under graduate thesis 2015-a comparative study of the compression strength of timber from thinned...

THE COPPERBELT UNIVERSITY

SCHOOL OF NATURAL RESOURCES

DEPARTMENT OF BIOMATERIALS SCIENCE AND TECHNOLOGY

A comparative study of the compression strength of timber from thinned and un-thinned P. kesiya stands.

By

Wankumbu Rabecca Nalungwe

SIN: 12454597

A special project report submitted in partial fulfilment for the award of a Bachelor of Science Degree in Wood Science and Technology

June 2016

A comparative study of the compression strength of timber from thinned and unthinned Pinus kesiya.

DECLARATION

I Wankumbu Rabecca Nalungwe do hereby declare and confirm that this work is my own

work and has not been previously presented or submitted at the Copperbelt University or any

other Institution for similar purposes in addition I strongly declare that the work of others has

been duly acknowledged.

Student………………………. Date…………………………………

(Wankumbu Rabecca Nalungwe)

Supervisor……………………… Date……………………………….

(Mr Fabian Malambo)

AUTHOR: WANKUMBU RABECCA NALUNGWE Page i


ABSTRACT

This paper aims at finding the comparison of the compression strength of unthinned and

thinned P.kesiya parallel to the grain because in structural applications, strength is the most

important factor when selecting which timber to use. Timber that does not meet design

strength requirements is of no use in structural applications. The timber was tested for

compression strength parallel to the grain and the moisture content was determined according

to ASTM D143-94.

Silvicultural interventions carried out during the rotation of a stand of trees have a bearing on

the resulting properties and yield of timber that is obtained at the end of the rotation. One

such intervention is thinning. In forestry, thinning is the term describing the removal of some

trees from a stand to give others more space and resources to grow. Due to a shortage of raw

materials, most saw millers will harvest whatever stands is allocated to them regardless of

whether the trees growing in these stands meet with the quality requirements of sawmilling

and design strength specifications. Hence the study will enlighten the timber users on the

effects of thinned and unthinned stands of P. Kesiya in line with its compression strength

while it is in service as well as during its growth. This will open up other avenues of research

that will be exploited in the future by other researchers and necessary to evaluate more

mechanical strength properties and their impacts on wood. P.kesiya is one of the common

species in use for multipurpose applications in industrial and domestic service and high

strength is required. Resistance to crushing is an important property in parallel to grain.

The main objective of this study is to assess the effect failure to thin has on the strength in

compression of Pinus kesiya timber used in structural applications. Thinning helps in

improving the growth and quality of trees including the quality of timber produced. The

samples were collected and dried at favourable moisture content and were then subjected to a

load for compression strength. The means of the compressive strength of unthinned and

thinned samples parallel to the grain were found to be 43 N/mm2 and 59.2 N/mm2

respectively. Though there is a difference in the compressive strengths, the results still show

that unthinned wood can still be used in situations that suit them best in terms of strength

properties because the difference isn’t much but considered.

The concluded results were based on the compression strengths and means of the

compressive strengths. The results suggest that thinning can produce improvements in the

investigated wood property, although subsequent studies must be better designed to minimise

AUTHOR: WANKUMBU RABECCA NALUNGWE Page ii


some effects and maximise treatment effects. More information is needed about the

investigated specie to determine if fibre length is affected by thinning or if thinning can affect

tensile or shear strengths.

AUTHOR: WANKUMBU RABECCA NALUNGWE Page iii


DEDICATION

I dedicate this paper to my lovely mother and young brother Ms Enala Mwenda and

Emmanuel Silungwe, who helped me reach this far. It wasn’t going to be easy on my own, I

thank you so much for being there for me and I thank God for everything. May Jehovah

continue to bless you.

AUTHOR: WANKUMBU RABECCA NALUNGWE Page iv


ACKNOWLEDGEMENTS

Many thanks go to Jehovah God for seeing me through in all and without HIM, I wouldn’t

have come this far.

To mum Ms Enala Mwenda and brother, Emmanuel Silungwe thank you so much for always

being there for me, the encouragements, assistance and care that was shown to me throughout

the entire time of the research was really helpful, may God bless you.

My sincere thanks go to my supervisor Mr Fabian Malambo for his unfailing guidance that

helped me accomplish the task ensuring that the project was a success. I would also like to

thank Mr Francis Munalula, Mr Chester Kalinda and Benny Lubemba for their help, wisdom,

expertise, encouragements and suggestions. My words can never be enough to express my

appreciation for their invaluable help.

Mr Kamanga and Mr Mushota all thanks to you for the huge assistance that you rendered

upon me all the way from the start of data collection, helping me acquire the raw material to

carry out my experiment and research it wouldn’t have been an easy task.

Special thanks also goes to Ntasimulwa, Lupenga, Taonga and former roommates for the

love, encouragement and support, thank you very much and may God bless you all.

All the lecturers that taught me, thank you so much for the knowledge that you imparted in

me. I really appreciate.

To all my classmates and friends, thank you so much for the support that you gave me. May

Jehovah bless you all.

AUTHOR: WANKUMBU RABECCA NALUNGWE Page v


TABLE OF CONTENTSDECLARATION......................................................................................................................................... i

ABSTRACT.............................................................................................................................................. ii

DEDICATION.......................................................................................................................................... iv

ACKNOWLEDGEMENTS..........................................................................................................................v

TABLE OF CONTENTS............................................................................................................................vi

LIST OF FIGURES..................................................................................................................................viii

LIST OF TABLES...................................................................................................................................... ix

CHAPTER ONE......................................................................................................................................10

1.0 INTRODUCTION.......................................................................................................................11

1.1 BACKGROUND INFORMATION............................................................................................12

1.2 STATEMENT OF THE PROBLEM...........................................................................................13

1.3 OVERALL OBJECTIVE..................................................................................................................13

1.3.1 SPECIFIC OBJECTIVES..........................................................................................................13

1.4 ASSUMPTIONS.......................................................................................................................13

1.5 HYPOTHESES.............................................................................................................................13

1.5.1 NULL HYPOTHESIS...............................................................................................................13

1.5.2 ALTERNATE HYPOTHESIS.....................................................................................................13

1.6 JUSTIFICATION..........................................................................................................................14

1.7 SCOPE AND LIMITATIONS.........................................................................................................14

CHAPTER TWO.....................................................................................................................................15

2.0 LITERATURE REVIEW......................................................................................................................16

2.1 FORESTRY...................................................................................................................................16

2.2 SILVICULTURE............................................................................................................................16

2.3 THINNING..................................................................................................................................16

2.4 IMPORTANCE OF THINNING......................................................................................................18

2.5 STRENGTH OF WOOD................................................................................................................18

