Forestry, Faculty of
DSpace
UBCV
Xiang, Liuzhen
Master of Science - MSc
University of British Columbia
This research study focuses on the experimental testing and modeling of nail connections in Mid-ply 2 shear wall (MPSW2) systems with the objective to understand the lateral resistance of these connections and develop reliable models for further analysis. The research includes monotonic and reversed cyclic loading tests with loading directions parallel to the grain, specific gravity, and moisture content tests, as well as nail bending tests. These evaluations aim to assess the mechanical performance of the connections, encompassing peak load, stiffness, and ductility. The test results indicated the failure mode was dominated by dowel bearing failures of the OSB sheathing and not the classical nail withdrawal failures observed in traditional light wood frame shear walls. The load-slip data was fitted to load-slip equations (Foschi, 1974) and a mechanic-based load-slip model, HYST algorithm (Foschi, 2000). The results demonstrate that the fitted load-slip equation and the calibrated HYST model effectively capture the monotonic and reversed cyclic backbone load-slip behaviour of the connections. The information can serve as input parameters for sophisticated numerical structural analysis models to predict and model the lateral resistance performance of MPSW2 systems and buildings. The findings from this thesis can be applied in future MPSW2 connection and wall studies to enhance their practical applications.
LATERAL RESISTANCE OF NEW MID-PLY SHEAR WALL (MPSW2) CONNECTIONS - PERFORMANCE OF DIFFERENT MATERIALS by Liuzhen Xiang B.Sc., The University of British Columbia, 2020 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Forestry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) July 2024 © Liuzhen Xiang, 2024 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis entitled: Lateral Resistance of New Mid-ply Shear Wall (MPSW2) Connections â Performance of Different Materials submitted by Liuzhen Xiang in partial fulfillment of the requirements for the degree of Master of Science in Forestry Examining Committee: Dr. Frank Lam, Professor, Department of Wood Science, UBC Supervisor Dr. Minghao Li, Associate Professor, Department of Wood Science, UBC Supervisory Committee Member Dr. Haibo Feng, Assistant Professor, Department of Wood Science, UBC Supervisory Committee Member Dr. Ricardo O. Foschi, Professor Emeritus, Department of Civil Engineering,UBC Additional Examiner iii Abstract This research study focuses on the experimental testing and modeling of nail connections in Mid-ply 2 shear wall (MPSW2) systems with the objective to understand the lateral resistance of these connections and develop reliable models for further analysis. The research includes monotonic and reversed cyclic loading tests with loading directions parallel to the grain, specific gravity, and moisture content tests, as well as nail bending tests. These evaluations aim to assess the mechanical performance of the connections, encompassing peak load, stiffness, and ductility. The test results indicated the failure mode was dominated by dowel bearing failures of the OSB sheathing and not the classical nail withdrawal failures observed in traditional light wood frame shear walls. The load-slip data was fitted to load-slip equations (Foschi, 1974) and a mechanic-based load-slip model, HYST algorithm (Foschi, 2000). The results demonstrate that the fitted load-slip equation and the calibrated HYST model effectively capture the monotonic and reversed cyclic backbone load-slip behaviour of the connections. The information can serve as input parameters for sophisticated numerical structural analysis models to predict and model the lateral resistance performance of MPSW2 systems and buildings. The findings from this thesis can be applied in future MPSW2 connection and wall studies to enhance their practical applications. iv Lay Summary This thesis investigated nail connections of new shear wall design Midply-2 (MPSW2) in wooden structures through experimental tests and modeling. The results showed that thicker sheathing panels had higher load-carrying capacities but lower stiffness. The properties of nails from different suppliers were comparable. Calibrated mathematical models accurately predicted connection behavior. The developed fundamental understanding of the nail connection can be used to guide the design and construction of the new MPSW2 wooden building systems. v Preface This research project was under guidance of Dr. Frank Lam to investigate more about the load deformation behaviours of the connections in the new Midply-2 shear walls, The connection experiment tests in Chapter 2 were conduced Liuzhen Xiang, with the help of George Lee and Amir Kari. The modeling in Chapter 7 was carried out by Liuzhen Xiang with the help of Amir Kari. The energy dissipation calculation in Chapter 3, nail bending tests in Chapter 4, drying test in Chapter 5 and the Fitting in Chapter 6 were completed by Liuzhen Xiang. vi Table of Contents Abstract ....................................................................................................................... iii Lay Summary ............................................................................................................... iv Preface ........................................................................................................................... v Table of Contents ......................................................................................................... vi List of Tables ................................................................................................................. x List of Figures .............................................................................................................. xii List of Abbreviations ................................................................................................... xv Acknowledgements ..................................................................................................... xvi Chapter 1: Introduction and Literature Review .......................................................... 1 1.1 Research Background .......................................................................................... 1 1.2 Research Introduction ......................................................................................... 2 1.3 Research Objectives ............................................................................................. 8 1.4 Literature Review ................................................................................................ 9 1.4.1 MIDPLYâ¢ Sheathing .............................................................................................. 9 1.4.2 Midply Shear Wall System (MIDPLYâ¢) Connection ........................................... 10 1.4.3 MIDPLYâ¢ versus Conventional Shear Wall System............................................ 11 1.4.4 MIDPLYâ¢ Models ................................................................................................. 14 Chapter 2: Connection Testing ................................................................................... 16 vii 2.1 Connection Test under Monotonic Loading ..................................................... 16 2.1.1 Testing Purpose....................................................................................................... 16 2.1.2 Materials ................................................................................................................. 16 2.1.3 Test Apparatus ........................................................................................................ 21 2.1.4 Loading Protocol ..................................................................................................... 22 2.1.5 Methods of Data Analysis ....................................................................................... 22 2.1.6 Test Results ............................................................................................................. 27 2.2 Connection Testing under Reversed Cyclic Loading ........................................ 35 2.2.1 Testing Purpose....................................................................................................... 35 2.2.2 Materials ................................................................................................................. 35 2.2.3 Test Apparatus ........................................................................................................ 39 2.2.4 Loading Protocol ..................................................................................................... 40 2.2.5 Methods of Data Analysis ....................................................................................... 41 2.2.6 Test Results ............................................................................................................. 41 Chapter 3: Energy Dissipation .................................................................................... 48 Chapter 4: Nail Bending Test ..................................................................................... 50 4.1 Testing Purpose .................................................................................................. 50 4.2 Materials ............................................................................................................. 50 4.3 Test Apparatus ................................................................................................... 50 4.4 Loading Protocol ................................................................................................ 51 viii 4.5 Test Results ........................................................................................................ 51 Chapter 5: Specific Gravity and Moisture Content Test ........................................... 53 5.1 Testing Purpose .................................................................................................. 53 5.2 Testing Materials ............................................................................................... 53 5.3 Test Apparatus and Method .............................................................................. 54 5.4 Test Results ........................................................................................................ 54 Chapter 6: Model Fitting ............................................................................................ 58 6.1 Fitting Purpose ................................................................................................... 58 6.2 Fitting Method ................................................................................................... 58 6.3 Fitting Results and Discussion ........................................................................... 60 Chapter 7: Calibration of HYST Model for the Reversed Cyclic Backbone Experimental Curve .................................................................................................... 68 7.1 Modeling Purpose .............................................................................................. 68 7.2 Modeling Method ............................................................................................... 68 7.3 Modeling Results ................................................................................................ 69 Chapter 8: Conclusion and Future Research ............................................................. 74 8.1 Conclusion .......................................................................................................... 74 8.1.1 Monotonic and Reversed Cyclic Tests .................................................................... 74 8.1.3. Model Fitting .......................................................................................................... 75 8.1.4 Calibration of HYST Model ................................................................................... 75 ix 8.2 Future Research ................................................................................................. 76 References .................................................................................................................... 78 Appendix ...................................................................................................................... 84 x List of Tables Table 1. Connection Test Matrix ................................................................................... 20 Table 2. Mechanical properties of Engineered Wood Association connections under monotonic loading ......................................................................................................... 