Investigation of the Suitability of Finger Jointed Structural Timber for Use in Nail Plated Roof Trusses
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University of Southern Queensland Faculty of Engineering and Surveying Investigation of the Suitability of Finger Jointed Structural Timber for Use in Nail Plated Roof Trusses A dissertation submitted by Anthony Glen Dakin In fulfilment of the requirements of Courses ENG4111 and ENG4112 Research Project Towards the degree of Bachelor of Engineering (Civil Engineering) Submitted: October, 2011 Abstract The most common method of roof framing employed by Australian builders in modern construction is the use of pre-fabricated nail plated timber roof trusses. These trusses are predominantly manufactured from structural framing timber limited in length to a maximum of 6 metres. The style and size of houses increasingly preferred by Australian homeowners means that trusses are regularly required to span further than 6 metres. Truss manufacturers therefore use larger or additional nail plates to splice members during fabrication, and the assembly process becomes far more complex. Finger jointing of sawmill off-cuts and other short lengths of timber is a means of manufacturers economically producing timber in longer lengths. This dissertation investigates the suitability of using finger jointed structural timber for the fabrication of nail plated roof trusses. Physical testing and statistical analysis has been used to compare the performance of finger jointed structural timber with standard structural framing timber normally used in truss fabrication. This study involved characterizing the mechanical properties of the timber, as well as assessing the performance of joints including mechanical fasteners. These methods, along with the static modelling of loading situations, were also used to quantify the probability of inducing failures unique to finger jointed timber, during the truss fabrication and erection process. These investigations concluded that finger jointed timber could be produced with equivalent mechanical properties to standard framing timber. Joints manufactured from finger jointed and solid structural timber also exhibited no significant difference in performance. Furthermore, failures unique to finger jointed timber could occur during fabrication and erection, however, the probability of these, under normal use conditions, is generally quite low. i ii Certification I certify that the ideas, designs and experimental work, results, analyses and conclusions set out in this dissertation are entirely my own effort, except where otherwise indicated and acknowledged. I further certify that the work is original and has not been previously submitted for assessment in any other course or institution, except where specifically stated. Anthony Glen Dakin Student Number: 0050039573 Signature Date iii Acknowledgements I would like to thank the following people for providing assistance throughout the completion of my research. Associate Professor Karu Karunasena for his time and support as my research supervisor. My employer, Hyne and Son Pty Ltd, for their sponsorship of this research, including the provision of manufacturing equipment, materials, testing equipment and generous amounts of staff time. Mr Geoff Stringer and Mr Stephen Bolden from Hyne and Son, my „external‟ supervisors, for providing invaluable timber industry expertise, as well as on-going support and motivation. Mr Steve Blanch from Sid‟s Place for his valuable truss industry expertise, and the provision of hardware and fabrication of test samples. My family and friends for their unwavering support throughout the duration of my studies. Without their support the successful completion of this project would not have been possible. Anthony G Dakin University of Southern Queensland October, 2011 iv Table of Contents Abstract .................................................................................................................................. i Acknowledgements .................................................................................................... iv List of Figures ............................................................................................................. x List of Tables ............................................................................................................ xiv Chapter 1 Introduction .......................................................... 1 1.0 Outline of the study ......................................................................................... 1 1.1 Background ..................................................................................................... 2 1.2 Project Aim and Scope .................................................................................... 5 1.3 Project Objectives ........................................................................................... 6 1.4 Overview of the Dissertation ........................................................................... 7 Chapter 2 Literature Review ................................................ 8 2.0 Introduction ..................................................................................................... 8 2.1 In-Service Performance................................................................................... 9 2.1.1 Truss Action........................................................................................................ 9 2.1.1.1 Details of Material in Application .............................................................12 2.1.1.2 Test Methods ............................................................................................13 2.1.2 Truss Joints and Connections..............................................................................14 2.1.2.1 Truss Joints ...............................................................................................14 2.1.2.1.1 Details of Material in Application ........................................................16 2.1.2.1.2 Test Methods .......................................................................................17 2.1.2.2 Connections ..............................................................................................18 2.1.2.2.1 Details of Material in Application ........................................................19 2.1.2.2.2 Test Methods .......................................................................................22 2.1.3 Fabrication Issues ...............................................................................................22 2.1.3.1 Modelling of Handling Stresses .................................................................23 2.1.3.2 Test Methods ............................................................................................24 v 2.1.4 Truss Erection Issues ..........................................................................................25 2.1.4.1 Modelling of Temporary Construction Stresses .........................................26 2.1.4.2 Test Methods ............................................................................................26 Chapter 3 Manufacture of Finger Jointed Timber ............ 28 3.0 Introduction ................................................................................................... 28 3.1 Materials ........................................................................................................ 29 3.1.1 Timber Feedstock ...............................................................................................29 3.1.2 Adhesive ............................................................................................................30 3.2 Process ........................................................................................................... 30 Chapter 4 Methods of Testing and Assessment ................. 33 4.0 Introduction ................................................................................................... 33 4.1 Mechanical Properties ................................................................................... 34 4.1.1 Assessment ........................................................................................................34 4.1.2 Testing and Analysis Methods ............................................................................34 4.1.2.1 Bending Strength and Stiffness .................................................................34 4.1.2.2 Tension Strength .......................................................................................37 4.1.2.3 Shear Strength ..........................................................................................40 4.1.2.4 Compression Strength ...............................................................................42 4.2 Truss Joints and Connections ....................................................................... 45 4.2.1 Assessment ........................................................................................................45 4.2.2 Testing and Analysis Methods ............................................................................46 4.2.2.1 Nail Plate Parallel to Timber Grain – Stiffness and Strength ......................46 4.2.2.2 Nail Plate Perpendicular to Timber Grain ..................................................49 4.2.2.4 MultiGrip Connection of Roof Truss to Supporting Wall ...........................54 4.2.2.5 Screw Connection of Girder Bracket to Truss Chord .................................56 4.3 Fabrication Issues .......................................................................................... 58 4.3.1 Assessment ........................................................................................................58