Browsing by Author "Shrive, Nigel Graham"

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    Effects of FRP Cross-wall Connectors in Multi-wythe Masonry Walls
    (2016-01-13) Elrayes, Mahmoud; Shrive, Nigel Graham; Valluzzi, Maria Rosa; Nowicki, Edwin Peter; Wong, Ron Chik-Kwong; Lissel, Shelley Lynn; Shrive, Nigel Graham; Priest, Jeffrey Alan
    The seismic performance of multi-wythe masonry walls is known to be generally poor, as they can exhibit local failure modes by wythe separation and collapse of the external wythes. For retrofitting them, it is widely acceptable to install transverse ties in combination with other intervention methods to provide proper connections between the wythes. The value of using transverse ties in heritage multi-wythe masonry walls has been questioned in recent research. Different finite element models were developed to simulate the behaviour of traditional transverse ties installed in multi-wythe walls. A simplified micro-model provided insight regarding stress transfer between the different elements of the system, and suggested that the traditional distribution of ties is inefficient. Macro-models were used to investigate the role of a single tie in resisting different loading conditions and found that the effect is minimal in most cases. The findings were in agreement with previous experimental research. An experimental program was performed to investigate non-traditional configurations and distributions of transverse ties. Large scale three-wythe walls were constructed and subjected to axial compression and lateral in-plane cyclic loads. Transverse ties made of FRP rebar were installed at different angles to the wall surface as opposed to the traditional leveled and perpendicular to the wall surface approach. Differences in the behaviour of the ties were observed including connection technique to the wall as well as the ability to transfer shear loads if placed in certain locations. Inclined transverse ties were grouped to form semi-continuous vertical, horizontal and diagonal elements to produce certain improvements in the structural performance of the wall in terms of lateral strength, stiffness degradation, energy dissipation, and post-peak behaviour.
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    An Experimental and Numerical Study on Metakaolin-based Geopolymers
    (2021-01-26) Ershad, Mohamadmahdi (Armin); Khoshnazar, Rahil; Moshirpour, Mohammad; Shrive, Nigel Graham
    Portland cement concrete, in its most basic form, is produced by mixing aggregate, Portland cement (PC), and water. High energy consumption and CO2 emissions associated with the production of PC have caused serious environmental issues, and PC production is now responsible for about 5-8% of the global CO2-equivalent greenhouse gas emissions. Extensive research has been conducted to develop new and more sustainable binders that can replace PC paste in concrete without compromising its performance. Geopolymers (GPs) are a class of these alternative binders attracting significant attention in the past few decades. They are produced by mixing an aluminosiliceous powder such as metakaolin (MK) with an alkaline solution. Several parameters such as composition and curing conditions influence the characteristics of GPs, and appropriate selection of material proportions is necessary to achieve the desired performance. This research aims to (i) model the compressive strength of MK-based GPs based on their composition and (ii) suggest new methods for enhancing the compressive strength of MK-based GPs. In the first part of this research, different GPs were prepared with two different grades of MK and various compositions. Machine learning models were then used to classify and predict the compressive strength of GPs using the dataset driven from the experimental plan of this research and the literature. Different models were tested, among which the extreme gradient boosting algorithm was able to classify the GPs with 80% accuracy in three levels of ‘low’, ‘medium’, and ‘high’ strength and predict the strength with R2 = 0.80 given the composition and test age. In the second part, a seeding method was used to improve the compressive strength of GPs. Three different types of zeolite seeds (hydrogen faujasite, sodium faujasite, mordenite) were used. The results showed that all the zeolites could improve the strength of GPs although hydrogen faujasite and mordenite seemed to be more effective than sodium faujasite.
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    Hydro-Mechanical Coupling and Failure Behavior of Argillaceous Sedimentary Rocks: A Multi-Scale Approach
    (2019-04-26) Eghbalian, Mahdad; Wan, Richard G.; Wong, Ron Chik-Kwong; Epstein, Marcelo; Priest, Jeffrey Alan; Regueiro, Richard A.; Shrive, Nigel Graham
    This thesis aims at characterizing the hydro-mechanical behavior of argillaceous sedimentary rocks within a novel poro-elasto-plasticity framework that encompasses micro-mechanics and a multi-scale approach. The developed model considers argillaceous sedimentary rocks to be comprised of a mixture of clay aggregates and rock-type inclusions. The clay fraction has a dual porosity arising from micropores at the clay aggregate level and nanopores between the clay platelets that form the clay aggregates. The rock-type inclusions also have a dual porosity due to the presence of microcracks embedded into a nano-porous rock matrix. As such, the work develops multi-scale modeling techniques that elucidate the complex macroscopic characteristics observed in clay-rich rocks by advocating only the primitive physical laws at their fundamental scales. The outcome is an analytical constitutive law that transcends the various scales: from nano- to macro-scale. Therefore, the swelling stress originating in the nano-pores of clay particles and capillary stresses in the porous network, as well as micro-crack growth can be readily computed as a function of microstructure and physics across the various scales. The developed model is implemented within numerical modeling frameworks such as Finite Element Method (FEM) and eXtended FEM. Lab experimentally observed phenomena in argillaceous sedimentary rocks such as plastic/swelling deformations of clay aggregates and the failure of rock inclusions through micro-crack growth are successfully replicated.