2.5.1 COMPRESSIVE STRENGTH.......................................................................................................19

CHAPTER THREE...................................................................................................................................23

3.0 MATERIALS AND METHODS...........................................................................................................24

3.1 STUDY AREA..............................................................................................................................24

3.2 MATERIALS................................................................................................................................24

3.3 FIELD SAMPLING.......................................................................................................................24

3.3.1 Sample preparation............................................................................................................25

AUTHOR: WANKUMBU RABECCA NALUNGWE Page vi


3.4 DRYING AND SAMPLE PREPARATION.........................................................................................28

3.4.1 Compression parallel to the grain.......................................................................................28

3.5 RESEARCH DESIGN.....................................................................................................................30

3.5.1 PROCEDURE........................................................................................................................30

3.6 DATA ANALYSIS...................................................................................................................31

CHAPTER FOUR....................................................................................................................................32

4.0 DATA ANALYSIS AND RESULTS.......................................................................................................33

4.1 INTRODUCTION.........................................................................................................................33

4.2 MOISTURE CONTENT.................................................................................................................33

4.3 COMPRESSION PARALLEL TO THE GRAIN:................................................................................35

4.3.1 ANALYSIS:............................................................................................................................37

4.4 DISCUSSION...............................................................................................................................44

CHAPTER FIVE......................................................................................................................................45

5.0 CONCLUSION AND RECOMMENDATION........................................................................................46

5.1 CONCLUSION.............................................................................................................................46

5.2 RECOMMENDATIONS................................................................................................................46

REFERENCES........................................................................................................................................47

APPENDICES.........................................................................................................................................49

AUTHOR: WANKUMBU RABECCA NALUNGWE Page vii


LIST OF FIGURES

Figure 1 Compression parallel to the grain..........................................................................................21Figure 2 Piece of wood of Pinus kesiya under the compressive strength test......................................21Figure 3 shows the 60 x 60 square sawing sections of the bolt (ASTM D 5536 – 94).........................25Figure 4 A sketch showing the markings on a roller............................................................................25Figure 5 Quarter sawn pieces of 55mm x 55mm x 1.2m stacked and air dried....................................26Figure 6 Randomly selected pieces of timber......................................................................................26Figure 7 Measuring of timber pieces and marked to required lengths.................................................27Figure 8 Manual hydraulic compressive test machine.........................................................................29Figure 9 Samples after loading to failure.............................................................................................29Figure 10 Variations of compressive strengths of unthinned and thinned samples..............................39Figure 11 Histogram of samples from thinned stand...........................................................................41Figure 12 Pie Chart of Thinned...........................................................................................................42Figure 13 Histogram of Unthinned samples........................................................................................42Figure 14 Pie Chart of Unthinned samples..........................................................................................43

AUTHOR: WANKUMBU RABECCA NALUNGWE Page viii


LIST OF TABLESTable 1 Determination of moisture content (MC) for thinned samples of Pinus kesiya.......................34

Table 2 Shows the moisture content (MC) for unthinned samples of Pinus kesiya.............................35

Table 3 Force at peak of thinned samples (N).....................................................................................36

Table 4 Compressive strength results for each thinned sample tested.................................................37

Table 5 Compressive strength results for each unthinned sample tested..............................................38

AUTHOR: WANKUMBU RABECCA NALUNGWE Page ix

CHAPTER ONE


1.0 INTRODUCTION

Man has been using timber as a structural building material for millennia and is still using it

today. This is because few building materials possess the environmental benefits of wood.

Wood is not only the most widely used building material but also one with characteristics that

make it suitable for a wide range of applications (Falk, 2010). Timber's superior strength

qualities provide a versatile and reliable building material for a wide range of structural

applications - from beams, walls and flooring through to formwork and large timber panels.

Sawn timber, particularly in seasoned form, is highly valued in structural applications for its

favourable strength-to-weight ratio, durability and dimensional stability. When used in large

engineering construction, its strength performance is based on visual grading and the

durability rating of the species. For domestic construction, mechanical grading is also utilised

(Shmulsky et al., 2011). Wood, as with other materials, exhibits variation in properties.

Kretschmann (2010) states that because wood is a natural material and the tree is subject to

many constantly changing influences (such as moisture, soil conditions, and growing space),

wood properties vary considerably, even in clear material.

The practice of forestry makes timber for various applications available (Ford-Robertson,

1971). Forestry is practiced in plantations and natural stands. Forest trees often grow close

together for the development of wood, suitable for timber harvesting (Norman, 2011). The

forest manager is today looking for ways to improve the economics of forest production by

increasing yields, reducing production costs, and improving quality (Wagner, 2005).

However, the success of forest management cannot be measured simply in terms of reduced

costs per unit volume of production since the forester will need to satisfy the user that the

timber he grows is an acceptable product (Wagner, 2005). Thinning of forest stands is likely

to be tried much more in forest management efforts to improve growth. Following thinning,

trees in the thinned areas show a response in diameter increment. This response is the result

of improved growing space for the tree crowns, reduced competition for root soil moisture

and nutrients, and better exposure of branches to lateral light (Wagner, 2005). The

implications of such a cultural practice for producing a greater wood supply are now well

known and much research has been done on many tree species to measure the growth

responses to intensive forest management. Secondary growth (stem diameter growth) is best

indicator of competitive stress (Wagner, 2005).

AUTHOR: WANKUMBU RABECCA NALUNGWE Page 11


In forestry, thinnings offer the opportunity to gain access to the control of density in a forest

stand through the harvest of trees. It is essential that wood scientists and technologists have a

thorough understanding of the structural properties of timber. In addition, for most products

that are not viewed as strictly “structural” products like furniture, an understanding of the

mechanics of wood is still required to ensure a reliable and durable end-product.

1.1 BACKGROUND INFORMATION

Silvicultural interventions carried out during the rotation of a stand of trees have a bearing on

the resulting properties and yield of timber that is obtained at the end of the rotation. One

such intervention is thinning. In forestry, thinning is the term describing the removal of some

trees from a stand to give others more space and resources to grow. At establishment of a

stand, more trees are planted than present at end of rotation. As these trees grow, each places

increasing demands upon the site's resources. In time, the larger trees simply need more

water, nutrients, and sunlight than they did when smaller. Eventually, the site reaches a point

where it can no longer support all of the young forest's trees. Growth rates decline and

individual trees best suited to the site outgrow the others. The most important property in

wood used in construction is its strength properties. The research focused mainly on

comparing the compression strength of thinned and un-thinned P.kesiya. Pinus kesiya timber

can be used for a wide range of applications, including boxes, paper and pulp, and temporary

electric poles. It is intensely used for construction timber, both sourced in natural forests and

plantations (Luu et al., 2004) and in many applications for structural purposes; these

applications affect timber to behave differently in relation to the loads they are subjected to

(Lucky, 2013). It is important to gain a thorough understanding of the different factors that

influence timber and wood as a structural material. The effects of thinning on tree growth are

discussed, and their effects on strength properties of sawn timber are compared.



