UNIVERSITI TEKNOLOGI MARA
STRUCTURAL PERFORMANCE OF GFRP DOWELLED MORTISE AND TENON
CONNECTIONS MADE OF SELECTED TROPICAL SPECIES
ROHANA HASSAN
Thesis submitted in fulfillment of the requirements for the degree of
Doctor of Philosophy
Faculty of Civil Engineering
August 2011
ABSTRACT
The mortise and tenon is widely seen as one of the most important traditional timber structural joint. However, report and guidelines on its structural performance is very limited. Therefore in order to study the load-carrying capacity and performance of the structural mortise and tenon joint, the existing theoretical back ground of timber joint design is made as a reference. Current equations applicable in estimating the load-carrying capacity of timber joint is using European Yield Model (EYM).
However, the existing EYM equation use to estimate load-carrying capacity of timber joints is only established and limited to steel fasteners. This caused the difficulties in
designing the structural connection using other types of fastener material such as glass fibre reinforced polymer (GFRP) or wood wherever it is in need to substitute the steel dowels. The advantages of using steel as a fastener in timber joint are well known to the construction industry; however the use of GFRP as a new material in the construction especially in the timber industry is also proven to be successful.
Therefore, the main aim of this research is to determine the applicability of GFRP dowel to substitute steel and wood dowel as a fastener in strengthening structural mortise and tenon joints.
In this research, the load-carrying capacities of double shear joint performed experimentally were compared to the strength value calculated theoretically using EYM equations. The outcomes of the comparison were then used as guidelines and comparisons as well as to investigate the reliability of EYM in predicting the load- carrying capacity of mortise and tenon structural joint. The double shear joint test is currently the only method was developed in determining the timber joint capacity.
In order to determine the load-carrying capacity of the double shear joint, the complimentary test that is the dowel-bearing strength and dowel bending yield test is necessary. Thus, the laboratory experimental work comprising of the dowel-bearing strength tests, dowel bending tests and double shear strength tests were done to experimentally determine the performance of the structural mortise and tenon and compared with the theoretical equations. All experimental work was done using three dowels, one at a time either steel, GFRP or wood dowel. The steel dowels are used to validate the findings since the EYM is mean for the steel fastener and the results of wood dowel were used as a comparison to the performance resulted from the GFRP dowel. Structural mortise and tenon tests were performed in accordance to shear, bending and tension laterally loaded. All experimental work was done using Kempas species and repeated with Kapur species for comparison purposes.
The results from this research enhance the understanding of the performance of the structural mortise and tenon fastened with GFRP dowel and on the use of the existing National Design Specification (NDS), 2005 in estimating the load-carrying capacity of this type of connections. The existing EYM, NDS, 2005 are found applicable in estimating the GFRP dowelled mortise and tenon joints. The EYM equations are found reliable and sufficient in estimating the GFRP dowelled mortise and tenon joints subjected to tensile load. However the EYM equations under predicted the GFRP dowelled mortise and tenon joints subject to shear and bending load. Therefore the factor of safety values for the mortise and tenon joints dowelled with GFRP subjected to the shear and bending load are presented in this thesis for future references.
ACKNOWLEDGEMENTS
In preparing this thesis, with the Graciousness and Mercifulness of ALL THE MIGHTY ALLAH SWT., I wish to express my sincere appreciation to my main supervisor, Associate Professor Dr. Azmi Ibrahim for the priceless encouragement, ideas, and guidance in contributing towards my understanding and thoughts. I would also like to extent my gratitude to Associate Professor Dr. Zakiah Ahmad for always not just being the co-supervisor, but with her full-hearted support that she gave. Both of them provided me with the environment of ease of comfort to carry out my research work in a situation of immense pressure. I will cherish the guiding lesson that they have taught me which I should emulate in the future of my own work.
I would also like to thank adjunct professor; Prof. Pete Walker from Bath University for his guidance and all valuables comments given through-out this study.
Also, the laboratory technicians at the Concrete and Heavy Structural Laboratory of the Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam for their assistance in preparing the specimens for the testing, and also on highlighting the uses and condition of equipment and facilities at the laboratory. I also appreciate the extra hours of work that they have spent in order for me to complete the experimental work.
I would like also to recognise my colleagues who were sharing similar situations and experience in finishing their PhD, Jurina Jaafar and Marina Yusof and long lasting list to all friends in the faculty for their support and their invaluable views. Also, a special thanks to Wan Ahmad Fahmi Wan Kamaruddin for tremendously and sincerely being helpful in preparing the necessary laboratory work.
A special acknowledgement to all my family members, my parents, my husband and children, my mother in-law and my nine siblings-Othman, Mohd Nor, Isnah, Rahimah, Rohani, Rosmawati, Azlieynda, Nurin Hafilah and Mohd Jazlan and their family for their relentless prayer throughout these challenging years and also throughout my whole life in pursuing my academic dreams. M Pm* uVueu Ma&
TABLE OF CONTENTS
Page
CANDIDATE'S DECLARATION ii
ABSTRACT iii ACKNOWLEDGEMENTS iv
TABLE OF CONTENTS v LIST OF TABLES xi LIST OF FIGURES xiv LIST OF SYMBOLS xxii LIST OF ABBREVIATIONS xxiv
CHAPTER 1 : INTRODUCTION 1.1
1.2 1.3 1.4 1.5
Background Problem Statement Objectives of Study Scope of Study Structure of Thesis
1 4 7 8 11
CHAPTER 2 : TIMBER CONNECTIONS
2.1 Introduction 14 2.2 Ductility 15 2.3 Mechanical Timber Connections 16
2.3.1 Key Parameters Influencing Connections Capacity and Behaviour22
2.4 Mortise and Tenon Connections 24 2.5 Structural Behaviour of Mortise and Tenon Joints 32
2.5.1 Bending Moments 33 2.5.2 Shear Capacity 37
2.5.3 Tensile Capacity 38 2.6 Joint Design Using Malaysian Standard 40
2.7 Strength Group and Grade Identification 43
2.7.1 Kempas Species 44 2.7.2 Kapur Species 45 2.8 Characteristics of GFRP 46 2.9 GFRP in Timber Applications 47
2.10 Conclusions 50
CHAPTER 3 : LOAD-CARRYING CAPACITY OF TIMBER JOINTS
3.1 Introduction 52 3.2 European Yield Model (EYM) 52
3.3 National Design Standard (NDS, 2005) 57 3.4 EYM Modification for Wood Dowel Applications 63
3.5 Dowel Bending Strength 67 3.6 Dowel-bearing Strength 69
3.6.1 Influence of Dowel Diameter and Grain Directions 80
3.6.2 Influence of Specific gravity 86 3.6.3 Influence of Moisture Content 87
3.6.4 Influence of Density 88
3.7 Factor of Safety 89 3.8 Conclusions 92
CHAPTER 4 : RESEARCH METHODOLOGY
4.1 Introduction 94 4.2 Preparations of Dowel Specimens 97
4.3 Bending Strength Properties of Dowels 98
4.3.1 Sample Preparations 98
4.3.2 Test Method 99 4.3.3 Evaluation of Dowel Bending Yield Strength Properties 100
4.3.4 Evaluation of Toughness Properties of Dowels 102
4.3.5 Evaluation of Ductility 103
