Midply shear wall, which was originally developed by researchers at Forintek Canada Corp. (predecessor of FPInnovations) and the University of British Columbia, is a high-capacity shear wall system that is suitable for high wind and seismic loadings. Its superior seismic performance was demonstrated in a full-scale earthquake simulation test of a 6-storey wood-frame building in Japan. In collaboration with APA–The Engineered Wood Association and the American Wood Council (AWC), a new framing arrangement was designed in this study to increase the vertical load resistance of midply shear walls and make it easier to accommodate electrical and plumbing services. In this study, a total of 12 midply shear wall specimens in four wall configurations with different sheathing thicknesses and nail spacing were tested under reversed cyclic loading. Test results showed that the modified midply shear walls have approximately twice the lateral load capacity of a comparable standard shear wall. The drift capacity and energy dissipation capability are also greater than comparable standard shear wall. Seismic equivalency to standard shear walls in accordance with ASTM D7989 was also conducted. Results show that an overstrength factor of 2.5 and can be used to assign allowable design strengths of midply shear walls with 7/16” and nail spacing at 4” or 3” on center. For midply shear walls with 19/32” OSB, a higher overstrength factor must be used to meet the ductility criteria. The information from this study will support code implementation of the midply shear walls in Canadian and US timber design standards, thereby providing more design options for light wood frame structures in North America.
In order to enhance the bearing capacity of structural components, save materials, and reduce cost, a glued laminated timber (glulam) I-beam that is theoretically suitable for engineering application was proposed. In this study, 18 glulam specimens were fabricated using larch dimension lumber and resorcinol–formaldehyde resin. Four-point bending tests were carried out to compare the ultimate bearing capacity, strain, and deflection of various specimens. The results showed that: (1) The typical failure mode at bending is the web shear failure parallel to grain. Before the failure, cracks and sounds appear at the beam web, which represent the sudden brittle failure. (2) The cross-sectional strain of glulam beam changed linearly with the beam height, indicating that the plane section assumption was basically established. (3) Stiffener could improve the initial flexural stiffness of glulam beam, which experiences an increase of 28.21%. Larger the shear span ratio, smaller the initial flexural stiffness. The initial flexural stiffness improves by 10–23.5% with the increase in the thickness of the lower flange. (4) The effects of stiffener and shear-span ratio on shear strength are relatively significant. After the stiffeners are set at the support and the loading point in pairs, the shear strength of the glulam beam increases by 15.05% averagely. With the increase in the shear-span ratio, the shearing strength of the glulam I-beam gradually reduces. The equation of the shearing strength with the shear span ratio is obtained, which is shown by high fitting precision. (5) The shear strength correlation, as proposed by Soltis and Rammer, is suitable not only for rectangular beams, but also for glulam I-beams.
Innovations in the use of wood as a structural material have included the invention of engineered wood products including Cross-Laminated Timber (CLT) for which markets are expanding. One such market is residential construction where many structures are built using light-frame construction techniques. These structures have shown vulnerabilities to hazards such as tornadoes; whereas, CLT has shown potential to withstand these hazards.
The project had two main components: an experimental test phase and an analytical phase. Results from experimental debris impact testing demonstrated that 3-ply CLT could reliably resist the debris associated with EF-2 and EF-3 level events while failing approximately 50% of the time when subject to EF-5 level hazards. CLT shear wall tests on assemblies with and without out-of-plane walls sought to quantify the performance of configurations that would likely be present in residential structures with more box-like geometries and behavior. In addition, it was determined that out-of-plane walls could resist the uplift forces that develop due to lateral loads. A simplified analytical method for determining the capacity of CLT shear wall assemblies was proposed based on the connection capacities of the assembly.
The analytical phase of the project included the development of a structural performance model for residential archetypes designed using CLT. Results from this study indicated that the archetypes experienced a 10% probability of failure in EF-4 events. In comparison, light-frame construction has shown vulnerabilities to EF-0 and EF-1 level events. In addition, the hazard assessment of light-frame structures based on historical tornado data showed that significant portions of the United States exhibited a reliability index less than the target reliability described in ASCE 7-16, dropping to nearly 0% when built using CLT. A comparative cost analysis shows that for locations with high tornado hazard, it would take up to 100 years for CLT construction to be economically competitive with light-frame construction considering only the differences in upfront construction costs and tornado-induced losses.