1.2 STATEMENT OF THE PROBLEM

Pinus kesiya is extensively used for construction in Zambia for example in the manufacture

of roof trusses. Quality requirements for timber from Pinus kesiya stands demand that timber

produced be from well managed stands. Though thinning is an important part of the

management of plantations, it has been observed that for various reasons it is not always

either carried out at the scheduled time or it is not carried out at all in some of the Pine stands

on the Copperbelt in Zambia. Prescribed thinning schedules for Pine species may not always

be followed, resulting in some stands reaching rotation age with more stems per ha than they

should. Due to a shortage of raw materials, most saw millers will harvest roundwood from

whatever stand is allocated to them regardless of whether the trees growing in these stands

meet with the quality requirements of sawmilling and end-use requirements or not.

1.3 OVERALL OBJECTIVE

The overall objective of this study was to investigate the influence thinning has on the

strength in compression of Pinus kesiya timber used in structural applications

1.3.1SPECIFIC OBJECTIVES

The specific objectives of this study were to determine;

i. the compression strength of P. kesiya wood from thinned compartments.

ii. the compression strength of P. kesiya wood from unthinned compartments.

iii. if there is a significant difference in the means of the strength values from thinned and

unthinned stands.

1.4 ASSUMPTIONS

i. The timber sampled will be representative of the product coming out of similar stands.

ii. All other factors affecting design strength are constant.

1.5 HYPOTHESES

1.5.1 NULL HYPOTHESIS

Ho: There is no significant difference in the compression strength between P. Kesiya wood

from thinned and unthinned compartments.

1.5.2 ALTERNATE HYPOTHESIS

HA: There is a significant difference in the compression strength between P. Kesiya wood

from thinned and un-thinned compartments.



1.6 JUSTIFICATION

Timber, like all other materials of construction, has the ability to resist applied external

forces. It is essential to have a basic knowledge of the strength properties of a timber and the

factors that affect it to be able to use it effectively

1.7 SCOPE AND LIMITATIONS

The study only considered the compressive strength of wood from unthinned and thinned

Pinus kesiya. The tests were carried out in accordance with ASTM D143 (Standard Test

Methods for Small Clear Wood Specimens, 2000) and the tests carried out were Compression

parallel to grain and determination of moisture content.



CHAPTER TWO

2.0 LITERATURE REVIEW2.1 FORESTRY

Forestry is the practical application of scientific, economic and social principles used in the

establishment and management of forests. It encompasses the management of natural forests



and woodlands, plantations, and the various combinations of trees and agriculture known as

agro forestry or farm forestry it may also be defined as the science, art and craft of creating,

managing, using, conserving and repairing forests and associated resources, in a suitable

manner to meet desired goals, needs and values for human benefit.

Thinning is a forest management practice that is generally performed at some point(s) in time

during the course of the growth and development of pine stands. Thinning (as a forest

management practice) can be defined as the calculated removal of certain trees from an

existing stand and is usually conducted with a specific objective in mind (David et al. 2014).

There are various reasons why thinning should be employed as a management practice in

pine stands. Thinning promotes the growth of individual trees within a stand by removing

surrounding trees, which compete for water, sunlight, and soil nutrients. Most natural and

planted stands require thinning at certain stages of their development in order to sustain good

tree growth throughout the life of the stand. Thinning is beneficial to the overall health of a

stand of trees. Certain methods of thinning allow for the removal of a greater portion of

diseased trees and trees that are of poor quality and form. Many of these poorly formed,

cankered trees will die before the final harvest. The reasons for thinning clearly show that it

is a practice that we can’t do away with if we are to produce high quality timber.

2.2 SILVICULTURE

Silviculture is a process for creating, maintaining, or restoring an appropriate balance of

essential components, structures, and functions that ensure long-term ecosystem vitality,

stability and resiliency (Smith et al., 1997). Silviculture also focuses on making sure that the

treatment(s) of forest stands are used to preserve and to better their productivity (Hawley and

Smith 1954).

2.3 THINNING

Matthews (1991) defines thinning as a silvicultural operation where the main objective is to

reduce the density of trees in a stand, improve the quality and growth of the remaining trees

and produce a saleable product. Kerr (2011) further states that thinning can also achieve other

objectives such as altering the species composition of a stand, improving the health of the

remaining trees or disturbing an established ground flora to enhance opportunities for natural

regeneration. It’s these objectives that define when and how a thinning operation should be

conducted (Punches 2004). Repeated thinning may be needed to promote growth of large

trees with plenty of open space below. An objective of keeping a forest healthy may be met



by removing any trees that show signs of decline, thereby minimizing stress on the remaining

trees. For landowners that want to hold their forests in “big” trees for longer periods of time,

additional commercial thinning is required. This final objective requires trees to be thinned

out frequently enough to prevent the remaining trees from having too much of their crowns

(living branches) become shaded out – so timing of thinning operations becomes critical.

Punches (2004) states that it’s important to understand the following few basics before

undertaking thinning:

(i) Tree species vary in tolerance to shade. Some species grow best when exposed to full

sunlight, while others need to be in the shade. Thus, a species that is intolerant of

shade may respond best when widely spaced in a stand, while a shade tolerant species

may perform well in a stand with much closer spacing. Douglas-fir is classified as

intermediate in shade tolerance, and grows well in stands that are managed to

maintain moderate densities.

(ii) With many species, trees grown in dense stands for too long may exhibit a negative

response to thinning when it does occur. Trees in these stands may have thin bark that

makes them susceptible to sun-scald (damage to the cambium from overheating), they

may have needles that are not well adapted to direct sunlight, and they may have only

a small crown area. By thinning before a stand begins to stagnate, growth rates can be

maintained and tree health can be maintained.

(iii) To achieve maximum usable fibre yields, thin when the crowns of the trees are

beginning to overlap. (This is typically called a precommercial thinning, because the

material removed is too small to go to a sawmill). Thinning before this point has little

impact because the trees are not yet competing significantly. Waiting beyond this

point will result in reduced growth rates and smaller trees. A second thinning is

probably not economical if final harvest will occur before the stand reaches 45 years

of age.

(iv)Recurrent thinning may be needed to grow older, larger trees. Tree value (and stand

form, health, and aesthetic appeal) are almost always best improved by removal of

trees with poor form and/or lower growth rates. Close attention must be paid to crown

extent. Trees should be thinned before the crowns recede, as discussed in item 2,

above.



