Applied Science, Faculty of
Civil Engineering, Department of
DSpace
UBCV
Gerber, Adam Reynold
Master of Applied Science - MASc
University of British Columbia
Timber-Concrete Composite (TCC) systems are comprised of a timber element connected to a concrete slab through a mechanical shear connection. When TCC are used as flexural elements, the concrete and timber are located in compression and tension zones, respectively. A large number of precedents for T-beam configurations exist; however, the growing availability of flat plate engineered wood products (EWPs) in North America in combination with a concrete topping has offered designers and engineers greater versatility in terms of architectural expression and structural and building physics performance. The focus of this investigation was to experimentally determine the properties for a range of proprietary, open source, and novel TCC systems in several Canadian EWPs. Strength and stiffness properties were determined for 45 different TCC configurations based on over 300 small-scale shear tests. Nine connector configurations were selected for implementation in full-scale bending and vibration tests. Eighteen floor panels were tested for elastic stiffness under a quasi-static loading protocol and measurements of the dynamic properties were obtained prior to loading to failure. The tests confirmed that both hand calculations according to the γ-method and more detailed FEM models can predict the basic stiffness and dynamic properties of TCC floors within a reasonable degree of accuracy; floor capacities were more difficult to predict, however, failure did usually not occur until loading reached 10 times serviceability requirements. The research demonstrated that all selected connector configurations produced efficient timber-concrete-composite systems.
TIMBER-CONCRETE COMPOSITE CONNECTORS IN FLAT-PLATE ENGINEERED WOOD PRODUCTS by ADAM REYNOLD GERBER B.ASc., The University of British Columbia, 2016 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2016 © Adam Reynold Gerber, 2016 ii Abstract Timber-Concrete Composite (TCC) systems are comprised of a timber element connected to a concrete slab through a mechanical shear connection. When TCC are used as flexural elements, the concrete and timber are located in compression and tension zones, respectively. A large number of precedents for T-beam configurations exist; however, the growing availability of flat plate engineered wood products (EWPs) in North America in combination with a concrete topping has offered designers and engineers greater versatility in terms of architectural expression and structural and building physics performance. The focus of this investigation was to experimentally determine the properties for a range of proprietary, open source, and novel TCC systems in several Canadian EWPs. Strength and stiffness properties were determined for 45 different TCC configurations based on over 300 small-scale shear tests. Nine connector configurations were selected for implementation in full-scale bending and vibration tests. Eighteen floor panels were tested for elastic stiffness under a quasi-static loading protocol and measurements of the dynamic properties were obtained prior to loading to failure. The tests confirmed that both hand calculations according to the γ-method and more detailed FEM models can predict the basic stiffness and dynamic properties of TCC floors within a reasonable degree of accuracy; floor capacities were more difficult to predict, however, failure did usually not occur until loading reached 10 times serviceability requirements. The research demonstrated that all selected connector configurations produced efficient timber-concrete-composite systems. iii Preface This thesis is the original work of Adam Gerber, executed under the supervision of Dr. Thomas Tannert. The identification and design of the research program was performed largely independently; however, some suggestions were incorporated from industry professionals and suppliers regarding specific connections to be tested. All parts of the research reported herein were performed primarily by myself, with occasional assistance as needed from friends, colleagues, and technicians from the faculties of Civil Engineering and Wood Science. The analysis of all data generated over the course of the research program was performed by myself, in consultation with my supervisor, Dr. Thomas Tannert. A portion of the experimental results for the small-scale tests have been published in collaboration with Dr. Thomas Tannert as part of the proceedings of the ASCE Structures Congress 2015 in Portland, USA. A second manuscript has been accepted for publication at the 2016 World Conference on Timber Engineering in Vienna, Austria. A test report on the full scale bending tests was prepared in order to fulfill the requirements of the funding received by Forestry Innovation Investment. iv Table of Contents Abstract .......................................................................................................................................... ii Preface ........................................................................................................................................... iii Table of Contents ......................................................................................................................... iv List of Tables .............................................................................................................................. viii List of Figures .................................................................................................................................x Acknowledgements ................................................................................................................... xvii Chapter 1. Introduction ..............................................................................................................1 1.1. Timber-Concrete Composite Systems ............................................................................ 1 1.1.1. Overview ................................................................................................................... 1 1.1.2. Advantages of Timber Concrete Composite (TCC) Construction ............................ 2 1.2. Engineered Wood Products ............................................................................................. 3 1.2.1. Overview ................................................................................................................... 3 1.2.2. Laminated Strand Lumber ........................................................................................ 3 1.2.3. Laminated Veneer Lumber ....................................................................................... 4 1.2.4. Vertical Laminated Veneer Lumber ......................................................................... 4 1.2.5. Cross-Laminated Timber .......................................................................................... 5 1.3. Connectors ...................................................................................................................... 5 1.3.1. Introduction ............................................................................................................... 5 1.3.2. Geometric Interlock Connections ............................................................................. 6 1.3.3. Mechanical Fasteners ................................................................................................ 7 1.3.4. Screw-Type Connectors ............................................................................................ 7 1.3.5. Adhesive Connections .............................................................................................. 8 1.4. Design of TCC ................................................................................................................ 9 1.4.1. Overview ................................................................................................................... 9 1.4.2. Gamma Method ...................................................................................................... 10 1.4.3. Long-Term Behaviour ............................................................................................ 11 1.4.4. Vibration Performance ............................................................................................ 11 v 1.4.5. Finite Element Modeling ........................................................................................ 12 1.5. Research Need and Objectives ...................................................................................... 13 1.5.1. Research need ......................................................................................................... 13 1.5.2. Objectives ............................................................................................................... 13 Chapter 2. Small-Scale Shear Tests .........................................................................................15 2.1. Materials ....................................................................................................................... 15 2.1.1. Overview ................................................................................................................. 15 2.1.2. Engineered Wood Products..................................................................................... 15 2.1.3. Concrete .................................................................................................................. 16 2.1.4. Insulation................................................................................................................. 17 2.1.5. Adhesive ................................................................................................................. 17 2.1.6. Plastic Separation Layer ......................................................................................... 17 2.2. Connectors .................................................................................................................... 18 2.2.1. Overview ................................................................................................................. 18 2.2.2. Self-Tapping Wood Screws .................................................................................... 18 2.2.3. FT-Connector .......................................................................................................... 20 2.2.4. HBV System ........................................................................................................... 20 2.2.5. Transverse Notch Connection ................................................................................. 22 2.2.6. Localized Concrete Dowel Connection .................................................................. 23 2.2.7. Adhesive and Hybrid Adhesive and Screw Connections ....................................... 23 2.3. Experimental Design ..................................................................................................... 24 2.3.1. Investigated Parameters .......................................................................................... 24 2.3.2. Specimen Geometry and Connector Layout ........................................................... 27 2.4. Methods ......................................................................................................................... 32 2.4.1. Specimen Fabrication.............................................................................................. 32 2.4.2. Test Setup and Instrumentation .............................................................................. 33 2.4.3. Loading Protocol ..................................................................................................... 34 2.4.4. Analysis Methods.................................................................................................... 35 2.5. Results and Discussion ................................................................................................. 38 2.5.1. Overview ................................................................................................................. 38 2.5.2. Fully Threaded Screws Installed at 30° .................................................................. 38 vi 2.5.3. Fully Threaded Screw Pairs Installed at 45° ........................................................... 41 2.5.4. Partially Threaded Screws with Bearing Washer ................................................... 43 2.5.5. Fully Threaded Screws with FT Connector ............................................................ 44 2.5.6. Fully Threaded Screws Installed at 45° with 25mm Insulation Layer ................... 46 2.5.7. HBV System without Insulation Layer ................................................................... 47 2.5.8. HBV System with 25mm Insulation Layer ............................................................. 49 2.5.9. Transverse Notch Connections ............................................................................... 50 2.5.10. Localized Concrete Dowel Connections ............................................................. 50 2.5.11. Adhesive Connections ......................................................................................... 51 2.5.12. Hybrid Adhesive/Screw Connections ................................................................. 52 2.6. Discussion ..................................................................................................................... 54 2.6.1. Comparison of Normalized Connector Performance .............................................. 54 2.6.2. Characteristic Connector Values............................................................................. 60 2.6.3. Influence of Interlayer............................................................................................. 62 2.6.4. Influence of EWP and Wood Density ..................................................................... 63 2.6.5. Influence of Screw Embedment .............................................................................. 65 2.6.6. Influence of Screw Diameter .................................................................................. 66 2.6.7. Influence of Moisture Condition ............................................................................. 68 Chapter 3. Full-Scale Bending Tests .......................................................................................69 3.1. Design of Specimens ..................................................................................................... 69 3.1.1. Overview ................................................................................................................. 69 3.1.2. Panel Specifications ................................................................................................ 70 3.2. Specimen Fabrication .................................................................................................... 75 3.2.1. Overview ................................................................................................................. 75 3.2.2. Self-Tapping Screw Connectors ............................................................................. 75 3.2.3. HBV Steel Mesh Connectors .................................................................................. 76 3.2.4. Concrete Casting ..................................................................................................... 77 3.3. Methods ......................................................................................................................... 77 3.3.1. Design of Panels Using FEM .................................................................................. 77 3.3.2. Test Set-up .............................................................................................................. 81 3.3.3. Dynamic Test Procedure ......................................................................................... 82 vii 3.3.4. Quasi-Static Test Procedure .................................................................................... 84 3.3.5. Analysis Methods.................................................................................................... 85 3.4. Results ........................................................................................................................... 85 3.4.1. Bending Stiffness .................................................................................................... 85 3.4.2. Vibration Results .................................................................................................... 91 3.4.3. Panel Capacity ........................................................................................................ 92 3.4.4. Failure Modes ......................................................................................................... 98 3.5. Discussion ................................................................................................................... 105 3.5.1. Differences Between FEM Model and Experiment .............................................. 105 3.5.2. Difference Between Small and Full Scale Tests ................................................... 105 3.5.3. Importance of Failure Modes ................................................................................ 106 3.5.4. ULS vs. SLS Considerations................................................................................. 106 Chapter 4. Conclusion ............................................................................................................108 Bibliography ...............................................................................................................................109 Appendices ..................................................................................................................................114 Appendix A - Load-Displacement Curves for Phase I Specimens ......................................... 114 Appendix B - Pictures of Failure Modes of Phase I specimens .............................................. 137 Appendix C - Design of Phase II Specimens According to Gamma Method ......................... 139 Appendix D - Pictures of Failure Modes of Phase II specimens ............................................ 143 viii List of Tables Table 1: EWP Mechanical Properties ........................................................................................... 16 Table 2: Concrete Properties ......................................................................................................... 16 Table 3: STS Properties ............................................................................................................... 19 Table 4: HBV Properties (per mm length) .................................................................................... 21 Table 5: ASSY SK Partially Threaded Screw Connector with Washer Heads ............................ 