Final Report - Timber 2 (2)

QUT

Timber Practical: Report Flexural Properties of Timber Members

SANDRA LISTER N7457499 ENB273 – Civil Materials

5/6/2011

Investigation into relative performance of various timbers and timber products

SANDRA LISTER N7457499

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Executive Summary

This report presents the results and evaluations of the flexural properties of four types of timber

products, namely softwood, hardwood, chipboard and plywood that are of interest to design

engineers and architects. The aim of this experiment was to gain a more meaningful understanding

of how various types of timber products vary in terms of stress, elastic limits, and resistance to

bending.

The approach taken was the standard three-point flexure test. Included are particulars on visual

strength grading, testing methods, results, calculations and comment on Modulus of Elasticity and

Modulus of Rupture. Furthermore, an investigation into how moisture content influences the

strength of timber, specifically the Modulus of Elasticity and Modulus of Rupture is included.

The overall objectives were met and show that there was a correlation between density and the

Modulus of Elasticity where elasticity generally improved as density increased. Additionally, the

composite materials, chipboard and plywood, engineered for specific structural applications were

found to have elastic and maximum stress values that fell in the scope specified by the Australian

Wood Panels Association. The values for the Modulus of Rupture for all specimens were determined

thus allowing appropriate design for strength in terms of structural application, however direct

comparison was difficult since the beam section dimensions were varied between samples.


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Table of Contents Executive Summary ................................................................................................................................. 1

List of Tables ........................................................................................................................................... 3

List of Figures .......................................................................................................................................... 3

Introduction ............................................................................................................................................ 4

1 Testing Method ............................................................................................................................... 4

1.1 Visual Strength Grading and the Effects of Defects ................................................................ 4

1.2 Three-point Flexure Testing Procedure .................................................................................. 5

2 Results ............................................................................................................................................. 6

3 Load vs. Deflection Graph ............................................................................................................... 6

4 Calculations ..................................................................................................................................... 7

4.1 Density .................................................................................................................................... 7

4.2 Moment of Inertia (mm4) ........................................................................................................ 8

4.3 Modulus of Elasticity ............................................................................................................... 8

4.3.1 Softwood ......................................................................................................................... 8

4.3.2 Hardwood ....................................................................................................................... 9

4.3.3 Chipboard ........................................................................................................................ 9

4.3.4 Plywood ........................................................................................................................... 9

4.4 Modulus of Rupture (MOR) .................................................................................................. 10

4.4.1 Softwood ....................................................................................................................... 10

4.4.2 Hardwood ..................................................................................................................... 11

4.4.3 Chipboard ...................................................................................................................... 11

4.4.4 Plywood ......................................................................................................................... 11

5 Evaluation of Density, Elastic Modulus & Modulus of Rupture .................................................... 11

6 The Effects of Moisture on E and MOR ......................................................................................... 13

7 Applications in Building ................................................................................................................. 14

7.1 Softwood ............................................................................................................................... 14

7.2 Hardwood ............................................................................................................................. 15

7.3 Chipboard .............................................................................................................................. 15

7.4 Plywood ................................................................................................................................. 16

8 Conclusions ................................................................................................................................... 16

9 Works Cited ................................................................................................................................... 17

10 Appendix A - Elastic Constants and Defect Illustrations ........................................................... 18

11 Appendix B – Australian Wood panel Association: Facts about Particleboard and MDF ......... 19


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12 Appendix C – Raw Data ............................................................................................................. 20

List of Tables Table 1: Visual Sample Characteristics .................................................................................................... 4

Table 2: Sample Measurements ............................................................................................................. 6

Table 3: Load Deflection Characteristics ................................................................................................. 6

Table 4: Sample Densities ....................................................................................................................... 7

Table 5: Moments of Inertia ................................................................................................................... 8

Table 6: Engineering Characteristics Summary ..................................................................................... 11

List of Figures Figure 1: Illustration of Three Point flexure Test .................................................................................... 5

Figure 2: Plot of Load vs. Deflection for all Samples ............................................................................... 7


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Introduction

Timber from well-managed forest plantations is one of the most sustainable building resources

available. It has a high to strength to weight ratio and is capable of transferring both tensile and

compressive forces and therefore, as might be expected, is highly suitable as a flexural member

(Porteous and Kermani 2007). There are a number of other distinctive characteristics that make

timber an ideal construction material, these being its durability and insulating properties against

heat and sound as well as its natural growth characteristics such as grain patterns and availability in

many species, sizes and shapes that render it an extraordinarily versatile material (Porteous and

Kermani 2007).