(v) Foresters use various guidelines to help them determine how many trees to leave on a

site. These may be based on tree diameter, crown closure, site conditions, and several

other factors. The important thing is to use a guideline to ensure that you will meet

your management objectives.

(vi)The objectives of management define when and how much to thin. If a primary

objective is to maximize value, remove the trees with poor form and lower growth

rates. For maximum timber volume

Competition arises when individual organisms are sufficiently close together to incur growth

constraint through mutual modification of the local environment (Milthorpe 1961). Plants

may compete for light, moisture and nutrients, but seldom for space per se. Vegetation has

management directed more of the site’s resources into usable forest products, rather than just

eliminating all competing plants (Buse and Baker 1991). Ideally, site preparation ameliorates

competition to levels that relieve the out plant of constraints severe enough to cause

prolonged check.

2.4 IMPORTANCE OF THINNING

Thinning removes surplus trees to concentrate timber production on a limited number of the

best trees in the plantation resulting in increased diameter growth and producing more

valuable larger diameter trees.

If forests are left unthinned, there is a high incidence of mortality in the forest i.e. trees will

progressively die, leading to a reduction in total timber volume production. If these trees are

removed by thinning operations, a proportion of the timber volume can be salvaged resulting

in an increase in volume production over similar unthinned stands (Farrelly and Hynes,

2007).

2.5 STRENGTH OF WOOD

Design strengths are defined as the product of the relevant strength reduction factor,

characteristic stress, section property, and modification factors for the condition expected in

service. Strength properties are the ultimate resistance of a material to applied loads. In the

case of wood, strength varies significantly depending on species, loading condition, load

duration and a number of other material and environmental factors (Ross, 2010).When one is

talking about strength of wood one should be very clear whether one is referring to a piece of

clear wood or a piece of timber with knots and other defects present. Strength is defined in

terms of the ability of a material to sustain a load (Bier, 1986). The magnitude of the load that



can be sustained varies with the shape and size of the sample being tested, which is

inconvenient. Therefore strength is defined in terms of stress that is the load or force per unit

area. If the failure load is known, the failure stress is obtained by dividing the failure load by

the area over which it acts. For all materials there is a critical stress at which they will fail. At

less than the critical stress the material will simply be compressed, stretched or bent, often by

almost imperceptible amounts. Loads can be applied in tension, in compression, in shear, or

in some combination. Unfortunately with wood the situation is more complicated still. Wood

is anisotropic, so it is necessary to define the direction of the stress with respect to the grain

of the wood. Wood tested in tension or compression and loaded parallel to the grain is

considerably stronger than when loaded perpendicular to the grain, but the reverse applies in

shear (Walker 1993). Good Silvicultural practices affect wood properties. In softwoods, good

thinning and proper spacing can enhance growth rates, strength and other properties.

Moreover, spacing can be tailored to the targeted product. For pulpwood species proper

spacing can produce high quality fibre and yield which may not be the same as high volume.

For trees destined for structural lumber, spacing can be done to produce a growth rate giving

optimum strength. For yard lumber (general construction lumber) - where volume is the main

goal-other spacing prescriptions apply. In hardwood, quality is more important than volume.

Fairly high growth rates in diffuse-porous woods are desirable. For ring porous species,

extremely high growth rates are not desirable nor are extremely slow growth rates. Where

strength is a factor six rings per inch is a minimum. When building with wood, consider how

each part will bear the load that will be placed upon it. Also consider how the wood joints

will transfer the loads from part to part. There are three mechanical properties that are

commonly measured and represented as strength properties of wood. These, according to

Forest Products Laboratory (2010), include modulus of rupture in bending, maximum stress

in compression parallel to grain, and shear strength parallel to grain.

2.5.1 COMPRESSIVE STRENGTH

The compressive strength is the capacity of a material or structure to withstand loads tending

to reduce its size. It can be measured by plotting applied force against deformation in a

testing machine. Some materials fracture at their compressive strength limit; others deform

irreversibly, so a given amount of deformation may be considered as the limit for

compressive load. Compressive strength is a key value for design of structures. Compressive

strength is often measured on a universal testing machine; these range from very small table-



top systems to ones with over 53 MN capacity (Urbanek et al. 2014). Measurements of

compressive strength are affected by the specific test method and conditions of measurement.

Compressive strengths are usually reported in relationship to a specific technical standard.

Compressive strength tells you how much of a load a wood species can withstand parallel to

the grain. Compression of wood and wood-based materials plays an important role in almost

any construction projects. If the compression strength or bending strength of a 2-inch by 4-

inch beam is not known, deflection due to bearing a load may cause significant deformation,

which could even lead to its failure during service life. Therefore, most softwood

construction lumber is graded based on allowable load resistance, which can be determined

from a stress test. However, strength properties of hardwood lumber are not that critical

because a majority of it is used for furniture manufacturing and is not exposed to substantial

loads. Compression or shear strength of a wood beam or truss are used extensively for

construction. Compressive strength is measured on materials, components (Urbanek et al.

2014) and structures (Ritter and Oliva 1990).

There are a number of applications where assessments of this property are important and

particularly with building supplies, which need to be strong enough to with stand failure

during and after construction (Thelandersson et al 1999). By definition, the ultimate

compressive strength of a material is that value of uniaxial compressive stress reached when

the material fails completely. The compressive strength is usually obtained experimentally by

means of a compressive test. The apparatus used for this experiment is the same as that used

in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive

load is applied. As can be imagined, the specimen (usually rectangular) is shortened as well

as spread laterally.



Figure 1 Compression parallel to the grain

When put under compression (or any other type of stress), every material will suffer some

deformation, even if imperceptible, that causes the average relative positions of its atoms and

molecules to change. The deformation may be permanent, or may be reversed when the

compression forces disappear. In the latter case, the deformation gives rise to reaction forces

that oppose the compression forces, and may eventually balance them.

Figure 2 Piece of wood of Pinus kesiya under the compressive strength test

Various forms of materials, wood inclusive can be tested for compressive strength. The

technician or experimenter will take note of the signs of failure that may begin to appear

when subjected to load such as cracking or splitting, recording the point of failure were the

materials or wood pieces break or fully fail. With materials such as wood, multiple tests may

be run to generate a range of readings.



Because it is important to produce wood quickly and efficiently, thinning has become

common practice in Turkish forestry. Thinning has proven to be an effective method in

increasing radial increment of P. brutia and has been the subject of numerous studies.

Correlations between wood properties, such as ring width, wood density, fibre length and

strength properties, and the quality of wood would have long been established and are

classically used to characterize wood for the forest product industry (Guller 2006).