31 Table 3. Descending order of stiffness Ke with COV ..................................................... 32 Table 4. Descending order of peak load Fmax with COV ................................................. 32 Table 5. Descending order of ductility D with COV ...................................................... 33 Table 6. Reversed Cyclic Loading Tests ........................................................................ 36 Table 7. Loading protocol data for reversed cyclic tests ................................................. 40 Table 8. Mechanical properties of Engineered Wood Association and FPInnovations connections under reversed cyclic loading ..................................................................... 44 Table 9. Descending order of Stiffness Ke with COV under reversed cyclic loading....... 45 Table 10. Descending order of Peak Load Fmax with COV under reversed cyclic loading45 Table 11. Descending order of Ductility D with COV under reversed cyclic loading ..... 45 Table 12. Energy Dissipation of Connections Made of APA Resources ......................... 48 Table 13. Energy Dissipation of Connections Made of FPInnovations Resources .......... 48 Table 14. Average Data of Nail Bending Test ................................................................ 52 Table 15. Properties of the Tested Monotonic Specimens .............................................. 56 Table 16. Properties of the Tested Reversed Cyclic Specimens ...................................... 57 Table 17. Monotonic Test Fitting Parameters (units) ..................................................... 66 Table 18. Reversed Cyclic Test Fitting Parameters (units) ............................................. 67 Table 19. Fixed fastener properties of APA connections in HYST modeling ................. 70 Table 20. Fixed fastener properties of FPI connections in HYST modeling.................... 70 xi Table 21. Resulted connection properties by HYST ....................................................... 71 xii List of Figures Figure 1. Three-dimensional view of a MIDPLYâ¢ connection ................................................... 5 Figure 2. Three-dimensional view of a MPSW2 connection ......................................................... 6 Figure 3. Top view of MIDPLYâ¢ and MPSW2 shear walls ........................................................ 7 Figure 4. Top view of MIDPLYâ¢ and MPSW2 shear walls ...................................................... 18 Figure 5. Three-dimensional view of the specimen under monotonic loading ............................. 19 Figure 6. Test setup for single-nail specimen under monotonic loading ...................................... 21 Figure 7. Loading Protocol of Connection test under Monotonic Loading .................................. 22 Figure 8. Monotonic experimental curves of 7/16â thick OSB sheathing (APA) ......................... 23 Figure 9. Monotonic experimental curves of 15/32â thick OSB sheathing (APA) ....................... 23 Figure 10. Monotonic experimental curves of 7/16â thick OSB sheathing (FPI) ......................... 24 Figure 11. Monotonic experimental curves of 19/32â thick OSB sheathing (FPI) ....................... 24 Figure 12. Monotonic experimental curves of 7/16â thick OSB sheathing (SPF) ........................ 25 Figure 13. Monotonic experimental curves of 19/32â thick OSB sheathing (SPF) ...................... 25 Figure 14. Determination of parameters in accordance with ASTM E2126-19-19 ...................... 27 Figure 15. Typical failures of monotonic test (APA) .................................................................. 28 Figure 16. Typical failure of monotonic test (FPI) ..................................................................... 29 Figure 17. Typical failures of monotonic test (SPF) ................................................................... 29 Figure 18. Nail deformation type d and g (from left to right, respectively) ................................. 30 Figure 19. Configurations of single-nail and double-nail specimen under reversed cyclic loading ................................................................................................................................................. 37 Figure 20. Three-dimensional view of the specimen under reversed cyclic loading .................... 38 Figure 21. Test setup for single-nail specimen under reversed cyclic loading ............................. 39 Figure 22. Loading protocol of connection reversed cyclic tests ................................................. 41 xiii Figure 23. Average MTS experimental curves of 7/16â thick OSB connections from reversed cyclic tests (APA) ..................................................................................................................... 42 Figure 24. Average MTS experimental curves of 15/32â thick OSB connections from reversed cyclic tests (APA) ..................................................................................................................... 43 Figure 25. Average MTS experimental curves of 7/16â thick OSB connections from reversed cyclic tests (FPI) ....................................................................................................................... 43 Figure 26. Average MTS experimental curves of 19/32â thick OSB connections from reversed cyclic tests (FPI) ....................................................................................................................... 44 Figure 27. Dissipated Energy of Each Cycle .............................................................................. 49 Figure 28. Accumulated Dissipated Energy ............................................................................... 49 Figure 29. Nail Bending Test Setup ........................................................................................... 51 Figure 30. Averaged experimental and fitting curves of 11.1 mm (7/16â) thick OSB connections from monotonic tests (APA) ...................................................................................................... 61 Figure 31. Averaged experimental and fitting curves of 11.9 mm (15/3â) thick OSB connections from monotonic tests (APA) ...................................................................................................... 61 Figure 32. Averaged experimental and fitting curve of 11.1 mm (7/16â) thick OSB connections from monotonic tests (FPInnovations) ....................................................................................... 62 Figure 33. Averaged experimental and fitting curve of 15.1 mm (19/3â) thick OSB connections from monotonic tests (FPInnovations) ....................................................................................... 62 Figure 34. Averaged experimental and fitting backbone curves of 11.1 mm (7/16â) thick OSB connections from reversed cyclic tests (APA) ............................................................................ 64 Figure 35. Averaged experimental and fitting backbone curves of 11.9 mm (15/32â) thick OSB connections from reversed cyclic tests (APA) ............................................................................ 64 Figure 36. Averaged experimental and fitting backbone curves of 11.1 mm (7/16â) thick OSB connections from reversed cyclic tests (FPInnovations) ............................................................. 65 xiv Figure 37. Averaged experimental and fitting backbone curves of 13.1 mm (19/32â) thick OSB double-nail connections from reversed cyclic tests (FPInnovations) ........................................... 65 Figure 38. HYST modeling and experimental curves of APA 7/16â ........................................... 72 Figure 39. HYST modeling and experimental curves of APA 15/32â ......................................... 72 Figure 40. HYST modeling and experimental curves of FPI 7/16â ............................................. 73 Figure 41. HYST modeling and experimental curves of FPI 19/32â ........................................... 73 Figure 42. HYST Connection data for APA 7/16" ..................................................................... 84 Figure 43. HYST Connection data for APA 15/32â ................................................................... 84 Figure 44. HYST Connection data for FPI 7/16â ....................................................................... 85 Figure 45. HYST Connection data for FPI 19/32â...................................................................... 85 xv List of Abbreviations APA Engineered Wood Association ASTM American Society for Testing and Materials COV Coefficient of variance CSA 086 Canadian Code on Engineering Design in Wood FPI FPInnovations MIDPLYâ¢ Mid-ply MPSW2 Mid-ply 2 SPF Spruce Pine Fir UBC The University of British Columbia xvi Acknowledgements To commence, and most importantly, I would like to express my sincere appreciation to my supervisor Dr. Frank Lam for his unwavering guidance throughout my study in the field of Timber Engineering. Dr. Lam's patience, expertise, and insightful advice have been invaluable, contributing significantly to my academic journey. Heartfelt thanks were also extended to my parents, Xiuqiong Wen and Zhaolong Xiang, for their enduring and unwavering support throughout my life. Their consistent encouragement and belief in my journey have been a source of strength and inspiration. The companionship of my little puppy, Duoduo, has brought me comfort and relaxation, positively impacting my well being. I am also deeply grateful to my grandparents, Yongqun He, Guangyin Xiang, Renfang Wang and Huisheng Wen for their care and concern all the time. They made me feel treasured and loved. A special appreciation is reserved for Mr. and Mrs. Yao, who provided abundant emotional comfort and solace during my challenging moments. Their support has significantly contributed to fostering a more mature perspective on life for me. xvii I am also truly thankful for the supportive members within our research group who have played a crucial role in my academic journey. Special gratitude to Xing Zhang and Wancheng Gao for their help in data processing and analysis, Zhen Liang for valuable suggestions and advice in data analysis, Chao Zhang and George Lee for their assistance in test conduction and data analysis, and lastly, Amir Kari for his contributions to test designs, as well as insightful suggestions throughout the study. The collective efforts of these friendly and knowledgeable group members have greatly enriched my academic experience. At the end, I want to express my gratitude to all the friends I've made during my eight years at UBC. Their support and unwavering presence have illuminated this chapter of my life, making it truly special and memorable. 1 Chapter 1: Introduction and Literature Review 1.1 Research Background Earthquake is an abrupt and transient movement of earthâs surface. As a common natural disaster on the planet, earthquake can generate huge damages in an instant. This phenomenon can lead to catastrophic events and is of serious concern in many parts of the world. Numerous earthquakes take place worldwide annually, with recorded instances reaching into the millions. North America has witnessed some of the most severe earthquakes in recent history. One significant occurrence was the massive earthquake that struck Alaska, USA, in 1964, with a magnitude of 9.2 on the Richer magnitude scale (Oluwafemi et al., 2018). This earthquake was recorded to be the second largest earthquake taken place in the world. It affected an area of nearly 502,000 square miles (1,300,000 square km) (Britannica, 2023). Well designed and built light wood frame construction is well recognized to process good seismic resistance forces primary due to the relatively light weight and high ductility of the building system. It is noted British Columbia process an abundant and sustainable supply of wood construction. The BC forestry industry is successful in cultivating and managing forests to ensure a continuous supply of high-quality timber. Through sustainable practices such as reforestation, selective logging, and forest management programs, the industry maintains the balance between timber extraction and 2 environmental preservation. This approach allows for the replenishment of forests and ensures a long-term supply of wood resources for various applications, including construction. Utilization of this renewable resource as value added products to create cost effective seismic resistance building solutions is of interest to government and society. 