreteReinforced Concrete


Reinforced Concrete Engineered Wood Products

09/10/2011

Composites - examples Fibre Reinforced Polymers (FRP) Fib Fibres Carbon Glass Aramid Nylon Silicone


Polymer Epoxy Polyurethanes

09/10/2011

09/10/2011

48352/S2011/L10/RS 28

Composites - examples Concrete Cement Aggregate Sand Admixtures


Composites - examples Reinforced Concrete Concrete Reinforcement Bars


09/10/2011

48352/S2011/L10/RS 29

Composites - examples Engineered Wood Products Timber Glue Reinforcement


Application – FRP for strengthening

48352 L10 Spring Semester 2011 58Source: Taljsten (2003)

09/10/2011

09/10/2011

48352/S2011/L10/RS 30

Application - FRP for Strengthening


Strengthening of a reinforced masonry archSource: International Institute for FRP in Construction

FRP Photo Competition '05:http://www.iifc-hq.org/photocompetition05/

09/10/2011

Application - FRP Reinforcement


Laying Aslan 100 GFRP Rebar: Sierrita de la Cruz Creek Bridge near Amarillo Texas USA Spreading concrete over a grid of

carbon fibre reinforcing barsSource: International Institute for FRP in ConstructionFRP Photo Competition '05:http://www.iifc-hq.org/photocompetition05/

09/10/2011

09/10/2011

48352/S2011/L10/RS 31

Application - All FRP


The Johnson County, Kentucky Swinging Bridge, USA, is 128 m long. It is the

longest FRP bridge superstructure in the world.

FRP cable stayed bridge inJiansu Province, China

Source: International Institute for FRP in ConstructionFRP Photo Competition '05:http://www.iifc-hq.org/photocompetition05/

09/10/2011


h l k d ( k


The Clear Creek Bridge (Kentucky, USA) is 18.3 m (60 ft) long and is the first bridge to use hybrid carbon/glass

FRP pultruded beams.

First Highway-rated All-Composite Bridge in Missouri,

USA (span = 9m)Source: International Institute for FRP in ConstructionFRP Photo Competition '05:http://www.iifc-hq.org/photocompetition05/

09/10/2011

09/10/2011

48352/S2011/L10/RS 32



60-foot RStandard(tm) Modular Composite Utility Pole

FRP handrails

Source: International Institute for FRP in ConstructionFRP Photo Competition '05:http://www.iifc-hq.org/photocompetition05/

09/10/2011

Phases Continuous – Matrix Metal Polymer

Discrete – Fibres, Particles


09/10/2011

48352/S2011/L10/RS 33

Matrix Metal High strength Abrasion resistance High operating temperature Corrosion Weight


Matrix Polymer Low cost Low weight Corrosion resistant Sensitive to temperature UV light Low elastic modulus


Low elastic modulus

09/10/2011

09/10/2011

48352/S2011/L10/RS 34

Composites - Classification Microscopic – fibres, particles m Fibre Reinforced Particle Reinforced

Macroscopic – larger size constituents e.g. aggregate, rebars


Microscopic composites Two phaseContinuous – matrix (polymer, metal)Dispersed – fibres/particles

Property governed by distributed phaseShapeSizeDistribution


DistributionOrientation

09/10/2011

09/10/2011

48352/S2011/L10/RS 35

Fibre reinforced composites Fibres – dispersed phase Fibres main load carrying components Fibres – main load carrying components Matrix – binds fibres in place Fibre types

Carbon Aramid Glass Nylon


Nylon Silicone

Superior properties due to fewer internal defects in fibres

09/10/2011

Important parameters Fibre volume Type of fibre Type of resin Fibre orientation Quality control during manufacturing


09/10/2011

48352/S2011/L10/RS 36

Tensile strength


Tension test set-up Tensile failure of plate

09/10/2011

Particle reinforced composites Particles dispersed through matrix Particle size 0.01 to 0.1 micronMatrix – main load carrying components Particles prevents dislocation of matrix

Particle size > 0.1 micron Load shared by particles and matrix Particles act as fillers


Particles act as fillers

09/10/2011

09/10/2011

48352/S2011/L10/RS 37

Macroscopic composites Concrete

Cement pastep aggregate

Reinforced concrete Cement paste Aggregate Reinforcement bars

EWP Glue Wood

A h lt t


Asphalt concrete Bitumen Aggregate Filler

09/10/2011

Lect 10 - Wood and Composites

Documents

Transcript of Lect 10 - Wood and Composites