24 Table 6: FT Connector with ASSY VG Fully Threaded Screws with Countersunk Heads ......... 25 Table 7: ASSY VG Fully Threaded Screw Connector with Cylinder Heads ............................... 25 Table 8: HBV Glued in Steel Mesh System ................................................................................. 26 Table 9: Transverse Notched Connections ................................................................................... 26 Table 10: Localized Concrete Dowel Connections ...................................................................... 26 Table 11: Adhesive and Hybrid Connections ............................................................................... 27 Table 12: Calculated Parameters .................................................................................................. 36 Table 13: 8x240, 10x240, and 10x300 ASSY VG at 30º Average Results (per screw) ............... 40 Table 14: 10x200 ASSY VG Pairs at 45º Average Results (per screw pair)................................ 42 Table 15: 10x260 ASSY SK at 30º Average Results (per screw) ................................................ 44 Table 16: 10x240 and 10x300 ASSY VG with FT Connector Average Results (per connector) 45 Table 17: 10x220 ASSY VG Pairs at 45º + 25mm Insulation Average Results (per screw pair) 47 Table 18: 90mm HBV System Average Results (per mm length)................................................ 48 Table 19: 120mm HBV System + 25mm Insulation Layer (per mm length) ............................... 50 Table 20: Adhesive only Connection Averaged Results (per mm length) ................................... 52 Table 21: Hybrid Adhesive/Screw Connections Average Results (per screw) ............................ 52 Table 22: Equivalent ULS and SLS Performance in LSL ............................................................ 55 Table 23: Equivalent ULS and SLS Performance in LVL ........................................................... 55 ix Table 24: Equivalent ULS and SLS Performance in CLT ............................................................ 56 Table 25: Equivalent ULS and SLS Performance through 25mm Insulation ............................... 56 Table 26: Adhesive and Hybrid Adhesive and Self-Tapping Screw Characteristic Strengths ..... 60 Table 27: Self-Tapping Screw Characteristic Connector Strengths ............................................. 61 Table 28: HBV Characteristic Connector Strengths ..................................................................... 62 Table 29: Influence of Removing Slip Membrane ....................................................................... 63 Table 30: Influence of Wood Density on Strength and Stiffness of 10x240 ASSY VG .............. 64 Table 31: Influence of Wood Density on Strength and Stiffness of all STS Connectors ............. 64 Table 32: Influence of Screw Embedment for 10mm Diameter ASSY VG Screws in CLT........ 66 Table 33: Influence of Screw Diameter in LSL ............................................................................ 67 Table 34: Influence of Screw Diameter in all EWPs .................................................................... 67 Table 35: Influence of Moisture Condition .................................................................................. 68 Table 36: Connector Description Used for Full-Scale Bending Tests .......................................... 69 Table 37: Full-Scale Panel Configurations ................................................................................... 70 Table 38: FEM Model Parameters ................................................................................................ 78 Table 39: Analysis Methods for Full-Scale Tests ......................................................................... 85 Table 40: Panel Stiffness - EIeff (1012 N*mm2) ............................................................................. 86 Table 41: Panel Vibration Results ................................................................................................ 92 Table 42: Panel Capacities ............................................................................................................ 93 Table 43: Panel Failure Modes ..................................................................................................... 99 x List of Figures Figure 1: ASSY VG CYL (left), ASSY VG CSK (middle), and ASSY SK (right) .................... 19 Figure 2: FT Connector ................................................................................................................. 20 Figure 3: HBV Connector Installation .......................................................................................... 21 Figure 4: Transverse Notch Connection ....................................................................................... 22 Figure 5: Localized Concrete Dowel Connection ......................................................................... 23 Figure 6: VG1-11, SK1-3, FT1-5 (137 Specimens) ..................................................................... 28 Figure 7: VG12-14 (18 Specimens) .............................................................................................. 28 Figure 8: VG15-17 (17 Specimens) .............................................................................................. 29 Figure 9: AB1,AB5 (12 Specimens) ............................................................................................. 29 Figure 10: AB6-8 (24 Specimens) ................................................................................................ 30 Figure 11: GM1-4 (40 Specimens) ............................................................................................... 30 Figure 12: GM5-7 (18 Specimens) ............................................................................................... 31 Figure 13: TN1-3 (18 Specimens) ................................................................................................ 31 Figure 14: LD1-5 (30 Specimens) ................................................................................................ 32 Figure 15: Shear-Test Specimens: Inclined STS Connectors (top) Epoxied with STS Backup (bottom left), HBV Mesh (bottom, middle and right) .................................................................. 33 Figure 16: Shear Test Setup: Schematic (left) and Photo (right) .................................................. 34 Figure 17: Loading Protocol ......................................................................................................... 35 Figure 18: Calculation of Strength and Stiffness Parameters ....................................................... 36 Figure 19: Averaged Sample Curve .............................................................................................. 37 Figure 20: 8x240 ASSY VG at 30º Average Results (per screw) ................................................ 39 Figure 21: 10x240 and 10x300 ASSY VG at 30º Average Results (per screw) ........................... 40 Figure 22: 10x200 ASSY VG Pairs at 45º Average Results (per screw pair) .............................. 42 xi Figure 23: 10x260 ASSY SK at 30º Average Results (per screw) ............................................... 44 Figure 24: 10x240 and 10x300 ASSY VG with FT Connector Average Results (per connector) 46 Figure 25: 10x220 ASSY VG Pairs at 45º + 25mm Insulation Average Results (per screw pair)47 Figure 26: 90mm HBV System Average Results (per mm length) .............................................. 48 Figure 27: 120mm HBV System + 25mm Insulation Layer (per mm length) .............................. 49 Figure 28: Adhesive only Connection Averaged Results (per mm length) .................................. 51 Figure 29: Hybrid Adhesive/Screw Connections Average Results (per screw) ........................... 53 Figure 30: AB7 – SikaDur32 Adhesive + 10x240 ASSY VG at 30º in LSL ............................... 53 Figure 31: ULS Strength Matched Connectors in LSL ................................................................ 57 Figure 32: SLS Stiffness Matched Connectors in LSL ................................................................. 57 Figure 33: ULS Strength Matched Connectors in LVL ................................................................ 58 Figure 34: SLS Stiffness Matched Connectors in LVL ................................................................ 58 Figure 35: ULS Strength Matched Connectors in CLT ................................................................ 59 Figure 36: SLS Stiffness Matched Connectors in CLT ................................................................ 59 Figure 37: ULS and SLS Strength and Stiffness Matched Connectors through Insulation .......... 60 Figure 38: Interlayer Influence (8x240 ASSY VG in LSL and LVL) .......................................... 63 Figure 39: Influence of Wood Density on 10x240 ASSY VG Performance ................................ 64 Figure 40: Influence of Screw Embedment for 10mm Diameter ASSY VG Screws in CLT ...... 66 Figure 41: Influence of Screw Diameter in all EWPs................................................................... 67 Figure 42: Layout of Typical Panel with Inclined STS (S1, S2, S3) ............................................ 71 Figure 43: Detail A (inclined STS) ............................................................................................... 71 Figure 44: Layout of Typical Panel with Pairs of Inclined STS Through Rigid Insulation (S4) . 71 Figure 45: Detail B (Pairs of Inclined STS through Rigid Insulation) ......................................... 72 Figure 46: Layout of Typical Panel with Adhesive Layer and Inclined STS (S5) ....................... 72 xii Figure 47: Detail A (Adhesive Layer and Inclined STS) ............................................................. 72 Figure 48: Layout of Typical Panel with HBV Mesh (S6, S7, & S8) .......................................... 73 Figure 49: Detail C (HBV Mesh).................................................................................................. 73 Figure 50: Section C-C` (HBV Mesh) .......................................................................................... 73 Figure 51: Layout of Typical Panel with HBV Mesh through Rigid Insulation (S9)................... 74 Figure 52: Detail D (HBV Mesh through Rigid Insulation) ......................................................... 74 Figure 53: Section D-D` (HBV Mesh through Rigid Insulation) ................................................. 74 Figure 54: Installation of Inclined STS ......................................................................................... 75 Figure 55: Installation of HBV Mesh ........................................................................................... 76 Figure 56: Concrete Casting ......................................................................................................... 77 Figure 57: FEM Model of Set-up with Elastic Beam Elements and Springs at Fastener Locations....................................................................................................................................................... 79 Figure 58: Close up of FEM Model at Springs ............................................................................. 79 Figure 59: Nonlinear Spring Calibration ...................................................................................... 80 Figure 60: Test Setup and Instrumentation ................................................................................... 81 Figure 61: Photo of Full-Scale Bending Test ............................................................................... 82 Figure 62: Acceleration Time History from Heel Strike (left) and Fundamental Frequency Determination using FFT (right) ................................................................................................... 83 Figure 63: Full Scale Loading Protocol ........................................................................................ 83 Figure 64: Load vs. Displacement of Series 1 up to Service Level .............................................. 87 Figure 65: Load vs. Displacement of Series 2 up to Service Level .............................................. 87 Figure 66: Load vs. Displacement of Series 3 up to Service Level .............................................. 88 Figure 67: Load vs. Displacement of Series 4 up to Service Level .............................................. 88 Figure 68: Load vs. Displacement of Series 5 up to Service Level .............................................. 89 Figure 69: Load vs. Displacement of Series 6 up to Service Level .............................................. 89 xiii Figure 70: Load vs. Displacement of Series 7 up to Service Level .............................................. 90 Figure 71: Load vs. Displacement of Series 8 up to Service Level .............................................. 90 Figure 72: Load vs. Displacement of Series 9 up to Service Level .............................................. 91 Figure 73: Load vs. Displacement of Series 1 .............................................................................. 94 Figure 74: Load vs. Displacement of Series 2 .............................................................................. 94 Figure 75: Load vs. Displacement of Series 3 .............................................................................. 95 Figure 76: Load vs. Displacement of Series 4 .............................................................................. 95 Figure 77: Load vs. Displacement of Series 5 .............................................................................. 96 Figure 78: Load vs. Displacement of Series 6 .............................................................................. 96 Figure 79: Load vs. Displacement of Series 7 .............................................................................. 97 Figure 80: Load vs. Displacement of Series 8 .............................................................................. 97 Figure 81: Load vs. Displacement of Series 9 .............................................................................. 98 Figure 82: Load vs Shear Slip of Series 1................................................................................... 100 Figure 83: Load vs Shear Slip of Series 2................................................................................... 100 Figure 84: Load vs. Shear Slip of Series 3.................................................................................. 101 Figure 85: Load vs. Shear Slip of Series 4.................................................................................. 101 Figure 86: Load vs. Shear Slip of Series 5.................................................................................. 102 Figure 87: Load vs. Shear Slip of Series 6.................................................................................. 102 Figure 88: Load vs. Shear Slip of Series 7.................................................................................. 103 Figure 89: Load vs. Shear Slip of Series 8.................................................................................. 103 Figure 90: Load vs. Shear Slip of Series 9.................................................................................. 104 Figure 91: VG1 - 8x240 ASSY VG at 30˚ in LSL .................................................................... 114 Figure 92: VG2 – 8x240 ASSY VG at 30˚ + Friction in LSL ................................................... 114 Figure 93: VG3 – 10x240 ASSY VG at 30˚in LSL ................................................................... 115 xiv Figure 94: VG4 - 8x240 ASSY VG at 30˚in LVL..................................................................... 115 Figure 95: VG5 – 8x240 ASSY VG at 30˚ + Friction in LVL .................................................. 116 Figure 96: VG6 – 10x240 ASSY VG at 30˚ in LVL ................................................................. 116 Figure 97: VG7 – 8x240 ASSY VG at 30˚ in Brisco LVL ....................................................... 117 Figure 98: VG8 – 10x240 ASSY VG at 30˚ in Brisco LVL ..................................................... 117 Figure 99: VG9 - 8x240 ASSY VG at 30˚ in CLT .................................................................... 118 Figure 100: VG10 – 10x240 ASSY VG at 30˚ in CLT ............................................................. 118 Figure 101: VG11 – 10x300 ASSY VG at 30˚ in CLT ............................................................. 119 Figure 102: VG12 – 10x200 ASSY VG Pairs at 45˚ in LSL ..................................................... 119 Figure 103: VG13 – 10x200 ASSY VG Pairs at 45˚ in LVL .................................................... 120 Figure 104: VG14 – 10x200 ASSY VG Pairs at 45˚ in CLT .................................................... 120 Figure 105: VG15 – 10x220 ASSY VG Pairs at 45˚ through 25mm Insulation in LSL ........... 121 Figure 106: VG16 - 10x220 ASSY VG Pairs at 45˚ through 25mm Insulation in LVL ............ 121 Figure 107: VG17 - 10x220 ASSY VG Pairs at 45˚ through 25mm Insulation in CLT ............ 122 Figure 108: SK1 – 10x260 ASSY SK at 30˚ in LSL .................................................................. 122 Figure 109: SK2 – 10x260 ASSY SK at 30˚ in LVL ................................................................. 123 Figure 110: SK3 – 10x260 ASSY SK at 30˚ in CLT .................................................................. 123 Figure 111: FT1 – 10x240 ASSY VG plus FT-Connector at 30˚ in LSL .................................. 124 Figure 112: FT2 – 10x240 ASSY VG plus FT-Connector at 30˚ in LVL .................................. 124 Figure 113: FT3 – 10x240 ASSY VG plus FT-Connector at 30˚ in Brisco LVL ...................... 125 Figure 114: FT4 – 10x240 ASSY VG plus FT-Connector at 30˚ in CLT .................................. 125 Figure 115: FT5 – 10x300 ASSY VG plus FT-Connector at 30˚ in CLT .................................. 126 Figure 116: AB1 – SikaDur 32 Adhesive and LVL (Wet/Dry) .................................................. 126 Figure 117: AB5 – SikaDur 32 Adhesive and LVL (Wet/Wet) ................................................. 127 xv Figure 118: AB6 – Hybrid Adhesive plus 10x240 ASSY VG at 30˚ in LVL ............................ 127 Figure 119: AB7 – Hybrid Adhesive plus 10x240 ASSY VG at 30˚ in LSL ............................. 128 Figure 120: AB8 – Hybrid Adhesive plus 10x240 ASSY VG at 30˚ in CLT ............................ 128 Figure 121: LD1 – Localized Concrete Dowels in LSL with Slip Membrane ........................... 129 Figure 122: LD2 – Localized Concrete Dowels in LSL without Slip Membrane ...................... 129 Figure 123: LD3 – Localized Concrete Dowels in LVL with Slip Membrane .......................... 