1.2 Research Introduction As one of the major building materials, wood has obtained a high reputation due to its natural and mechanical properties. Low carbon emission during production, sustainability and embodied energy are three important attributes of wood obtained from well managed sustainable forestry practices. It is known that the construction sector is one of the main contributors to global greenhouse gas emissions. Construction accounted for 23% of the total global CO2 emission in 2009, emitting 5.7 billion tons of CO2 (Huang & et al., 2018). More recently reported by the United Union, the building sector contributed 3.1 billion tonnes of CO2 emission in 2022 (UNEP, 2022). In recent years, there has been a growing awareness and focus on environmental protection. One essential aspect of this awareness is photosynthesis. Throughout the growth period, leaves assimilate CO2 and water from the atmosphere, utilizing the energy of the sun to catalyze a series of reactions resulting in the production of organic compounds, such as sugars, that serve as a source of nutrients for the tree. As carbon is stored in the wood fibre, using wood from well managed sustainable forestry practices allows wood to be considered as carbon neutral building material. The release of oxygen during tree growth also adds to the environment 3 friendly attribute of wood. Furthermore, by using life cycle assessment (LCA) methodology, wood is proven to have a lower environmental impact than alternative construction materials (Werner & Richter, 2007). In addition to its environmental benefits, certain mechanical properties of wood, such as high ductility and strength-weight ratio, are also significant. For instance, timber-frame buildings were documented to have enough lateral resistance against strong motion earthquakes compared to the buildings made of other materials (Blass & et al., 1994). Besides that, well designed timber buildings can have good fire-resistance performance. The combustion of timber leads to the charring of its outer layer, creating a protective barrier against fire and slowing down the thermal degradation (pyrolysis), thereby insulating the inner part of the timber (Hurley, 2016). This distinctive characteristic holds significant value in ensuring building safety. Based on these attributes, remarkably, light-frame wood buildings have occupied 90% of the residential construction market in North America (Mulder, 2017), playing a pivotal role in construction area. Shear walls perform a vital function in timber structures by transferring lateral loads in the parallel direction along the wall plane to the ground. However, post-and-beam timber frame buildings are known for their low lateral stiffness (Shu et al., 2019), leading to a surge of interest in light wood frame constructions in the field of low-rise wood construction. To address this issue, MIDPLYâ¢ (Mid-ply) was developed as a high-performance light wood frame shear wall system by E. Varoglu, formerly with Forintek Canada Corp. and Prof. S.F. Stiemer from the University of British Columbia (US Patent 4 US5782054) between 1990s and the 2000s. MIDPLYâ¢ (Mid-ply) features two parallel studs with their wide faces in contact with a sheathing panel (Oriented Strand Board or plywood) in between, as shown in Figure 1. When facing lateral loads, double shear is generated on the sheathing panel and the nail in the connection. In addition, the nail heads, situated on the framing membersâ surfaces, are not pulled through the studs during the loads (Lungu, 2000). By fastening the sheathing panel to the wide faces of studs, the lateral load capacity of MIDPLYâ¢ shear wall system can be enhanced by providing edge distance to fasteners, while reducing the chip-out failure mode (Buitelaar, 2001). The National Building Code of Canada (NBCC) (2015) noted the challenges of constructing mid-rise buildings in high seismic areas while meeting seismic requirements, but MIDPLYâ¢ shear walls can address this issue and be employed to meet the national requirements. According to Varoglu et al. (2007), MIDPLYâ¢ exhibits comparable drift capacity to standard shear walls while showcasing over 2.5 times the carrying capacity. Therefore, MIDPLYâ¢ is a better performed shear wall type against the in-plane lateral loads than the conventional ones in timber construction industry. Van de Lindt et al. (2011) conducted a full-scale shake table experiments on a six-story light-frame timber building to further verify its performance in lateral resistance under a series of earthquakes. Due to its effectiveness in mid-rise and large-scale timber structures, MIDPLYâ¢ has been broadly promoted by Canada Wood Japan and recognized as one of the most effective designs (Midplyâ¢ Shearwall System, 2021). 5 Figure 1. Three-dimensional view of a MIDPLYâ¢ connection However, MIDPLYâ¢ has some limitations that restrict its utilization. Builders on site have identified difficulties in accommodations of services such as piping and wiring within the wall due to insufficient space. Additionally, buckling failure may occur in MIDPLYâ¢ wall studs under high vertical loads due to their high slenderness ratio, shape of cross section and small moment of inertia. To address these issues, the Engineered Wood Association (APA) introduced a new mid-ply shear wall system (MPSW2), as illustrated in Figure 2. In MPSW2 shear wall system, the orientation of the studs is different from the Midply. Instead of being parallelly positioned with a sheathing panel being sandwiched, the two studs are positioned perpendicular to each other. One stud is placed flatwise with the sheathing panel, while the other one is placed edgewise with its 6 narrow side in contact with the sheathing panel. A nail goes through these three elements with its head positioned at the flatwise placed stud. Figure 3 illustrates the comparison between MPSW2 and MIDPLYâ¢ in terms of the top view of their walls. Due to this new design, the space between the edgewise placed stud and the sheathing panel can be used for wiring and piping accommodation. Moreover, the resulting T-shape cross-section provides a higher stability and moment of inertia. All these advantages and potentials mentioned of MPSW2 have made it a more competitive option in wood building construction. Figure 2. Three-dimensional view of a MPSW2 connection MIDPLYâ¢ 7 MPSW2 Figure 3. Top view of MIDPLYâ¢ and MPSW2 shear walls As aforementioned, the MPSW2 design concept has the potential to bring significant benefits to the development of timber-frame buildings. However, limited research has been conducted on this innovative design, impeding its widespread adoption in the market. Given the critical role of connections in the lateral response of wood frame shear walls, particularly under reversed cyclic loading conditions (Gu & Lam, 2004), as well as the growing demand for improved shear wall performance, this study aims to investigate the connection behaviour of MPSW2. A range of connection tests and analyses, including monotonic loading, reversed cyclic loading, specific gravity and moisture content tests, and nail bending tests, have been conducted to comprehensively evaluate the performance of MPSW2 connections. Such research efforts are essential to further promote the development of wood frame structures and enhance their structural performance. 8 The accurate modeling of connection characteristics is a crucial component in predicting the behaviour of wood shear walls during the investigation of a new design. In this regard, the HYST algorithm which was developed by Foschi in 2000 is calibrated in this thesis against the reversed cyclic backbone hysteresis characteristics of nail connections for utilization in modeling MPSW2 shear wall connections. This algorithm requires the input of nail characteristics including nail length, diameter and yield strength, and outputs a set of data representing connection characteristics (such as stiffness and peak load) that best models the real connection load-slip curves. These data can be further utilized as input in finite-element wood shear wall model such as WALL2D (Li et al., 2012). 1.3 Research Objectives The research objectives in this study are: Conduct connection tests to establish the load-slip behaviour of the connections under monotonic and reversed cyclic loading. Calibrate HYST to represent the connection behaviour and verify its applicability in modeling MPSW2. 9 Utilize the data obtained from connection tests and to calculate and analyse the essential connection characteristics. 1.4 Literature Review 1.4.1 MIDPLYâ¢ Sheathing Bringing the consideration and application of oversized sheathing panel in light wood frame shear wall, Lam et al. (1997) demonstrated the potential benefits of utilizing nonstandard oversized panels in light wood frame shear wall to enhance their mechanical performance. The monotonic loading test results indicated that the utilization of the oversized panels could improve their stiffness and lateral resistance; however, this modification did not have positive impact on the ductility or energy dissipation. The study by Durham et al. (2001) presented similar results from their tests: large (2.4 x 2.4 m) and standard (1.2 x 2.4 m) size OSB panels were employed for the comparisons of their behaviour under quasi-static monotonic, reversed cyclic and dynamic loads. A 26% greater shear resistance was observed in the walls with large OSB panels than the standard one when using the conventional nail spacing resulting in fewer nails in the large panel; a 104% improvement in shear capacity was noticed with the use of large panels with intense perimeter spacing resulting in the same number of nails for both the 10 small and large panel cases. Nail-pullout and tear-out were observed to be the main failure modes during reversed cyclic tests. 1.4.2 Midply Shear Wall System (MIDPLYâ¢) Connection The response of the connections dominates the performance of the shear walls in light wood frame buildings. Thus, the connections have been investigated by researchers to predict the wall behaviours based on the connection responses in the past decades. In the report presented by Karacabeyli et al. (2000), the double shear plane design was proven to have 80% higher capability of lateral resistance than the single shear design; the stiffness of double shear design was around 3 times as high as in the single shear design. As discussed in the work, the thickness of the sheathing panel was also an important influence in shear wall performance in peak load and stiffness. Tests have been conducted to study and compare the maximum load and stiffness of the 12.5 mm (1/2â) and 19 mm (3/4â) thickness Canadian Softwood Plywood (CSP). For both monotonic loading and reversed cyclic loading tests, the results showed higher values of 12.5 mm (1/2â) CSP than 19 mm (3/4â) CSP in maximum load and higher values in 19 mm (3/4â) CSP than 12.5 mm (1/2â) CSP in initial stiffness. Same results were also presented by Buitelaar (2001). 11 Zheng et al. (2015) also conducted the tests on the connections of MIDPLYâ¢ shear wall system. According to the test results, the failure modes of the tested connections were influenced by the sheathing thickness and edge distance. The results of the tests suggested that increasing the nail edge-distance and sheathing thickness can considerably enhance the strength and ductility of the connections, while leaving their stiffness mostly unaffected. As the significance of sheathing thickness as a variable has been emphasized, this thesis will investigate OSB sheathing in different thicknesses as a main factor. 