CHAPTER THREE



3.0 MATERIALS AND METHODSThis section presents the methods and materials that were used in this research. It clearly

states the frame work, tools and technique that were used in data collection.

3.1 STUDY AREA

The research or study was conducted in Kitwe at The Copperbelt University Civil

engineering Laboratory using samples obtained from Chati Plantation in Kalulushi, which is

owned by the Zambia Forestry and Forest Industries Corporation (ZAFFICO).

3.2 MATERIALS

Mechanical properties are the characteristics of a material in response to externally applied

forces. They include elastic properties, which characterise resistance to deformation and

distortion, and strength properties which characterise resistance to applied loads. The

mechanical property values of wood are obtained from laboratory tests of defect-free wood

samples. For this study, a total of 30 test samples (15 from a thinned stand and 15 from an

unthinned one) were used.

3.3 FIELD SAMPLING

In the field, sampling was carried out as outlined in the American Society for Testing of

Materials, ASTM D5536- 94. Random Sampling was done from the forest plantation where

materials were collected. ASTM D5536- 94 states that materials shall be collected from the

trees selected under a series of steps provided in the standard, the procedure is as follows:

a) From the five selected rollers, 2.4 sections were marked to afford information on the

variation of properties with height on a roller.

b) The process in (a) above was repeated until all the rollers were sectioned

c) Representative pieces were cut on the rollers conforming to the measurements in (b)

above.

d) The north side of each roller was marked in same manner for easy identification.

e) Each roller was sawn into nominal 55 x 55 mm square sticks of length 1.2m.

The sawing was from north to south and from east to west of the cross section of the bolt. As

shown below



Figure 3 shows the 60 x 60 square sawing sections of the bolt (ASTM D 5536 – 94)

3.3.1 Sample preparation

The dimension of class A pieces was 50mm x 50mm x 200mm and for class B was 50mm x

50mm x 200mm. Pieces for compression parallel to the grain were prepared and that the end

grain surface was parallel to each other and at right angles to the longitudinal. When cutting

pieces to the dimensions named above circular saw and measuring tape tools were used. The

following were the steps of cutting rollers to 50mm cube pieces.

Step 1 The rollers was marked as shown below

Figure 4 A sketch showing the markings on a roller.



Step 2 A roller was quarter sawn.

Step3 A quarter sawn roller was cut to dimensions of 55mm square by 1.2m length pieces.

55mm x 55mm x 1.2m pieces after sawing using quarter sawing method. Then the pieces were

stuck and air dried as below;

Figure 5 Quarter sawn pieces of 55mm x 55mm x 1.2m stacked and air dried

Step 4 from the above pieces of timber stack 4 pieces were picked randomly and made sure they

were clear with no defects.

Figure 6 Randomly selected pieces of timber



Step 5 the pieces were measured to mark the required length and an extension in length was

required so that when the samples were planed the required 200mm was attained.

Figure 7 Measuring of timber pieces and marked to required lengths.

Step 6 the pieces were then collected and placed on the ripper to be ripped into dimensions of

50mm x 50mm

Step 7 the planed pieces were then collected and placed on the cross cutter to get the required

lengths of 200mm

Step 8 from the pieces that were cut, 30 clear pieces were collected (15 for unthinned and 15 for

thinned Pinus kesiya).



3.4 DRYING AND SAMPLE PREPARATION

After the preparation of samples from the saw mill, the samples were oven dried constant a

required moisture content of 12 to 13%.

The samples were dried according to ASTM D143. First, the samples were weighed and their

mass before drying (W) noted. The samples were then placed in an oven and then dried at a

temperature of 103± 2 °C for 24 hours, after which the samples where re-weighed and the

oven-dry mass, Wo, was obtained. The loss in weight expressed as a percentage of the final

oven-dry weight was taken as the moisture content of the test piece. The value so obtained

shall be recorded with the results of the particular test to which it refers.

Moisture content will be calculated for all pieces using the formula;

MC % = wet weight (W )−ovendry weight (Wo)

ovendry weight(Wo)×100

When tested the pieces were stored at temperature of 20 + 30c.

3.4.1 Compression parallel to the grain

To determine the compression strength parallel to the grain, the samples were prepared in

accordance with the standard (ASTM D143). According to the standard, a total of 15

unthinned samples and 15 thinned samples were considered, having the dimensions of 50mm

x 50mm x 200mm. The samples were then placed in between the two plates of the manual

hydraulic compressive test machine where the load was applied to the cross section axially as

Figure 3.9 in order to obtain the maximum force the samples can withstand. The samples

failed as shown in Figure 3.10.

Compression parallel to the grain determines the load that may be carried, high strength is

required for use. The main purpose of carrying out this test was to come up with information

of the maximum load of the wood from the two (unthinned and thinned samples) can support

when subjected to different types of loads



Figure 8 Manual hydraulic compressive test machine

Figure 9 Samples after loading to failure



3.5 RESEARCH DESIGN

3.5.1 PROCEDUREThe unthinned samples were acquired from Chati plantation where rows were assigned and

stands were picked randomly after picking the rows, systematic sampling was used to select

trees from compartment number 467. After this, the selected trees were felled, billets of 1.2

metres each were cut for easier transportation. The same method was done for the thinned

stands though the samples were collected from the log yard at Chati sawmill where logs were

picked randomly and were cut to required dimensions. Sawing was done at the sawmill in

Chati so as to maximise the output out of the billets. The sawn and dried pieces of timber

were further sawn and planed to meet the dimensional requirements for the compressive test

machine.

After the samples were processed and cut as needed for tests, there were 30 samples in total

for both unthinned and thinned.

Clear wood samples of Pinus kesiya were tested for compression parallel to grain. BS 373-

1954 standard was used during the testing process, a Testometric Testing Machine could not

be used because the forces at peak of each sample could not exceed 100 KN (Which is the

maximum force of the machine). Instead, a manual hydraulic compressive test machine was

used. According to BS 373-1954 the dimensions for small clear pieces were 50mm × 50mm

× 200mm for compression parallel to grain.

A load was applied parallel to the span of the wood sample. This was done piece after

the other.

The readings were recorded as Spu1,Spu2,Spu3……Spu15 for readings of unthinned Pinus

kesiya and Spt1,Spt2,Spt3………Spt15 for readings of thinned Pinus kesiya.

Stress was calculated as;

σ ℮ = F

A0

Where, F= load applied [N], A0= original specimen Area [m2].



3.5.1.1 COMPRESSIVE STRENGTH

The samples were subjected to a manual hydraulic compressive test machine, were each piece

of wood was placed in its vertical direction and then a known force was applied continually

until the piece of wood developed some form of failure (cracking or splitting).