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    Mechanisms of Early Filling in the Left Ventricle
    (2021-01-08) Urroz Lopez, Maryell Giofred; Tyberg, John V. T.; Shrive, Nigel Graham; Belenkie, Israel; Sheldon, Robert Stanley; Fewell, James E.
    The mechanism by which ventricular filling occurs has been debated for centuries. Originally, it was believed that ventricular filling was an entirely passive process. However, in the 20th-century, researchers proposed that LV played a role in its own filling sucking blood into itself. At the early phase of diastole, the LV enlarges faster than it is able to fill passively by the Left Atrium (LA); therefore, aspirating blood into itself. Diastolic suction (DS) is the term applied to the phenomenon whereby the left ventricle (our study will be limited to the LV), in part, fills itself. Two approaches to study DS are the volume of filling due to suction, VDS (Katz’ approach), and the energy of the Backward Decompression Wave, BDW (Wang’s approach). Our first aim was to determine if DS exists at LV volumes that exceed the unstressed volume. Our second aim was to compare Katz’ Criterion to the energy of the BDW generated by the LV (Wang’s approach). The study was performed using a porcine model. Hemodynamics and mitral blood flow velocity were measured over a range of filling pressures during baseline, inferior vena cava occlusion (IVCO), and volume loading. Our findings suggests that the LV generates suction when ESV is greater than ESV at baseline (ESVB), which opposes the view that the LV is not capable of generating suction at increasing ESV’s. We found non-zero values of VDS and IW-DS when ESV>ESVB which suggest a non-recoil mechanism responsible for suction. In addition, our data shows that both approaches to DS, measured by VDS and IW-DS, are indeed related as they responded in the same manner to changes in EDV, ESV, and EDP.
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    Safety Analysis of a Historical Structure: Turner Valley Gas Plant - Absorption Building
    (2023-06-01) Burzic, Emina; Duncan, Neil Alexander; Shrive, Nigel Graham; Sudak, Leszek Jozef; Wong, Ron Chik-Kwong
    Canada is beginning to shift towards the reuse of existing structures to reduce environmental impacts [5]. This shift has created a new culture of structural conservation and the need for engineers to understand the procedure of structural assessment of existing buildings. Historical structures are a specific niche of existing structures that require a closer assessment. Many historic structures in Canada are deemed unsafe and are closed or of limited access to the public. An “unsafe” steel and concrete heritage building rebuilt between 1929 and 1933, known as the absorption building, has been analysed structurally with respect to the National Building Code of Canada (NBCC) and the Standards and Guidelines for the Conservation of Historic Places (SGCHP) [7] [4]. The building is located at the Turner Valley Gas Plant (TVGP) National Historic site [8]. The TVGP was Alberta’s first natural gas plant built and thus the birthplace of the energy sector in Western Canada [8]. Throughout the building lifespan the structural skeleton has been adapted to accommodate changes in the oil and gas processing. The load path, effects of modified and missing members, and capacity of elements were assessed. Due to a lack of historical records and the building designation, Non-destructive and Minor destructive testing methods were used to determine building geometric and material properties. Five finite element models were developed to conduct a linear-elastic analysis of the buildings structural integrity. A load test was performed to validate the models. Results confirmed the load path and the effects of modifying members as an initial assessment towards a complete safety analysis. Based on the NBCC if the past performance of the structure is considered insufficient and a structural analysis is conducted the results show plastic hinges will begin to form in the roof of the structure due to the applied loads. The research exposed gaps within current NBCC and SGCHP guidelines. Technical testing and clarification on the potential interpretations of the NBCC and SGCHP are recommended additions based on the research conducted. As standards are developed the research provided can guide future engineers on conducting a structural safety analysis of heritage structures.