130 Figure 124: LD4 – Localized Concrete Dowels in LVL without Slip Membrane ..................... 130 Figure 125: LD5 – Localized Concrete Dowels in CLT with Slip Membrane ........................... 131 Figure 126: TN1 – Transverse Notch in LSL ............................................................................. 131 Figure 127: TN2 – Transverse Notch in LVL ............................................................................ 132 Figure 128: TN3 – Transverse Notch in CLT ............................................................................. 132 Figure 129: GM1 – 300mm HBV Mesh in LSL ......................................................................... 133 Figure 130: GM2 – 300mm HBV Mesh in LVL ........................................................................ 133 Figure 131: GM3 – 300mm HBV Mesh in Brisco LVL ............................................................. 134 Figure 132: GM4 – 300mm HBV Mesh in CLT ........................................................................ 134 Figure 133: GM5 – 300mm HBV Mesh through 25mm Insulation in LSL ............................... 135 Figure 134: GM6 – 300mm HBV Mesh through 25mm Insulation in LVL .............................. 135 Figure 135: GM7 – 300mm HBV Mesh through 25mm Insulation in CLT ............................... 136 Figure 136: HBV Yielding Failure ............................................................................................. 137 Figure 137: FT Connector and Tensile Failure of Screw ........................................................... 137 Figure 138: ASSY VG Failing Bond Between Threads and Concrete ....................................... 137 Figure 139: Concrete Shear Failure for Transverse Notch (left) and Localized Dowel (right) Connections................................................................................................................................. 138 Figure 140: Series 1 Panel Failing Due to Concrete Crushing and Timber Tensile Fracture .... 143 xvi Figure 141: Series 2 Panel Failing by Screw Withdrawal Followed by Tensile Failure of Timber..................................................................................................................................................... 143 Figure 142: Series 3 Panel Exhibiting Tensile Failure Prior to Connector Yielding or Concrete Crushing ...................................................................................................................................... 144 Figure 143: Series 4 Panel Failing by Screw Withdrawal through 25mm Rigid Insulation ....... 144 Figure 144: Series 7 Panel with HBV Connector Prior to (left) and After Yielding (right) ....... 145 Figure 145: Series 9 Panel with HBV Connector Yielding through 25mm Rigid Insulation..... 145 Figure 146: Series 5 Panel Failures (a) Initial Failure of Adhesive Bond Line Followed by (b) Screw Withdrawal Failure and Finally (c)(d) Timber Tensile Failure ....................................... 146 xvii Acknowledgements This project would not have been possible without the generous contributions of many parties. The industry support allowed us to perform a comprehensive study that is expected to provide a meaningful contribution to the development and use of TCC systems in Canada. The help of the students from Dr. Tannert’s research team, my colleagues and friends, and the technicians at the UBC and FPInnovations laboratories is greatly appreciated. Funding Partners: Forest Innovations Investment through Wood First Program NSERC through Engage program Industry Sponsors: Weyerhaeuser – official NSERC partner and sponsorship of LSL Louisiana Pacific – sponsorship of LVL Brisco Manufacturing – sponsorship of vertically laminated LVL Structurlam Products – sponsorship of CLT MyTiCon Timber Connectors Inc. – sponsorship of self-tapping screws and FT connectors TiComTec – sponsorship of HBV mesh Sika Canada – sponsorship of adhesive Lafarge – sponsorship of concrete Collaborators: FPInnovations – full scale testing UBC Centre for Advanced Wood Processing –fabrication of test specimens Equilibrium Consulting – design considerations 1 Chapter 1. Introduction 1.1. Timber-Concrete Composite Systems 1.1.1. Overview Timber-concrete composite (TCC) systems were first introduced at the end of WWI due to widespread shortages in steel and concrete (Yeoh et al. 2011). They are generally comprised of a timber beam or deck element connected compositely to a concrete topping above. The materials are arranged such that their inherent strengths complement each other in flexure under gravity loads. Concrete is strong and stiff in compression, as is timber in tension, so they are located at the top and bottom of the section, respectively. The efficiency of TCCs depends largely on the properties of the shear connection between them. Ceccotti (2002) identifies four categories of connectors ranging from low-stiffness, where only partial composite behaviour is achieved, to rigid connectors where composite sections can be evaluated based on Euler-Bernouli beam theory assumptions that plane sections remain plane (i.e. the transformed section method). TCCs offer significant improvements over conventional reinforced concrete and light wood-frame flooring systems with regard to strength, section depth, stiffness, and vibration performance. Yeoh et al. (2011) identified three fundamental design criteria for this technique to be utilized efficiently: (1) the neutral axis of the composite cross-section should be located near the timber-concrete interface to ensure both components act efficiently with concrete purely compressed (and therefore un-cracked) and the timber mostly subjected to tensile stresses; (2) the connection system must be strong and stiff enough to transfer the design shear force and provide an effective composite action; and (3) the timber part (joist/beam or solid deck made from individual planks 2 nailed together on edge) must be strong enough to resist bending tensile stresses induced by gravity loads applied on the composite beam. Awareness of and familiarity with the behaviour and design methods of TCCs are important for this type of construction to become a viable option for the building industry. 1.1.2. Advantages of Timber Concrete Composite (TCC) Construction Traditional reinforced concrete and light wood-frame floors suffer from several unique weaknesses that are resolved by a TCC system. The design of wood floors is often governed by serviceability criteria such as deflections and vibrations, and are plagued with a reputation for poor acoustic and fire performance without significant steps toward mitigation. Reinforced concrete floors on the other hand make inefficient use of material, with up to 60% of the gross cross section being cracked in tension and not contributing to the load bearing resistance. This necessitates greater section depths (and resulting CO2 emissions) and introduces vulnerabilities to corrosion and fire for reinforcing steel that is left exposed (Gutkowski et al. 2008). TCC construction offers several advantages over conventional systems, such as (1) increased stiffness, mass and damping compared to timber-only floors; (2) up to 50% reduction in slab depths; (3) increased acoustic and insulation performance, particularly with the introduction of rigid insulation at the interlayer; and (4) reduced heating and cooling costs due to increased thermal mass (Ceccotti 2002; Gutkowski et al. 2008; Yeoh et al. 2011). Composite technology is already familiar to builders of steel-concrete composite floors and the transition to TCC should be relatively straightforward by adapting existing practices (Yeoh et al. 2011). Additionally, the introduction of a timber element in place of the cracked section of concrete allows for the following benefits: (1) reduced installation time and cost as a result of 3 permanent formwork for the concrete topping, reduced shoring & lower-weight elements to be installed; (2) reduced foundation loads compared to conventional concrete system; (3) low embodied energy; (4) reduced seismic demands due to lower floor weight; and (5) improved resistance to wind induced vibrations in tall wood structures (Yeoh et al. 2011; Green et al. 2012). Significant benefits can also be realized in the rehabilitation of existing timber structures through the introduction of a lightweight concrete topping which improves the strength and serviceability performance of the structure (Jorge et al. 2011). 1.2. Engineered Wood Products 1.2.1. Overview Engineered wood products (EWP) are created by bonding together graded strands, veneers or lumber into larger structural elements. This process results in stable products with more uniform strength and stiffness than traditional lumber products. Additionally, large sections are produced using smaller feed-in stock which can be cultivated according to sustainable forest practices. While many EWPs are commonly available, only those available in large panel format in North America will be discussed in the following. 1.2.2. Laminated Strand Lumber Laminated Strand Lumber (LSL) is manufactured from strands of wood species or, combinations of species, blended with an isocyanate-based adhesive, where the strands are oriented parallel to the length of the member (CCMC 12627-R, 2015). The product is first pressed into billets, which are typically cut into smaller sizes depending on their intended use. Commonly available dimensions include panels with thicknesses of either 45mm or 89mm and widths up to 1220mm. 4 1.2.3. Laminated Veneer Lumber Laminated Veneer Lumber (LVL) is manufactured by laminating graded wood veneers coated with an exterior-type structural adhesive (CCMC 11518-R, 2015). LVL can be ordered with or without cross-plies, although products without cross-plies are most common. The products are typically identified by bending strength and stiffness. For example, a specification of 2900Fb-2.0E LVL refers to an LVL product with an allowable bending strength of 2900psi (carried over from allowable stress design), and an apparent modulus of elasticity (MOE) of 2.0x106psi. Strength values are differentiated for “plank” versus “beam” orientations, which refers to loads being applied to the wide versus narrow face of the member respectively. LVL is produced in large billets, which are generally 1220mm wide and range in thickness from 19mm to 89mm. Typically, the billets are cut into smaller sizes at the plant for use as joists and beams, however, full-dimension panels are available by special order up to 24.4m length (CCMC 08675-R, 2012). 1.2.4. Vertical Laminated Veneer Lumber Brisco Fine LineTM vertical veneer panels are a proprietary product produced by secondary lamination of primary LVL products. Panel strength and stiffness properties are specified in accordance with CCMC 11518-R (2015), which covers the primary LVL product used for secondary lamination (Brisco 2016). This approach allows greater versatility in specifying panel dimensions over conventional LVL products, which have a maximum panel thickness of 89mm. In addition to panels being available in widths up to 1220mm, depths ranging from 80mm to 292mm, and lengths up to 18.4m, architectural quality planed and sanded finishes can also be specified. Plank versus beam orientation are again differentiated, and grade specifications reference the apparent MOE in units of 106psi. 5 1.2.5. Cross-Laminated Timber Cross-Laminated Timber (CLT) is a structural wood panel product built up from dimensional lumber. “CLT panels consist of several layers of boards stacked crosswise (typically at 90 degrees) and glued together on their wide faces and, sometimes, on the narrow faces as well. A cross-section of a CLT element has at least three glued layers of boards placed in orthogonally alternating orientation to the neighboring layers. In special configurations, consecutive layers may be placed in the same direction, giving a double layer (e.g. double longitudinal layers at the outer faces and additional double layers at the core of the panel) to obtain specific structural capacities. CLT products are usually fabricated with three to seven layers and even more in some cases” (CLT EN-2012). 1.3. Connectors 1.3.1. Introduction The concrete and timber elements of TCCs are required to be joined by some shear connection in order to achieve composite behavior. As a result, the efficiency of TCC’s depends largely on the properties of the shear connection between. A generalized form of efficiency for composite beams and slabs was proposed by Gutkowski et al. (2008): 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝐷𝑁−𝐷𝐼𝐷𝑁−𝐷𝐶∗ 100% (1) where D stands for the mid-span deflection; and the subscripts N, I, and C indicate non-composite (calculated as stacked elements with no shear transfer), incomplete composite (measured deflection of TCC system), and fully composite (estimated using transformed section method) systems respectively. Ceccotti (2002) divides connectors into four categories that range 6 from relatively weak and flexible connectors such as dowels or nails to very stiff connectors such as glued-in plates or notches cut into the timber. The performance characteristics (i.e. strength, stiffness & ductility) for serviceability and ultimate limit states (SLS and ULS) are most often determined through direct shear push-out tests according to EN 26891 (1991) where strength is defined as the maximum load before failure occurs in the specimen, and stiffness is quantified by the slip modulus at three different load levels (40, 60, and 80% of the mean maximum load) corresponding to SLS, ULS and near-collapse load levels respectively (Yeoh et al. 2011). A large variety of proprietary and open-source connectors have been proposed and implemented in TCC projects around the world. A selection of these connectors will be discussed in the following sections. 1.3.2. Geometric Interlock Connections Mechanical interlocking and notched connections are characterized by high strength and stiffness and have been used extensively to create TCC. In their most general form, notches are cut directly into the timber beam or slab and the concrete fills the notch upon casting; thus creating a tight fitting connection with concrete bearing directly on timber in the parallel to grain direction. While these connections are both strong and stiff, they are also governed by brittle failure modes, including block shear of timber, tensile rupture of timber, crushing of concrete, and shear failure of concrete at the notch (Gutkowski et al. 2008, Deam et al. 2008, Yeoh et al. 2009, Jorge et al. 2010, Khorsandnia et al. 2012, Lukaszewska et al. 2008, Van der Linden 1999). Attempts to improve the post-peak performance of these connections have seen the introduction of lag screws or other mechanical anchors which provide some ductility and load carrying capability following failure of the notch, and in certain instances, an initial pre-stressing force to 7 provide clamping and resistance to any uplift force components generated at a notch (Gutkowski et al. 2008). Other factors affecting notch performance include the length of notch, presence of dowel-type fastener, and its depth of penetration into timber (Yeoh et al. 2011). Yttrup (1996) investigated embedment of dimpled timber beams into a concrete slab a where 19mm diameter holes were drilled 10mm deep and spaced along the length of the embedded top portion of the beam. Double-tee sections were tested in full-scale bending using LVL and glulam. In the LVL specimens, failure was observed as localized fibre crushing at the location of the concrete dimples, while the denser Glulam specimens showed no damage at the dimples and failed in tension at the bottom of the beam. 1.3.3. Mechanical Fasteners Mechanical connectors such as nails, lag screws and dowels are generally characterized by lower stiffness and strength but higher ductility. They are therefore less efficient than notched connections but have the advantage of improved deformation capacity. Deam et al. (2008) performed shear tests on a wide variety of fasteners both on their own and used in reinforced notches in LVL beams. In general, the reinforced notches and dowel type fasteners showed good strength and deformation capacity whereas unreinforced notch and brace anchors showed undesirable rapid decline in post peak load carrying capacity. 1.3.4. Screw-Type Connectors A number of screw-type connectors have been implemented in TCC, and in their most efficient form, are installed at an angle to the grain to engage them axially rather than as a dowel. SFS provides a proprietary “SFS – VB jointing system”, (Z-9.1-342, 2015) which consists of screw pairs installed at 45° with concrete cast over. Aligning screws at an angle provides a significant 8 increase in stiffness over fasteners installed perpendicular to the shear plane. Other systems include the “Timtec plus VG screw” or so-called “FT connector” system, (ETA-12/0196) which allows for either integrally cast-in fully threaded screws or the use of a cast-in connector. The system utilizes cast-in plastic sleeves, which allow for easy installation of the screws on site at an angle of 30° from the plane of the panel. This provides greater embedment and up to 87% utilization of the screw’s tension strength in shear at the wood-concrete interface. 1.3.5. Adhesive Connections Adhesive bonded connections are able to provide very stiff connection between concrete and timber and have been shown to achieve up to 97% stiffness and 99% strength of a perfectly composite member (Clouston et al. 2005). The HBV system (TiComTec, 2015) resembles an expanded steel mesh that is glued into a saw cut in the timber member and then concrete is cast on top. The adhesive and the concrete fill the voids in the mesh creating a mechanical “adhesive dowel” connection, which, if designed properly, will yield in the steel mesh before dowel failure. Glued in rebar, both angled and straight, has been investigated with failure resulting from tension in the timber beam after full plasticization of the connectors (Ceccotti et al. 2006). Connections created entirely by adhesive bonding have also been investigated with the majority of research using moisture insensitive epoxies where the adhesive was applied first to the timber elements and concrete was subsequently cast before the epoxy had hardened. Tests at the Bern University of Applied Sciences in Switzerland (Tannert et al. 2014) as well as at Metropolitan State University of Denver (Balogh, 2013) have shown that full composite behavior is obtained and failure ultimately occurs as tensile rupture of the timber element or concrete failure depending on the material and geometric specifications. 