Department of Civil Engineering Graduate Theses

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    Seismic Performance of Bolted Glulam Timber Brace Connections with Internal Steel Plates
    Civil Engineering; Woods, Joshua; Viau, Christian
    Mass timber braced frame systems achieve their ductility through the brace connections. Canadian design standards currently lack guidance on how to detail bolted brace connections to achieve a target system-level ductility as per the National Building Code of Canada. This research aims to develop guidelines on how to detail bolted glulam timber brace connections to achieve moderate or limited ductility. To accomplish this objective, 4, 8, and 12-storey prototype buildings were designed to determine realistic brace design forces. Experimental tests were conducted on brace connections from the prototype buildings and finite element models using ABAQUS were developed to predict and compare to the experimental brace behaviour. A total of 12 brace specimens with one or two slotted-in steel plates and two different bolt sizes were studied with the aim to determine the ductility of the connections and brace assemblies. The use of self-tapping screws as perpendicular-to-grain reinforcement to prevent splitting and enhance brace ductility was also investigated. The results of the experimental study showed that both end connections in a brace can experience larger plastic deformations if the connections exhibit a post-yield hardening response. To ensure a post-yield hardening response, connections can be designed with bolt spacing greater than the minimum allowable in Canadian Wood design standards with the addition of self-tapping screws perpendicular to grain to minimize splitting. The experimental yield strengths were compared to the design yield resistance and the results showed that the design yield resistance was more accurate for connections with two slotted-in steel plates than those with only one. The results of the experimental tests were then compared to finite element models of two of the connections that were calibrated for a connection with a single dowel. The finite element models were reasonably accurate for the connection with the two slotted-in plates and less accurate for the connection with a single slotted-in plate.
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    Performance of Hooked-End Superelastic Shape Memory Alloy and Steel Fibre Reinforced Concrete and Stiffness of Ankle Foot Orthosis With Superelastic Shape Memory Alloy Hinges
    Menna, Demewoz; Civil Engineering; Green, Mark; Genikomsou, Aikaterini
    Civil engineering structures are vulnerable to damage from aging and hazards such as earthquakes and fire. Engineers are therefore seeking innovative materials that can adapt to environmental changes, function in harsh environments, and extend the service life of the structure. Superelastic shape memory alloys (SMA) and steel fibre reinforced concrete (FRC) have recently emerged as viable materials. A novel superelastic SMA fibre production method was proposed. The fibres were fabricated from heavily cold worked SMA wire followed by heat treatment, with the goal of enhancing fibre pullout performance and simplifying the fibre production process. The heat treatment conditions significantly affected the pullout load, re-centering ratio, and average and equivalent bond strength values. The cyclic flexural responses of hooked-end superelastic SMA and steel fibre reinforced concrete prisms were examined. The superelastic fibres were fabricated from a heavily cold worked, 1 mm diameter NiTi alloy, followed by a 40-minute heat treatment at 350ºC. For fibre volume fractions ranging from 0.25% to 1.00%, the increased volumetric ratio of the fibres increased the ductility, tensile strength, flexural stress, and cumulative energy dissipation characteristics of the FRC. The SMA FRC exhibited significantly better performance than that of its steel FRC counterpart. To investigate the potential application of FRCs in retrofitting existing structures, the punching shear response of concrete slabs strengthened with a thin layer of ultra high-performance FRC (UHPFRC) was studied using finite element methods. The model was verified by analyzing previously tested slab-column connections from literature. Parametric studies showed that the punching shear capacity of the retrofitted slab increased with an increase in the thickness of the UHPFRC layer. Applications of superelastic SMA in ankle foot orthoses (AFO) were examined in Chapters Six and Seven of this thesis. AFOs are orthotic devices used by patients who have an abnormal gait caused by conditions such as foot drop syndrome. A systematic review was conducted and the mechanical characterization of AFOs equipped with SMA hinges was investigated experimentally. The results indicate that producing AFO hinges from heavily cold worked superelastic SMA followed by an optimum heat treatment could be an effective alternative to existing AFOs.
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    The Chemical Durability of Elastomeric Bituminous Geomembranes (BGMS) in Different Geoenvironmental Applications at Elevated Temperatures
    Samea, Alireza; Civil Engineering; Abdelaal, Fady
    The chemical durability of elastomeric bituminous geomembranes (BGMs) is investigated using laboratory accelerated immersion tests for different geoenvironmental applications. The effects of elevated temperatures, thickness, and incubation media on the mechanical, rheological, and chemical properties of BGMs are examined. Exposure to elevated temperatures resulted in the thermo-oxidative degradation of the bituminous coat that increased its rigidity. Concurrently, the BGM exhibited degradation in the reinforcement layer resulting in the loss of its mechanical properties. The rate of degradation in the BGM components is shown to be different and dependent on the incubation media. In air, the BGM exhibited thermo-oxidative degradation in the bitumen coat, leading to its brittleness before any degradation in the mechanical strengths. In contrast, exposure to water resulted in fast degradation of the mechanical properties, while the bitumen coat exhibited substantially less degradation than in air. Immersing a 4.8 mm thick BGM in pH 0.5, 9.5, and 11.5 synthetic mining solutions shows that the degradation rates of all properties are faster in high pHs than in pH 0.5. Additionally, the degradation of this BGM is compared to a 4.1 mm thick BGM produced by the same manufacturer when immersed in synthetic municipal solid waste (MSW) leachate. It is shown that the 4.1 mm has slightly faster degradation in its chemical, mechanical, and rheological properties than the 4.8 mm BGM. Relative to the mining solutions, the degradation in the bitumen coat was slower in the MSW leachate, while the degradation in the reinforcement layer was much faster. The time to nominal failure (tNF) of the BGM is predicted in air, water, mining solutions, and MSW leachate at field temperatures using Arrhenius modelling. Using a custom-designed apparatus to age the BGM under single-sided exposure, it is shown that degradation times are substantially longer in single-sided than in double-sided immersion experiments only for the mechanical properties. However, the bitumen coat degradation is not affected by the ageing method. Additionally, factors established from the relative degradation in the double-sided and single-sided experiments were used to shift the predictions of the tNF at field temperatures to the single-sided field exposure condition.