This report provides an account of the engineering properties of four types of timber products,

namely; softwood, hardwood, chipboard and plywood that are of interest to design engineers and

architects. Included are particulars on visual strength grading, testing methods, results, calculations

and comment on Modulus of Elasticity (E) and Modulus of Rupture (MOR). Furthermore, the report

will consider how moisture content influences the strength of timber, specifically the Modulus of

Elasticity (E) and Modulus of Rupture (MOR).

1 Testing Method

1.1 Visual Strength Grading and the Effects of Defects

This form of grading is a manual process whereby a sample is inspected visually, since this process

involves experience and personal judgment, the results are inherently subjective. Four samples of

were examined, each piece to inspect the size and frequency of specific physical characteristics or

defects such as knots, slope of grain, wane, shakes and distortion, bending or twisting. The results

are shown in the table 1.

Table 1: Visual Sample Characteristics

Sample Visual Analysis

Softwood Edge Grain with one knot, no other defects present

Hardwood Edge Grain, no visual defects present

Chipboard Visible particles, no visual defects present

Plywood Layered appearance ( 3 layers), no visual defects present

The slope of the grain is critical when grading timber products as it can affect the strength properties of the wood as well as the type of warping which may occur under certain conditions. For instance boards with a straight or edge grain, as in the case of the above softwood and hardwood, where the board has been cut so that the fibres run up and down the length of the board will result in the greatest strength. In contrast, cross grain boards, will result in the least wood strength (Singh 2007).


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A knot, a portion of a branch enclosed by the natural growth of the tree (Porteous and Kermani

2007), found on the softwood may have had adverse effects on the mechanical properties of the

timber sample since knots alter the fibers surrounding them, causing discontinuity and stress

concentrations or non-uniform stress distributions (Mamlouk and Zaniewski 2011). Their effects are

further magnified in members subjected to tensile stress. The presence of the knot on the lower side

of a member, being subjected to tensile stresses, has a greater effect on the load capacity of the

member than a similar knot on the upper side being subjected to compressive stresses (Porteous

and Kermani 2007).

Other defects include cracks, fissures, decay and wanes, all natural defects, none of which were

present in any of the test samples. The effect of a wane is a reduction in the cross-sectional area

resulting in reduced strength properties due to a reduced second moment of Area (Kermani 1999).

Further defects may be possible from uneven drying during the seasoning process and may result in

splitting or cupping (Porteous and Kermani 2007).

1.2 Three-point Flexure Testing Procedure

For each of the four timber specimens provided, softwood, hardwood, plywood and chipboard, the

cross section dimensions, length and mass were recorded. The test span, distance between the

supports, was also recorded. Each test specimen, in turn, was placed in the testing rig and a dial

gauge placed beneath the load point of the sample, ensuring it that it just touched the underside of

the sample. The dial gauge was then zeroed, and care was taken to ensure that the loading arm was

not placed on the sample at this time. The loading arm was then placed on the sample and the

corresponding deflection measured. The deflection was again measured in increments of 0.5 kg up

to a maximum of 3.5 kg. After this point the dial gauge was removed and loading continued until

failure. Using these results the Elastic Modulus (E) and Maximum Tensile Stress (or Modulus of

Rupture MOR) for each samples were determined.

Figure 1: Illustration of Three Point flexure Test

Point load

L = 550

Point

load

mm Deflection (mm)

Dial Gauge


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2 Results

Table 2: Sample Measurements

Sample Mass (gm) Length (mm) Width (mm) Depth (mm)

Softwood 65.5 749 19 11 Hardwood 42.5 600 9 9 Chipboard 170.8 750 20 16 Plywood 46.3 701 20 6 Test Span: 550mm

Table 3: Load Deflection Characteristics

Load Deflection (mm)

Load (kg) Newtons Softwood Hardwood Chipboard Plywood 0 0 0 0 0 0 0.5 4.905 1.9 2.76 1.64 9.95 1.0 9.81 2.74 3.92 2.3 14.28 1.5 14.715 3.65 4.96 2.98 18.33 2.0 19.62 4.58 6.05 3.65 22.82 2.5 24.525 5.42 7.11 4.34 26.78 3.0 29.43 6.32 8.09 5.05 31.71 3.5 34.335 7.23 9.16 5.76 36.79 Failure Load 21.5 kg (210.9N) 14.5kg (142.2N) 7.5kg (73.6N) 6kg (58.9N)