The compressive strength will be calculated using the formula below;

σ ℮ = F

A0 (N/mm2)

Where;

σ ℮ ; maximum load before failure in compression

F ; load applied

3.6 DATA ANALYSIS.

The collected data was analysed quantitatively using Minitab statistical package for

calculation in which the student t-test was based on 5% and 1% significance levels (95% and

99% level of confidence) because the number of samples was 30.



CHAPTER FOUR



4.0 DATA ANALYSIS AND RESULTS

4.1 INTRODUCTION

The results presented in this chapter were obtained from tests of “clear” and “straight

grained” pieces of wood which, as explained by Kretschmann (2010), are usually considered

“homogeneous” in wood mechanics.

4.2 MOISTURE CONTENT

The results that were obtained from the weighed samples are shown in appendix. From these

results the moisture content was calculated for each test piece.

The mean of samples was calculated using the formula:

Mean (ϰ) = Σ moisture contentNo . of specimens

The samples were at the required moisture content of between 12 to 14 %, at which timber is

stable in use. Results are shown in table 4.1 below for thinned samples of Pinus kesiya;



Table 1 Determination of moisture content (MC) for thinned samples of Pinus kesiya

Sample Number:

Weight before drying (g)

Weight after oven drying (g)

Moisture Content (%)

1 211.5 187.5 12.82 259.5 230.0 12.83 246.5 211.5 16.54 252.5 225.0 12.25 229.0 202.5 13.16 217.0 191.5 13.37 270.0 241.0 12.08 252.0 224.0 12.59 261.5 231.5 12.9

10 213.5 187.5 13.911 255.0 227.5 12.112 258.0 229.0 12.713 257.0 227.5 12.914 250.0 214.5 16.515 245.5 217.5 12.9

Mean 245.2 216.5 13.3SD 17.9 24.8 1.3

CI (±) 9.1 8.4 0.7

Moisture content Sample mean, Sample standard deviation, and Confidence interval

The study was carried out with a sample size of 15 test specimen. The sample of timber

pieces from a thinned stand had a mean moisture content of 13.3, a standard deviation of 1.3,

and a desired confidence level of 95%, the corresponding confidence interval was found to be

± 0.7. That is to say that one can be 95% certain that the true moisture content mean falls

within the range of 12.6 to 14% MC



Table 2 Shows the moisture content (MC) for unthinned samples of Pinus kesiya

Sample number: Weight before drying (g)

Weight after drying 9g) Moisture content (%)

1 206.5 181.6 13.72 220.5 196.6 12.13 213 187.2 13.84 174.5 153.8 13.45 208 183 13.76 164 144 13.97 200.5 177.5 12.98 244 216.8 12.59 171 151 13.2

10 169 150.6 12.211 258.5 227 13.912 187.5 165 13.613 220.5 196.6 12.114 238.5 207.5 14.915 206.5 183.2 12.7

Mean 205.5 181.42 13.24SD 27.62 24.26 0.78

CI (I±) 13.98 12.28 0.4

For a survey using 15 test samples from an unthinned stand, a mean score of 13.24, a

standard deviation of 0.78, and a desired confidence level of 95%, the corresponding

confidence interval was determined to be ± 0.4. That is to say that you can be 95% certain

that the true moisture content mean falls within the range of 12.84 to 13.64% MC

4.3 COMPRESSION PARALLEL TO THE GRAIN:

A compressive test was carried out in order to determine the compressive strength of the

samples and this was done parallel to the grain. Table 4.3 shows the results that were

obtained after the tests were carried out on thinned samples.



Table 3 Force at peak of thinned samples (N)

Test Sample No

FORCE AT PEAK (KN)

Thinned Unthinned1 150.00 150.002 175.00 85.003 125.00 150.004 180.00 110.005 125.00 110.006 150.00 115.007 195.00 100.008 185.00 75.009 145.00 110.0010 135.00 95.0011 100.00 85.0012 175.00 110.0013 175.00 115.0014 55.00 125.0015 150.00 85.00Mean 148.00 108.00

SD 35.58 21.35

CI ± 18.01 10.8

For tests pieces from a thinned stand, a mean score of 148KN, a standard deviation of 35.58,

and a desired confidence level of 95%, the corresponding confidence interval was found to be

± 18.01. This means that you can be 95% certain that the true strength mean for timber from

thinned stands would fall within the range of 129.99 to 166.01 KN.

For a similar number of samples but from an unthinned stand, a mean score of 108.00, a

standard deviation of 21.356, and working with a desired confidence level of 95%, the

corresponding confidence interval would be ± 10.8. That is to say that you can be 95%

certain that the true strength value mean would fall within the range of 97.2 to 118.8



4.3.1 ANALYSIS:

Compression strength

σ = PA

Where; σ = Compressive strength (N/mm2)

P = force at peak, (N)

A = Cross section Area, (mm2)

The above formula was used to calculate for each sample and the results that were obtained

were recorded in the table below:

Table 4 Compressive strength results for each thinned sample tested.

Test Sample No

Force at Peak (N)

Area (mm2)

Stress at Peak (N/mm2)

1 150 000 2 500 602 175 000 2 500 703 125 000 2 500 504 180 000 2 500 725 125 000 2 500 506 150 000 2 500 607 195 000 2 500 788 185 000 2 500 749 145 000 2 500 5810 135 000 2 500 5411 100 000 2 500 4012 175 000 2 500 7013 175 000 2 500 7014 55 000 2 500 2215 150 000 2 500 60Max 195 000.00 2 500.00 78Min 55 000.00 2 500.00 22Mean 148 000.00 2 500.00 59.2SD 35 580.89 14.23CI (±) 7.2



Table 5 Compressive strength results for each unthinned sample tested.

Test Sample No

FORCE AT PEAK

(N)

AREA (mm2)

STRESS AT PEAK

(N/mm2)

1 150000.00 2500.00 60

2 85000.00 2500.00 34

3 150000.00 2500.00 60

4 110000.00 2500.00 44

5 110000.00 2500.00 44

6 115000.00 2500.00 46

7 100000.00 2500.00 40

8 75000.00 2500.00 30

9 110000.00 2500.00 44

10 95000.00 2500.00 3811 85000.00 2500.00 34

12 110000.00 2500.00 44

13 115000.00 2500.00 46

14 125000.00 2500.00 50

15 85000.00 2500.00 34

Max 150000.00 2500.00 60

Min 75000.00 2500.00 30

Mean 108000.00 2500.00 43

SD 21354.16 0.00 8.54CI (±) 4.32



sample 1

sample 2

sample 3

sample 4

sample 5

sample 6

sample 7

sample 8

sample 9

sample 10

sample 11

sample 12

sample 13

sample 14

sample 15

60

70

50

72

50

60

7874

5854

40

70 70

22

6060

34

60

44 44 4640

30

4438

34

44 4650

34

variations of compressive strengths of unthinned and thinned samples

thinned unthinned

com

pres

sive

str

engt

h (N

/mm

)

Figure 10 Variations of compressive strengths of unthinned and thinned samples

4.3.1.1 Statistical Analysis:

The t-statistic calculation was divided into two categories;

- Compressive strength of unthinned samples – Number of samples, n = 15.