Ultimately, CLT exhibits an increased level of performance compared to light-frame residential construction in tornado events. Further developments in the mass timber market could make such an alternative to light-frame construction more realistic.
Cross-laminated timber (CLT) is an innovative engineering wood product made by gluing layers of solid-sawn lumber at perpendicular angles. The commonly used wood species for CLT manufacturing include spruce-pine-fir (SPF), douglas fir-larch, and southern pine lumber. With the hope of broadening the wood species for CLT manufacturing, the purposes of this study include evaluating the mechanical properties of black spruce CLT and analyzing the influence of CLT thickness on its bending or shear properties. In this paper, bending, shear, and compressive tests were conducted respectively on 3-layer CLT panels with a thickness of 105 mm and on 5-layer CLT panels with a thickness of 155 mm, both of which were fabricated with No. 2-grade Canadian black spruce. Their bending or shear resisting properties as well as the failure modes were analyzed. Furthermore, comparison of mechanical properties was conducted between the black spruce CLT panels and the CLT panels fabricated with some other common wood species. Finally, for both the CLT bending panels and the CLT shear panels, their numerical models were developed and calibrated with the experimental results. For the CLT bending panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios can even slightly reduce the characteristic bending strength of the black spruce CLT. For the CLT shear panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios has little enhancement on their characteristic shear strength. For the CLT bending panels, their effective bending stiffness based on the Shear Analogy theory can be used as a more accurate prediction on their experiment-based global bending stiffness. The model of the CLT bending specimens is capable of predicting their bending properties; whereas, the model of the CLT shear specimens would underestimate their ultimate shear resisting capacity due to the absence of the rolling shear mechanism in the model, although the elastic stiffness can be predicted accurately. Overall, it is attested that the black spruce CLT can provide ideal bending or shear properties, which can be comparable to those of the CLT fabricated with other commonly used wood species. Besides, further efforts should focus on developing a numerical model that can consider the influence of the rolling shear mechanism.
Board width-to-thickness ratios in non-edge-glued cross laminated timber (CLT) panels influence the in-plane shear stiffness of the panel. The objective is to show the impact of board width-to-thickness ratios for 3- and 5-layer CLT panels. Shear stiffnesses were calculated using finite element analysis and are shown as reduction factors relative to the shear stiffnesses of edge-glued CLT panels. Board width-to-thickness ratios were independently varied for outer and inner layers. Results show that the reduction factor lies in the interval of 0.6 to 0.9 for most width-to-thickness ratios. Results show also that using boards with low width-to-thickness ratios give low reduction factors. The calculated result differed by 2.9% compared to existing experimental data.
The main goal of this study was to analyze glue line on eucalyptus wood. In order to do that, thickness of main and secondary glue lines were measured as well their interaction with apparent density of elements glued with resorcinol-formaldehyde (RF) and castor polyurethane (CP) adhesives. Anatomical wood characterization of Eucalyptus grandis × Eucalyptus urophylla was performed by correlating glue line thickness. According to normative instruction, specimens were produced for delamination tests. The experiment was conducted in a completely random 2 × 2 design factorial scheme (two classes of apparent density and two adhesives). Pearson correlation was performed among variables. It was found that there was adhesive penetration into wood pots and rays. Glue line thickness was higher in woods with density higher than 0.58 g cm-3 glued with RF adhesive. There was low correlation among density, vessel diameter, main and secondary glue lines.