3 Load vs. Deflection Graph

The load versus deflection graphs with the line of best fit shown for all timber samples are plotted

below, care was taken to include the 0kg loads and deflections, since these points will affect the

gradient of each plot. The equation of each line of best fit was used to determine the gradient, thus:

𝒚 = 𝒎𝒙 + 𝒄: 𝑠𝑢𝑐 𝑡𝑎𝑡: 𝑚 = 𝑡𝑎𝑛𝜃 =𝐶𝑎𝑛𝑔𝑒 𝑖𝑛 𝐷𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛 (𝑚𝑚)

𝐶𝑎𝑛𝑔𝑒 𝑖𝑛 𝐿𝑜𝑎𝑑 (𝑁)=

𝐿3

48𝐸𝐼


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Figure 2: Plot of Load vs. Deflection for all Samples

4 Calculations

4.1 Density

Table 4: Sample Densities

Sample Mass (gm) Length (cm) Width (cm)

Depth (cm)

Volume (cm^3)

Density (g/cm^3)

Density (kg/m^3)

Softwood 65.5 74.9 1.9 1.1 156.541 0.418420733 418.4207332

Hardwood 42.5 60 0.9 0.9 48.6 0.874485597 874.4855967

Chipboard 170.8 75 2 1.6 240 0.711666667 711.6666667

Plywood 46.3 70.1 2 0.6 84.12 0.550404184 550.4041845

y = 0.2218x

y = 0.2882x

y = 0.1778x

y = 1.1162x

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40

De

fle

ctio

n (

mm

)

Load (N)

Softwood

Hardwood

Chipboard

Plywood

Linear (Softwood )

Linear (Hardwood )

Linear (Chipboard )

Linear (Plywood)


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4.2 Moment of Inertia (mm4)

𝑰 = 𝒃𝒅𝟑

𝟏𝟐

Where: I = Moment of Inertia (mm4)

B = Breadth (mm) D = Depth (mm)

Table 5: Moments of Inertia

Sample Depth (mm) Breadth (mm) I (mm4)

Softwood 11.00 19.00 2107.42

Hardwood 9.00 9.00 546.75

Chipboard 16.00 20.00 6826.67

Plywood 6.00 20.00 360.00

4.3 Modulus of Elasticity

4.3.1 Softwood

𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑙𝑖𝑛𝑒 𝑜𝑓 𝑏𝑒𝑠𝑡 𝑓𝑖𝑡: 𝑦 = 𝑚𝑥 + 𝑐

𝑦 = 0.2218𝑥 + 0

𝑚 = 0.2218 = 𝑡𝑎𝑛𝜃

𝑇𝑎𝑛𝜃 = 𝐶𝑎𝑛𝑔𝑒 𝑖𝑛 𝐷𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛 (𝑚𝑚)


𝐿3

48𝐸𝐼

𝑚 =𝐿3

48𝐸𝐼

0.2218 =5503

48𝐸(2107.42)

𝐸 =5503

48 0.2218 (2107.42)

𝑬 = 𝟕𝟒𝟏𝟓.𝟑𝟗 𝑴𝑷𝒂


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4.3.2 Hardwood


𝑦 = 0.2882𝑥 + 0

𝑚 = 0.2882 = 𝑡𝑎𝑛𝜃



𝐿3

48𝐸𝐼

𝑚 =𝐿3

48𝐸𝐼

0.2882 =5503

48𝐸(546.75)

𝐸 =5503

48 0.2882 (546.75)

𝑬 = 𝟐𝟏𝟗𝟗𝟕 𝑴𝑷𝒂

4.3.3 Chipboard


𝑦 = 0.1778𝑥 + 0

𝑚 = 0.1778 = 𝑡𝑎𝑛𝜃



𝐿3

48𝐸𝐼

𝑚 =𝐿3

48𝐸𝐼

0.1778 =5503

48𝐸(6826.67)

𝐸 =5503

48 0.1778 (6826.67)