- Compressive strength of thinned samples – Number of samples, n = 15.

Statistical analysis was carried out using Stats Calculator (McCallum Layton, 2016)

Compressive strength test results for pieces from thinned and unthinned stands are shown in

tables 4.5 and 4.6, respectively.

Table 4.3.1 T-test results

Groups 1 21 Yes2 Yes



‘YES’ indicates that there is a significant difference between the two mean scores at the 95%

confidence level, i.e. the mean score for strength of timber from thinned stands is

significantly higher than the mean score for timber from unthinned stands.

Table 4.9: Student’s T-test results

Tabulated t-value Calculated t-value Conclusion

Thinned samples VS

Unthinned samples 1.761 3.23

Reject null hypothesis

Paired T-Test and CI: THINNED, UNTHINNED

Table 4.10: Paired T for thinned – unthinned samples

N Mean St Dev SE Mean

Thinned 15 59.20 14.73 3.80

Unthinned 15 43.20 8.84 2.28

Difference 15 16.00 19.18 4.95

95% CI for mean difference: (5.38, 26.62)

T-Test of mean difference = 0 (vs not = 0):

T-Value = 3.23 P-Value = 0.006



80706050403020

5

4

3

2

1

0X_

Ho

Thinned

Freq

uenc

y

Histogram of Thinned(with Ho and 95% t-confidence interval for the mean)

Figure 11 Histogram of samples from thinned stand



78

224050545860707274

Category

Pie Chart of Thinned

Figure 12 Pie Chart of Thinned

60555045403530

6

5

4

3

2

1

0

-1X_

Ho

Unthinned

Freq

uenc

y

Histogram of Unthinned(with Ho and 95% t-confidence interval for the mean)

Figure 13 Histogram of Unthinned samples



6034444640303850

Category

Pie Chart of Unthinned

Figure 14 Pie Chart of Unthinned samples



4.4 DISCUSSION

The timber samples were tested at a favourable moisture content of 12% - 15% and thinning,

as shown in table 4.5 and 4.6, appears to influence strength of timber. This corresponds with

the results from other studies (Punches 2004) and (Guller 2006). The values of thinned and

unthinned Pinus kesiya samples were analysed statistically as presented in table 4.10. Based

on the t-test result and p-value of 0.006, it shows there’s high significant difference between

the compression strengths of thinned and unthinned wood of Pinus kesiya. This can be clearly

shown in the individual failure loads for all samples as they were subjected to a load.

Despite having a difference in the values of compression strengths found, the compression

strength values for thinned samples of timber clearly show that they are ideal and suitable for

construction purposes and as construction material because they are able to withstand load for

quite a long time. Recurrent thinning may be needed to grow older, larger trees. Tree value

(and stand form, health, and aesthetic appeal) are almost always best improved by removal of

trees with poor form and/or lower growth rates. Close attention must be paid to crown extent.

Trees should be thinned before the crowns recede (Punches 2004).

If the calculated t value exceeds the tabulated value we say that the means are significantly

different at that level of probability which is the case in the results found. Hence, the results

rule in favour of the alternative hypothesis which states; there is a significant difference in the

compression strength between P. Kesiya wood from thinned and un-thinned compartments.

Good Silvicultural practices affect wood properties. In softwoods, good thinning and proper

spacing can enhance growth rates, strength and other properties. Moreover, spacing can be

tailored to the targeted product.

Mortality occurs at a faster pace when the density is higher. After a thinning from below,

mortality in a thinned stand is lower than in an unthinned stand of the same density (Dennis

2010).

Wood has been used by humans since the earliest recognition that they could make use of the

materials they found around them. As they used it to meet a varying array of human needs, in

peace and in war, in farming and in industry, people gradually came to understand something

of the unique nature of wood. Its properties were first understood by experience, more

recently by systematic research and refined observation (Perlin, 1989).



CHAPTER FIVE



5.0 CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION This research was carried out in order to compare the compressive strengths of clear wood

specimens from thinned Pinus kesiya and unthinned Pinus kesiya stands. This was a

comparative study whose overall objective of this study was to assess the influence thinning

has on the strength in compression of Pinus kesiya timber of the same age that is used in

structural applications.

Test results show that the failure load for the samples from unthinned stands was significantly

lower than that of samples from thinned stands

We can thus reject the null hypothesis which states that there is no significant difference in

the compression strength between P. Kesiya wood from thinned and unthinned

compartments.

5.2 RECOMMENDATIONS

The study was mainly focused on Pinus kesiya and to make generalisation, more research is

required on this subject to make full use of the locally grown timber. The current results

suggest that thinning can produce improvements in the investigated wood property, although

subsequent studies must be better designed to minimise some effects and maximise treatment

effects. More information is needed about the investigated specie to determine if fibre length

is affected by thinning or if thinning can affect tensile or shear strengths.

Timber provides a cleaner, safe or environmentally friendly material were environmental

issues are concerned. Therefore, diverse studies should be done as to how other species can

be managed, the complete utilisation of forest resources, for this will improve the economy

and industry at large for they will be used in various applications that may be beneficial for

all.

Studies on other species should be carried to determine if thinning has the same effect on the

strength of all species



REFERENCES

1. ASTM, D. (2000). 143-94e1.Standard Test Methods for Small Clear Specimens of Timber. ASTM International.

2. ASTM D5536-94 (2000): Practice for sampling the Forest Trees for Determination of Clear Wood Properties: United States of America.

3. Bier, H. (1986). Log quality and the strength and stiffness of structural timber. NZJ For. Sci, 16(2), 176-186.

4. Buse, L.J.; Baker, W.D. (1991). Determining necessity and priority for tending in young spruce plantations in north-western Ontario. Ont. Min. Nat. Resour., North-western Ont. For. Technol. Devel. Unit, Thunder Bay ON, Tech. Note TN-08. 4 P.

5. Dennis P. Dykstra (2010). Forest growth and timber quality: crown models and simulation methods for sustainable forest management.