Cross-laminated timber (CLT) is gaining popularity in residential and non-residential applications in the North American construction market. CLT is very effective in resisting lateral forces resulting from wind and seismic loads. This research investigated the in-plane performance of CLT shear wall for platform-type buildings under lateral loading. Analytical models were proposed to estimate the in-plane stiffness of CLT wall panels with openings based on experimental and numerical investigations. The models estimate the in-plane stiffness under consideration of panel thickness, aspect ratios, and size and location of the openings. A sensitivity analysis was conducted to reduce the number of model parameters to those that have a significant impact on the stiffness reduction of CLT wall panels with openings. Finite element models of CLT wall connections were developed and calibrated against experimental tests. The results were incorporated into models of CLT single and coupled shear walls. Finite element analyses were conducted on CLT shear walls and the results in terms of peak displacements, peak loads and energy dissipation were in good agreement when compared against full-scale shear wall tests. A parametric study on single and coupled CLT shear walls was conducted with variation of number and type of connectors. The seismic performance of 56-single and 40-coupled CLT shear walls’ assembles for platform-type construction were evaluated. Deflection formulas were proposed for both single and coupled CLT shear walls loaded laterally in-plane that in addition to the contributions of CLT panels and connections, also account for the influence of adjacent perpendicular walls and floors above and illustrated with examples. Analytical equations were proposed to calculate the resistance of CLT shear walls accounting for the kinematic behaviour of the walls observed in experimental investigations (sliding, rocking and combined sliding-rocking) and illustrated with examples. Different configurations (number and location of hold-downs) of single and coupled CLT walls were considered. The findings presented in this thesis will contribute to the scientific body of knowledge and furthermore will be a useful tool for practitioners for the successful seismic design of CLT platform buildings in-line with the current CSA O86 provisions.
In the US, codified seismic design procedure requires the use of seismic performance factors which are currently not available for CLT shear wall systems. The study presented herein focuses on the determination of seismic design factors for CLT shear walls in platform type construction using the FEMA P-695 process. Results from the study will be proposed for implementation in the seismic design codes in the US. The project approach is outlined and selected results of full-scale shear wall testing are presented and discussed. Archetype development, which is required as part of the FEMA P-695 process, is briefly explained with an example. Quasi-static cyclic tests were conducted on CLT shear walls to systematically investigate the effects of various parameters. The key aspect of these tests is that they systematically investigate each potential modelling attribute that is judged within the FEMA P-695 uncertainty quantification process. Boundary constraints and gravity loading were both found to have a beneficial effect on the wall performance, i.e. higher strength and deformation capacity. Higher aspect ratio panels (4:1) demonstrated lower stiffness and substantially larger deformation capacity compared to moderate aspect ratio panels (2:1). However, based on the test results there is likely a lower bound for aspect ratio (at 2:1) where it ceases to benefit deformation capacity of the wall. This is due to the transition of the wall behaviour from rocking to sliding. Phenomenological models were used in modelling CLT shear walls. Archetype selection and analysis procedure was demonstrated and nonlinear time history analysis was conducted using different wall configurations.
The effect of glass fiber reinforced polymer (GFRP) on the technical properties of LSL made from poplar (Populus deltoids L.) employing pMDI and UF as binders was investigated. Technical properties such as modulus of rupture (MOR), Modulus of elasticity (MOE), shear strength (SS), compression strength parallel to the grains (CS //), impact strength (IS), water absorption (WA) and thickness swelling (TS) were determined. Results confirmed that resin type and GFRP have significant effects on the LSL properties. It was revealed that the most beneficial effect of GFRP is on MOR, MOE, IS, SS and CS respectively. The Highest properties were obtained by using pMDI as the resin and GFRP as the reinforcement, where properties such as MOR, MOE, IS, SS and CS were improved by 123, 114, 100, 94, and 90%, respectively, compared to control samples. Furthermore, GFRP incorporation led to alteration of fracture place from tension side to compression side. Depending on the treatment type, the WA and TS values of the LVLs improved between 23% to 68% and 19.5% to 78%, respectively.
This work focuses on optimization of the laminated lap-joint lengthening technology that is used to produce large-size bamboo bundle laminated veneer lumber (BLVL). A three-factor Box-Behnken design was developed in which lap-joint length (x1), board density (x2), and thickness of lap veneer (x3) were the three factors. Multi-objective optimization of response surface model was used to obtain 17 optimum Pareto solutions by a genetic algorithms method. The mechanical properties of BLVL predicted using the model had a strong correlation with the experimental values (R2 = 0.925 for the elastic modulus (MOE), R2 = 0.972 for the modulus of rupture (MOR), R2 = 0.973 for the shearing strength (SS)). The interaction of the x1 and x3 factors had a significant effect on MOE. The MOR and shearing SS were significantly influenced by the interaction of x2 and x3 factors. The optimum conditions for maximizing the mechanical properties of BLVL lap-joint lengthening process were established at x1 = 16.10 mm, x2 = 1.01 g/cm3, and x3 = 7.00 mm. A large-size of BLVL with a length of 14.1 m was produced with the above conditions. Strong mechanical properties and dimensional stability were observed.
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