𝑬 = 𝟐𝟖𝟓𝟓.𝟔𝟔 𝑴𝑷𝒂

4.3.4 Plywood



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𝑦 = 1.1162𝑥 + 0

𝑚 = 1.1162 = 𝑡𝑎𝑛𝜃



𝐿3

48𝐸𝐼

𝑚 =𝐿3

48𝐸𝐼

1.1162 =5503

48𝐸(360)

𝐸 =5503

48 1.1162 (360)

𝑬 = 𝟖𝟔𝟐𝟓.𝟖𝟔𝑴𝑷𝒂

4.4 Modulus of Rupture (MOR)

Load at Failure Softwood Hardwood Chipboard Plywood

21.5 kg (210.9N) 14.5kg (142.2N) 7.5kg (73.6N) 6kg (58.9N)

** Plywood sample did not rupture; deflection became too great for further consideration and thus was deemed to have failed.

𝑀𝑂𝑅 =𝑀𝑦

𝐼

Where: M = Bending Moment at Failure = PL/4 Y=Distance from Neutral Axis to extreme fibres = d/2 P = Load at Failure I= Moment of Inertia

4.4.1 Softwood

𝑀𝑂𝑅 =

211 ∗ 5504 ∗

112

2107

𝑴𝑶𝑹 = 𝟕𝟓. 𝟕 𝑴𝑷𝒂


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4.4.2 Hardwood

𝑀𝑂𝑅 =

142 ∗ 5504 ∗

92

547

𝑴𝑶𝑹 = 𝟏𝟔𝟎. 𝟔 𝑴𝑷𝒂

4.4.3 Chipboard

𝑀𝑂𝑅 =

74 ∗ 5504

∗162

6827

𝑴𝑶𝑹 = 𝟏𝟏. 𝟗 𝑴𝑷𝒂

4.4.4 Plywood

𝑀𝑂𝑅 =

59 ∗ 5504 ∗

62

360

𝑴𝑶𝑹 = 𝟔𝟕. 𝟔 𝑴𝑷𝒂

5 Evaluation of Density, Elastic Modulus & Modulus of Rupture

Abdy Kermani, in his book, ‘Structural Timber Design, 1999’ states that density is the best indicator

when determining a timbers material properties. Such properties may include strength, stiffness,

and hardness, ease of machining, fire resistance and drying characteristics. On average,

hardwood is of higher density than softwood, but there can be considerable variation in actual

density in both classifications (National Association of Forest Industries 2004). A summary of the

flexural characteristics of the four test samples is shown below in Table 6.

Table 6: Engineering Characteristics Summary

Sample Density (gm/cm^3)

Moment of Inertia (mm^4)

Elastic Modulus (MPa)

Modulus of Rupture (Mpa)

E/ ρ Mpa/(kg/m^3)

MOR/ρ Mpa/(kg/m^3)

Softwood 0.418 2107.42 7415.39 75.7 17.74 0.181 Hardwood 0.874 546.75 21997 160.6 25.17 0.183 Chipboard 0.712 6826.67 2855.66 11.9 4.01 0.017 Plywood 0.550 360.00 8625.86 67.6** 15.68 0.122 ** Plywood sample did not rupture; deflection became too great for further consideration and thus was deemed to have failed.

http://www.diffen.com/difference/Than_vs_Then


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The presence of moisture in timber not only increases the mass of the timber, but it also results in

the swelling of the timber, and hence both mass and volume are affected. Thus, in the

determination of density both the mass and volume must be determined at the same moisture

content (Dinwoodie 2000).

As can be observed from Table 6, the softwood possesses the lowest density, hardwood the highest

with chipboard and plywood lying between. The physical substance that makes up the cell walls has

a basic density of approximately 1500 kg/m3 (Dinwoodie 2000). However, as timber comprises both

wood substance and voids, such as the central cavities in cells, density can vary considerably due to

the cell structure between softwoods, hardwoods, different species and different trees within the

same species. Since softwoods are generally faster growing, have higher moisture content and

thinner cell walls, they are generally less dense when compared to hardwoods at the standard

moisture content of 12 percent which is often referred to as the air-dry density (National Association

of Forest Industries 2004).