9 1.4. Design of TCC 1.4.1. Overview The design of TCC is not addressed in the majority of timber standards around the world, with the exception of Eurocode 5, Part 2, Annex B (CEN 2004a). In the case of semi-rigid connectors, which constitute the vast majority available, a relative slip between the concrete and timber layers will occur. This violates the Euler-Bernouli assumption that plane sections remain plane, therefore requiring an alternative to the transformed section method commonly known to structural designers for determination of composite bending stiffness and stress distribution. Additionally, timber, concrete, and connectors all exhibit varying time-dependent properties specifically related to creep and shrinkage. Any TCC design must take into account these two limitations. Several composite theories exist for the calculation of effective bending moduli and determination of element stresses of partially composite sections. The most widely accepted methodology is the so called “gamma method”, which is described in detail in section 1.4.2 but it is worth noting that other methodologies have been implemented successfully for a variety of composites products including TCC and CLT. An elastoplastic solution has been proposed for situations in which TCC failure occurs after full yielding of connectors. This situation is expected from connectors that exhibit low strength and stiffness and high ductility such as dowel-type connectors. Frangi and Fontana (2003) claimed that this method provides an accurate prediction of the failure load; however, it is not widely used in design. Additionally, the shear analogy method and K-method, which are commonly used to determine the properties of CLT could be used for TCC as well. 10 1.4.2. Gamma Method The so-called gamma method is a linear-elastic solution, initially proposed by Möhler (1956) for the analysis of timber-timber composite beams, and was later recommended by Ceccotti (2002) for the analysis of TCC. The assumption that all materials (timber, concrete, and connector) remain elastic allows for straightforward determination of stresses in component materials at various states. The effect of non-linear behaviour of the connector is captured by using the secant stiffness, determined from push-out tests according to EN 26891 (1991), in calculations at SLS and ULS load levels to predict the level of slip and resulting stress distributions in the concrete and timber elements. The solutions obtained using the gamma method are exact for a simply supported beam with a sinusoidal varying bending moment along its length. The effective flexural rigidity of this system (EI)eff is: (𝐸𝐼)𝑒𝑓𝑓 = ∑ (𝐸𝑖𝐼𝑖 + 𝛾𝑖𝐸𝑖𝐴𝑖𝑎𝑖2)2𝑖=1 (2) Where EI and A are the flexural rigidity and cross sectional area of each element respectively, a is the distance from neutral axis of the composite to neutral axes of the elements, and γ is the ‘connection efficiency factor’: 𝛾1 =11+𝜋2𝐸1𝐴1𝑠1𝑛𝑟𝐾𝑙2 (3) where l is the beam span, K is the connector stiffness, s1 is the spacing between rows, and nr is the number of fasteners per row. Importantly, (EI)eff depends on the load distribution and span so it is not a fundamental cross-sectional property (Ceccotti 2002). Element stresses are calculated by linear superposition of flexural and axial contributions. Detailed formulae are presented in Eurocode 5 Part 2 Annex B (CEN 2004a). 11 1.4.3. Long-Term Behaviour Extensive numerical studies which account for the phenomena affecting the long-term behaviour of TCC, such as creep, mechano-sorptive creep, shrinkage/swelling, and temperature variations have been conducted and validated by long-term tests (Fragiacomo 2006, Jorge et al. 2010, Fragiacomo and Ceccotti 2006, Ceccotti et al. 2005, Fragiacomo and Lukaszewska 2013, Fragiacomo 2012, Yeoh et al. 2009, Khorsandnia et al. 2013). Different approaches have been proposed for dealing with the creep and shrinkage, e.g. Ceccotti (2002) proposed the utilization of a reduced modulus by dividing the average material modulus by a creep factor determined for each component at the end of service life. The use of this less rigorous approach is justified by experimental evidence, which shows that deformation tends to stabilize after a few years under quasi-permanent design loads. Therefore, correct final deformation values can be predicted by adopting these approaches. An approach developed by Fragiacomo and Ceccotti (2004) captures the inelastic strains due to environmental variations of relative humidity and temperature and shows good agreement with results from numerical modelling making it suitable for use by practitioners. 1.4.4. Vibration Performance The vibration performance of floors is affected by a number of factors relating to both the loading type (i.e. amplitude and frequency), and structural dynamic properties (i.e. mass, damping, and stiffness). Vibration controlled floor spans have typically been achieved by simple approximations like the static deflection method (CLT EN-2012) or by requiring the fundamental vertical frequency to be above threshold values, typically near 8.0Hz (Bachmann et al. 1995). Different values are often prescribed by codes for occupancies that may have higher or lower likelihood of inducing a resonant response as well as sensitivity to perception of vibrations (e.g. 12 standing vs. sitting) (Bachmann et al. 1995). Jorge et al. (2010) compared the natural frequencies and effective bending stiffness of several CLT-concrete composite floors. Bending stiffness was increased by up to 4.7 times over bare CLT floors with higher increases with increasing connector stiffness and span. The natural frequencies of composite systems increased by 20 to 70%. This modest increase in natural frequency is due to the added mass, which counteracts part of the increased stiffness to lower the natural frequency. The additional mass, damping and stiffness provided by the concrete topping significantly reduces the likelihood that human induced vibrations will be perceived as annoying or uncomfortable if natural frequencies lie above the threshold values provided by building codes. 1.4.5. Finite Element Modeling A number of finite element method (FEM) models have been shown to provide reliable estimates of performance of TCC systems. Of particular interest to this investigation is a method presented by Lopes et al. (2012), which makes use of commercially available software and readily available test data. The model is implemented in SAP2000® and assumes that both the timber and concrete sections remain elastic and that all the nonlinearity occurs in the shear connection. Shear connectors are modeled as shear springs (axially rigid) connecting the centroids of the concrete and timber elements. The springs are calibrated to the non-linear load-deformation response available from push-out tests. The models showed good correlation with test results of full-size specimens (Lopes et al. 2012) and have the added advantage that they can accurately predict the shear force in discrete connectors, or regions of “smeared” connectors (e.g. at beam ends), even under non-uniform loading conditions. Dynamic investigations can be performed using modal analysis tools to predict the fundamental vertical frequencies and mode shapes of 13 the structures as well as the response to periodic excitation. These responses can subsequently be compared with experimental results and building code requirements. 1.5. Research Need and Objectives 1.5.1. Research need Opportunities exist to expand the use of mass-timber products in what has traditionally been a concrete market. By replacing the cracked and ineffective portion of a concrete slab with a mass-timber element, benefits are seen through reduced CO2 and embodied energy, thinner slabs, lower weight buildings, and enhanced aesthetics. Designers are looking for ways to make use of the versatility offered by flat-plate EWPs: their strength and vibration performance, which often governs design, can easily be enhanced by connecting them compositely to a concrete topping. The main barrier preventing widespread implementation of TCCs in North America is a lack of design guidance, specifically: i) lack of agreed upon design approach; ii) lack of appropriate test data in North American EWP’s; iii) lack of readily available connector properties (majority of connector systems are proprietary and cannot be easily compared across the range of materials); and iv) uncertainty regarding the long-term performance of TCC systems. 1.5.2. Objectives A test program for TCC was developed to systematically address all of the identified barriers to TCC implementation for North American engineers, designers and suppliers, thereby creating new opportunities for the utilization of timber and providing another potential layer of value-added services to the industry. The specific objectives were to investigate i) the properties of a 14 variety of shear connectors in small-scale shear tests and ii) the bending and vibration properties of selected TCC systems in full-scale bending tests. 15 Chapter 2. Small-Scale Shear Tests 2.1. Materials 2.1.1. Overview Timber-concrete composites are generally comprised of timber slabs or beams, a concrete slab, occasionally an interlayer consisting of rigid foam insulation or plywood, and some shear connection to join them all together. As with any design scenario, there are innumerable possibilities for material selection and specification; however, the focus of this research is not only to investigate the properties of various shear connectors, but to do so in a way that is most easily incorporated into current engineering practice. The latter objective requires strategic selection of which materials to test with which connectors in order to obtain a reasonable degree of confidence in identifying material influence on connector performance, while also ensuring testing in materials that will be implemented in real projects. 2.1.2. Engineered Wood Products Engineered wood products represent an ideal partner in the marriage of timber and concrete. Their inherent stability and consistent engineering properties make optimization and efficient design possible. Coupled with the growing desire for increased prefabrication and rapid on-site installation, makes incorporation of EWPs an attractive alternative to conventional methods. All EWP’s were donated by several industry sponsors for both phases of the experimental work. The material’s mechanical properties, as summarized in Table 1, are taken from the manufacturer’s specifications: (CCMC 12627-R, 2015 for LSL, CCMC 11518-R, 2015 for LVL and Brisco LVL, and Crosslam™ Design Guide Version 11, 2015 for CLT). 16 Table 1: EWP Mechanical Properties Material Properties (MPa) (1) Material Supplier MOE Ft Fc Fb Fv Fcp LSL (1.55E) Weyerhaeuser 10,685 20.4 22.6 33.3(2) 1.95(2) 6.10(2) LVL (2.0E) LP Corp. 13,790 18.6 35.2 37.6(2) 1.79(2) 6.90(2) CLT (SPF No.1/No.2) Structurlam 9,500 5.5 11.5 11.8 0.50(3) -- Brisco LVL (2.0E) Brisco Manufacturing 13,790 18.6 35.2 37.0 3.65 9.41 (1) MOE = Modulus of elasticity; Ft, Fc, Fb, Fv, Fcp = specified strengths in tension, compression, bending, shear, and compression perpendicular to grain respectively. (2) Strength properties for plank orientation (3) Rolling shear (Longitudinal shear = 1.5 MPa) 2.1.3. Concrete Phase I specimens were prepared in batches of 20-30 specimens at a time which required a relatively small volume of concrete per casting session. As such, pre-mixed concrete was prepared in an electric barrel type mixer and cast by hand into the specimen forms. For the full-scale specimens tested in Phase II, Lafarge provided 10m3 ready-mix concrete to cast all specimens as well as additional small scale specimens which would complement the initial Phase I tests. The mechanical properties of the concrete are summarized in Table 2. Table 2: Concrete Properties Material Supplier f’c (MPa) Max aggregate size (mm) Weight 60lb. Bags Concrete Mix QUIKRETE 28(1) Unknown Normal Ready-Mix Concrete Lafarge 30(2) 19 Normal (1) Average cylinder strength = 28.2 MPa (2) Average cylinder strength at time of testing = 45.5 MPa 17 2.1.4. Insulation Insulation is sometimes desired for enhanced acoustic performance of TCC floors. The layer of insulation also increases the static moment arm between the timber and concrete without adding any significant weight. In this way it is possible to increase the stiffness of the panel and potentially improve the vibration performance provided the shear connector can connect effectively through the insulation. In this project, Foamular® C-200 extruded polystyrene rigid insulation was utilized, which is commonly available and has a compressive strength of 140kPa according to the manufacturers Technical Bulletin No. SC33 (2009). 2.1.5. Adhesive Investigation of adhesive bonded TCC panels required the specification of a moisture insensitive adhesive that is capable of bonding wet concrete to timber. Sikadur®32 Hi-Mod was selected, a moisture insensitive, two-component structural epoxy suitable for bonding fresh, plastic concrete to hardened concrete and steel or as a structural adhesive for concrete, masonry, metal, and wood. According to the Sikadur®32 Hi-Mod product data sheet (2012), it has a shear strength after 14 days of 41MPa and a pot life of 30-38 minutes. 2.1.6. Plastic Separation Layer In order to prevent moisture ingress into the timber elements and also to limit influence of friction on determination of connector strength and stiffness properties, a plastic separation layer was typically placed between the timber and concrete elements. The layers were cut from rolls of clear 6mil polyethylene sheeting material which is a heavy-duty plastic and used commonly as vapour and moisture barriers as well as for various other construction applications. 18 2.2. Connectors 2.2.1. Overview A large number of connectors are available for the implementation of TCC, the focus was limited to those which achieve high stiffness and therefore high composite efficiency. Five main connector types were investigated which included: i) adhesive bonded steel mesh, ii) fully and partially threaded self-tapping screws, iii) epoxied and hybrid epoxied and screwed connections, iv) FT connector and v) mechanical interlocking connections. Within the TCC systems, additional parameters were varied which included: EWP type, presence of slip membrane, presence of rigid insulation interlayer, screw angle, screw embedment length, and screw diameter. 2.2.2. Self-Tapping Wood Screws Self-Tapping Screws (STS) do not usually require pre-drilling and are therefore faster to install than traditional lag screws or wood screws, making them a cost efficient connector appropriate for many timber structures. STS with continuous threads are hardened to produce a high yield moment, tensile, and torsional strength while the large threads provide reliable embedment in the timber elements (Dietsch and Brandner 2015). The ability of STS to be effectively embedded at angles to the grain provides the opportunity to utilize the high axial strength and stiffness of the connectors and makes them an excellent choice for shear connections in TCC, which typically are required to resist high forces parallel to the axis of the timber at the highest stiffness possible. Screws have the additional advantage that they can be installed at all temperatures and with significantly fewer quality control measures than other available solutions. 19 The screws investigated in this research, as shown in Figure 1, were provided by MyTiCon Timber Connectors Inc. Timber Connectors; their relevant properties are summarized in Table 3. The technical specifications of the screws are provided by the product evaluation report (CCMC 13677-R, 2013). Table 3: STS Properties Partial-(PT) or Full-Thread (FT) “SWG ASSY®” Type Head Type Diameter (mm) Length (mm) Thread Length (mm) Tension Strength (kN)(1) FT VG CYL 8 240 240 18.9 FT VG CYL 10 240 240 24.0 FT VG CYL 10 300 300 24.0 FT VG CYL 10 200 200 24.0 FT VG CYL 10 220 220 24.0 FT VG CSK 10 240 240 24.0 FT VG CSK 10 300 300 24.0 PT SK Washer 10 260 100 24.0 (1) Unfactored resistance Figure 1: ASSY VG CYL (left), ASSY VG CSK (middle), and ASSY SK (right) 20 2.2.3. FT-Connector The “FT connector”, shown in Figure 2, is a proprietary product used to facilitate the installation of precast concrete panels to timber elements on site to improve overall quality, construction time, and prevent contact of wet concrete to the timber elements. The connector provides a hollow sleeve, inclined at 30° from horizontal with a large steel bearing washer through which a 10mm diameter fully threaded STS is installed to provide the necessary anchorage of the concrete to the timber. The slab is required to be 70mm thick to allow proper access to the concealed component. The connector has a European technical approval (ETA-12/0196, 2012). Figure 2: FT Connector 2.2.4. HBV System The proprietary glued-in steel connector system Holz-Beton-Verbund (HBV), shown in Figure 3, has proven a viable option in terms of achieving TCC strength, stiffness, and ductility, although there are some concerns regarding the assurance of stringent quality control measures and complexity of on-site applications. The HBV system has product approvals for being used with epoxy and polyurethane based adhesives (Z-9.1-557, 2012). CR-421 by Purbond®, a two component polyurethane adhesive was applied. The adhesive system has been successfully tested and approved for use with insulation interlayers and maintains a high degree of stiffness 21 and load bearing capacity even through an unsupported separation layer (Lehringer 2014). The connector consists of a 2.0mm thick expanded metal mesh that comes in 1m segments in heights of 90mm, 105mm, and 120mm depending on whether it is required to extend through an insulation layer or not. The installation requires cutting a kerf into the timber element, followed by filling the cleaned out kerf with adhesive and then inserting the mesh. Characteristic strength and stiffness values were calculated from the Technical Dossier HBV-Systems (2011) and are presented in Table 4. Table 4: HBV Properties (per mm length) Height (mm) Insulation Thickness (mm) Embed in Timber (mm) Embed in Concrete (mm) Kser(1) (N/mm) Kult(2) (N/mm) Tk(3) (N) 90 0 45 45 825 550 160 120 25 45 50 349 232 120 (1) Stiffness at service level (2) Stiffness at failure – equal to 2/3*Kser (3) Characteristic strength presented – convert to design strength using technical approval Figure 3: HBV Connector Installation 22 2.2.5. Transverse Notch Connection Notches are the oldest form of composite connection for TCC and have proven to provide very efficient composite sections. In this research, two wood-concrete connections were investigated: i) the traditional transverse notch; and ii) a localized concrete dowel type connection based on the work of Yttrup (1996). Transverse notches are realized by removing a portion of the timber which is later filled with concrete as the slab is cast. Shear forces resulting are resisted primarily through bearing of the concrete on the notch, which loads the timber in