1.4.3 MIDPLYâ¢ versus Conventional Shear Wall System Buitelaar (2001) studied the comparison of the mechanical performance between MIDPLYâ¢ shear walls and comparable conventional shear walls. The MIDPLYâ¢ wall exhibited a lateral resistance that was more than twice as much as the conventional wall. Additionally, due to its exceptional strength, the test apparatus was unable to fully cause the failure of the MIDPLYâ¢ wall, indicating the potential of wall to bear even higher loads. MIDPLYâ¢ was also confirmed by Chen et al. (2002) to have twice the lateral load capacity as well as superior drift capacity and energy dissipation capability compared to conventional shear walls; however, while MIDPLYâ¢ demonstrated such features, it appeared to have lower ductility than conventional shear walls. Similar wall tests were carried out by Varoglu et al. (2006) to compare the mechanical performance of MIDPLYâ¢ with the conventional shear walls, whose results showed a better performance of MIDPLYâ¢. A conventional shear wall and a comparable MIDPLYâ¢ wall underwent reversed cyclic loads in the tests, with only one studâs 12 orientation perpendicular and all other features remained unchanged. They were compared in several perspectives: the load-carrying capacity of MIDPLYâ¢ system was more than 3 times that of conventional shear walls; the stiffness of MIDPLYâ¢ was around 2 to 3 times that of corresponding conventional shear walls; the energy dissipation capability was twice more than that of conventional shear walls. MIDPLYâ¢ shear wall system was confirmed to have a better performance with regards to the mentioned characteristics. In construction projects, cost is a significant factor to be considered. MIDPLYâ¢ has been evaluated in comparison with conventional shear walls in terms of cost-effectiveness. The preliminary cost (considered materials (lumber, sheathing and nail) and labour on site) of a MIDPLYâ¢ shear wall was 20% to 30% less than a conventional shear wall, with the lateral resistance of MIDPLYâ¢ shear walls twice as much as that of the conventional ones (Karacabeyli et al., 2000). Buitelaar (2001) also did the cost calculations based on MIDPLYâ¢ walls with 600 mm (24â) stud spacing and conventional walls with 400 mm (16â) and spacing. The MIDPLYâ¢ walls with and without exterior sheathing generated less cost than the conventional walls: 30% and 20% respectively for equal lateral resistance. Therefore, considering the initial capital required to commence building construction, it is a favorable choice and opportunity to promote the utilization of MIDPLYâ¢ shear wall systems on a wide scale. In terms of the failure modes of shear walls, the most common ways the conventional shear walls with OSB sheathing failed in were identified by Buitelaar (2001) as follows: ï· Pull-through failure: nail pulling through the sheathing 13 ï· Tear-out failure: nail tearing through the edges of the sheathing ï· Nail-fatigue: applies to cyclic loading ï· Sheathing rupture: due to high shear stress ï· Frame failure Buitelaar (2001) also presented the failure modes observed from the MIDPLYâ¢ shear wall tests. Compared to conventional shear walls, the new failure modes of MIDPLYâ¢ wall included: ï· Transverse buckling: due to the vertical loads applied ï· Disconnection of the studs: when the nails used to fasten the sheathing to the framing failed ï· Rupture of the end studs: due to the uplift forces In this thesis, the failure modes of MPSW2 connections will be analyzed comparing with those found in MIDPLYâ¢âs. The aim is to identify potential weaknesses in the connection design and to develop strategies to improve its mechanical performance and prevent failures. By investigating and understanding the failure modes, it is possible to make informed decisions about the design, materials, and construction methods of the MPSW2 connection system, which will ultimately lead to the development of safer and more resilient structures. 14 1.4.4 MIDPLYâ¢ Models Apart from the first introduction and development of HYST by Foschi in 2000, Foschi et al. (2000) also investigated the modeling performance of HYST. It showed the possibility to obtain connectionsâ behaviour under either monotonic or cyclic loads with the embedment properties being considered. Gu and Lam (2004) and Li et al. (2012) investigated in the application of HYST in the prediction of wood shear wallâs hysteresis behaviour. Li et al. (2012) modified the original HYST algorithm, which already included considerations for pinching effects, by adding a new feature. This new feature considered the stiffness degradation of the wood embedment medium under repeated loading to completely tackle the strength and stiffness degradation effect in nail hysteresis. This study verified that the modified HYST algorithm was able to accurately reproduce load-slip response of specimens evaluated with standard monotonic and the backbone load-slip response under reversed cyclic test protocols. Much effort has been directed toward the study of shear wall behaviour prediction. An investigation on the numerical modeling was carried out for the prediction of light frame wood structuresâ seismic performance (Mulder, 2017). A detailed numerical model called M- CASHEW2 was applied, and the results showed its ability for accurate predictions of light-frame wood buildingsâ performance under monotonic and reversed cyclic lateral loads; another global model called Timber3D was confirmed to predict the accurate hysteretic and time history response. However, Timber3D was not able to capture the accumulative damage from the previous runs. 15 Studies about MIDPLYâ¢ employed models for load-slip behaviour were also carried out. Guo et al. (2020) developed and applied a finite-element numerical model for the predictions, which were confirmed in future research to investigate MIDPLYâ¢âs lateral hysteretic behaviours with various configurations. The models showed a sensible conservative result to avoid overvalued stiffness and strength due to the brittle failure observed in the tests. 16 Chapter 2: Connection Testing 2.1 Connection Test under Monotonic Loading 2.1.1 Testing Purpose An empirical study was undertaken to investigate the lateral load-slip behaviour of connection specimens in the sorted specimen groups under monotonic loads, including the peak load (Fmax), shear stiffness (Ke) and Ductility (D). Given the small size of the nails used, the loading direction was restricted to be parallel to the grain due to the negligible impact expected from varying the load direction, as specified in the standard CSA O86. The Fmax value obtained from this test will serve as critical input for the protocol design of the subsequent reversed cyclic test. 2.1.2 Materials The assemblies were constructed in accordance with ASTM D1761-20, following the single-nail and double-nail configurations of the specimens depicted in Figure 4. A three-dimensional view of the connection is also presented in Figure 5. The end distance for the nail was set at 101.6 mm (4â) and the edge distance was 44.5 mm (1.75â). In these assemblies, the two studs were positioned perpendicular to each other, with an OSB sheathing panel sandwiched. The connection was established by driving a nail through the flatwise placed stud, effectively joining the three members. The studs were made of either No. 2 and better grade Douglas fir or SPF (Spruce-Pine-Fir) lumbers, with a dimension of 38 mm x 89 mm (1.5 x 3.5 inch or 2 x 4 inch nominal) and a length of 280 mm (11â). The Douglas fir lumber used in this study was sourced from two 17 organizations: APA-The Engineered Wood Association (APA) and FPInnovations. Douglas fir is widely recognized for its exceptional strength and hardness, making it suitable for various construction applications, such as bridges, residential and commercial buildings. SPF lumber, constituted of Lodgepole pine, interior spruce and subalpine fir, were known for their high strength-to-weight ratio. Kiln-dried SPF lumber is frequently used as framing members in residential, commercial and industrial buildings. OSB was chosen to be the sheathing panel material in this study. The two sources of sheathing panel specimens were APA and FPInnovations. For the APA panels, two types were tested: Structural I with a thickness of 11.1 mm (7/16â) and 11.9 mm (15/32â); the FPInnovations panels were also Structural I but with a thickness of 11.1 mm (7/16â) and 15.1 mm (19/32â). The nails used were all F1667 NL CM PS-37B in a length of 88.9 mm (3.5â) and a diameter of 3.327 mm (0.131â), also provided by APA and FPInnovations. A total of 45 specimens were tested in this study, with 5 replicates for each specimen group. All monotonic tests and their needed materials are listed in Table 1. 18 Figure 4. Top view of MIDPLYâ¢ and MPSW2 shear walls (1 inch = 25.4 mm) 19 Figure 5. Three-dimensional view of the specimen under monotonic loading 20 Table 1. Connection Test Matrix Test Type Number of Replicates Stud OSB Thickness (in.) Material Source1 Single nail2 5 D. Fir (A)3 7/16 APA Double nail4 5 D. Fir (A) 7/16 APA Single nail 5 D. Fir (A) 15/32 APA Double nail 5 D. Fir (A) 15/32 APA Double nail 5 D. Fir (F) 5 7/16 FPInnovations Single nail 5 D. Fir (F) 19/32 FPInnovations Double nail 5 D. Fir (F) 19/32 FPInnovations Double nail 5 SPF 7/16 FPInnovations Single nail 5 SPF 19/32 FPInnovations Note: *the nominal thickness of 7/16â, 15/32â and 19/32â OSB are 11.1 mm, 11.9 mm and 15.1 mm, respectively; 1 inch = 25.4 mm. 1: Include nail, stud and sheathing sources 2: One nail connecting sheathing and studs 3: Douglas fir lumber provided by APA 4: Two nails connecting sheathing and studs 5: Douglas fir lumber provided by FPInnovations 21 2.1.3 Test Apparatus The monotonic loading tests for the connections were conducted utilizing a universal testing machine - MTS 810 (Material Testing System). Figure 6 illustrates the setup, which involved the installation of two Linear Voltage Displacement Transducers (LVDTs) to measure the relative displacements between the studs and sheathing. The loading head was in tight contact with the OSB sheathing to apply the monotonic load. To prevent the specimens opening up at the bottom during loading, two steel tubes bolted to the testing base were placed next to the studs. Figure 6. Test setup for single-nail specimen under monotonic loading 22 2.1.4 Loading Protocol In accordance with the specifications outline from ASTM D1761 (2020), the loading speed for the test was set to be 3 mm/min. The tests were terminated under two conditions: either when the load decreased 20% from the peak load or when the loading device reached a downward displacement of 45 mm. Figure 7 illustrates the loading protocol. Figure 7. Loading Protocol of Connection test under Monotonic Loading 2.1.5 Methods of Data Analysis The nail deformation, peak load (Fmax), shear stiffness (Ke) and Ductility (D) of each specimen group were compared to determine the performance order. The definitions of these parameters were based on the guidelines provided by ASTM standards. Reasons contributing to the order will be discussed. The nail deformation was categorized based on Figure 17, referred to the standard CSA 086 (2019). The peak load (Fmax) represents 051015202530354045500 200 400 600 800 1000Displacement (mm)Time (s) 23 the maximum load value before a displacement of 25 mm, following the general trend observed in all load-slip curves depicted in Figure 8 to Figure 13. Figure 8. Monotonic experimental curves of 7/16â thick OSB sheathing (APA) Figure 9. Monotonic experimental curves of 15/32â thick OSB sheathing (APA) 00.511.522.533.544.550 10 20 30 40Load (KN)Displacement (mm)Monotonic Experimental CurvesSingle-nail 1Single-nail 2Single nail 3Single-nail 4Single-nail 5Double-nail 1Double-nail 2Double-nail 3Double-nail 4Double-nail 500.511.522.533.544.550 10 20 30 40Load (KN)Displacement (mm)Monotonic Experimental CurvesSingle-nail 1Single-nail 2Single nail 3Single-nail 4Single-nail 5Double-nail 1Double-nail 2Double-nail 3Double-nail 4Double-nail 5 24 Figure 10. Monotonic experimental curves of 7/16â thick OSB sheathing (FPI) Figure 11. Monotonic experimental curves of 19/32â thick OSB sheathing (FPI) 00.511.522.533.544.550 10 20 30 40Load (KN)Displacement (mm)Double-nail 1Double-nail 2Double-nail 3Double-nail 4Doubke-nail 500.511.522.533.544.550 10 20 30 40Load (KN)Displacement (mm)Single-nail 1Single-nail 2Single-nail 3Single-nail 4Single-nail 5Double-nail 1Double-nail 2Double-nail 3Double-nail 4Doubke-nail 5 25 Figure 12. Monotonic experimental curves of 7/16â thick OSB sheathing (SPF) Figure 13. Monotonic experimental curves of 19/32â thick OSB sheathing (SPF) 00.511.522.533.544.550 10 20 30 40Load (KN)Displacement (mm)Single-nail 1Single-nail 2single-nail 3Single-nail 400.511.522.533.544.550 10 20 30 40Load (KN)Displacement (mm)Single-nail 1Single-nail 2Single-nail 3Single-nail 4Single-nail 5 26 Ke, the shear stiffness, is defined as the initial slope of the load-slip curves. ð¾ð =0.4 ð¹ððð¥ð¢40 Where u40 represents the corresponding displacements at 40% Fmax. The ductility D was calculated based on the equation: ð· = ð¢ð¢ð¢ð¦ Where uu represents the ultimate displacement when load dropped to 80% of the maximum load Fmax, as shown in Figure 14; the yielding displacement uy was determined referring to the energy elastic-perfectly-plastic (EEEP) method in ASTM E2126-19 (2019). In this study, the ultimate displacement could not be established due to their high ductility for most of the specimens tested. Hence, the reference deformation was obtained in accordance with EN 12512, with the ultimate slip at 30 mm (1.18â) for the specimens whose load never dropped to 80% Fmax. 27 Figure 14. Determination of parameters in accordance with ASTM E2126-19-19 2.1.6 Test Results 2.1.6.1 Failure Mode The failures observed in the monotonic loading tests were primarily governed by the dowel bearing resistance of the OSB sheathing. This occurred due to the interaction between the nail and OSB sheathing. Under the compressive dowel bearing load, the fibres of