The Elastic modulus of the softwood sample at 7415 MPa is almost three times less than the

hardwood at 21997 MPa. A study on ‘Estimation of Basic Density and Modulus of Elasticity of

Eucalypt Clones in Southern China,2010’ by S.J Wu et al, found that the correlation between basic

density and the Modulus of Elasticity was significantly positive, in line with the results of this

investigation where elasticity is increasing with density, disregarding plywood and chipboard which

are composite materials. The Modulus of Rupture of the hardwood was significantly greater than all

other specimens, while the softwood was similar to the plywood. The modulus of Rupture depends

on the beam section properties and the arrangement of loading. Given that all specimens were

loaded in the same manner but the section dimensions were varied, in this case it is difficult to give a

straightforward comparison.

The density of the Chipboard sample is relatively high as compared to the plywood and the

softwood. Chipboard is a manufactured timber product whereby wood particles are coated with a

resin, then formed into a mat and pressed to produce a board of particular thickness. Chipboard is

available in a range of densities which depend on type and size of wood particles used, ratio of wood

particles to amount of resin and the amount of pressure used to reduce voids. Different types of

boards with different engineering properties can be formed in this way (Australian Wood Panels

Association Incorporated 2008). The Modulus of Rupture (MOR) is relatively low at 11.9 MPa and is

close to the standard particleboard MOR as per the Australian Wood panel Association’s range for

boards of this thickness at 15 MPa, refer to Appendix B. The chipboard in this case is not high

performance and should not be used for structural applications such as flooring which requires a

depth of at least 19mm and a MOR of 24 MPa. Comparatively, the Modulus of Elasticity is low at

2855 MPa, which implies that the material will reach plastic deformation relatively quickly. Since the

elastic modulus is an inherent material property, it will vary with the quality and quantity of

ingredients used in manufacture.

Plywood is made from thinly sliced wood veneers glued together to form a board of desired

thickness. The grain direction is alternated layer by layer so that the sheet has similar areas of grain

in the direction of the width of the sheet and the length of the sheet (Forest & Wood Products

Australia 2007). Therefore, plywood has properties that are relatively the same in both directions

with regard to the plane of the sheet. Since only thin slices of timber are used in the manufacture of


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this product, the size and influence of any natural characteristic is limited to the thickness of the

veneer. Structural properties of plywood tend to have less variability than those for sawn timber

meaning that the mechanical properties are generally higher than the properties of the pure timber

from which it was made (Forest & Wood Products Australia 2007). In terms of this experiment, the

Elastic modulus and Modulus of Rupture is comparable to that of the softwood, meaning that it may

have been manufactured from timber of lesser quality than the softwood but the manner of

construction has rendered the product more stable and robust. It is important to note however, that

the plywood specimen did not actually rupture at the ultimate load stated, deflection was excessive

and was not longer able to be measured, and consequently specimen was deemed to have failed at

this point.

The Elastic modulus per unit density and Modulus of Rupture per unit density as shown in Table 6,

may be useful in comparing the material flexural properties per unit mass of a certain volume, and

thus can be used to compare wood products with other materials such as Steel and Concrete.

Relating these values obtained from the experiment to table 14.7 shown in Appendix A, we can see

that the softwood and hardwood are approximately in the range specified.

6 The Effects of Moisture on E and MOR

Timber properties, unlike other structural materials such as steel or concrete, are very sensitive to

environmental conditions. For instance, timber is very sensitive to moisture content, which has a

direct effect on the strength, stiffness and swelling or shrinkage and resistance to decay (Kermani

1999). Most timber is air dried or kiln dried to a moisture content of approximately 12% which is

below fiber saturation point meaning that the cell walls are still saturated but moisture is removed

from within the cells. Further reduction in moisture content will result in shrinkage, the amount of

shrinkage pertaining to the particular species (Kermani 1999).

Figure 3: General relationship between strength & moisture content

Kermani. A, 1999, Structural Timber Design, Chapter 1, Page 8


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Figure 3, shows the general relationship between strength of timber and its moisture content.

Illustrating that there is an almost linear loss in strength and stiffness as moisture increases to

approximately 30% which is consistent with the fiber saturation point (Kermani 1999). Any further

increase in moisture content has no influence on strength. In terms of physical properties, it must be

noted that as moisture content decreases shrinkage will increase.