compression parallel to grain at the notch and longitudinal shear beyond the notch. In cases where the shear resistance exceeds the parallel to grain bearing capacity of the timber, composite sections tend to fail in combined tension and bending at mid-span; however other failure modes including concrete shear at the notch or concrete crushing are possible depending on the system and notch geometry. The force distribution at notches creates a small uplift force resulting from eccentricity of the loading and reaction points within the section, so mechanical fasteners are often located at notches to provide uplift resistance while also enhancing post-peak behavior in scenarios where a notch has failed. This program pursued fully unreinforced notches and obtained the uplift resistance by fabricating a tapered cavity, which “locks” the concrete tightly to the timber, see Figure 4 and section 2.3.2. Figure 4: Transverse Notch Connection 23 2.2.6. Localized Concrete Dowel Connection The localized concrete dowel connection was proposed as an extension of the work performed by Yttrup (1996). In the original work, circular holes were drilled in the timber at the concrete timber interface to create an interlocking mechanism which provided the shear connection between timber and concrete. The objective of the connection tested in this program was to obtain a pure concrete and timber connection solution that makes use of CNC fabrication technology and does not require any additional mechanical fasteners. The concrete dowels were given an elongated shape to promote compression failure of the timber rather than shear failure of concrete. Additionally, a longitudinal dovetail was provided to add uplift resistance to the connection. The tested connection geometry is depicted in Figure 5 and detailed in section 2.3.2. Figure 5: Localized Concrete Dowel Connection 2.2.7. Adhesive and Hybrid Adhesive and Screw Connections Adhesive connections are able to achieve “pure” composites such as glued laminated beams. The challenge in obtaining reliable adhesive connections in TCC is non-trivial however, and must account for a number of factors including: moisture sensitivity of adhesive, proper mixing, proper surface preparation, pot life and proper distribution/dosing of the adhesive (Brunner at al. 24 2007). In light of these considerations, most designers do not trust that the adhesive could be applied in a fully reliable and consistent way in the field. The approach taken in this experimental program was to provide enough adhesive bond to obtain full composite action of the TCC for SLS, and to provide a redundant but less stiff connection of STS which satisfies the load-resisting requirements at ULS. This way, less adhesive is required than if designing for the ULS and fewer screws are required than if designing for SLS and a higher overall performance is obtained with predictable failure modes. 2.3. Experimental Design 2.3.1. Investigated Parameters The objectives of experimental program were to provide a comprehensive set of test data for a variety of connectors in the most widely utilized EWPs and the relative influence of several connection parameters on the performance of TCC systems. While some parameters are connector specific such as fastener diameter d, or embedment length L, some are generic such as presence of a slip membrane or EWP. Table 5 - Table 11 identify the parameters of all test series. Table 5: ASSY SK Partially Threaded Screw Connector with Washer Heads Label INS. S.M. L (mm) Screw Angle No. Conn d (mm) Material No. Reps. SK1 X 170 30º 4 10 LSL 6 SK2 X 170 30º 4 10 LVL 6 SK3 X 170 30º 4 10 CLT 5 Total: 17 INS. – indicates use of 25mm insulation layer S.M. – indicates use of polyethylene slip membrane 25 Table 6: FT Connector with ASSY VG Fully Threaded Screws with Countersunk Heads Label INS. S.M. Lembed (mm) Screw Angle No. Conn Screw Diameter (mm) Material No. Reps. FT1 X 150 30º 4 10 LSL 6 FT2 X 150 30º 4 10 LVL 4 FT3 X 150 30º 4 10 Brisco LVL 3 FT4 X 150 30º 4 10 CLT 6 FT5 X 210 30º 4 10 CLT 6 Total: 30 Table 7: ASSY VG Fully Threaded Screw Connector with Cylinder Heads Label INS. S.M. Lembed (mm) Screw Angle No. Conn Screw Diameter (mm) Material No. Reps. VG1 X 150 30º 4 8 LSL 6 VG2 150 30º 4 8 LSL 6 VG3 X 150 30º 4 10 LSL 12 VG4 X 150 30º 4 8 LVL 6 VG5 150 30º 4 8 LVL 6 VG6 X 150 30º 4 10 LVL 12 VG7 X 150 30º 4 8 Brisco LVL 6 VG8 X 150 30º 4 10 Brisco LVL 12 VG9 X 150 30º 4 8 CLT 6 VG10 X 150 30º 4 10 CLT 12 VG11 X 210 30º 4 10 CLT 6 VG12 X 110 45º pairs 2 10 LSL 6 VG13 X 110 45º pairs 2 10 LVL 6 VG14 X 110 45º pairs 2 10 CLT 6 VG15 X 110 45º pairs 4 10 LSL 6 VG16 X 110 45º pairs 4 10 LVL 6 VG17 X 110 45º pairs 4 10 CLT 5 Total: 125 26 Table 8: HBV Glued in Steel Mesh System Label INS. S.M. Lconn (mm) No. Conn Material No. Reps. GM1 X 300 1 LSL 12 GM2 X 300 1 LVL 12 GM3 X 300 1 Brisco LVL 5 GM4 X 300 1 CLT 11 GM5 X 300 1 LSL 6 GM6 X 300 1 LVL 6 GM7 X 300 1 CLT 6 Total: 58 Table 9: Transverse Notched Connections Label INS. S.M. Lnotch (mm) No. Conn Material No. Reps. TN1 X 45 2 LSL 6 TN2 X 45 2 LVL 6 TN3 X 45 2 CLT 6 Total: 18 Table 10: Localized Concrete Dowel Connections Label INS. S.M. Width (mm) Length (mm) No. Conn Material No. Reps. LD1 X 20 60 6 LSL 6 LD2 20 60 6 LSL 6 LD3 X 20 60 6 LVL 6 LD4 20 60 6 LVL 6 LD5 X 20 60 6 CLT 6 Total: 30 27 Table 11: Adhesive and Hybrid Connections Label Aadhesive (mm2) S.M. Lembed (mm) Screw Angle No. Conn Screw Diameter (mm) Material No. Reps. AB1 27500 X 0 LVL 6 AB5 27500 X 0 LVL 6 AB6 27500 X 150 30º 4 10 LVL 12 AB7 27500 X 150 30º 4 10 LSL 6 AB8 27500 X 150 30º 4 10 CLT 6 Total: 36 2.3.2. Specimen Geometry and Connector Layout The specimen geometry was designed based on a variety of factors which included constructability, ease of handling, desire not to have bracing, fit within testing machine, and expected failure to occur within desired range of machine loading capacity. With these considerations in mind, a skewed specimen geometry according to EN 408 (2012) was selected which aligns the loading and reaction surfaces resulting in no rotational moment during testing, thus eliminating the need for out of plane bracing. Additionally, the size was kept so that individual specimens did not exceed 22.5kg and could be handled safely by one person. Lastly, the number of fasteners per specimen was determined based on spacing requirements (CCMC 13677-R, 2013) to avoid group effects and obtain average “per connector” values. Each of the test specimens and their related series are detailed in Figure 6 - Figure 14. 28 Figure 6: VG1-11, SK1-3, FT1-5 (137 Specimens) Figure 7: VG12-14 (18 Specimens) 29 Figure 8: VG15-17 (17 Specimens) Figure 9: AB1,AB5 (12 Specimens) 30 Figure 10: AB6-8 (24 Specimens) Figure 11: GM1-4 (40 Specimens) 31 Figure 12: GM5-7 (18 Specimens) Figure 13: TN1-3 (18 Specimens) 32 Figure 14: LD1-5 (30 Specimens) 2.4. Methods 2.4.1. Specimen Fabrication The test specimens were prefabricated at the Center for Advanced Wood Processing (CAWP) at UBC. To the extent possible, specimens were cut on the Hundegger Robot Drive CNC machine according to the geometry shown in Figure 6 - Figure 14. Fabrication was then completed on the table saw and by hand as required. Typically, a slip membrane was spray-glued to the specimens, after which the connectors were installed using jigs and templates to ensure accurate installation at the angle and spacing specified. Once the connectors were installed, forms were built around them in preparation for concrete casting. Specimens were cast in batches of approximately 30 at a time and then moist cured until testing. Photos of several specimens at various stages of fabrication and testing are shown in Figure 15. 33 Figure 15: Shear-Test Specimens: Inclined STS Connectors (top) Epoxied with STS Backup (bottom left), HBV Mesh (bottom, middle and right) 2.4.2. Test Setup and Instrumentation The shear tests were performed at the UBC Structures Laboratory in a universal testing machine. The load was applied to the specimen through a steel bearing plate on the concrete at the top and the test specimens were supported by another steel bearing plate beneath the timber part of the specimen, see Figure 16. Owing to the skewed geometry, the line of force passes through the centre of the specimen and the upper and lower bearing plates produce a resultant force that is vertically aligned. This way no additional bracing was required for stability. Specimens were instrumented with linear voltage displacement transducers (LVDTs) on each side to measure the relative slip between the timber and concrete elements. The LVDTs were fastened directly to the 34 timber using wood screws and a mounting bracket, while a custom bracket was fabricated that was clamped tightly to the concrete without being in contact with the timber element. In this way, the relative slip was measured directly along the shear plane and related to the applied loads as recorded by a calibrated load cell. Figure 16: Shear Test Setup: Schematic (left) and Photo (right) 2.4.3. Loading Protocol Mechanical fasteners are understood to have varying degrees of inelastic slip upon first loading. The loading protocol and test procedure in EN 26891 (CEN 1991) accounts for this by initially loading up to 40% of the expected failure load, meant to represent service level, and then unloading before reloading the connection to failure. In this way tangent stiffness can be calculated which are not “softened” by the initial inelastic slip that would occur only once during the service life of the structure. The load-controlled protocol shown in Figure 17 was adapted 35 from EN 26891 for the expected loads for each connector type. Typically a prediction was made for the first test, and the protocol was adjusted to match the expected load to the failure load of the first replicate. Data was recorded at a sampling rate of 5Hz, which provided enough resolution to capture peak and post peak behavior. It is worthy of note that since it is a load-controlled protocol, once failure occurs, the displacement rate of the testing machine speeds up rapidly, this results in rapid failure of the specimens after the peak load has been obtained, even for ductile connectors. Figure 17: Loading Protocol 2.4.4. Analysis Methods The parameters of interest and the basis for comparison of connector performance for each of the series tested are summarized in Table 12 along with the equations used to calculate each parameter. The visual representations of these formulae on the measured data are shown in Figure 18. For each test series, characteristic (5th percentile) values were determined based on an assumed normal distribution of the parameters of interest. Within similar test series, the relative influence of parameters was also investigated by regression analysis. 36 Table 12: Calculated Parameters Description Equation Tangent stiffness at 40% of peak load (used for Serviceability Limit State calculations) 𝐾0.4 = (𝐹0.4 − 𝐹0.1∆0.4 − ∆0.1) [kN mm⁄ ] Tangent stiffness at 60% of peak load 𝐾0.6 = (𝐹0.6∆0.6 − ∆𝑟𝑒𝑠) [kN mm⁄ ] Tangent stiffness at 80% of peak load (used for Ultimate Limit State calculations) 𝐾0.8 = (𝐹0.8∆0.8 − ∆𝑟𝑒𝑠) [kN mm⁄ ] Tangent stiffness at peak load 𝐾𝑢𝑙𝑡 = (𝐹𝑢𝑙𝑡∆𝑢𝑙𝑡 − ∆𝑟𝑒𝑠) [kN mm⁄ ] Peak load recorded 𝐹𝑢𝑙𝑡 [𝑘𝑁] Inelastic slip after loading to service level ∆𝑟𝑒𝑠= ∆0.4 − 𝐹0.4𝐾0.4 [mm] Figure 18: Calculation of Strength and Stiffness Parameters 37 The individual connector results in section 2.5 are presented as averaged curves which are a piece-wise linear representation of the non-linear connector behaviour. The curves are produced by calculating the corresponding loads and displacements based on the averaged tangent stiffness for each connector type. For example, if the failure load is 100kN, then displacements would be calculated for F0, F0.4, F0.6, F0.8, and Fult and plotted together with their corresponding loads to generate the averaged piece-wise linear curve. If K0.4 is 100kN/mm then the displacement at F0.4 would be calculated as F0.4/K0.4 = (40kN / 100kN/mm) = 0.40mm. The curves are also plotted over the measured data in Appendix A however here they are shifted by the amount Δres to align with measured data. An example is presented in Figure 19. Figure 19: Averaged Sample Curve F (kN) K (kN/mm) Δ (mm) 0 0 0 40 100 0.4 60 60 1.0 80 45 1.8 100 20 5.0 38 2.5. Results and Discussion 2.5.1. Overview This section provides a summary of the strength and stiffness parameters determined from the Phase I tests and visual comparison between connectors of the same category. Calculated parameters along with averaged piece-wise linear curves are presented for each connection type as indicated in sections 2.5.2 – 2.5.12. Complete results including original load-slip curves are presented in Appendix A . Investigations of the statistical relevance of the results as well as insights into the relative influence of the parameters are presented in section 2.6. 2.5.2. Fully Threaded Screws Installed at 30° Fully threaded screws were tested at an angle to grain of 30° in order to utilize the axial strength and stiffness of the connectors to the greatest degree possible while still having a constructible connection. The tests were carried out in LSL, LVL, Brisco® LVL, and CLT. Within this subset of connector configurations, screw diameter, presence of a plastic layer, and embedment length of the screw were selectively varied. Figure 20 compares the relative strength and stiffness of 8x240 ASSY VG screws in each of the different EWP’s and additionally was tested with LSL and LVL without the plastic layer. Connections in LSL and LVL tend to exhibit higher strength and stiffness than connections in CLT, likely due to their higher density, which is correlated with increased withdrawal resistance of threaded fasteners in timber (CEN 1995). 39 Figure 20: 8x240 ASSY VG at 30º Average Results (per screw) The removal of the slip membrane resulted in very high measured stiffness as well as increased ultimate load carrying capacity. Since the screws are installed at a 30° angle and are oriented to carry loads in tension, the axial load in the screws create a clamping force equal to 50% of the axial load, thus causing large friction forces to develop in the absence of a non-slip plastic layer. In most instances, the screws would fail in tension for the specimens without the plastic layer, and a combination of screw withdrawal, tension failure, and concrete cracking for specimens with the plastic layer. Figure 21 presents the relative strength and stiffness of 10mm diameter ASSY VG screws in LSL, LVL, Brisco® LVL, and CLT. Average results for each specimen type are presented in Table 13. In CLT, the embedment length in timber was varied, using both 240mm and 300mm long screws. All specimens exhibited similar initial stiffness, and differences in strength and stiffness become more pronounced only at higher loads. 40 Figure 21: 10x240 and 10x300 ASSY VG at 30º Average Results (per screw) Table 13: 8x240, 10x240, and 10x300 ASSY VG at 30º Average Results (per screw) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps VG1 26.6 38.1 51.9 45.7 33.4 17.2 0.10 6 VG2 35.8 223.0 219.0 81.2 56.5 29.3 0.03 6 VG3 32.6 44.7 68.2 53.6 42.8 27.8 0.11 12 VG4 26.6 35.8 56.5 44.1 29.8 15.5 0.14 6 VG5 35.1 67.7 102.4 60.5 42.4 20.6 0.13 6 VG6 31.9 41.4 65.2 45.7 33.7 19.1 0.14 12 VG7 26.5 38.2 96.5 55.2 34.2 17.5 0.19 6 VG8 32.2 52.9 72.8 56.2 44.5 30.0 0.08 6 VG9 25.4 31.2 49.3 33.9 23.2 11.5 0.15 6 VG10 27.9 35.0 71.9 45.2 29.0 11.6 0.17 12 VG11 33.5 41.4 61.9 44.4 32.9 22.5 0.14 6 41 It is suspected that the initial deformation in the connection is related mostly to the localized crushing of wood fibres at the screw to timber interface and that axial withdrawal stiffness, which would be expected to increase with specimen density, is observed only once the initial deformation has taken place. This can be seen most clearly between the VG10 and VG11 specimens, which are the 10x240 and 10x300 ASSY VG screws installed in CLT respectively; where the initial stiffness appears very close initially, however, the ultimate load carrying capacity increased for the longer embedment length and the total deformation is reduced. A direct comparison of the 8x240 vs 10x240 screws demonstrates that strengths increase in the range of 10-25% and stiffness increases in the range of 15-45% by going to the larger diameter screw. While the larger screw will be more expensive, it is expected that the labour cost savings from installing fewer screws will at minimum break even with the cost premium of the screw, and the same result could be achieved in less time at the same or lower cost. For this reason, 10mm diameter screws were selected over 8mm diameter screws moving forward to the full-scale tests. 2.5.3. Fully Threaded Screw Pairs Installed at 45° By having the screws inclined at 45° in matching pairs, there is no normal force generated between the timber and concrete elements, thus the stiffness and strength of the connection is purely controlled by the proportioning and spacing of the connectors. The results presented in Figure 22 are for pairs of STS (i.e. one screw each in tension and compression) installed at 45° to the shear plane. The advantage to such a configuration is that there is no directional dependence as there is for the screws which are inclined in one direction only and must be oriented to align with the anticipated shear flow at every location. However, orienting the screws closer to vertical makes for a less efficient load carrying ability by simultaneously reducing the 42 component that is aligned with the applied force and reducing the amount of embedment that can be achieved prior to penetrating the bottom of the timber element. The configuration was tested in LSL, LVL, and CLT. Not surprisingly, the LSL specimens (ρ = 720kg/m3) showed the highest stiffness and strength of all specimens tested. However, the CLT specimens showed a higher initial stiffness than LVL. Ultimately however, the LVL did end up with higher strength and stiffness at the ULS. Average results for each specimen type are presented in Table 14. Table 14: 10x200 ASSY VG Pairs at 45º Average Results (per screw pair) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps VG12 49.0 67.1 74.4 57.1 41.0 19.2 0.06 6 VG13 34.9 40.2 55.6 45.5 30.2 10.3 0.14 6 VG14 30.6 44.7 67.5 41.5 22.4 8.8 0.13 6 Figure 22: 10x200 ASSY VG Pairs at 45º Average Results (per screw pair) 43 2.5.4. Partially Threaded Screws with Bearing Washer Partially threaded screws with a smooth shank and washer head were tested to see whether effective embedment in the concrete could be obtained by direct bearing of the washer head on the concrete rather than the bond-type connection obtained by embedding a fully threaded screw into wet concrete. Again, the screws were tested in LSL, LVL, and CLT. The thread length of a 10x260 ASSY SK screw is only 100mm which resulted in a portion of the unthreaded shank being embedded in the timber along with the threaded portion. The curves in Figure 23 clearly show the now familiar strength and stiffness relation between the three EWP’s, with both stiffness and strength increasing with timber density. Specimen failure tended to initiate in the form of screw withdrawal in the LVL and CLT specimens and a mixture of screw withdrawal and cracking in the unreinforced concrete around the connectors in the LSL specimen where failure occurred at higher loads. What is not evident in the curves is the significant residual displacement that was observed following the initial loading which is much higher than the specimens with fully threaded screws. This can be seen clearly in the individual load-displacement curves in Appendix A as well as in Table 15 which presents the average results for each series including the observed residual displacement. The additional residual displacement is thought to be from a combination of localized concrete crushing at the washer head, as well as local timber crushing at the screw/wood/concrete interface. Since the residual displacement does not appear to be correlated to timber density, it is suspected that most of the permanent deformation is taking place where the connector is in contact with the concrete. 