the OSB panels accumulated or piled up on the load bearing side of the hole which locally increased the density and stiffness of the region. The nail started to bend and yield. This can be observed from the elongation of the sheathing hole and the bending of the nail shown in Figure 15 to Figure 17. Simultaneously, the holes in the 28 studs which were generated from the insert of the nail were also elongated during the loading. Continued loading resulted in the gradual withdrawal of the nail end from the stud, thereby a relatively stable load without significant load drop was maintained. However, the nail deformation type could be different depending on the MOE under compression of the studs. A more elongated hole indicated a higher possibility of deformation type d, as depicted in Figure 18, and as described in the standard CSA 086 (2019). This observation can be supported by two findings: first, the typical failures of APA, FPI and SPF connection groups shown from Figure 15 to Figure 17 demonstrated that the SPF connection with SPF studs had larger elongation than the APA and FPI connections with Douglas-fir studs; second, the nail deformation of SPF connections was mainly regarded as type d, as illustrated in Figure 18 and Table 2. Further analysis on this phenomenon will be provided in subsequent sections, taking into account the data of mechanical properties presented in this chapter. Figure 15. Typical failures of monotonic test (APA) 29 Figure 16. Typical failure of monotonic test (FPI) Figure 17. Typical failures of monotonic test (SPF) 30 Figure 18. Nail deformation type d and g (from left to right, respectively) 2.1.6.2 Load-Slip Curve Table 2 presents the mechanical properties of stiffness (Ke), peak load (Fmax) and ductility (D) for the sorted monotonic connection tests of APA groups, FPI groups and SPF groups. The properties have been arranged in a descending order as presented from Table 3 to Table 5. One thing to be noticed is that, as shown in Figure 11, one test of the FPI 7/16â specimen stopped before reaching 30 mm, which was due to the early rupture on the top surface of OSB sheathing. However, this failure was the only OSB rupture observed and not regarded as a significant factor, it will not be included in the data analysis of this study. 31 Table 2. Mechanical properties of Engineered Wood Association connections under monotonic loading Connection Group OSB Thickness (in.) Stiffness Ke (kN/mm) Peak Load Fmax (kN) Ductility D Nail Deformation Number of Noticeably Deformed Nails Average Value COV Average Value COV Average Value COV APA 7/16 5.009 68.4% 3.74 13.6% 47.4 65.6% g 8 d 2 APA 15/32 4.123 70.2% 3.66 10.3% 41 64.9% g 6 d 4 FPI 7/16 0.665 28% 3.12 11.7% 7.6 47.4% g 4 d 1 FPI 19/32 2.07 29.4% 4.16 13.6% 18.5 44.7% g 4 d 6 SPF 7/16 1.468 67% 3.12 10.9% 17 73.3% g 1 d 3 SPF 19/32 1.924 35.5% 3.13 14.1% 20.3 32.6% g 0 d 5 Note: *1 inch = 25.4 mm 32 Table 3. Descending order of stiffness Ke with COV Stiffness Ke Specimen Group Average Value (kN/mm) COV APA 7/16â 5.009 68.4% APA 15/32â 4.123 70.2% FPI 19/32â 2.07 29.4% SPF 19/32â 1.924 35.5% SPF 7/16â 1.468 67% FPI 7/16â 0.665 28% Table 4. Descending order of peak load Fmax with COV Peak Load Fmax Specimen Group Average Value (kN) COV FPI 19/32â 4.16 13.6% APA 7/16â 3.74 13.6% APA 15/32â 3.66 10.3% SPF 19/32â 3.13 14.1% SPF 7/16â 3.12 10.9% FPI 7/16â 3.12 9.5% 33 Table 5. Descending order of ductility D with COV Ductility D Specimen Group Average Value COV APA 7/16â 47.4 65.6% APA 15/32â 41 64.9% SPF 19/32â 20.3 32.6% FPI 19/32 18.5 44.7% SPF 7/16â 17 73.3% FPI 7/16â 7.6 47.4% The examination of the tested specimens provides valuable insights into their stiffness characteristics. When comparing the APA, FPI, and SPF connection groups, APA connections stood out for their exceptional properties, demonstrating higher stiffness than the other two connection group. On the other hand, SPF connections exhibited low stiffness as shown in Table 3. To compare among all the test specimens, it was observed that APA 7/16â exhibited the highest stiffness, with a value of 5.009 kN/mm. However, although with the same type of OSB sheathing, nail and stud, FPI 7/16â connection had the lowest stiffness value of 0.665 kN/mm, even lower than that of the two SPF groups. This unexpected result could potentially be attributed to the sources of studs and sheathing panels. Although they were in the same grade, they came from different sources. Since the discrepancy between APA 7/16â and FPI 7/16â was obvious, more discussion about the stiffness will be provided in the sequent section based on the 34 reversed cyclic test results. It is also noticeable from the table that the SPF 7/16â has higher stiffness than FPI 7/16â. However, as mentioned in the subsection of failure mode, the loading first affected the OSB sheathing and subsequently impacted the nail during the tests. The nail then also transmitted the load to the bearing contact surface between the nail and studs. Given that SPF naturally has lower MOE under compression compared to the Douglas fir, it can be deduced that the SPF connection group is supposed to have lower stiffness attributed to the choice of stud material. Since the data does not agree with the rational and analysis, the FPI 7/16â deserves more comprehensive discussion in the subsection on the reversed cyclic connection tests. The evaluation of the tested specimens yielded valuable insights into their peak load characteristics. As clearly indicated in Table 4, similar to the findings regarding stiffness, APA 7/16â, APA 15/32â and FPI 19/32â demonstrated sightly higher peak loads than other specimen groups. Within the FPI connection group, the specimen group with 19/32â sheathing (the thickest among all groups) achieved the highest peak load, while the one with 7/16â sheathing panel had the lowest. In contrast, within the SPF connection group, no significant difference between the two peak loads could be found although they have the same OSB types as the FPI connections. This could be attributed to the lower MOE under compression of SPF. As explained earlier, the lower MOE under compressions of SPF compared to that of Douglas fir resulted in their nails elongating the stud holes at a lower load than in FPI and APA connections. The MOE under compression of the stud was found to influence the peak load in SPF connections. This also explained the higher peak load of APA connections compared to SPF connections. However, the unexpected low peak load of FPI 7/16â was noteworthy. 35 The determination of ductility D, based on the EEEP method referred to ASTM E2126-19, depends on the initial stiffness Ke, thereby showing a strong correlation between these two properties. All the specimen groups showed high ductility, which reflects the favorable ductility performance of the MPSW2. Overall, based on the three property orders, it is evident that APA 7/16â exhibited the highest performance, while FPI 7/16â demonstrated the lowest. Further tests and analysis will be conducted in the subsequent sections. 2.2 Connection Testing under Reversed Cyclic Loading 2.2.1 Testing Purpose The behavior of the connections under reversed cyclic loading was examined for all specimen groups to assess their response to earthquake conditions. Various indices, peak load (Fmax), shear stiffness (Ke), Ductility (D), and energy dissipation were obtained for further analysis and evaluation. These parameters provide insights into the performance and resilience of the connections under reversed cyclic loading conditions. 2.2.2 Materials The assemblies were constructed following the guidance of ASTM E2126-19 (2019). Configurations of single-nail and double-nail specimens are shown in Figure 19. The wood 36 materials and sources of the nails aligned with those used in the monotonic tests. Similar to the monotonic specimens, the reversed cyclic specimens had an end distance of 101.6 mm (4â) and an edge distance of 44.5 mm (1.75â). To facilitate the testing process, the specimens were cut to a length of 330 mm (13â) to provide more space to connect the specimens bottom and steel plate by bolts. As mentioned in the monotonic test analysis that SPF groups had low performance in all properties, a total of 20 specimens with Douglas-fir studs were tested in this study, with 5 replicates for each specimen group. The details of the tests and their corresponding materials used are listed in Table 6. Figure 20 shows a three-dimensional view of the specimen. Table 6. Reversed Cyclic Loading Tests Test Type Number of Replicates Stud OSB Thickness (in.) Nail Source OSB Source Single nail 5 D. Fir (A)1 7/16 APA APA Single nail 5 D. Fir (A) 15/32 APA APA Double nail 5 D. Fir (F) 7/16 FPInnovations FPInnovations Single nail 5 D. Fir (F) 19/32 FPInnovations FPInnovations 37 Figure 19. Configurations of single-nail and double-nail specimen under reversed cyclic loading 38 Figure 20. Three-dimensional view of the specimen under reversed cyclic loading 39 2.2.3 Test Apparatus The same loading machine and Linear Voltage Displacement Transducers (LVDTs) used in the monotonic loading tests were also employed in the reversed cyclic tests for this section. However, there were some adjustments on the test setup. To ensure the stability of the testing specimen during loading, three small OSB pieces were glued to the specimens before testing. Two of these pieces were attached to the two faces of the OSB at the top to increase the contact area between the specimen and the loading head, while one piece was glued to the bottom between the studs to prevent deformation caused by clamping from the steel tubes, as shown in Figure 21. Additionally, two rods were inserted through the top and bottom of the specimens to connect with MTS 810. Figure 21. Test setup for single-nail specimen under reversed cyclic loading 40 2.2.4 Loading Protocol The loading protocol for the reversed cyclic testing was designed in accordance with Test Method B of ISO 16679, referred in ASTM E2126-19 (2019). The loading speed was set to be 1 mm/sec. The reference deformation for creating the loading protocol was based on the displacement at which the load dropped below 80%Fmax or ultimate displacement in the monotonic loading test. The loading protocol data and its generated curve are presented in Table 7 and Figure 22, respectively. Table 7. Loading protocol data for reversed cyclic tests Amplitude. % of reference displacement Displacement (mm) 1.25 0.375 2.5 0.75 5 1.5 7.5 2.25 10 3 20 6 40 12 60 18 80 24 100 30 120 36 41 Figure 22. Loading protocol of connection reversed cyclic tests 2.2.5 Methods of Data Analysis The calculation methods for determining the mechanical properties in the reversed cyclic loading test were aligned with the same procedures as those used in the monotonic loading test. The stiffness (Ke), peak load (Fmax), and ductility (D) were calculated based on the respective formulas and definitions established in the earlier tests. By applying consistent calculation methods, the mechanical properties obtained from the reversed cyclic loading test could be compared directly with the results from the monotonic loading test for further analysis and evaluation. 