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    Structural Behaviour of Masonry Arch Retaining Walls
    (2024-06-19) Rathnayake, Hasini Sumuditha; Shrive, Nigel Graham; Duncan, Neil Alexander; Wong, Ron Chik-Kwong; Sudak, Leszek Jozef; Malomo, Daniele
    Recently, a novel experiment explored the possibility of employing low-rise arch masonry walls to resist earth pressure. The system proved to have several advantages: minimal deflection, ease of construction, cost-effectiveness, and aesthetic appearance. The authors established that the idea could work but did not study the influence of any of the parameters involved. To address this limitation and to further investigate the performance of arch masonry retaining walls, six masonry arch walls were constructed using half-scale concrete blocks and modular cored bricks. The test walls had an equivalent span of 2 m and two different span-to-rise ratio, 0.17 and 0.35. The walls were built inside a rigid concrete tank, and the arch bases were cemented to the concrete base with a mortar joint. Arches were subjected to soil pressure and surcharge load: displacements and strains were measured. The walls demonstrated stability and maintained their structural integrity without significant lateral deformations. The experiment yielded successful results, as the arch masonry walls exhibited deflections less than 0.1% of the backfill height. A simplified finite element micromodel has been developed using ABAQUS software to simulate and study the structure in detail, allowing variation of the parameters intrinsic to such walls. The influences of the rise-to-span ratio, height, and grouting pattern on the performance of the arch were explored. For a given wall width, a curved hollow arch wall profile was found to increase the maximum sustained pressure more so than grouting a flat wall: for the same height and span, a curved hollow arched wall with a rise-to-span ratio of 0.25 resisted 37% more pressure than a grouted planar wall. Thus, by combining the information obtained from the experiment and the numerical modelling, masonry arch retaining walls may be seen as an economical and stable alternative to conventional methods of constructing earth-retaining structures.
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    Structural Behaviour of Spatial Arch Bridges
    (2017) Hudecek, Martin; Shrive, Nigel Graham; Sparling, Bruce; El-Hacha, Raafat; Sudak, Leszek Jozef; Wong, Ron Chik-Kwong; Priest, Jeffrey Alan
    This thesis investigates particular aspects of the structural behaviour of a new form of bridge structure called spatial arch bridge (SAB). SABs are designed to be outstanding pieces of architecture. Due to the enhancement in graphical and structural analysis software, the number of SABs is increasing. However, the complexity of SABs results in certain challenges in structural analysis and design. The unique combination of the arch, hangers, and deck result in the development of out-of-plane loads that significantly influence the structural response. This work focuses on SABs with an inferior deck suspended on flexible hangers (cables) below the arch. Three different spatial arrangements of the arch and deck are developed and analyzed to fill particular gaps in the current state of knowledge. Finite element analysis (FEA) is employed as the main analysis tool. Both linear and nonlinear parametric models are developed to address the objectives of the research. Ratios of primary and secondary geometric variables including arch rise, span, deck reach, and inclination or rotation of the parabolic arch are established to identify the trends in the structural response and to consider the effects of various types of loads. The significance of variability in the bending stiffness of the arch and the deck is studied to determine the optimal combination of these parameters that results in spatial configurations with minimal susceptibility to buckling as a function of particular types of end conditions of the deck. The work describes aspects of advanced composite materials (ACM), such as a low modulus of elasticity and time-dependent material properties in all-composite assemblies, and determines the applicability of commonly used durable structural profiles in SABs taking into account the nonlinear character of the cables and the effect of additional tensioning of the cables. The results of the large number of analyses conducted are summarized in tables accompanied with charts and schematic sketches that are intended to serve as guidelines when analyzing or designing structures similar in nature to the ones described in this work. Design criteria are proposed.
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    Towards High-Strength and Low-Carbon Concrete Masonry Blocks Using Locally Available Materials
    (2023-04-21) Zarrinkoub, Mohammad; Khoshnazar, Rahil; Shrive, Nigel Graham; Wong, Joanna
    High-strength concrete masonry blocks are attracting attention to be used for loadbearing applications, such as tall walls. Such blocks can be achieved via modification of the dry mixture design and production methods. These modifications, however, may increase the carbon footprint of the concrete masonry blocks upon manufacturing. Careful selection of the mixture parameters is, therefore, necessary for the production of concrete blocks that have higher compressive strengths yet low carbon footprints. This study explored the effectiveness of using locally available materials for the production of dry concrete mixtures that can be used for the masonry block manufacturing. First, the suitability of utilizing pumice, sourced in British Columbia, as an alternative for Class F fly ash to partially replace the Portland cement in the concrete mixtures was studied. That was important as the availability of Class F fly ash is declining in Alberta and finding alternative replacements is imperative. To overcome the lower reactivity and strength development of pumice, a performance enhancing chemical admixture was used. Finally, recycled aggregates were obtained by crushing and pulverizing concrete masonry blocks that were used for structural testing in the laboratory. The so-produced aggregates were used as a replacement for the natural aggregates in the production of the dry concrete mixtures without and with pumice and chemical admixture. The resulting dry concrete mixtures were categorized into different classes of 30, 35, 40, and 50 MPa based on their average compressive strength at the age of 28 days in the laboratory conditions. Their mixture proportion with respect to their cement intensity (cement content per unit of strength) and application was discussed, and recommendations for future research were made. It is worth noting that although the results of this study were obtained for producing dry concrete mixtures, they can be extended for other concrete applications.