44 Table 15: 10x260 ASSY SK at 30º Average Results (per screw) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps SK1 33.1 23.7 52.3 30.7 23.1 14.9 0.31 6 SK2 23.9 21.5 53.2 41.7 27.1 15.3 0.34 6 SK3 23.2 17.6 37.8 24.8 16.4 6.4 0.30 5 Figure 23: 10x260 ASSY SK at 30º Average Results (per screw) 2.5.5. Fully Threaded Screws with FT Connector Tests utilizing the FT connector system were performed using 10x240 fully threaded screws in LSL, LVL, Brisco® LVL, and CLT. In the CLT specimens the screw length was varied and both 240mm and 300mm long screws were tested. This test series exhibited higher overall load carrying capacity than the cast-in screw connections for the same exact connector configuration and spacing. The increase is likely due to the large bearing washer which more uniformly transfers the tension stresses from the screw into compressive stresses in the concrete element. 45 Despite its higher overall load carrying ability, the results captured several drawbacks to the system as well. First, the connectors proved to be less stiff than cast-in connections utilizing the same screw configurations, and more importantly, they exhibited higher levels of residual displacement following initial loading which translates into potentially large unrecoverable deformations in the final structure. The larger residual deformations are likely a result of oversizing of the hole through which the screw is installed in the FT connector. The gap between the edge of the sleeve and the screw then needs to be closed before the stiffer axial load path can be activated. Figure 24 illustrates the overall performance of the FT connectors and the individual results are summarized in Table 16. The residual displacements are best illustrated in the load-slip curves presented in Appendix A In order for the maximum benefit to be obtained from the FT connectors, consideration of the initial inelastic slip should be accounted for and mitigated to the extent possible. Table 16: 10x240 and 10x300 ASSY VG with FT Connector Average Results (per connector) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps FT1 47.0 19.6 37.7 29.2 23.8 13.9 0.38 6 FT2 36.5 21.6 49.2 33.9 26.4 16.2 0.38 4 FT3 34.8 25.8 75.8 49.0 32.6 15.9 0.42 3 FT4 27.4 16.1 58.4 37.6 25.9 11.5 0.56 6 FT5 40.5 15.8 32.3 25.6 20.0 11.3 0.59 6 46 Figure 24: 10x240 and 10x300 ASSY VG with FT Connector Average Results (per connector) 2.5.6. Fully Threaded Screws Installed at 45° with 25mm Insulation Layer Fully threaded screws were installed in pairs at 45° through a 25mm layer of rigid insulation into specimens of LSL, LVL, and CLT. Screws at 45° pairs were selected so that no additional compressive stresses would result from the component of axial load in the screws, which would tend to crush the insulation. The strength and stiffness were lower than for pairs of screws installed without insulation, however, the results show that the difference is not large. The averaged load slip curves are presented in Figure 25 and individual parameters in Table 17. It should be noted that when it comes to the design of the full-scale composite, the addition of the insulation layer not only adds the benefit of improved acoustic performance, but also increases the static moment arm of the concrete and timber elements relative to their centroids. The result is a stiffer overall panel which weighs the same as a corresponding panel without insulation assuming a reasonable degree of connector strength and stiffness is maintained. 47 Table 17: 10x220 ASSY VG Pairs at 45º + 25mm Insulation Average Results (per screw pair) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps VG15 30.0 61.5 61.7 51.7 38.8 26.9 0.01 6 VG16 26.3 42.2 47.3 41.6 35.1 38.2 0.03 6 VG17 23.6 36.0 42.8 34.6 24.9 18.1 0.07 5 Figure 25: 10x220 ASSY VG Pairs at 45º + 25mm Insulation Average Results (per screw pair) 2.5.7. HBV System without Insulation Layer The HBV system was installed in specimens of LSL, LVL, Brisco® LVL and CLT. The mesh was 90mm deep and 300mm long and was installed to equal depth in both timber and concrete. This system exhibited a consistent load deformation response with low variation in both strength and stiffness, see Figure 26 and Table 18. The specimens all exhibited some degree of yielding however some specimens developed cracks along the length of the connector soon after yielding was initiated and as a result the length of the yield plateau is occasionally cut short. The 48 specimens were unreinforced in the small scale tests, however the full scale tests which included a sheet of welded wire mesh reinforcement showed no signs of cracking around connectors (refer to section 3.4.4 for additional detail). The system does show some variation in stiffness between the different EWP’s. It is suspected that the difference is due to the very high stiffness of the connector itself and that the testing also measured some shear deformation in the wood specimen, the effect of which would be less pronounced in less stiff connectors. Table 18: 90mm HBV System Average Results (per mm length) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps GM1 0.23 1.18 1.53 1.18 0.86 0.19 0.02 12 GM2 0.23 1.10 1.17 0.98 0.78 0.18 0.01 12 GM3 0.24 0.93 0.85 0.79 0.65 0.22 0.00 5 GM4 0.24 0.80 0.89 0.76 0.58 0.15 0.02 11 Figure 26: 90mm HBV System Average Results (per mm length) 49 2.5.8. HBV System with 25mm Insulation Layer The HBV system was installed in LSL, LVL, and CLT through a 25mm layer of rigid insulation. Typically, the mesh is fully braced against buckling by the wood and concrete; the insulation, however, is unable to provide the same degree of lateral restraint and the connector is less stiff and fails at lower loads when it is installed without the mesh. This effect is dealt with in the technical approval by providing a reduction in strength and stiffness that is related to the depth of insulation through which it is installed. The results, see Figure 27 and Table 19, showed a larger dependence on the EWP than was evident in specimens without insulation. For both parameters, strength and stiffness appear to be positively correlated with stiffer (denser) EWPs. Figure 27: 120mm HBV System + 25mm Insulation Layer (per mm length) 50 Table 19: 120mm HBV System + 25mm Insulation Layer (per mm length) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps GM5 0.21 1.40 1.54 1.35 1.05 0.47 0.01 6 GM6 0.18 0.92 1.00 0.86 0.71 0.28 0.01 6 GM7 0.16 0.72 0.64 0.55 0.41 0.12 0.00 6 2.5.9. Transverse Notch Connections The transverse notch connections tested as part of this investigation suffered from constructability issues, as well as minor oversights during specimen design. The casting of the concrete into the dovetail notch configuration, while intended to keep concrete “locked” to the timber and prevent uplift, ended up reducing the section at the critical location where shear and prying stresses were greatest. As a result, many specimens failed at very low loads and the loading protocol could not be completed as intended. Consequently, averaged load slip curves and the calculated strength and stiffness parameters were incoherent and are not presented here. Original load slip curves are included in Appendix A 2.5.10. Localized Concrete Dowel Connections The localized concrete dowel connections suffered tested as part of this investigation faced the same challenges as the transverse notch connections. In the case of the specimens which did not utilize the plastic sheet to separate the concrete and timber elements, the wood swelled due to moisture absorption from the concrete during and after casting. All specimens failed prior to completing the loading protocol and in some cases the longitudinal dovetail had failed before the specimen could even be tested due to the tension stresses induced in the concrete by the timber 51 swelling. As such, averaged load slip curves and strength and stiffness parameters are not presented here. Original load slip curves are available in Appendix A 2.5.11. Adhesive Connections Adhesive connections were tested with LVL to provide a baseline comparison to hybrid adhesive and self-tapping screw connections. The bond area was limited to 25% of the contact surface area between timber and concrete to limit the loads required to fail the specimen and to ensure the connection failed rather than the concrete or timber. Both wet/dry and wet/wet systems, where concrete was precast and then bonded and cast directly on wet epoxy respectively, exhibited very high stiffness up until failure. Both series had mixed failure modes with elements of bond failure (between smooth precast and epoxy), concrete shear failure, and timber shear failure. Failures were sudden and brittle as expected. Averaged load slip curves and strength and stiffness parameters are presented in Figure 28 and Table 20. Figure 28: Adhesive only Connection Averaged Results (per mm length) 52 Table 20: Adhesive only Connection Averaged Results (per mm length) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps AB1 0.2 2.9 2.4 2.6 2.4 1.8 0.00 5 AB5 0.2 2.8 2.2 2.5 2.4 1.7 0.00 6 2.5.12. Hybrid Adhesive/Screw Connections Hybrid adhesive/screw connections were tested in LSL, LVL, and CLT. Averaged load-slip curves are shown in Figure 29 and individual results are presented in Table 21. Failures in these specimens tended to occur in distinct phases. Initially, the bond provided an extremely stiff connection where almost no displacement was recorded. Eventually, the bond gave way and a transition period occurred where the concrete displaced without picking up additional load. This occurred due to the transfer from a very stiff connection (adhesive) to a less stiff connection (screws). Once the screws were fully engaged, they continued to pick up additional load and attained higher ultimate loads than screws on their own. It is suspected that some additional load was carried by friction generated between the rough failure surface along the adhesive bond and the significant clamping component provided by the inclined screws. The load slip curves for series AB7 series are shown in Figure 30 and demonstrate the transition between adhesive and screwed connection. The remaining individual load-slip curves are presented in Appendix A Table 21: Hybrid Adhesive/Screw Connections Average Results (per screw) Label Fult (kN) Kinit (kN/mm) K0.4 (kN/mm) K0.6 (kN/mm) K0.8 (kN/mm) Kult (kN/mm) Δres (mm) No. Reps AB6 40.6 403.7 284.4 244.7 162.1 51.4 0.01 12 AB7 51.5 298.3 287.5 237.9 181.7 32.0 0.00 6 AB8 45.2 190.2 209.9 160.2 111.4 39.1 0.02 6 53 Figure 29: Hybrid Adhesive/Screw Connections Average Results (per screw) Figure 30: AB7 – SikaDur32 Adhesive + 10x240 ASSY VG at 30º in LSL 54 2.6. Discussion 2.6.1. Comparison of Normalized Connector Performance This section compares the connector performance by looking at the quantity of connectors required to provide equivalent performance at ULS and SLS. Since the general trends within materials are reasonably consistent, each of the connector types are presented for each of the EWP’s separately. Two curves are presented for each EWP (Figure 31 to Figure 37) and show the relative strength and stiffness performance of each of the connectors based on achieving either equivalent stiffness or equivalent strength to a baseline connector. In this case, the HBV system was selected as the baseline. Strength matched curves show the relative connector stiffness provided by a specified connector density that matches the shear strength of 1m of HBV mesh. Stiffness matched curves show how connector strength changes when connectors are specified at a density to match the stiffness of 1m of HBV mesh. The connector quantities are summarized in Table 22 to Table 25. This section is not intended to provide a design basis for interchangeability of connectors, but to provide a qualitative indication of the level of effort, cost, and relative efficiency of various connector systems. Specimen geometry, material specification, construction considerations and desired performance level all influence the specification of connector type and spacing. 55 Table 22: Equivalent ULS and SLS Performance in LSL ULS SLS Connector Description Fk (kN) No. Conns K0.4 (kN/mm) No. Conns HBV 90x1000 203.9 1000mm 1525 1000mm 8x240 ASSY VG @ 30 24.7 8.3 51.9 29.4 8x240 ASSY VG + friction 33.1 6.2 219.0 7.0 10x240 ASSY VG @ 30 27.3 7.5 68.2 22.4 10x200 ASSY VG Pairs @ 45 43.1 4.7 74.4 20.5 10x260 ASSY SK @ 30 31.2 6.5 52.3 29.2 FT + 10x240 ASSY VG 45.9 4.4 37.7 40.4 SikaDur 32 Epoxy + 10x240 ASSY VG @ 30* 44.1 7.5 287.5 5.3 Table 23: Equivalent ULS and SLS Performance in LVL ULS SLS Connector Description Fk (kN) No. Conns K0.4 (kN/mm) No. Conns HBV 90x1000 188.7 1000mm 1170 1000mm 8x240 ASSY VG @ 30 25.6 7.4 56.5 20.7 8x240 ASSY VG + friction 32.2 5.9 102.4 11.4 10x240 ASSY VG @ 30 25.5 7.4 65.2 17.9 10x200 ASSY VG Pairs @ 45 27.4 6.9 55.6 21.0 10x260 ASSY SK @ 30 22.0 8.6 53.2 22.0 FT + 10x240 ASSY VG 32.2 5.9 49.2 23.8 SikaDur 32 Epoxy + 10x240 ASSY VG @ 30* 36.1 7.4 284.4 4.1 56 Table 24: Equivalent ULS and SLS Performance in CLT ULS SLS Connector Description Fk (kN) No. Conns K0.4 (kN/mm) No. Conns HBV 90x1000 220.4 1000mm 887 1000mm 8x240 ASSY VG @ 30 23.4 9.4 49.3 18.0 10x240 ASSY VG @ 30 20.8 10.6 71.9 12.3 10x300 ASSY VG @ 30 26.3 8.4 61.9 14.3 10x200 ASSY VG Pairs @ 45 25.1 8.8 67.5 13.2 10x260 ASSY SK @ 30 21.0 10.5 37.8 23.5 FT + 10x240 ASSY VG 22.4 9.9 58.4 15.2 FT + 10x300 ASSY VG 35.8 6.2 32.3 27.5 SikaDur 32 Epoxy + 10x240 ASSY VG @ 30* 28.8 10.6 209.9 4.2 Table 25: Equivalent ULS and SLS Performance through 25mm Insulation ULS SLS Material Fk (kN) No. Conns K0.4 (kN/mm) No. Conns HBV 120x1000 LSL 192.8 1000mm 1538 1000mm 10x220 ASSY VG Pairs @ 45 LSL 23.80 8.1 61.7 24.9 HBV 120x1000 LVL 167.0 1000mm 999.5 1000mm 10x220 ASSY VG Pairs @ 45 LVL 24.2 6.9 47.3 21.1 HBV 120x1000 CLT 155.2 1000mm 640.4 1000mm 10x220 ASSY VG Pairs @ 45 CLT 19.2 8.1 42.8 15.0 57 Figure 31: ULS Strength Matched Connectors in LSL Figure 32: SLS Stiffness Matched Connectors in LSL 58 Figure 33: ULS Strength Matched Connectors in LVL Figure 34: SLS Stiffness Matched Connectors in LVL 59 Figure 35: ULS Strength Matched Connectors in CLT Figure 36: SLS Stiffness Matched Connectors in CLT 60 Figure 37: ULS and SLS Strength and Stiffness Matched Connectors through Insulation 2.6.2. Characteristic Connector Values Characteristic connector values were derived based on the standard t-test using a one-tail distribution with 5% of the area beneath the tail. T-values range from 2.92 for DOF = 2 to 1.80 for DOF = 11 (Montgomery, 2007). Characteristic strengths are then determined by subtracting T*StdDev from the mean ultimate strength of the sample. A summary of the characteristic strengths and associated statistical parameters are presented in Table 26 – Table 28. Table 26: Adhesive and Hybrid Adhesive and Self-Tapping Screw Characteristic Strengths Label EWP Fult (kN) Fk (kN) DOF's COV Std Dev AB1 LVL 0.214 0.142 4 15.7% 0.034 AB5 LVL 0.152 0.120 5 10.6% 0.016 AB6 LVL 40.61 36.13 11 6.1% 2.50 AB7 LSL 51.54 44.13 5 7.1% 3.67 AB8 CLT 45.16 28.78 5 18.0% 8.13 61 Table 27: Self-Tapping Screw Characteristic Connector Strengths Label EWP Fult (kN) Fk (kN) DOF's COV Std Dev VG1 LSL 26.60 24.68 5 3.6% 0.96 VG2 LSL 35.79 33.07 5 3.8% 1.35 VG3 LSL 32.58 27.29 11 9.0% 2.95 VG4 LVL 26.61 25.60 5 1.9% 0.50 VG5 LVL 35.14 32.22 5 4.1% 1.45 VG6 LVL 31.92 25.46 11 11.3% 3.59 VG7 Brisco LVL 26.54 23.93 5 4.9% 1.30 VG8 Brisco LVL 32.21 29.52 5 4.1% 1.34 VG9 CLT 25.37 23.42 5 3.8% 0.97 VG10 CLT 27.93 20.85 11 14.1% 3.95 VG11 CLT 33.52 26.29 5 10.7% 3.59 VG12 LSL 49.01 43.14 5 5.9% 2.91 VG13 LVL 34.89 27.37 5 10.7% 3.73 VG14 CLT 30.60 25.06 5 9.0% 2.75 VG15 LSL 30.01 23.80 5 10.3% 3.08 VG16 LVL 26.27 24.24 5 3.8% 1.01 VG17 CLT 23.57 19.16 4 8.8% 2.07 SK1 LSL 33.15 31.23 5 2.9% 0.95 SK2 LVL 23.87 22.05 5 3.8% 0.90 SK3 CLT 23.21 20.97 4 4.5% 1.05 FT1 LSL 46.97 45.90 5 1.1% 0.53 FT2 LVL 36.48 32.17 3 5.0% 1.83 FT3 Brisco LVL 34.78 31.55 2 3.2% 1.11 FT4 CLT 27.42 22.35 5 9.2% 2.51 FT5 CLT 40.55 35.84 5 5.8% 2.34 62 Table 28: HBV Characteristic Connector Strengths Label EWP Fult (kN) Fk (kN) DOF's COV Std Dev GM1 LSL 0.227 0.204 11 5.6% 0.013 GM2 LVL 0.227 0.189 11 9.3% 0.021 GM3 Brisco LVL 0.237 0.209 4 5.5% 0.013 GM4 CLT 0.238 0.220 10 4.0% 0.009 GM5 LSL 0.214 0.193 5 5.0% 0.011 GM6 LVL 0.184 0.167 5 4.6% 0.008 GM7 CLT 0.164 0.155 5 2.7% 0.005 2.6.3. Influence of Interlayer The influence of the interlayer was checked for correlation and linear regression to determine whether the presence or lack of a slip membrane would create a statistically significant difference in the strength and stiffness of the specimens. Results presented in sections 2.6.3 to 2.6.7 were deemed to be significant when the probability of the observed relationship being a random error was less than 5 percent (ie. α = 0.05). It was found that the absence of an interlayer in STS connections produced a significant increase in both strength and stiffness. This was borne out clearly in the statistics which are presented in Table 29. This result is not surprising as the inclined screws create a normal (clamping) component which increases the portion of the load carried by friction and stiffens the connection. The initial stiffness is further bolstered by the fact that concrete fills all the little voids and imperfections on the wood surface making for a surface-bond type connection. It should be noted with caution that casting concrete directly onto the timber will increase the moisture content of the timber element and may take a long time to return to equilibrium with the environment depending on how the panels are detailed. 