COMPARATIVE ASSESSMENT OF THE STRENGTHS OF SOLID AND GLUED LAMINATED TIMBER

TABLE OF CONTENTS

Abstract

Table of contents

List of Symbols and Abbreviations

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background of the Study

1.2       Statement of Research Problem

1.3       Justification of the Study

1.4       Aim and Objectives

1.4.1 Aim

1.4.2 Objectives

1.5       Methodology

1.6       Analysis of Results

1.7       Scope and Limitation

1.8       Limitation

CHAPTER TWO

2.0       Literature review

2.1       Structural Glue Laminated Timber

2.2       Glued Laminated Timber Appearance Grade

2.3       Timber Species for Glued Laminated Timber Production

2.4       Adhesives

2.5       Challenges of Timber Utilization in Nigeria

2.5.1    Research

2.5.2    Technological Capability

2.5.3    Mode of Strength Assessment

2.5.4    Lack of Quality Control

2.5.5    Acceptability

2.5.6    Skewed dependence on a few species

2.5.7    Jointing Systems

2.5.8    Lack of Comprehensive Standard

2.6       Mechanical Properties of Wood and Wood Composite

2.6.1    Elastic properties

2.6.2    Modulus of Elasticity

2.6.3    Modulus of Rigidity

2.6.4    Poisson Ratio

2.6.5    Strength Properties

2.6.6    Bending Strength

2.6.7    Compressive strength

2.6.8    Compression Perpendicular to Grain

2.7       Grading of Timber

2.8       Glue Laminated Timber

2.8.1 Properties of Glue Laminated Timber

2.8.2    Effects of heat treatment

2.8.3    Glueability of Timber

2.8.4    Fabrication of glulam

2.8.5    Production Essentials

2.8.6    Indigenous Timber Species In Glulam Production

2.9       Adhesive

2.9.1    Structural Adhesives

2.9.2    Factors That Affect Adhesive Bonding

CHAPTER THREE

3.0       Experimental Procedure

3.1       Preamble

3.2       Materials

3.3       Experimental design

3.4       Methods

3.4.1    Bending strength test

3.4.2    Compressive strength test

3.4.3    Compressive strength test and temperature variation

3.4.4    Moisture content and density determination

CHAPTER FOUR

4.0       Presentation of Results Analysis and Discussion

4.1       Preamble

4.2       Results

4.3       Characteristic Material Properties

4.4       Discussion of Results

4.4.1 Static bending test

4.4.2 Variability in density

4.4.3 Compression parallel to grain

4.4.4 Compression perpendicular to grain

            Moisture content

4.4.6 Effects of temperature variation on compressive strength

4.4.7 Failure mode

4.4.8    Beam failure mode

4.4.9    Glue laminated timber beams

4.4.10  Compression members

CHAPTER FIVE

5.0       Summary, Conclusion and Recommendation

5.1       Summary

5.2       Conclusion

5.3       Recommendation

5.4       Recommendation for further studies

REFERENCES

Abstract

Timber is a construction material with unparalleled environmental credential. Howbeit, limitations of span and crossectional dimension, strength reducing defects and anisotropy limits its engineering application. Mechanical methods of jointing to address the earlier challenge has introduced serious wood fiber failure and increased the embodied energy in timber as a green material. However, developed societies have established in literature the possibility of overcoming these limitations to utilize timber beyond the traditional application in Nigeria being glueable for developing engineered wood products like glued laminated timber (glulam) using their timber species. Conversely, while little or no interest is shown in timber as a structural material in Nigeria, many of the few researches in timber have focused on solid timber elements leaving its limitations unattended. Consequently, its structural capabilities is yet unappreciated. Nevertheless, the fact remains that reconstituting natural timber as glulam is an effective way of optimizing this green material for limitless structural use. Whether these qualities are achievable with local timber is the main thrust of this research. The research therefore conducted laboratory experiments on selected timber species namely; Ire (Funtumia africana), Awun (Alstonia congensis) and Oriro (Antiaristoxicaria) being readily available and widely used species with no information on Oriro and Ire in NCP 2 of 1973. The aim was to assess their strength properties as glulam elements with the view to improving their structural capacity.It also set out to determine their glueability, the effects of temperature variation on compressive strength parallel to grain for glulam short columns by subjecting specimens ofequal dimension for the three species to different temperatures of 0 ⁰C, 40 ⁰C, 50 ⁰C, 70 ⁰C, 100 ⁰C and room temperature for 4 hours in an electric oven prior to testing; to compare the mechanical properties of solid and glulam elements. In furtherance, specimens were prepared and tested for; static bending strength, compression parallel and perpendicular to grain, density and moisture content in line with ASTM D193, EN 408(2003) and EN13183-1(2002). The research established that the species are; structurally glueable, that due to temperature increase compressive strength is lost in glulam columns from control temperature (30 ⁰C and 27.9⁰C) to 100 was 41% 14.4% and 21.6% in Ire, Awun and Oriro. Results showed that glulam elements developed 55%, 95% and 143% of clear solid wood bending strength and that bending strength of 65.22N/mm^2;36.44N/mm², 26.15N/mm²; 25N/mm² and 14N/mm²; 20N/mm² in solid and glulam in the species are structurally significant.The study has therefore demonstrated that the timber species studied can be engineered to load bearing glued laminated structural elements using polyvinyl acetate glue without severe loss of strength below and above room temperature.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background of the Study

The versatility of timber finds wide application in the construction industry spanning from simple framing in housing projects to large scale public facilities. However because sawnwood hasrestrictionsto spans and cross-sectional dimensions due to size of tree as well as strength reducing features which occur at growth, its value as a structural material for extensive structural applications is limited. Engineered wood products such as glue laminated timber (glulam) were thereforedeveloped to improve the use of natural timber beyond its natural limitations.

Structural glued laminated timber is an engineered structuraltimber glued up from suitably selected and prepared pieces ofstress graded lumber either in a straight or curved form with the grain of all pieces essentially parallel to the longitudinal axis of the member (APA, 1996; Manja et al., 2010). According to the American plywood association (APA, 2013), glulam has remained the most resource-efficient approach to wood building products when it comes to optimizing products from a carefully managed timber resource. Glued laminated wood can be built out of defective wood without losing its strength properties as reported by Reginaet al.,(2010). The application of glue laminated timber as a construction material would therefore make many species of timber previously regarded as non-merchantable useful for structural purpose. Clearly, this has the potential to revamp the forestry industry making it a massive employer of labor. Glulam can also be manufactured from small diameter fast growing tree, thereby bridging the supply deficit from slow growing trees(Evalinaet al.,2010). According to the American institute of timber construction....

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