Description
ABSTRACT
An experimental study of identification of the species and mechanical properties of some selected tropical timber species available locally in Sierra Leone was carried out. The fundamental aim of this paper is to establish the properties of timbers currently used in Sierra Leone, since manufacturing and preservation processes affect the properties of timber. Four chosen species, Albizia (Albizia ferruginea), Dahoma or Ekhimi (Piptadeniastrum africanum), Ekki (Lophira Alata) and Opepe (Nauclea diderichii), were obtained, and tests for their mechanical properties (compressive strength, modulus of rupture and modulus of elasticity) and physical properties (moisture content and density) were conducted. The mechanical properties of these species were compared to data published by international organisations. It was observed that woods from Sierra Leone had lower strength values, compared to average values published for these species. From the results, Albizia showed much lower strength properties than Ekhimi and Opepe. Ekki exhibited very high values of all mechanical properties, at 12% moisture content. It also had a very high density. Albizia had a low density and moisture content at its basic state, while Ekhimi and Opepe had medium moisture contents and densities at their basic states, respectively. From these results, their suitability as structural members was inferred, after having compared their mechanical properties.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
CHAPTER ONE
- INTRODUCTION
- BACKGROUND OF THE PROJECT
- STATEMENT OF RESEARCH PROBLEM
- JUSTIFICATION OF THE STUDY
- AIM AND OBJECTIVES
CHAPTER TWO
2.0 LITERATURE REVIEW
- OVERVIEW OF THE STUDY
- SIERRA LEONE BACKGROUND
2.2.1 HISTORY
2.2.2 CULTURAL, POLITICAL AND PHYSICAL GEOGRAPHY
- REVIEW OF SIERRA LEONE FOREST GOVERNANCE AND MANAGEMENT
- GLOBAL DEBATES AND ACTIVITIES: FOREST EXPLOITATION IN AFRICA
CHAPTER THREE
3.0 MATERIALS AND METHODS
- MOISTURE CONTENT DETERMINATION
- COMPRESSIVE STRENGTH DETERMINATION
- TENSILE STRENGTH DETERMINATION
- BENDING STRENGTH TEST
CHAPTER FOUR
- RESULTS
- DISCUSSION OF RESULT
CHAPTER FIVE
- CONCLUSION
- REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Timber is a major construction material that can be used in almost every facet of construction [1]. Timber in its simplest form can be said to be the hard, tough substance that forms the trunks of trees [2]. The Sierra Leone code of practice, NCP2 1973, defines timber as wood in a form suitable for construction of carpentry, joinery, or for manufacturing purposes [1, 2]. Basically, timber is a biological and organic material often used in its natural state; anisotropic and hydroscopic, with widely varying properties depending on species, geographical area where the tree grows, the growth conditions, size of the tree at harvest, sawing and any other manufacturing processes [3].
As a structural element, timber is usually used in areas in a structure where load-bearing is at the minimum or virtually non-existent, to maximize the workability, and minimise cost [4]. However, in some countries where timber is the major construction material for most structures, design of these structures is done with regard to timber, and special treatment is given to the wood before or after construction [5]. Also, particular species are used in construction, depending on the property required. Some species possess high resistance to bending and compression stresses, chemical or insect attack, or resistance to fire than others, which makes them desirable when these properties are needed [6].
In the tropics, timber abounds, and is one of the cheapest and highly available materials. In Sierra Leone, a wide range of species of timber are available, and selection of the appropriate species for a particular use is of utmost importance [7-9].
Significant reduction in compressive and static bending strength of these species could be attributed to many factors, among which are premature felling of the trees before they reach maturity; presence of defects in the wood; improper drying (seasoning) of the wood, and improper timber conversion processes; poor growth conditions (e.g. poor soil and nutrients for tree growth, etc.); position along the tree trunk from which the specimen was obtained (strength properties are usually greater towards the bottom of the trunk, and reduce as one travels upwards); discrepancies in the moisture content and density of the samples, which in turn, due to swelling and shrinkage, have a great influence on the moduli of elasticity of the samples; and the different locations of origin of the wood from which the different specimens used to undergo these tests were obtained [9-12]. Thus, this work intends to address the possible variation in properties of timber as a result of current manufacturing and production process in Nigeria. Thus, complementing the work of other researchers [9, 14, 15]. Table 1 to 3 show the mechanical properties of timber, which are not from Sierra Leone, published in literature.
The aim of this research is to ascertain the inherent physical and mechanical characteristics/properties of some selected species of tropical timber available in Sierra Leone. It has been shown that the location, climate, planting technique and specie could have significant impact on the physical and mechanical properties of timber [12-14].
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1.2 STATEMENT OF RESEARCH PROBLEM
Timber has been identified as a construction material with an excellent environmental credential that is unparalleled (Bradford, 2008). However, limitations in mechanical properties as well as growth defects have limited its extensive use for industrial purpose.
Several researches have shown the mechanical properties and performance of some indigenous timber species only in solid timber form, these studies have not focused on the use of Sierra Leone timber species in the development of glulam for structural purpose to enhance the structural capabilities of local timber species (Suhaimiet et al., 2004; Kimeng et al., 2014). That the properties of timber between and within species is diverse makes it imperative to understand the behavior of local timber species as glued laminated elements.
1.3 JUSTIFICATION OF THE STUDY
The need to situate the Nigerian construction industry within the context of the “Green” agenda is imperative as the subject of sustainability and environmental friendliness continues to top the agenda among the highest level of policy makers such as the G7 meetings where issues of global concern like climate change is discussed. Therefore setting the trajectory for the industry along the green path is to take advantage of locally available forest resources. Home grown and processed timber, when successfully glued for structural purpose could achieve the benefits of sustainability, environmental friendly construction and construction cost reduction working in tandem (Bradford Forest Inc. 2008;Anthony and Joshua, 2014).
Establishing the glueability of indigenous timber species for structural purpose would demonstrate to designers and engineers that local timber species can perform excellently as structural glulam elements as demonstrated with timber species used for important structures in the United kingdom and the United states of America; that they can compete favorably with other traditional construction material without compromising the tenets of structural safety.
1.4 AIM AND OBJECTIVES
Aim
The aim of this study is to identify the species and to determine the mechanical properties of local timbers used in the construction industry using Sierra Leone as the case study.
Objectives
The specific objectives are;
- To evaluate the effects of varied temperature on strength performance of timber
- To determine the mechanical properties such as static bending strength, compression parallel and perpendicular to grain of solid wood of the species
- To compare the mechanical properties of timber elements.
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