63 Table 29: Influence of Removing Slip Membrane Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) 0.973 0.000 8.95 0.948 22 K0.4 (kN/mm) 0.484 0.016 107 0.235 K0.6 (kN/mm) 0.736 0.000 19 0.541 K0.8 (kN/mm) 0.795 0.000 15 0.632 Kult (kN/mm) 0.720 0.000 7 0.518 * P-values >0.05 indicate results not statistically significant Figure 38: Interlayer Influence (8x240 ASSY VG in LSL and LVL) 2.6.4. Influence of EWP and Wood Density The influence of the different EWP’s on the performance of the connectors was tested by a linear regression model by looking at the strength and stiffness parameters as the dependent variables and the wood density as the independent variable. Data was analyzed first from specimens using just 10x240 ASSY VG connectors and then extended to use all specimens that used STS connectors. The results are presented in Table 30 and Table 31. 64 Table 30: Influence of Wood Density on Strength and Stiffness of 10x240 ASSY VG Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) 0.498 0.001 0.017 0.248 40 K0.4 (kN/mm) -0.049 0.755* -0.014 0.002 K0.6 (kN/mm) 0.268 0.086* 0.034 0.072 K0.8 (kN/mm) 0.584 0.000 0.050 0.341 Kult (kN/mm) 0.781 0.000 0.055 0.61 * P-values >0.05 indicate results not statistically significant Table 31: Influence of Wood Density on Strength and Stiffness of all STS Connectors Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) 0.193 0.008 0.017 0.037 183 K0.4 (kN/mm) 0.126 0.087* 0.111 0.016 K0.6 (kN/mm) 0.120 0.104* 0.074 0.014 K0.8 (kN/mm) 0.156 0.034 0.065 0.024 Kult (kN/mm) 0.166 0.024 0.024 0.028 * P-values >0.05 indicate results not statistically significant Figure 39: Influence of Wood Density on 10x240 ASSY VG Performance 65 Both regression models showed that a statistically significant increase in strength was observed with increasing wood density. Internationally, timber codes have recognized this and routinely account for it in calculations of withdrawal capacity of fasteners. Both models also showed that tangent stiffness at 40% and 60% of the ultimate capacity was not significantly affected by changes in wood density, while as fasteners progressed closer to failure, statistically significant increases in stiffness were detected. It is likely that the initial stiffness is more related to a bearing type crushing of the fastener against wood fibres due to their orientation at an angle to grain, while towards ULS loads, the stiffness is more dependent on the withdrawal stiffness of the fasteners which is expected to be correlated with wood density. Figure 39 shows the averaged curves of 10x240 ASSY VG screw connectors in the different EWPs. 2.6.5. Influence of Screw Embedment The embedment depth of 10mm diameter ASSY VG screws was varied in the CLT specimens in order to see the effect of screw length on performance as a shear connector for TCC. Data from 4 test series (VG10, VG11, FT4, and FT5) were analyzed to see if there was a noticeable influence on the strength and stiffness of the connection by increasing the embedment depth from 140 to 200mm. The averaged connector results are plotted in Figure 40 and analysis results are presented in Table 32. Increasing the embedment clearly has a favourable effect on the strength of the connection, however similar to what was observed with the increase in wood density, the stiffness at lower load levels did not increase statistically significant due to the increased embedment. In fact, a significant increase in stiffness was only observed at ULS levels of deformation. It is expected that this too is a result of bearing type deformations occurring while the screw is being engaged at an angle to the grain at lower load levels and that increased withdrawal stiffness only becomes noticeable at higher load levels. 66 Table 32: Influence of Screw Embedment for 10mm Diameter ASSY VG Screws in CLT Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) 0.765 0.000 0.156 0.586 28 K0.4 (kN/mm) -0.343 0.063* -0.341 0.118 K0.6 (kN/mm) -0.258 0.169* -0.100 0.067 K0.8 (kN/mm) -0.060 0.751* -0.012 0.004 Kult (kN/mm) 0.541 0.002 0.085 0.293 * P-values >0.05 indicate results not statistically significant Figure 40: Influence of Screw Embedment for 10mm Diameter ASSY VG Screws in CLT 2.6.6. Influence of Screw Diameter The influence of screw diameter on the strength and stiffness of connectors was investigated. It was determined that for both the full sample set, shown in Figure 41 and Table 34, as well as within individual series (LSL presented in Table 33), that strength showed a significant increase with increasing screw diameter. Once again, however, the increase in stiffness at the serviceability load levels was not significant. 67 Table 33: Influence of Screw Diameter in LSL Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) 0.772 0.000 3.025 0.596 16 K0.4 (kN/mm) 0.344 0.162* 8.225 0.118 K0.6 (kN/mm) 0.234 0.349* 3.075 0.055 K0.8 (kN/mm) 0.519 0.027 4.308 0.269 Kult (kN/mm) 0.812 0.000 4.954 0.660 * P-values >0.05 indicate results not statistically significant Table 34: Influence of Screw Diameter in all EWPs Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) 0.604 0.000 2.389 0.365 64 K0.4 (kN/mm) 0.094 0.453* 2.787 0.009 K0.6 (kN/mm) 0.170 0.171* 2.121 0.029 K0.8 (kN/mm) 0.360 0.003 3.072 0.130 Kult (kN/mm) 0.380 0.002 2.636 0.145 * P-values >0.05 indicate results not statistically significant Figure 41: Influence of Screw Diameter in all EWPs 68 2.6.7. Influence of Moisture Condition During the second casting session for Phase I samples (which occurred at the same time as full-scale specimen casting), some samples were inadequately protected from moisture while the concrete was left to cure. This resulted in the wood products reaching higher than desirable moisture contents ranging from 20 to 30%. By the time of testing, samples were at a moisture content which would be considered “dry” (below 15%), however there appeared to be a residual effect from the past moisture history. Samples which had replicates from both rounds of Phase I castings were tested for the effect of getting wet on connector performance through a linear regression model. While a slight decrease in strength was observed, this effect was determined not to be significant. However, very importantly, significant reductions in stiffness were observed across all load levels from SLS to failure which can be seen in Table 35. Based on this result extreme care should be taken to protect the wood elements from moisture during construction. While ultimately not dangerous, it may be the difference between satisfactory or unsatisfactory in service floor performance. Table 35: Influence of Moisture Condition Dependent Variable Correlation Coeff: R P-value Slope R2 DOF’s Fult (kN) -0.191 0.264* -1.511 0.037 34 K0.4 (kN/mm) -0.902 0.000 -58.838 0.814 K0.6 (kN/mm) -0.873 0.000 -24.939 0.762 K0.8 (kN/mm) -0.691 0.000 -12.583 0.477 Kult (kN/mm) -0.399 0.016 -5.694 0.159 * P-values >0.05 indicate results not statistically significant 69 Chapter 3. Full-Scale Bending Tests 3.1. Design of Specimens 3.1.1. Overview Nine different TCC systems were identified as those offering the most efficient implementation of TCC due to their high stiffness and strength. The connector types which were selected from the Phase I testing are summarized in Table 36. Table 36: Connector Description Used for Full-Scale Bending Tests Type Connector Description 1 ASSY VG CYL 10x240 Installed at 30° angle to grain (leff =140mm) 2 ASSY VG CYL 10x240 Pairs installed at 45 deg to grain through 25mm rigid insulation (leff=90mm) 3 ASSY VG CYL 10x240 and Sikadur32 Hi-Mod epoxy Sim to type 1 plus 2 continuous 50mm wide rows epoxy applied wet just prior to casting 4 HBV mesh (90x1000) Installed in 3mm wide saw kerf with PURBOND two part polyurethane adhesive 5 HBV mesh (120x1000) Sim to type 4 plus 25mm rigid insulation interlayer between timber and concrete Full-scale specimens were designed to exhibit composite efficiencies in the range of 85-95%, as defined in Equation (1), to allow comparing the connector requirements for similar overall performance. Calculations based on the γ-method were performed along with FEM models using the software package RFEM (Dlubal 2015). The models assume elastic concrete and timber elements but account for the non-linear behavior of the connectors. For the purpose of 70 predicting experimental results, mean values for material strength and stiffness were used. Where only specified values were available, (e.g. EWP’s), a coefficient of variation of 10% was assumed to convert characteristic values to mean values. A sample γ-method calculation for panel series 1 is presented in Appendix C and a summary of the FEM modeling techniques and input parameters is provided in Section 3.3.1. 3.1.2. Panel Specifications A summary of the panel configurations, including the connector type and spacing, is presented in Table 37. The parameters tc, tt, and ti refer to concrete, timber and interlayer thickness respectively, while rows refers to the number of rows of fasteners across the width of the panel and s1 and s2 refer to fastener spacing in the high and low shear zones of the panel respectively. The individual drawings for each connector type are shown in Figure 42 - Figure 53. Full scale panels were designed and built using the same material specifications as those for the Phase I tests (refer to section 2.1). Table 37: Full-Scale Panel Configurations Series EWP b (mm) L (mm) tc (mm) tt (mm) ti (mm) Conn type Phase I ID s1 (mm) s2 (mm) rows S1 LSL 610 6096 70 89 -- 1 VG3 150 300 3 S2 LVL 610 6096 70 89 -- 1 VG6 150 300 3 S3 CLT 600 6000 70 99 -- 1 VG10 150 300 3 S4 LSL 610 6096 70 89 25 2 VG17 300 -- 3 S5 LVL 610 6096 70 89 -- 3 AB6 300 -- 3 S6 LSL 610 6096 70 89 -- 4 GM1 -- -- 2 S7 LVL 610 6096 70 89 -- 4 GM2 -- -- 2 S8 CLT 600 6000 70 99 -- 4 GM4 -- -- 2 S9 LVL 610 6096 70 89 25 5 GM6 -- -- 2 71 Figure 42: Layout of Typical Panel with Inclined STS (S1, S2, S3) Figure 43: Detail A (inclined STS) Figure 44: Layout of Typical Panel with Pairs of Inclined STS Through Rigid Insulation (S4) 72 Figure 45: Detail B (Pairs of Inclined STS through Rigid Insulation) Figure 46: Layout of Typical Panel with Adhesive Layer and Inclined STS (S5) Figure 47: Detail A (Adhesive Layer and Inclined STS) 73 Figure 48: Layout of Typical Panel with HBV Mesh (S6, S7, & S8) Figure 49: Detail C (HBV Mesh) Figure 50: Section C-C` (HBV Mesh) 74 Figure 51: Layout of Typical Panel with HBV Mesh through Rigid Insulation (S9) Figure 52: Detail D (HBV Mesh through Rigid Insulation) Figure 53: Section D-D` (HBV Mesh through Rigid Insulation) 75 3.2. Specimen Fabrication 3.2.1. Overview All fabrication took place at CAWP and panels were then transported to FPInnovations for casting. The prefabrication process was carried out as follows for the various specimen types. 3.2.2. Self-Tapping Screw Connectors  Layout of screw spacing (varied spacing at panel ends and mid-span regions)  Predrill 6mm pilot holes approximately 40mm deep at prescribed angle (depends on connector configuration and presence of insulation) using hardwood jig  Install 6 mil poly layer to minimize friction between wood and concrete and protect wood from moisture ingress during casting  Mark screws using spray paint to ensure proper embedment length  Install screws using an electric drill until painted portion of screw fully embedded into panel  Install formwork around panel  Cut and install welded wire mesh reinforcing over screws (centered in concrete depth) Figure 54: Installation of Inclined STS 76 3.2.3. HBV Steel Mesh Connectors  Layout of connector rows  Cut 45mm deep saw kerfs along length of panel using circular saw with 3mm wide blade.  Blow out saw kerfs with compressed air and remove saw dust using shop vacuum  Install 6 mil poly layer to minimize friction between wood and concrete  Install wood screws at 1 metre intervals to prevent glue seepage and enable sequential connector installation  Inject two-part polyurethane adhesive supplied by TiComTec per manufacturer’s instructions into saw kerf intervals followed immediately by installation of steel mesh.  Install formwork around panel  Cut and install WWM reinforcing over steel mesh connectors Figure 55: Installation of HBV Mesh 77 3.2.4. Concrete Casting  All full-scale panels were laid out on tarps at the FPInnovations yard for sequential casting with a 10 cubic meter ready-mix delivery truck.  All formwork had drain holes so that water could not build up in panels prior to casting.  As panels were poured, they were vibrated, leveled, finished, and covered  For specimens which were epoxy bonded to the concrete in a wet-wet process, the epoxy was mixed just prior to concrete placement and applied to the panel in the appropriate zones.  15 test cylinders were also poured at the time of casting and left in the field to cure with the panels for testing near the time of full-scale panel testing. Figure 56: Concrete Casting 3.3. Methods 3.3.1. Design of Panels Using FEM The FEM modeling was performed in the software suite RFEM (Dlubal 2015). Each specimen was modeled according to the dimensions and material parameters presented in Table 38. Timber and concrete were modeled as elastic beam elements with their centroids offset by the distance e’ as shown in Figure 57. In the case of CLT, a definable stiffness element was used 78 due to the fact that the entire section is not capable of withstanding tensile stresses and that CLT too has an effective bending modulus due to the cross layers and variations in shear stiffness across its depth. The Ieff_t and Aeff_t parameters refer to the effective moment of inertia and effective tensile area used to model CLT. In order to accurately model the connectors, rigid-hinge link elements were connected to springs which lie in the shear plane between timber and concrete. The springs were calibrated according to the stiffness values presented in Section 1.1 for the appropriate series and implemented in RFEM as shown in Figure 59. Table 38: FEM Model Parameters Panel Series tc (mm) tt (mm) ti (mm) e’ (mm) γc (kN/m3) γt (kN/m3) Ec (GPa) Et (GPa) Ieff_t (x106 mm4) Aeff_t (x103 mm2) S1 70 89 -- 79.5 23.5 6.87 30.3 10.7 -- -- S2 70 89 -- 79.5 23.5 6.00 30.3 13.8 -- -- S3 70 99 -- 84.5 23.5 4.12 30.3 9.5 42.2 38.4 S4 70 89 25 104.5 23.5 6.87 30.3 10.7 -- -- S5 70 89 -- 79.5 23.5 6.00 30.3 13.8 -- -- S6 70 89 -- 79.5 23.5 6.87 30.3 10.7 -- -- S7 70 89 -- 79.5 23.5 6.00 30.3 13.8 -- -- S8 70 99 -- 84.5 23.5 4.12 30.3 9.5 42.2 38.4 S9 70 89 25 104.5 23.5 6.00 30.3 13.8 -- -- Dynamic analysis was performed using the DynamPro add-on module to RFEM. For the purpose of these tests, predictions of the fundamental natural frequency were the primary interest. In order to calculate the natural frequency of the panels, accurate estimations of the weight, connector stiffness, concrete stiffness, and timber stiffness were required. The software only considers the initial linear portion of the piece-wise linear representation of the connector 79 stiffness curve during dynamic analysis, which is reasonable given floor vibrations are typically very low amplitude and would not stress the connectors to where non-linearity would be expected. Under certain design scenarios, further dynamic analysis may be necessary and the model could easily be subjected to response spectra or time history excitations to further investigate the performance under a variety of dynamic loading scenarios. Figure 57: FEM Model of Set-up with Elastic Beam Elements and Springs at Fastener Locations Figure 58: Close up of FEM Model at Springs 80 Figure 59: Nonlinear Spring Calibration In addition to the dynamic analysis, the models were each subjected to an incrementally increasing load to predict the full non-linear behaviour of the panels. In this case, only the connectors were modeled as non-linear elements and were the only failure mode considered. In some cases, where the connector capacity exceeds the timber or concrete capacity, these non-linear “push-over” curves are non-conservative and predict higher load bearing capacity than could be expected. This result is illustrated clearly in the load-slip curves in section 3.4.3. 81 3.3.2. Test Set-up The panels were tested for strength and stiffness under four-point bending. The panels spanned 5.8m between roller supports to simulate a true simply supported condition. Load was applied to the panel at the third points by a steel spreader beam which was pin connected to a 100kip hydraulic actuator in a steel reaction frame. The loads were spread evenly across the width of the panel by way of steel HSS tubes. Roller bearings were located between the spreader beam and the HSS tubes ensuring that the specimens were entirely unrestrained by the test apparatus. A schematic of the complete test apparatus is shown in Figure 60 and a photo of one mounted test specimen in Figure 61. Loads were recorded using a calibrated load cell while vertical displacements were measured by a mid-span LVDT for the stiffness tests and lasers at the mid and third points for the entire test. Four additional LVDTs were installed to measure the relative slip between the concrete and timber at each of the four corners directly over the supports. Figure 60: Test Setup and Instrumentation 82 Figure 61: Photo of Full-Scale Bending Test 3.3.3. Dynamic Test Procedure The dynamic performance of each panel type was predicted based on established methods of mechanics (Chopra, 2012) using the effective bending stiffness determined by the γ-method and by dynamic analysis in the FEM software suite RFEM. The panels were initially subjected to dynamic excitation from a light impact (heel strike), and accelerations were monitored using a digital accelerometer. From these acceleration time histories, the fundamental frequency was obtained using a Fast Fourier Transform (FFT). A sample time history and FFT plot are shown in Figure 62. The FFT plot shows each test (i.e. initial, after first service level loading, and after second service loading) and the stabilized natural frequency. 83 Figure 62: Acceleration Time History from Heel Strike (left) and Fundamental Frequency Determination using FFT (right) Following the initial vibration test, the panels were loaded to service level (defined as the actuator load causing the same bending moment as would be obtained from a 4.8 kPa UDL), held for thirty seconds, then unloaded a minimum of two times or until the fundamental frequency determined from the vibration tests stabilized. At that point the panel was loaded to failure at a constant displacement rate of 6mm/min. The loading protocol is depicted in Figure 63. Figure 63: Full Scale Loading Protocol 84 3.3.4. Quasi-Static Test Procedure The test procedure for the full scale specimens was adapted from EN 26891 (CEN 1991), the test procedure for small scale shear tests, and extended to include investigations into the dynamic performance of the specimens. TCC connectors show varying degrees of initial inelastic displacement upon first loading, represented by Δres in the results tables presented in section 3.4, so an initial loading component was incorporated into the loading protocol to quantify the level of inelastic deflection (denoted as Δinelastic in Table 40), this causes in the panels as well as the potential changes in bending stiffness associated with the inelastic “set” of some connectors. The protocol was further adapted by converting from a load-controlled to displacement-controlled protocol. 