6. Falk RH (2010). Wood as a sustainable building material. In Forest Products Laboratory Wood Handbook: wood as an engineering material. General Technical Report FPL-GTR-190,USDA

7. Farrelly, N and Hynes, S. (2007). The practice of thinning forest crops. Teagasc Forest research.

8. Ford-Robertson F.C. (1971), SAFnet Dictionary/ Definition for [forestry]. Dictionary of forestry.org 2008-10-22. Retrieved 2014-03-15

9. Forest Products Laboratory (2010). Wood handbook: wood as an engineering material. USDA Forest services, forest products technical report FPL-GTR-190. Madison, Wisconsin.

10. Hawley, R.C. and D.M. Smith (1954). The practice of Silviculture. 6th edition. New York: John Wiley & Sons Inc.

11. Kerr, G., and Haufe, J. (2011). Thinning practice: a silvicultural guide. Edinburgh, forestry commission.

12. Kretschman D (2010) Mechanical properties of wood.

13. Luu, N. D. T., & Thomas, P. I. (2004). Conifers of Vietnam. An illustrated field guide for

the most important forest trees. Darwin Initiative, Hanoi, Vietnam, 86.

14. Matthews, J.D. (1991). Silvicultural systems. Oxford science Publications.



15. McCallum Layton (2016). Retrieved on 21 June 2016 from https://www.mccallum-

layton.co.uk/tools/statistic-calculators/independent-t-test-calculator/

16. Milthorpe, F.L. (1961). The nature and analysis of competition between plants of different species. P.330-355 in Mechanisms in Biological Competition. Sympos. Soc. Exp. Boil. 15, Cambridge univ. press, Cambridge, U.K

17. Perlin J. (1989). A forest journey: The role of wood in the development of civilisation. WW Norton, New York. 445 pp.

18. Punches, J. (2004). Thinning: An Important Forest Management Tool. Oregon state university extension service. Roseburg, OR.

19. Ritter, M A; Olivia (1990). Design of Longitudinal Stress-Laminated Deck Superstructures, Timber Bridges: Design Construction, Inspection and Maintenance (pdf), US Dept. of Agriculture, Forest Products Laboratory.

20. Ross, R. J. (2010). Wood handbook: Wood as an engineering material.

21. Shmulsky, R., & Jones, P. D. (2011). Forest products and wood science. John Wiley & Sons

22. Smith, D.M., (1997). The Practice of Silviculture: Applied Forest Ecology. 9th edition. New York: John Wiley & Sons, Inc.

23. Standard, B. BS 373 (1957) Methods of Testing Small Clear Specimens of Timber. British Standard Institution, ISBN 0, 580(00684), 0.

24. Thelandersson S. and Hansson M (1999). Reliability of timber structural systems: effects of variability in homogeneity. Lund University of Technology, Division of Structural Engineering.

25. Urbanek, T; Lee, Johnson (2010). “Column compression strength of tubular packaging forms made of paper” (pdf) 34, 6. Journal of testing and evaluation. pp 31-40.

26. Wagner, R.G. (2005). Top 10 principles for managing competing vegetation to maximise regeneration success and long term yields. Forest research information paper.

27. Walker, J. C. (2006).Primary wood processing: principles and practice. Springer Science &

Business Media.

28. Youngs R.L., (1995). Forests and Forest Plants-Vol. ii- History, Nature and Products of wood- professor Emeritus, Virginia Polytechnic Institute and State University.


https://www.mccallum-layton.co.uk/tools/statistic-calculators/independent-t-test-calculator/

https://www.mccallum-layton.co.uk/tools/statistic-calculators/independent-t-test-calculator/


APPENDICES



APPENDIX A:

MOISTURE CONTENT RESULTS FOR THINNED PINUS KESIYA SAMPLES

Sample Number: Weight before drying

(g):

Weight after oven

Drying (g):

Moisture Content:

(%)

1 211.5 187.5 12.8

2 259.5 230 12.8

3 246.5 211.5 16.5

4 252.5 225 12.2

5 229 202.5 13.1

6 217 191.5 13.3

7 270 241 12

8 252 224 12.5

9 261.5 231.5 12.9

10 213.5 187.5 13.9

11 255 227.5 12.1

12 258 229 12.7

13 257 227.5 12.9



14 250 214.5 16.5

15 245.5 217.5 12.9

MOISTURE CONTENT RESULTS FOR UNTHINNED PINUS KESIYA SAMPLES

Sample number: Weight before drying

(g):

Weight after drying

(g):

Moisture content:

(%)

1 206.5 181.6 13.7

2 220.5 196.6 12.1

3 213 187.2 13.8

4 174.5 153.8 13.4

5 208 183 13.7

6 164 144 13.9

7 200.5 177.5 12.9

8 244 216.8 12.5

9 171 151 13.2

10 169 150.6 12.2

11 258.5 227 13.9

12 187.5 165 13.6

13 220.5 196.6 12.1



14 238.5 207.5 14.9

15 206.5 183.2 12.7

APPENDIX B:

COMPRESSIVE STRENGTHS FOR THINNED PINUS KESIYA SAMPLES

SAMPLE TEST NO. FORCE AT PEAK (N):

AREA (mm2):

STRESS AT PEAK (N/mm2):

1 150000 2500 60

2 175000 2500 70

3 125000 2500 50

4 180000 2500 72

5 125000 2500 50

6 150000 2500 60

7 195000 2500 78

8 185000 2500 74

9 145000 2500 58

10 135000 2500 54

11 100000 2500 40

12 175000 2500 70



13 175000 2500 70

14 55000 2500 22

15 150000 2500 60

Max 195000 2500 78

Min 55000 2500 22

Mean 148000 2500 59.2

COMPRESSIVE STRENGTHS FOR UNTHINNED PINUS KESIYA

SAMPLE TEST NO: FORCE AT PEAK :

(N)

AREA:

(mm2)

STRESS AT PEAK:

(N/mm2)

1 150000 2500 60

2 85000 2500 34

3 150000 2500 60

4 110000 2500 44

5 110000 2500 44

6 115000 2500 46

7 100000 2500 40

8 75000 2500 30

9 110000 2500 44

10 95000 2500 38

11 85000 2500 34

12 110000 2500 44



13 115000 2500 46

14 125000 2500 50

15 85000 2500 34

Max 150000 2500 60

Min 75000 2500 30

Mean 108000 2500 43

APPENDIX C:

Paired T-Test and CI: THINNED, UNTHINNED

Paired T for THINNED - UNTHINNED

N Mean StDev SE MeanTHINNED 15 59.20 14.73 3.80UNTHINNED 15 43.20 8.84 2.28Difference 15 16.00 19.18 4.95

95% CI for mean difference: (5.38, 26.62)T-Test of mean difference = 0 (vs not = 0): T-Value = 3.23 P-Value = 0.006


under graduate thesis 2015-a comparative study of the compression strength of timber from thinned...

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