Seasoning is a controlled process whereby the moisture content of the timber is reduced so that it is

suitable for the intended use. Seasoning defects are directly related to the movements which occur

in timber due to changes in moisture content such as excessive or uneven drying, as well as other

factors like exposure to wind and rain. Uneven drying can be caused by inferior stacking during the

seasoning process and these can all produce defects in timber which ultimately reduce the strength

(Porteous and Kermani 2007). However, interestingly, the level of moisture content has almost no

effect on the tensile strength parallel to the grain. This strength property is determined by the

strength of the covalent bonding on the molecular level. Additionally the relationship between

moisture content and strength may not apply when the timber contains major defects as is the case

with structural size timber for example, it has been shown that the effect of moisture content on

strength decreases as the size of knots increase (Dinwoodie 2000)

Timber is hygroscopic meaning that it attempts to attain equilibrium moisture content with its

surrounding environment, resulting in variable moisture content. This property should always be

considered when using timber, particularly softwoods which are more porous and thus more

vulnerable to shrinkage and expansion than hardwoods (Kermani 1999). The strength of timber is a

function of several parameters including the species type, density, size and form of members and

presence of various strength reducing characteristics such as slope of grain, knots, fissures and

wane. Since moisture content can affect some of these properties it will in turn affect the strength

properties (Porteous and Kermani 2007).

The Elastic Modulus will also deceases with increased moisture content. This variation takes place

until the moisture content reaches the Fiber Saturation Point, which is around 30% for most species

as shown in figure 3. It must be noted that the influence of the moisture content over the Modulus

of Elasticity is not very significant (Dinwoodie 2000).

7 Applications in Building

7.1 Softwood

When compared to hardwoods, plantation softwood timber is less variable and thus, more

predictable as a raw material. It also provides larger yields of usable timber in a shorter timeframe.

Softwood dries quickly, is easily machine-processed, forms strong gluing bonds and is easy to treat

with preservatives for uses where durability is important (Willmott forests Limited 2011).

These properties make softwood extremely versatile, due it good strength to weight properties is

suitable for many applications such as, structural sawn timber, laminated beams and veneer lumber,

Pine poles, piles and fence posts and landscaping uses such as retaining walls. Its light colour, even

texture and low resin content also make it suitable for wood panels, such as Medium density


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fiberboard (MDF) as well as wide range of Pulp and Paper products. Residues of wood chips,

shavings and sawdust from the production of solid wood products are also a good source for these

products (Willmott forests Limited 2011).

7.2 Hardwood

Different species of hardwood afford themselves to a varied range of uses mainly due to the variety

of characteristics apparent in different timbers including, density, grain, pore size, growth pattern,

wood fiber pattern and flexibility. Hardwood with good strength characteristics lends itself to

structural applications where strength is a critical factor such as bearers, joists, lintels and roof

beams (Timber Development Association 2011).

Other suitable structural applications for some hardwoods may be small temporary bridges, wharf

timber or timber for use in wet conditions given that it is generally less porous than soft woods.

Additional uses for hardwoods may be pre-assembled trusses and frames for large structures and

other smaller objects such as furniture and musical instruments. Timbers for structural applications

where large loads may occur would need to be specially selected and well graded (Timber

Development Association 2011).

7.3 Chipboard

The Australian Standard AS/NZS 1859.1-2004 describes three types of Chipboard otherwise known

as particleboard, and each is engineered for specific structural applications.

Standard general purpose particleboard intended for internal use in dry conditions, such as in the

construction of furniture, cupboards and shelving. Moisture resistant general purpose particleboard

is intended for internal where humid conditions are present or where occasional wetting may occur.

It is however, not moisture proof and should not be used where there is persistent wetting the

particleboard is likely to degrade via adhesive failure and is prone to fungal attack. Continued

Exposure of particleboard to the weathering will have an effect on its internal bonding strength and

stiffness (Australian Wood Panels Association Incorporated 2008). High Performance particleboard is

engineered for use in continuously humid conditions and load bearing applications in dry and humid

conditions.

Chipboard can also used for flooring; there are two classes in this case, specifically Class 1 and Class

2 Flooring Board. Class 1 is stronger and is used for most internal flooring and is manufactured with

an adhesive which does not deteriorate in the presence of moisture. Class 2 is only suitable indoors

where there is no risk of dampness such as upper storey floors (Timber Development Association

2011).


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7.4 Plywood

Plywood is designed to have high strength and stiffness to weight ratios which renders it suitable for

installation very cost effective in applications such as residential and commercial flooring, shear-

walls and diaphragms, formwork and webbed beams (Forest & Wood Products Australia 2007). The

cross-laminated construction of plywood ensures that sheet sizes remain relatively stable under

changes of temperature and moisture, making it particularly suited to formwork applications. The

shear strength, approximately double that of solid timber due to its cross laminated structure,

makes it suitable for use in gussets for portal frames, webs of fabricated beams and thin plywood

bracing panels (Forest & Wood Products Australia 2007).