85 3.3.5. Analysis Methods The results were calculated for each phase of each test as described in Table 39. Table 39: Analysis Methods for Full-Scale Tests Parameter Description Equation Panel Stiffness, k (N/mm) Regression analysis of load vs displacement curves up to service level 𝑘 =𝑃𝑡𝑜𝑡𝑎𝑙2⁄∆𝑚𝑖𝑑𝑠𝑝𝑎𝑛 EIeff (N*mm2) 𝐸𝐼𝑒𝑓𝑓 = 𝑘 ∗ 𝑎24 (3𝑙2 − 4𝑎2) Natural Frequency, fn (Hz) FFT of acceleration time history from heel-strike impact at mid-span. Repeated for each loading cycle to service loads. Calculations performed in MathCad v.15 𝑋𝑘 = ∑ 𝑥𝑛𝑒−𝑖2𝜋𝑘𝑛𝑁𝑁−1𝑛=0 (𝑘 = 0, … , 𝑁 − 1) Mult (kN*m/m) See figure for EIeff b = panel width in metres 𝑀𝑢𝑙𝑡 = (𝑃𝑡𝑜𝑡𝑎𝑙2⁄ ) ∗ 𝑎𝑏 3.4. Results 3.4.1. Bending Stiffness Each of the full-scale specimens was subjected to multiple loadings up to service level as described in section 3.3.4, from which the effective bending stiffness (EIeff) was calculated according to the equations in Table 39. These results, along with the inelastic deformations 86 (Δinelastic) which remained after initial loading are summarized in Table 40 and compared with both FEM and γ-method predictions. Load vs. displacement curves up to service level for both initial and second loading are shown for each of the nine test series in Figure 64 to Figure 72. Table 40: Panel Stiffness - EIeff (1012 N*mm2) Measurements Predictions Series Replicate Initial Service FEM Difference γ-method Difference Δinelastic S1 1 3.21 3.41 3.11 -8.7 % 3.24 -5.0 % 1.12 2 2.78 3.22 -3.3 % 0.7 % 2.10 S2 1 3.61 3.83 3.58 -6.5 % 3.73 -2.6 % 1.11 2 3.50 3.81 -6.1 % -2.2 % 1.29 S3 1 2.65 2.90 2.74 -5.5 % 2.84 -2.0 % 1.76 2 2.83 3.16 -13.3 % -10.1 % 1.64 S4 1 3.97 4.65 4.39 -5.6 % 4.59 -1.2 % 1.68 2 4.24 4.34 1.1 % 5.8 % 0.42 S5 1 3.96 4.15 3.78 -8.9 % 3.88 -6.5 % 0.70 2 3.84 3.92 -3.6 % -1.1 % 0.21 S6 1 3.36 3.34 3.24 -3.0 % 3.35 0.4 % -- 2 2.92 3.16 2.6 % 6.1 % 1.42 S7 1 3.79 3.94 3.71 -6.0 % 3.85 -2.4 % 0.73 2 4.06 4.16 -10.8 % -7.4 % 0.24 S8 1 3.00 3.13 2.74 -12.5 % 2.85 -8.9 % 0.76 2 2.89 2.95 -7.3 % -3.5 % 0.69 S9 1 5.41 5.73 5.60 -2.3 % 5.87 2.4 % 0.58 2 6.14 6.13 -8.6 % -4.2 % 0.01 87 Figure 64: Load vs. Displacement of Series 1 up to Service Level Figure 65: Load vs. Displacement of Series 2 up to Service Level 88 Figure 66: Load vs. Displacement of Series 3 up to Service Level Figure 67: Load vs. Displacement of Series 4 up to Service Level 89 Figure 68: Load vs. Displacement of Series 5 up to Service Level Figure 69: Load vs. Displacement of Series 6 up to Service Level 90 Figure 70: Load vs. Displacement of Series 7 up to Service Level Figure 71: Load vs. Displacement of Series 8 up to Service Level 91 Figure 72: Load vs. Displacement of Series 9 up to Service Level 3.4.2. Vibration Results The vibration tests provided valuable, almost real-time, feedback during the testing since the results can be analyzed quickly with the use of programs such as MathCad. The vibration tests demonstrated that the inelastic behaviour that was expected at initial loading for some connectors had taken place once the measurements of the natural frequency stabilized between loading cycles. This indicated that it was appropriate to move on to destructive testing of the panels. Additionally, performing vibration tests made it possible to assess the accuracy with which the natural frequency of the panels could be determined by simplified and FEM methods, which is an essential step for designers looking to assess the vibration performance of floor systems. The results are presented in Table 41 for each panel. 92 Table 41: Panel Vibration Results Fundamental Frequency (Hz) Series Replicate Initial Service_1 Service_2 FEM γ-method S1 1 7.37 7.35 7.30 7.14 7.10 2 7.15 6.98 6.96 S2 1 7.76 7.66 7.70 7.78 7.75 2 7.91 7.83 7.81 S3 1 7.00 6.88 6.84 7.08 7.01 2 7.12 7.02 6.98 S4 1 8.35 8.20 8.21 8.48 8.44 2 8.15 8.13 8.13 S5 1 7.68 7.70 -- 8.05 7.90 2 7.93 7.93 7.91 S6 1 7.32 7.32 7.22 7.28 7.21 2 7.06 7.06 7.03 S7 1 7.96 7.93 7.93 7.93 7.87 2 8.10 8.10 8.10 S8 1 7.28 7.28 7.28 7.08 7.04 2 7.15 7.13 7.13 S9 1 9.08 8.88 8.88 9.74 9.71 2 9.59 9.57 9.55 3.4.3. Panel Capacity Following initial loading up to SLS and measurement of the fundamental frequencies of each panel, they were loaded to failure according to the procedure described in section 3.3.4. Each of the load slip curves are presented here along with the corresponding FEM predictions in Figure 73 to Figure 81. The results are also summarized in Table 42. As discussed in section 3.3.1, only the connectors were modeled as non-linear elements and therefore are the only predicted 93 failure mode from. In cases where the connector was not the governing failure mode, it is clear from the curves that the FEM model over-predicts capacity. Table 42: Panel Capacities Series Replicate Pmax (kN) Mult (kN*m/m) S1 1 127.2 201.5 2 115.4 182.7 S2 1 123.2 191.8 2 127.4 198.4 S3 1 74.4 117.8 2 93.1 147.3 S4 1 124.7 197.4 2 105.2 166.5 S5 1 105.6 164.5 2 90.1 140.3 S6 1 89.6 139.5 2 88.0 137.0 S7 1 89.3 139.1 2 90.3 140.6 S8 1 84.5 133.8 2 74.9 118.6 S9 1 91.5 142.5 2 90.4 140.7 94 Figure 73: Load vs. Displacement of Series 1 Figure 74: Load vs. Displacement of Series 2 95 Figure 75: Load vs. Displacement of Series 3 Figure 76: Load vs. Displacement of Series 4 96 Figure 77: Load vs. Displacement of Series 5 Figure 78: Load vs. Displacement of Series 6 97 Figure 79: Load vs. Displacement of Series 7 Figure 80: Load vs. Displacement of Series 8 98 Figure 81: Load vs. Displacement of Series 9 3.4.4. Failure Modes The failure modes for each panel type are summarized in Table 43 and are based on interpretation of the panel and connector load slip curves along with visual observations during testing. Each of the connector load slip curves are presented below with pictures of each failure type presented in Appendix D . Ultimate load carrying capacity varied between the panel types and was generally indicative of the failure type. Brittle failure modes such as concrete crushing and tensile fracture of timber elements occurred at much higher loads than more ductile failure modes such as connector yielding or screw withdrawal. 99 Table 43: Panel Failure Modes Series Replicate Failure type Description S1 1 brittle concrete crushing & timber fracture 2 brittle concrete crushing S2 1 combined screw withdrawal & timber fracture 2 combined screw withdrawal & timber fracture S3 1 brittle timber fracture 2 brittle timber fracture S4 1 ductile screw withdrawal 2 ductile screw withdrawal S5 1 combined bond, screw withdrawal, & timber fracture 2 combined bond, screw withdrawal, & timber fracture S6 1 ductile connector yielding 2 ductile connector yielding S7 1 ductile connector yielding 2 ductile connector yielding S8 1 brittle timber fracture 2 brittle timber fracture S9 1 ductile connector yielding 2 ductile connector yielding 100 Figure 82: Load vs Shear Slip of Series 1 Figure 83: Load vs Shear Slip of Series 2 101 Figure 84: Load vs. Shear Slip of Series 3 Figure 85: Load vs. Shear Slip of Series 4 102 Figure 86: Load vs. Shear Slip of Series 5 Figure 87: Load vs. Shear Slip of Series 6 103 Figure 88: Load vs. Shear Slip of Series 7 Figure 89: Load vs. Shear Slip of Series 8 104 Figure 90: Load vs. Shear Slip of Series 9 105 3.5. Discussion 3.5.1. Differences Between FEM Model and Experiment The FEM models and experimental results proved to be in reasonable agreement for predictions of bending stiffness and the fundamental frequency of vibration. The parameters which influence these properties are generally well understood and variation observed in measurements of individual samples (e.g. elastic modulus and weight of concrete and timber, and connector stiffness) tends to be smoothed out when incorporated in a large panel. The most significant shortcoming of the modeling was its inability to accurately predict the failure load and failure mode. The models utilized linear concrete and timber elements as it was assumed that damage would generally be limited to the connectors. This was not the case for several EWPs and connector combinations where the timber and or concrete failed prior to any observed connector failure. This increased connector capacity is a natural consequence of increasing connector density to achieve higher stiffness. Models could be modified to include either non-linear timber and concrete elements, or linear elements which will initiate failure at a given stress level. 3.5.2. Difference Between Small and Full Scale Tests The small scale tests showed a wider variety of failure modes than the full scale tests. This is likely due to the lack of transverse reinforcing in the small scale tests, as most connector types exhibited some level of cracking around the connectors when connector failure was initiated. It was expected that this failure mode would not be observed in the full-scale tests due to the additional wire mesh reinforcing as well as the inherent confinement provided by a larger mass of concrete when compared with a small unconfined piece of concrete as in the small scale specimens. It is relatively easy to measure the shear deflection under bending, however much 106 more difficult to measure accurately the load in connectors. This is due to fact that the generation of shear flow forces, which are carried by the connectors, is dependent on the stiffness of the connector. What we can observe is that good agreement was obtained between predicted overall bending stiffness of panels and experimental results. This indicates that stiffness values obtained in small-scale shear tests as calculation input are an appropriate characterization of the connector stiffness under realistic bending conditions. 3.5.3. Importance of Failure Modes The understanding of the structural load path, and expected and possible failure modes are important pre-requisites for any competent design. The experimental work showed that TCC can fail in a number of ways which are characterized generally as either ductile or brittle. Where connector strength is the governing failure mode, it is possible to introduce ductility to the system where it would otherwise experience either concrete compression or timber tensile failure. Both of these brittle failure modes were observed during testing. However, it was observed that brittle failures tended to occur at very high load levels; always in excess of four times service load and as high as ten times service load. This demonstrates that these brittle failures are unlikely to be the governing failure mode within the structure; as a result, the failure mode is no longer of much practical importance or consequence since the TCC floor stands a very small chance of being a weak link in the overall structural load path. 3.5.4. ULS vs. SLS Considerations The conventional wisdom surrounding design of slender floor systems are that serviceability related issues tend to govern rather than strength requirements. In the case of lightweight floors such as light wood frame joisted floors, deflections under service loads are limited both to 107 prevent cracking of finishes on the ceiling below and to ensure a minimum amount of stiffness is achieved to prevent occupant discomfort resulting from transient vibrations. In heavier floors, such as reinforced concrete flat slabs, long-term creep deflection is generally the governing criteria which limits span. Although the vibration frequencies of these floors often fall within the range of susceptibility for human induced vibration, their significant mass limits the motion that is perceived by occupants. TCC floors do not fit neatly into either of these categories as they are neither lightweight nor particularly heavy. As such, the serviceability requirements are less well understood and may require additional investigation to ensure satisfactory performance is attained from a given design. At a minimum, attention should be paid to the following to achieve a satisfactory floor using TCC:  Service load level deflections;  total long-term deflection which accounts explicitly for creep of timber, concrete, and connector, as well as deflection caused by inelastic “set” of connectors; and  fundamental vibration frequency. What was abundantly clear from the full-scale tests was that panels which are designed to perform satisfactorily under SLS conditions generally have significant reserve capacity and have easily meet ULS requirements. 108 Chapter 4. Conclusion The work presented herein is a summary of the experimental work performed at UBC on the topic of Timber Concrete Composites using flat-plate engineered wood products. A two phase experimental program was developed which focused first on performance of 45 different TCC configurations (variety of proprietary, off-the-shelf, and novel connectors in combination with four different EWPs) in small-scale shear tests. The results were presented and relative performance of the various connectors was discussed with respect to both strength and stiffness. Nine TCC configurations were selected for implementation in full-scale bending and vibration tests. The full-scale test specimens were designed according to the γ-method to achieve similar composite efficiencies, in the range of 90%, so that comparisons would be based on equivalent overall performance. Specimens were tested for elastic stiffness under a quasi-static loading protocol and measurements of the dynamic properties were obtained using an accelerometer. The results showed that calculations according to the γ-method and detailed FEM models were able to predict the stiffness and dynamic properties of the panels within a reasonable degree of accuracy. Predictions of the capacity were less easily validated with simplified models, however panels which were designed to meet or exceed serviceability requirements had significant reserve capacity and were capable of sustaining loads up to 10 times service loads before failure. As TCC technology advances and is implemented into building codes, it will be important to address their long-term performance and to quantify the relative contributions of concrete, timber, and connectors to the overall creep of TCC. 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New Orleans, Louisiana, USA. , 3 304-308. 114 Appendices Appendix A - Load-Displacement Curves for Phase I Specimens Figure 91: VG1 - 8x240 ASSY VG at 30˚ in LSL Figure 92: VG2 – 8x240 ASSY VG at 30˚ + Friction in LSL 115 Figure 93: VG3 – 10x240 ASSY VG at 30˚in LSL Figure 94: VG4 - 8x240 ASSY VG at 30˚in LVL 116 Figure 95: VG5 – 8x240 ASSY VG at 30˚ + Friction in LVL Figure 96: VG6 – 10x240 ASSY VG at 30˚ in LVL 117 Figure 97: VG7 – 8x240 ASSY VG at 30˚ in Brisco LVL Figure 98: VG8 – 10x240 ASSY VG at 30˚ in Brisco LVL 118 Figure 99: VG9 - 8x240 ASSY VG at 30˚ in CLT Figure 100: VG10 – 10x240 ASSY VG at 30˚ in CLT 119 Figure 101: VG11 – 10x300 ASSY VG at 30˚ in CLT Figure 102: VG12 – 10x200 ASSY VG Pairs at 45˚ in LSL 120 Figure 103: VG13 – 10x200 ASSY VG Pairs at 45˚ in LVL Figure 104: VG14 – 10x200 ASSY VG Pairs at 45˚ in CLT 121 Figure 105: VG15 – 10x220 ASSY VG Pairs at 45˚ through 25mm Insulation in LSL Figure 106: VG16 - 10x220 ASSY VG Pairs at 45˚ through 25mm Insulation in LVL 122 Figure 107: VG17 - 10x220 ASSY VG Pairs at 45˚ through 25mm Insulation in CLT Figure 108: SK1 – 10x260 ASSY SK at 30˚ in LSL 123 Figure 109: SK2 – 10x260 ASSY SK at 30˚ in LVL Figure 110: SK3 – 10x260 ASSY SK at 30˚ in CLT 124 Figure 111: FT1 – 10x240 ASSY VG plus FT-Connector at 30˚ in LSL Figure 112: FT2 – 10x240 ASSY VG plus FT-Connector at 30˚ in LVL 125 Figure 113: FT3 – 10x240 ASSY VG plus FT-Connector at 30˚ in Brisco LVL Figure 114: FT4 – 10x240 ASSY VG plus FT-Connector at 30˚ in CLT 126 Figure 115: FT5 – 10x300 ASSY VG plus FT-Connector at 30˚ in CLT Figure 116: AB1 – SikaDur 32 Adhesive and LVL (Wet/Dry) 127 Figure 117: AB5 – SikaDur 32 Adhesive and LVL (Wet/Wet) Figure 118: AB6 – Hybrid Adhesive plus 10x240 ASSY VG at 30˚ in LVL 128 Figure 119: AB7 – Hybrid Adhesive plus 10x240 ASSY VG at 30˚ in LSL Figure 120: AB8 – Hybrid Adhesive plus 10x240 ASSY VG at 30˚ in CLT 129 Figure 121: LD1 – Localized Concrete Dowels in LSL with Slip Membrane Figure 122: LD2 – Localized Concrete Dowels in LSL without Slip Membrane 130 Figure 123: LD3 – Localized Concrete Dowels in LVL with Slip Membrane Figure 124: LD4 – Localized Concrete Dowels in LVL without Slip Membrane 131 Figure 125: LD5 – Localized Concrete Dowels in CLT with Slip Membrane Figure 126: TN1 – Transverse Notch in LSL 132 Figure 127: TN2 – Transverse Notch in LVL Figure 128: TN3 – Transverse Notch in CLT 133 Figure 129: GM1 – 300mm HBV Mesh in LSL Figure 130: GM2 – 300mm HBV Mesh in LVL 134 Figure 131: GM3 – 300mm HBV Mesh in Brisco LVL Figure 132: GM4 – 300mm HBV Mesh in CLT 135 Figure 133: GM5 – 300mm HBV Mesh through 25mm Insulation in LSL Figure 134: GM6 – 300mm HBV Mesh through 25mm Insulation in LVL 136 Figure 135: GM7 – 300mm HBV Mesh through 25mm Insulation in CLT 137 Appendix B - Pictures of Failure Modes of Phase I specimens Figure 136: HBV Yielding Failure Figure 137: FT Connector and Tensile Failure of Screw Figure 138: ASSY VG Failing Bond Between Threads and Concrete 138 Figure 139: Concrete Shear Failure for Transverse Notch (left) and Localized Dowel (right) Connections 139 Appendix C - Design of Phase II Specimens According to Gamma Method 140 141 142 143 Appendix D - Pictures of Failure Modes of Phase II specimens Concrete Crushing and Timber Tensile Failure Figure 140: Series 1 Panel Failing Due to Concrete Crushing and Timber Tensile Fracture Connector Failure Followed by Brittle Panel Failure Figure 141: Series 2 Panel Failing by Screw Withdrawal Followed by Tensile Failure of Timber 144 Brittle Tensile Failure of Timber Figure 142: Series 3 Panel Exhibiting Tensile Failure Prior to Connector Yielding or Concrete Crushing Ductile Screw Withdrawal Failure Figure 143: Series 4 Panel Failing by Screw Withdrawal through 25mm Rigid Insulation 145 Ductile Connector Yielding Failure Figure 144: Series 7 Panel with HBV Connector Prior to (left) and After Yielding (right) Ductile Connector Yielding Failure Through Rigid Insulation Figure 145: Series 9 Panel with HBV Connector Yielding through 25mm Rigid Insulation 146 Bond Failure, Screw Withdrawal and Timber Tensile Failure Figure 146: Series 5 Panel Failures (a) Initial Failure of Adhesive Bond Line Followed by (b) Screw Withdrawal Failure and Finally (c)(d) Timber Tensile Failure
Thesis/Dissertation
eng
Civil Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Timber-concrete composite connectors in flat-plate engineered wood products
Text