2.2.6 Test Results The load-slip curves of all specimen groups are presented in Figure 23 to Figure 26, displaying the average experimental results. Table 8 provides the mechanical properties obtained from the -40-30-20-100102030400 5 10 15 20 25Displacement (mm)Cycle number 42 sorted reversed cyclic connection tests of APA groups and FPI groups. The properties arranged in a descending order are provided in Table 9 to Table 11. It should be noted that due to the small initial slips in the protocol, and the potential discrepancy between the recorded slips by the LVDTs and the actual slip occurred on the OSB sheathing in the specimen, the initial loops of the loadâslip were not adequately formed. Figure 23. Average MTS experimental curves of 7/16â thick OSB connections from reversed cyclic tests (APA) -4-3-2-101234-45 -35 -25 -15 -5 5 15 25 35 45Load (kN)Displacement (mm) 43 Figure 24. Average MTS experimental curves of 15/32â thick OSB connections from reversed cyclic tests (APA) Figure 25. Average MTS experimental curves of 7/16â thick OSB connections from reversed cyclic tests (FPI) -4-3-2-101234-45 -35 -25 -15 -5 5 15 25 35 45Load (kN)Displacement (mm)-4-3-2-101234-45 -35 -25 -15 -5 5 15 25 35 45Load (kN)Displacement (mm) 44 Figure 26. Average MTS experimental curves of 19/32â thick OSB connections from reversed cyclic tests (FPI) Table 8. Mechanical properties of Engineered Wood Association and FPInnovations connections under reversed cyclic loading Connection Group OSB Thickness (in.) Stiffness Ke (kN/mm) Peak Load Fmax (kN) Ductility D Average Value COV Average Value COV Average Value COV APA 7/16 1.165 67.9% 3.604 20.2% 10.737 44.3% APA 15/32 1.596 29% 3.755 4.17% 9.844 28.4% FPI 7/16 1.77 35% 3.396 12.8% 18.14 24.6% FPI 19/32 1.533 33.9% 3.578 11.4% 11.53 48.2% -4-3-2-101234-45 -35 -25 -15 -5 5 15 25 35 45Load (kN)Displacement (mm) 45 Table 9. Descending order of Stiffness Ke with COV under reversed cyclic loading Stiffness Ke Specimen Group Average Value (kN/mm) COV FPI 7/16â 1.77 35% APA 7/16â 1.65 29% APA 15/32â 1.596 11.4% FPI 19/32â 1.533 33.9% Table 10. Descending order of Peak Load Fmax with COV under reversed cyclic loading Peak Load Fmax Specimen Group Average Value (kN) COV APA 15/32â 3.755 4.17% APA 7/16â 3.604 20.2% FPI 19/32â 3.578 11.4% FPI 7/16â 3.396 12.8% Table 11. Descending order of Ductility D with COV under reversed cyclic loading Ductility D Specimen Group Average Value COV FPI 7/16â 18.144 24.6% APA 7/16â 11.532 48.2% APA 15/32â 10.737 44.3% FPI 19/32â 9.844 28.4% 46 Table 9 highlights an important observation that requires careful consideration: the stiffness of FPI 7/16â in the reversed cyclic tests is the highest among all specimen groups, which contradicts its lowest stiffness in the monotonic loading tests. Conversely, the stiffness values of the other three specimen groups align well with their performance in the monotonic tests. This discrepancy may be attributed to the potential material quality inconsistencies from production, leading to lower performance of the FPI 7/16â specimens in the monotonic test, which could only be revealed from the observed OSB rupture in one of the FPI 7/16 tests. The inconsistencies in the production quality of OSB could have affected the mechanical properties of the FPI 7/16" specimens, resulting in their lower stiffness values compared to the reversed cyclic test. When comparing within each connection group, a notable trend was found that specimen groups with thicker sheathing panel tend to have lower stiffness compared to the specimen groups with thinner sheathing. The inclusion of thicker sheathing panels can have a notable influence on the behavior of fasteners within the connection. As the thickness of the sheathing increases, the length of the fastener embedded in the sheathing also increases proportionally. Consequently, the extended length of the fastener embedded contributes to a greater extend of bending and deformation, leading to a reduction in the overall stiffness of the connections. Table 10 provides a descending order of the peak load values observed in the tested specimens. When examining the data of each specimen group, a pattern became apparent: specimen groups with thicker sheathing panels (APA 15/32â and FPI 19/32â) tended to exhibit higher load-carrying capacities compared to those with thinner sheathing (APA 7/16â and FPI 7/16â). As 47 previously discussed, this phenomenon can be attributed to the increasing dowel bearing capacity of the OSB panel as its thickness increases. Furthermore, a noticeable difference in performance can be observed when comparing the two connection groups: the APA specimen groups consistently outperform the FPI specimen groups in terms of peak load. This distinction in the peak load could be attributed to the material sources of the two connection groups. Factors such as variations in material properties or manufacturing processes between the APA and FPI sources may have contributed to the observed differences in peak load capacity. The ductility exhibited in the reversed cyclic tests corresponds to the results obtained for stiffness. All specimen groups demonstrated excellent performance in terms of ductility, with connections with thinner sheathing panels exhibiting higher ductility compared to those with thicker sheathing. Overall, the specimen groups with thicker sheathing in general demonstrated higher load-carrying capacity. Among the tested connections, the APA specimen groups consistently performed well in all measured mechanical properties. It is also noted that the thickest sheathing panel, FPI 19/32â connection group exhibited lower stiffness and load-carrying capacity compared to the other groups. The material source, production and quality control also play a crucial role in achieving desired performance. 48 Chapter 3: Energy Dissipation As can be seen from Table 12 and Table 13 that, FPI 7/16â dissipated the most energy, followed by FPI 19/32â, APA 7/16â and APA 15/32â. Table 12. Energy Dissipation of Connections Made of APA Resources Cycle Number APA 7/16â (Each cycle) APA 7/16â (Accumulated) APA 15/32â (Each cycle) APA 15/32â (Accumulated) 0.5 1.53 1.53 1.26 1.26 1 1.74 3.27 1.34 2.60 1.5 2.93 6.20 2.38 4.99 2 3.31 9.51 2.26 7.25 2.5 4.05 13.56 3.24 10.49 3 4.21 17.77 2.98 13.47 3.5 13.23 31.00 10.14 23.61 4 13.34 44.35 9.36 32.97 4.5 32.92 77.26 22.55 55.52 5 30.14 107.41 21.73 77.25 Note: *decimal cycle numbers refer to loading during positive displacement while integer cycle numbers refer to loading during negative displacement Table 13. Energy Dissipation of Connections Made of FPInnovations Resources Cyclic Number FPI 7/16â (Each cycle) FPI 7/16â (Accumulated) FPI 19/32â (Each cycle) FPI 19/32â (Accumulated) 0.5 0.57 0.57 0.95 0.95 1 0.33 0.90 1.01 1.95 1.5 1.25 2.16 1.88 3.83 2 0.91 3.07 1.80 5.63 2.5 1.81 4.88 2.73 8.35 3 1.47 6.34 2.60 10.96 3.5 6.81 13.15 9.22 20.18 4 5.96 19.11 8.91 29.09 4.5 17.22 36.32 21.07 50.15 5 16.67 52.99 21.66 71.82 5.5 23.25 76.24 21.52 93.34 6 22.25 98.50 25.06 118.40 6.5 24.41 123.10 7 24.47 147.57 Note: *decimal cycle numbers refer to loading during positive displacement while integer cycle numbers refer to loading during negative displacement 49 Figure 27. Dissipated Energy of Each Cycle Figure 28. Accumulated Dissipated Energy 051015202530350 1 2 3 4 5 6 7 8Dissipated Energy (KN.mm)Cycle NumberAPA 7/16APA 15/32FPI 7/16FPI 19/320204060801001201401600 1 2 3 4 5 6 7Accumulated Dissipated Energy (KN.mm)Cycle NumberAPA 7/16APA 15/32FPI 7/16FPI 19/32 50 Chapter 4: Nail Bending Test 4.1 Testing Purpose Nails are widely employed as mechanical fasteners in wooden buildings, playing a critical role in determining the capacities of nailed connections. They significantly impact the overall mechanical analysis of the structures. The bending yield strength of nails is calculated to validate the nominal resistance of these connections. Furthermore, the calculated values will be utilized in the modeling process in Chapter 7. This chapter focuses on comparing the bending yield strength values obtained from two different sources to assess any variations between them. 4.2 Materials Two groups of F1667 NL CM PS-37B having a diameter of 3.327 mm (0.131â) and in a length of 88.9 mm (3.5â) were the only needed materials. The measured average length of the nails was 3.277 mm (0.129â). 10 replicates for each nail source (APA and FPInnovations) were tested for analysis. 4.3 Test Apparatus The nail bending tests under centre point loading were conducted to establish the bending yield strength, in accordance with ASTM F1575_F1575M (2021). Similar to the connection tests, MTS 810 was used for the nail bending tests. The nails were centrally positioned on two bolts connected to the test fixtures, as illustrated in Figure 28. 51 Figure 29. Nail Bending Test Setup 4.4 Loading Protocol A load with a rate of 3 mm/min was applied at the centre of the nail to create a load-deformation graph. The loading rate used in the nail bending tests was consistent with that applied in the monotonic loading tests of the connections. The loading process was halted when the displacement reached 45 mm. 4.5 Test Results The bending yield strength of the nails was calculated following the guidelines specified in ASTM F1575/F1575M (2021) standard. The calculated values of the bending yield strength from the nail bending tests are presented in Table 14. The average bending yield strength for APA nails was found to be 838 MPa, which is only 1.8% higher than that of FPI nails. To assess the correlation between the two nail groups, a single Anova test was conducted, yielding a p-value of 0.097. A p-value greater than 0.05 indicates the absence of significance at conventional 5% 52 significance level, suggesting that the nails from these two providers do not have a significant impact on the results. Table 14. Average Data of Nail Bending Test Source Bending Yield Strength (MPa) APA 838 FPInnovations 823 53 Chapter 5: Specific Gravity and Moisture Content Test 5.1 Testing Purpose During the testing process, the moisture content, density (as received), and specific gravity (based on oven-dried weight and volume) of the tested specimens were measured. Wood is known to be hygroscopic, and its strength can be significantly affected by its moisture content. A too low or too high moisture content can have a great impact on the performance evaluation. Therefore, in this chapter, the moisture content of both the OSB sheathing panels and the studs underwent testing to confirm that it would not emerge as a significant factor capable of influencing the results of the connection test. Density is another crucial attribute of wood that influences its strength and stiffness. Generally, higher density is associated with increased strength and stiffness. Hence, specific gravity (SG) (oven dried density of wood compared to density of water) can influence the test results. By measuring the density and specific gravity of the wood specimens, their influence on the overall performance can be assessed. 5.2 Testing Materials Once the required connection tests were completed, all the tested connection members, including the two studs and one OSB sheathing panel of each connection specimen, were cut into smaller sections with dimensions of 88.9 mm x 25.4 mm (3.5â x 1â). 54 5.3 Test Apparatus and Method The cut members were placed in a drying oven and subjected to a temperature of 100 â for 48 hours, following the guidelines outlined in ASTM D4442 (2020). The weight and dimensions of the specimens were measured both before and after the drying process with a wight scale and caliper. The moisture content was calculated using the formula in ASTM D4442 (2020): ðð¶ = (ðð â ðð)/ðð, where Wg represents the weight of green wood while Wo represents the weight after oven drying. The as-tested density was calculated using the formula: ð· = (ð/ (ð»ð âðð â ð¿ð), where ð· represents density, ð, ðð, ð»ð and ð¿ð represent the weight, height, width, and length of the specimen. The specific gravity (SG) was determined in accordance with standard ASTM D2395 (2022). It was calculated using the formula ððº = ðð / (ð»ð â ðð â ð¿ð), where Ho represents the oven-dry height, Wo represents the oven-dry weight, and Lo represents the oven-dry length of the specimens. 5.4 Test Results Table 15 displays the average values of moisture content, density, and specific gravity for the lumbers and OSB specimens subjected to monotonic tests. These values were obtained through direct measurements and oven-drying tests. Similarly, Table 16 presents the same properties for specimens tested under reversed cyclic loading. For the specimens experienced monotonic loadings, their moisture content of the studs ranges from 10.5% to 11.7%, which is close to the equilibrium moisture content (EMC) of indoor-use wood at 11.7%. The determination of EMC was conducted based on the EMC table in Wood 55 Handbook: Wood as an Engineering Material, with a temperature of 26.7°C and a relative humidity of 65%. The moisture content of the OSB sheathing panel ranges from 7.1% to 7.3%. The densities of the studs exhibit a relatively small variation, ranging from 511 kg/m3 to 554 kg/m3. On the other hand, the densities of the OSB sheathing panels show a larger range, with values ranging from 466 kg/m3 for FPI 7/16â groups to 655 kg/m3 for APA 15/32â groups. The specific gravity values range from 0.479 to 0.517 for the studs and from 0.444 to 0.620 for the OSB sheathing panels. These specific values are within the expected range of the wood species under consideration. For the specimens under reversed cyclic loadings, their moisture content of the studs and OSB panels range from 11.0% to 12.2%. and from 7.3% to 7.6%. The densities of the two materials are from 513 to 537 kg/m3 and from 566 to 655 kg/m3, respectively. The specific gravities are from 0.481 to 0.518 and from 0.551 to 0.638, respectively. These acceptable variations do not exert a significant influence on the comparison of results. 