Plywood, as with most timber products, has the ability to accommodate the occasional short term

load up to twice the design load. This property is beneficial for applications such as loading docks

where short term vehicle impact can be expected or in buildings subject to seismic activity or

cyclonic winds. Plywood may also be utilized as interior panelling; decorative plywoods are

frequently used as internally for their aesthetic value (Forest & Wood Products Australia 2007).

8 Conclusions

This report has provided an account of the flexural properties of four types of timber products,

namely; softwood, hardwood, chipboard and plywood that are of interest in terms of structural

design. It was found that the softwood had the lowest density, hardwood the highest with

chipboard and plywood lying between.

The test and research demonstrated that there was a correlation between density and the Modulus

of Elasticity where elasticity generally improved as density increased. The composite materials, the

chipboard and plywood, engineered for specific structural applications were found to have elastic

and maximum stress values that fell in the scope specified by the Australian Wood Panels

Association.

The values for the Modulus of Rupture for all specimens were determined thus allowing appropriate

design for strength in terms of structural application, however direct comparison was difficult in this

case since the beam section dimensions were varied. An overview of the effects of defects on

Strength and structural applications for all specimens as well as brief outline visual grading and

effects of Moisture of timber was also incorporated.


17

9 Works Cited Australian Wood Panels Association Incorporated. Facts about Particleboard and MDF. Coolangatta:

Australian Wood Panels Association Incorporated, 2008.

Dinwoodie, J M. Timber Its Nature and Behaviour. New York: Spon Press, 2000.

Forest & Wood Products Australia. “Plywood.” Timber.org.au. 2007.

http://www.timber.org.au/ntep/menu.asp?id=104 (accessed May 13, 2011).

Kermani, Abdy. Structural Timber Design. Oxford: Blackwell Publishing , 1999.

Mamlouk, Michael S, and John P Zaniewski. Materials for Civil and Construction Engineers. New

Jersey: Pearson, 2011.

McKenzie, William M C, and Binsheng Zhang. Design of Structural Timber to Eurocode 5. New York:

Palgrave Macmillan, 2007.

National Association of Forest Industries. Timber Species and Properties: Timber Manual Datafile 1.

Sydney: National Association of Forest Industries, 2004.

Porteous, Jack, and Abdy Kermani. Structural Timber Design to Eurocode, 5. Oxford: Blackwell

Publishing, 2007.

Singh, Harbhajan. Design of Masonry and Timber Structure. Chandigarh: Abhishek Publications, 2007.

Timber Development Association. “Structural Timber.” Timber.net.au. 2011.

http://www.timber.net.au/index.php/Structural-Timber.html (accessed May 13, 2011).

Willmott forests Limited. “About the Softwood Industry.” Willmott Forests. 2011.

http://www.willmottforests.com.au/default.asp?id=about_the_softwood_industry (accessed May

13, 2011).


18

10 Appendix A - Elastic Constants and Defect Illustrations


19

11 Appendix B – Australian Wood panel Association: Facts about

Particleboard and MDF


20

12 Appendix C – Raw Data

Sample Mass (gm) Length (mm) Width (mm) Depth (mm)

Softwood 65.5 749 19 11

Hardwood 42.5 600 9 9

Chipboard 170.8 750 20 16

Plywood 46.3 701 20 6

Test Span: 550mm

Load Deflection (mm)

Load (kg) Newtons Softwood Hardwood Chipboard Plywood

0 0 0 0 0 0

0.5 4.905 1.9 2.76 1.64 9.95

1.0 9.81 2.74 3.92 2.3 14.28

1.5 14.715 3.65 4.96 2.98 18.33

2.0 19.62 4.58 6.05 3.65 22.82

2.5 24.525 5.42 7.11 4.34 26.78

3.0 29.43 6.32 8.09 5.05 31.71

3.5 34.335 7.23 9.16 5.76 36.79

Failure Load 21.5 kg (210.9N)

14.5kg (142.2N) 7.5kg (73.6N) 6kg (58.9N)

Documents

Final Report - Timber 2 (2)