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    Hurricane-generated ocean wave propagation and impacts on a fringing reef in Hawai’i
    Zimmerman, Zoe; Civil Engineering; Mulligan, Ryan P.
    The Pacific Ocean surrounding the Hawaiian Islands is a region subject to strong storm events. Hurricane Hector and Hurricane Lane, successive offshore storms, had strong winds that generated large waves and impacted the islands in the summer of 2018. This study aims to investigate the ocean surface wave response to hurricane wind forcing across the ocean at a large scale and to understand the finer-scale processes of energy dissipation and the corresponding wave-driven circulation as waves break over a steep fringing reef. Hydrodynamic and wave modelling frameworks are used to develop two numerical models using SWAN and Delft3D-SWAN at different scales to investigate the ocean and coastal responses to the two hurricanes. In the first part of this study, a large-scale model that encompasses the entire Hawaiian Archipelago is developed and the surface waves generated using four different large-scale spatially varying wind fields are compared. These include a detailed atmospheric model input (CFSv2), a simple parametric hurricane wind model, the parametric model blended with CFSv2 winds, and this blended product with a limited maximum wind speed. The results indicate that the blended and limited wind field produces wave model predictions in the best agreement with bulk wave statistic observations at several ocean wave buoys. The model provides valuable results for the large-scale propagation of hurricane winds and waves, but the relatively low-resolution and large scale limits the use in providing detailed predictions at coastal observation sites. In the second part of this study, a fine-scale coupled hydrodynamic-wave model is developed for the south coast of Moloka’i. This area is comprised of a fringing coral reef and numerical model grids were developed to resolve the detailed reef morphology with high resolution. Results from the two energetic ocean wave events generated by the distant passing hurricanes were validated with wave and current measurements collected at multiple observation stations deployed by the US Geological Survey across a 1200 m wide cross-reef transect. The model, in combination with analysis of the field observations, was used to evaluate wave breaking over a steep reef face and the corresponding wave-driven energy dissipation and circulation to provide predictions of nearshore processes resulting from wave events generated by offshore hurricanes.
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    Biostabilization of mine tailings for improving wind erosion resistance
    Rezasoltani, Samira; Civil Engineering; Champagne, Pascale; Mann, Vanessa
    One of the leading anthropogenic origins of wind erosion is mine tailings; therefore, finding a sustainable practice for mitigating dust emissions from mine tailings is of critical importance. Cyanobacteria have shown promising results in the surface stabilization of erosion-susceptible soils in desert regions and moving dunes. However, little information is available on their application in mine tailings. Experimental studies were conducted to identify potential cyanobacteria that can survive in gold mine tailings. The experiments were carried out in Pb-containing BG110 media to stimulate nutrient-poor and metal-enriched conditions in gold mine tailings while isolating the impact of other variables. Two nitrogen‐fixing cyanobacteria, Anabaena sp. and Nostoc muscorum, were tested. Both cyanobacteria could sustain growth. However, Anabaena sp. showed better performance in resisting Pb(II) inhibitory effects. Hence, Anabaena sp. was selected for the tailings experiments due to its high resistance to metal toxicity, and N. muscorum was selected due to its reported ability to create biocrusts. The performance of Anabaena sp. and N. muscorum, individually and as a consortium, in creating biocrusts on gold mine tailings was investigated (inoculation-based method). The cyanobacteria showed complementary traits in improving the biophysicochemical properties of the mine tailings and inoculation using the consortium led to the formation of a stronger structure. The cyanobacterial consortium inoculation successfully created stable biocrusts, which significantly reduced wind erosion (0.85% vs. 81.99% mass loss), increased compressive strength (1.90 vs. 0.1 kg cm-2), and improved organic carbon (17.23 vs. 3.26 mg g-1 tailings) and nitrogen (3.89 vs. 0.036 mg g-1 tailings). A photosynthetically induced carbonate precipitation approach was assessed by inoculating N. muscorum with an essential substrate. The biocemented crusts showed superior performance in reducing wind erodibility compared to the inoculation-based crusts. The proposed strategy could not only overcome the environmental drawbacks of the ureolysis-driven carbonate precipitation but also take advantage of the beneficial effects of cyanobacteria in surface stabilization, biological CO2 sequestration, and N2 fixation. The work outlined in this thesis has contributed to mitigating dust emissions from gold mine tailings in an environmentally friendly and energy-efficient manner while laying the groundwork for the subsequent establishment of vegetation covers.