56 Table 15. Properties of the Tested Monotonic Specimens (APA & FPInnovations) Source Configuration OSB Thickness(in.) Element Moisture Content Density (kg/m3) Specific Gravity APA Single nail & Double nail 7/16 Front Stud 11.7% 547 0.503 FPInnovations Double nail 7/16 Front Stud 11.1% 521 0.494 APA Single nail & Double nail 15/32 Front Stud 11.6% 515 0.491 FPInnovations Single nail & Double nail 19/32 Front Stud 10.5% 511 0.485 APA Single nail & Double nail 7/16 Back Stud 11.7% 554 0.517 FPInnovations Double nail 7/16 Back Stud 10.6% 514 0.490 APA Single nail & Double nail 15/32 Back Stud 11.6% 531 0.504 FPInnovations Single nail & Double nail 19/32 Back Stud 10.5% 511 0.479 APA Single nail & Double nail 7/16 OSB Sheathing 7.2% 594 0.578 FPInnovations Double nail 7/16 OSB Sheathing 7.3% 466 0.444 APA Single nail & Double nail 15/32 OSB Sheathing 7.3% 655 0.620 FPInnovations Single nail & Double nail 19/32 OSB Sheathing 7.1% 581 0.564 SPF Double nail 7/16 Front Stud 11.2% 416 0.394 SPF Double nail 7/16 Back Stud 10.9% 383 0.362 SPF Double nail 7/16 OSB Sheathing 7.5% 598 0.378 57 Note: *the nominal thickness of 7/16â, 15/32â and 19/32â OSB are 11.1 mm, 11. 9 mm and 15.1 mm, respectively Table 16. Properties of the Tested Reversed Cyclic Specimens Tests Configuration OSB Thickness (in.) Element Moisture Content Density (kg/m3) Specific Gravity APA Single nail 7/16 Front Stud 11.8% 522 0.499 FPInnovations Double nail 7/16 Front Stud 11.0% 544 0.518 APA Single nail 15/32 Front Stud 11.8% 513 0.481 FPInnovations Single nail 19/32 Front Stud 11.4% 545 0.509 APA Single nail 7/16 Back Stud 11.7% 515 0.483 FPInnovations Double nail 7/16 Back Stud 11.2% 526 0.489 APA Single nail 15/32 Back Stud 12.2% 520 0.493 FPInnovations Single nail 19/32 Back Stud 11.5% 537 0.507 APA Single nail 7/16 OSB Sheathing 7.8% 655 0.638 FPInnovations Double nail 7/16 OSB Sheathing 7.6% 568 0.555 APA Single nail 15/32 OSB Sheathing 7.3% 583 0.567 FPInnovations Single nail 19/32 OSB Sheathing 7.5% 566 0.551 Note: *the nominal thickness of 7/16â, 15/32â and 19/32â OSB are 11.1 mm, 11. 9 mm and 15.1 mm, respectively 58 Chapter 6: Model Fitting 6.1 Fitting Purpose In fitting the experimental curves, parameters of functional relationships are obtained to gain a deeper understanding of the underlying mathematical significance of data. The resulting parameters from these functions facilitate further analysis without the need for the original experimental data. 6.2 Fitting Method The experimental curves were fitted to a non-linear load (p)-slip (w) model first introduced by Foschi in 1974: ð = (ð0 + ð1âð¤) â (1 â ðâðâð¤ð0 ). Three model parameters were involved in this p-w model: p1 represents the initial slope of the experimental curve which can be directly estimated using regression analysis. The parameters k and po represent the slope and the zero-intercept of an asymptotic line for the experimental curve. Both parameters were estimated by using the MS Excel Solver function. Using the p-w model with the estimated p1 and an assumed set of k and po values as input, a load can be calculated for a given displacement to generate an estimated load-displacement curve. Comparing it to the experimentally obtained load displacement curve, a sum of squared estimate of errors (SSE) was obtained. This process was repeated with different sets of k and po values using the MS Excel Solver function to establish the best fit that minimized the SSE between the fitted and experimental load-displacement curve. This process only considered the experimental 59 data before the declining branch at a âturningâ point. For all the monotonic tests, 25 mm was chosen to be the turning point based on the overall trends of the experimental curves as shown in Figure 8 to Figure 13. As p1 is positive for all experimental curves (increased load leads to increased deformation), the p-w relationship can only model the ascending portion of the experimental curve. Hence a linear line with a negative slope is added to the p-w relationship beyond the âturningâ point by considering the declining branch of the experimental load displacement curve as linear between the âturningâ point and load at 30 mm of displacement. The linear model of the declining branch can be solved by a linear equation with 2 unknowns: p= a*w +b. a is the slope, and b is the intercept of the vertical axis and the reverse extended linear line. This fitting method works for both the model based on the averaged experimental curve and the one based on the averaged parameter values. The only difference between these two fitting curves is the parameters used. For the model based on the averaged experimental curve, the parameters were obtained by doing a new fitting to the averaged experimental data; and for the model based on the averaged parameter values, the parameters were obtained by averaging the existed corresponding parameters of each tested specimen. The two ways of parameter calculations contributed to two different fitting curves. The fitting process of reversed cyclic experimental curves before 0 mm (when the test machine was applying a tensile load) was achieved by fitting to a curve with positive load and displacement axes after mirroring the experimental curves that were with negative axes. 60 6.3 Fitting Results and Discussion Figures 29 and 30 depict the average experimental and fitted curves of 11.1 mm (7/16â) and 11.9 mm (15/32â) thick OSB connections from APA monotonic tests, respectively. Similarly, Figures 31 and 32 display the corresponding curves from FPInnovations monotonic tests. In Figures 29 and 30, it is apparent that a noticeable disparity exists between the fitting curve based on the averaged parameter values and the experimental data for APA 11.1 mm (7/16â) connections, while the fitting based on average experimental curve worked very well. In Figures 31 and 32, the fitting curves made based on the average experimental curves aligned well with the experimental curves, except for a slight offset at the initial slips of the experimental curves. However, it is also quite clear from Figures 31 and 32 that the models based on the averaged parameter values do not perform as well as the other one, which is most obvious near the slip at the peak load. 61 Figure 30. Averaged experimental and fitting curves of 11.1 mm (7/16â) thick OSB connections from monotonic tests (APA) Figure 31. Averaged experimental and fitting curves of 11.9 mm (15/3â) thick OSB connections from monotonic tests (APA) 62 Figure 32. Averaged experimental and fitting curve of 11.1 mm (7/16â) thick OSB connections from monotonic tests (FPInnovations) Figure 33. Averaged experimental and fitting curve of 15.1 mm (19/3â) thick OSB connections from monotonic tests (FPInnovations) 63 Figures 33 and 34 show the experimental and fitted backbone curves for the two OSB thicknesses from APA reversed cyclic tests, and Figures 35 and 36 show those curves from FPInnovations reversed cyclic tests. In Figures 33 and 34, the resulting fitting curves based on the averaged experimental curves had a very good match to the experimental curves. Minimal offsets can be observed in the backbones of the reversed cyclic tests. However, significant deviations can be noticed between the fitting curves based on the averaged parameter values and the experimental curve within the range from -20 mm to 20 mm, but they deviate considerately from experimental curve in the two descending parts. In Figure 34, offsets are observed in the range from -15 mm to 0 mm and from 13 mm to 15 mm. When comparing the two fitting methods, the models based on the averaged experimental curves demonstrate excellent agreement, while the model based on the averaged parameter values only exhibits good alignment within the range of 0 mm to 12 mm in the 15/32â thickness connections. Figures 35 and 36 illustrate a good agreement of the models based on the averaged experimental curves in both connections of the two thickness. The alignment between these models and the experimental curves is clearly demonstrated throughout the test range. However, the models based on the averaged parameter values show significant deviations from the experimental curves, particularly in the descending parts. Additionally, the left ascending part of the 19/32â thickness connection does not align well with the experimental curves, as demonstrated in Figure 64 36. This suggests that the models based on the averaged parameter values may not accurately represent the behaviour of the connections in these specific cases. Figure 34. Averaged experimental and fitting backbone curves of 11.1 mm (7/16â) thick OSB connections from reversed cyclic tests (APA) Figure 35. Averaged experimental and fitting backbone curves of 11.9 mm (15/32â) thick OSB connections from reversed cyclic tests (APA) 65 Figure 36. Averaged experimental and fitting backbone curves of 11.1 mm (7/16â) thick OSB connections from reversed cyclic tests (FPInnovations) Figure 37. Averaged experimental and fitting backbone curves of 13.1 mm (19/32â) thick OSB double-nail connections from reversed cyclic tests (FPInnovations) 66 In general, the models constructed using the averaged experimental curves exhibit excellent performance and provide a close match to the experimental data. However, the models based on the averaged parameter values do not accurately capture the behaviour of the connections and are not recommended for fitting purposes in this case. It is advisable to utilize the suggested fitting method and the corresponding fitting data for future research in related areas. These models can serve as valuable tools for analyzing and predicting the behavior of similar connections. Table 17 displays the parameter values obtained for the models of each monotonic test, while Table 18 presents the parameters for each reversed cyclic test. These parameter values were derived using the suggested fitting method. Table 17. Monotonic Test Fitting Parameters Test po (kN) p1 (kN/mm) k (kN/mm) a b 7/16 Average (APA) 2.76929 0.03581 1.60318 -0.02642 4.32514 15/32 Average (APA) 2.90149 0.02678 1.25550 -0.01159 3.86058 7/16 Average (FPInnovations) 1.64114 0.06226 0.61534 0.03189 2.38711 19/32 Average (FPInnovations) 2.70538 0.04493 0.96987 0.03531 2.94486 7/16 Average (SPF) 1.84910 0.05563 1.40608 -0.05186 4.53323 19/32 Average (SPF) 2.19514 0.04916 1.49722 -0.04187 4.07096 67 Table 18. Reversed Cyclic Test Fitting Parameters Test po (kN) p1 (kN/mm) k (kN/mm) a b Pull 7/16 Average (APA) 1.76531 0.05087 7.07000 -0.68935 -19.18810 Push 7/16 Average (APA) 1.59937 0.10276 3.87065 -1.01469 25.86644 Pull 15/32 Average (APA) 2.19216 0.06098 12.91230 -1.84382 -30.51973 Push 15/32 Average 2.15210 0.09836 3.97775 -0.74932 12.60101 Pull 7/16 Average (FPI1) 1.89441 0.06282 2.34580 -0.07603 -3.97514 Push 7/16 Average (FPI) 1.49460 0.11127 3.41391 -0.11100 4.94557 Pull 19/32 Average (FPI) 1.46565 0.13399 3.39499 -0.36413 -7.05351 Push 19/32 Average (FPI) 2.06433 0.10586 3.28743 -0.40082 7.65656 68 Chapter 7: Calibration of HYST Model for the Reversed Cyclic Backbone Experimental Curve 7.1 Modeling Purpose The objective of modeling the experimental data is to quantify the load-slip behaviour for the tested nail connections with a test prototype independent mechanic-based model software HYST. Such model obtained from HYST will be further implemented into Wall2D. Kari et al. (2024) explored an efficient technique called the Pseudo-nail method to predict the reversed cyclic behavior of six MPSW2 wall configurations without extensive testing. This approach started with monotonic and reversed cyclic tests on double-shear nail joints which were performed as reported in this thesis. Subsequently, Kari et al. (2024) utilized the HYST software to create representative nail joint models for each configuration. These models were then incorporated into the Wall2D software to predict the backbone curves of MPSW2 walls. By leveraging HYST, Kari et al. (2024) transformed each backbone curve into a Pseudo-nail model, enabling the prediction of the reversed cyclic behavior of MPSW2 walls. This method offers significant time and cost savings while maintaining computational efficiency. Even though the Pseudo-nail study is beyond the scope of this thesis, this approach allows for further analysis of the structural behaviour of the wall elements. 7.2 Modeling Method The output parameters obtained from HYST represent the embedment property data of the nail connection, which is based on the experimental curve model. Since the data obtained is intended for use as input representing the load-slip lateral resistance behaviour of the nail connection in 69 WALL2D for wall behaviour modeling. As a first step, the modeled load-slip curve should closely match the corresponding backbone curve depicting the reversed cyclic load-slip behaviour of the connection. In cases where the fitting curve generated by HYST using fixed property data is considered not to match close enough to the experimental curve, the fixed properties of the nails were adjusted to improve the modeling accuracy. It is important to note that the loading behavior beyond the ultimate displacement of 30 mm is not considered valid for the purposes of this study. Therefore, the R-squared value obtained from the entire curve is only used as a reference for evaluating the goodness of fit between the modeling results and the backbone curves of the experimental data. 7.3 Modeling Results The modeling conducted by HYST focused on the loading data up to a displacement of 30 mm. Despite this limitation, the modeling results, as evident from the comparison of the modeling and experimental curves in the figures, indicate that HYST performed effectively in capturing the loading behavior of the connections. The close alignment between the modeled and experimental curves demonstrates the accuracy and reliability of HYST in representing the connection loading behavior within the specified displacement range. Tables 19 and 20 present the fastener properties utilized in HYST modeling for APA and FPI, respectively. In addition, Table 21 displays the resulting connection properties derived from the HYST modeling. Figures 37 to 40 showcase the backbones of the reversed cyclic tests alongside the HYST models. These figures demonstrate that the HYST models effectively replicate the 70 experimental curves up to a displacement of 30 mm. Despite slight discrepancies within this range, HYST offers reliable predictions suitable for application in WALL2D. The data of each connection in HYST is shown in Appendix. Table 19. Fixed fastener properties of APA connections in HYST modeling Fastener properties Diameter (mm) Length (mm) Yield (kN/mm^2) E (kN/mm^2) Ey/E Value 3.20 90 0.838 200 0.001 Table 20. Fixed fastener properties of FPI connections in HYST modeling Fastener properties Diameter (mm) Length (mm) Yield (kN/mm^2) E (kN/mm^2) Ey/E Value 3.27 88.9 0.823 200 0.001 71 Table 21. Resulted connection properties by HYST Connection test groups Embedment properties Qo (kN/mm) Q1 (kN/mm^2) Q2 Ko (kN/mm^2) Dmax (mm) R square APA 7/16 Bottom layer 0.129 0.038 1.6 105.683 22.389 0.919 Top layer/sheathing 2.495 0.154 1.6 83.734 33.776 APA 15/32 Bottom layer 0.214 0.024 1.6 67.775 16.699 0.936 Top layer/sheathing 4.67 0.166 1.6 7.255 4.764 FPI 7/16 Bottom layer 0.327 0.064 1.6 29.36 28.229 0.986 Top layer/sheathing 4.513 0.347 1.6 13.364 13.713 FPI 19/32 Bottom layer 0.129 0.038 1.6 105.683 22.389 0.919 Top layer/sheathing 2.495 0.154 1.6 83.734 33.776 72 Figure 38. HYST modeling and experimental curves of APA 7/16â Figure 39. HYST modeling and experimental curves of APA 15/32â 73 Figure 40. HYST modeling and experimental curves of FPI 7/16â Figure 41. HYST modeling and experimental curves of FPI 19/32â 74 Chapter 8: Conclusion and Future Research 8.1 Conclusion This thesis investigated the lateral behavior under loading parallel to the grain direction and the mechanical performance of nail connections in Mid-ply 2 (MPSW2) shear wall systems. The study utilized various stud species and OSB sheathing materials and a certain type of nail. The research encompassed several key areas, including experimental testing, specific gravity and moisture content test, fitting methods, and calibration of the HYST algorithm for the reversed cyclic backbone experimental curve. The results from this study can be further used in further MPSW2 connection and wall study. 8.1.1 Monotonic and Reversed Cyclic Tests The experimental testing involved monotonic and reversed cyclic loading tests on connections made of various materials, including sheathing panels, studs, and nails, to assess their mechanical performance. The results provided valuable insights into the connections' peak load, stiffness, and ductility. Among Douglas fir studs, thicker sheathing led to higher peak loads due to the enhanced bearing capacity of the OSB. However, it also resulted in lower stiffness because the larger embedment of the nail into the sheathing caused greater deformation when the load was applied. All connections demonstrated good ductility. However, the monotonic test results for FPI 7/16â did not perform as expected. The failure mode in the monotonic tests was attributed to the dowel bearing capacity of the OSB sheathing panel in the MPSW2 connection. SPF's lower MOE under compression compared to Douglas fir contributed to the lower stiffness of SPF connections yet resulted in similar peak loads among SPF connections. 75 8.1.2 Specific Gravity and Moisture Content Tests The conducted tests played a crucial role in evaluating the moisture content, density, and specific gravity of the specimens. These tests were vital in ensuring the moisture content do not become a factor that could impact the connection test results. By assessing these properties, the thesis confirmed that the moisture content was within an acceptable range, mitigating any potential effects on the performance. Furthermore, the nail bending tests were conducted to verify the quality of the nails from different sources. The results of these tests demonstrated that the nails obtained from both sources exhibited similar quality characteristics, which confirmed the consistent quality from the two sources of the nails used in the connections. 8.1.3. Model Fitting Fitting methods were employed using the equation developed by Foschi (2000) to establish parameters for the functional relationships to represent the experimental data. The results suggested that the fitting based on the averaged experimental curves successfully captured the loading characteristics of the connections, thereby generating reliable models for further analysis. 8.1.4 Calibration of HYST Model The HYST algorithm was calibrated against the reversed cyclic backbone load-deformation curve. The calibrated HYST model yielded closely matched reversed cyclic backbone curves compared to the test results which demonstrated the capability of HYST in representing the connection loading behaviour within the specified displacement range. 76 Overall, the findings of this thesis contribute to a deeper understanding of nail connections in MPSW2 shear wall systems. The experimental testing and modeling results provide valuable insights into the behavior and performance of these connections, which can be used to facilitate further analysis and prediction of wall behavior using the WALL2D algorithm. These findings can inform the design and optimization of nail connections in construction practices, ultimately enhancing the structural integrity and performance of MPSW2 shear wall systems. Nevertheless, it is important to acknowledge that this study has some limitations that should be taken into consideration. One of the limitations is the limited range of sheathing panel choices used in the experimental tests, which may restrict the comprehensiveness of the study. This limitation should be considered when interpreting the results and applying them to real-world scenarios. Further research with a wider range of sheathing panel choices could provide additional insights and enhance the understanding of the topic. 8.2 Future Research Future research in this field can build upon the methodologies and findings presented in this thesis to further advance the understanding and application of nail connections in construction engineering given the limitations of this study, such as restricted sheathing types, nail types, and stud species. Additional tests could be conducted on connections with 7/16â OSB sheathing panels to verify their mechanical properties and address any concerns about the materials. Furthermore, studying connections with different nail types can validate the findings from this thesis. Additionally, testing connections with various stud materials will provide more comprehensive results. Moreover, MPSW2 shear walls with plywood sheathing can greatly facilitate construction. Conducting full-scale testing of walls with MPSW2 nail connections 77 under reversed cyclic loadings in real-world applications will further validate the findings of this thesis. 78 References ASTM D1761 (2020). Standard Test Methods for Mechanical Fasteners in Wood and Wood-Based Materials. American Society for Testing and Materials. ASTM D2395 (2022). Standard Test Methods for Density and Specific Gravity (Relative Density) of Wood and Wood-Based Materials. American Society for Testing and Materials. ASTM D4442 (2020). Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials. American Society for Testing and Materials. ASTM E2126-19 (2019). Standard Test Methods for Cyclic (Reversed) Load Test for Shear Resistance of Vertical Elements of the Lateral Force Resisting Systems for Buildings. American Society for Testing and Materials. ASTM F1575/F1575M (2021). Standard Test Method for Determining Bending Yield Moment of Nails. American Society for Testing and Materials. doi: 10.1520/F1575_F1575M-21 Blass, H., Ceccotti, A., & Dyrbe, M. (1994). Behaviour of Timber Structures under Seismic Actions. Materials and Structures, 157-184. 79 Buitelaar, M. (2001). Static and dynamic testing of midply TM shear wall system (Master's thesis, University of British Columbia, 2001). Vancouver: University of British Columbia. Britannica, T. Editors of Encyclopaedia (2023). Alaska earthquake of 1964. Encyclopedia Britannica. https://www.britannica.com/event/Alaska-earthquake-of-1964 CSA O86 (2019). Engineering design in wood, Canadian Standards Association Durham. (2001). Seismic resistance of wood shear walls with large OSB panels. Journal of Structural Engineering, 127(12), 1460-1466. doi:10.1061/(asce)0733-9445(2001)127:12(1460) European Committee for Standardization. (2001). Timber structuresâTest methodsâCyclic testing of joints made with mechanical fasteners (EN 12512). Forest Products Laboratory. (2000). 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Journal of Structural Engineering, 138(1), 99-108. doi:10.1061/(asce)st.1943-541x.0000438 Lungu, D. (2000). Testing and analysis of midply(TM) shear wall system. (Master's thesis, University of British Columbia, 2000). Vancouver: University of British Columbia. doi:10.14288/1.0063774 Marisa J. Mulder, M. J. (2017). Numerical Modeling of Seismic Performance of Light-Frame Wood Buildings (Unpublished master's thesis). The University of British Columbia. Midplyâ¢ Shearwall System. (2021, April 19). Retrieved from https://canadawood.org/case-study/midply/ 82 National Building Code of Canada. 2015. Associate committee on the national building code. Ottawa, ON, Canada: National Research Council of Canada Oluwafemi, John & Ofuyatan, Olatokunbo & Ede, Anthony & Oyebisi, Solomon & Akinwumi, Isaac & Babaremu, Kunle. (2018). Review of earthquakes in Nigeria: An understudied area. International Journal of Civil Engineering and Technology. 9. 1023-1033. Shu, Z., Li, Z., Yu, X., Zhang, J., & He, M. (2019). Rotational performance of glulam bolted joints: Experimental investigation and analytical approach. Construction and Building Materials, 213, 675-695. doi:10.1016/j.conbuildmat.2019.03.002 Karacabeyli, E., Ni, C., Stiemer, S., & Lungu, D. (2000). MIDPLYâ¢ wall system: Final report (40031st ed., Canadian Forest Service NO.20, Rep.). United Nations Environment Programme UNEP (2022). International Organizations. Retrieved from the Library of Congress, https://www.unep.org/resources/annual-report-2022 Varoglu, E., Karacabeyli, E., Stiemer, S., & Ni, C. (2006). Midply wood shear wall system: Concept and performance in static and cyclic testing. Journal of Structural Engineering, 132(9), 1417-1425. doi:10.1061/(asce)0733-9445(2006)132:9(1417) 83 Varoglu, E., Karacabeyli, E., Stiemer, S., Ni, C., Buitelaar, M., & Lungu, D. (2007). Midply wood shear wall system: Performance in dynamic testing. Journal of Structural Engineering, 133(7), 1035â1042. https://doi.org/10.1061/(asce)0733-9445(2007)133:7(1035) Werner, F., & Richter, K. (2007). Wooden building products in comparative LCA. The International Journal of Life Cycle Assessment, 12(7), 470-479. doi:10.1065/lca2007.04.317 Jiang, G., & Lam, F. (2004). Simplified mechanics-based wood frame shear wall model. Proceedings. 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada Zheng, W., Lu, W., Liu, W., Wang, L., & Ling, Z. (2015). Experimental investigation of laterally loaded double-shear-nail connections used in midply wood shear walls. Construction and Building Materials, 101, 761-771. doi:10.1016/j.conbuildmat.2015.10.100 84 Appendix Figure 42. HYST Connection data for APA 7/16" Figure 43. HYST Connection data for APA 15/32â 85 Figure 44. HYST Connection data for FPI 7/16â Figure 45. HYST Connection data for FPI 19/32â
Thesis/Dissertation
eng
Forestry
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Lam, Frank C. F.
Lateral resistance of new mid-ply shear wall (MPSW2) connections â performance of different materials
Text