Browsing by Author "Shrive, Nigel"
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- ItemOpen AccessAn Experimental Approach to Explore Abdominal Aortic Aneurysms in Rabbit Model(2017) Altamimi, Manal Nasser; Di Martino, Elena; Mitha, Alim; Shrive, Nigel; Appoo, JehangirThe diagnosis of an Abdominal Aortic Aneurysm (AAA) is currently made based on maximum diameter, which fails to accurately predict risks of rupture. The purpose of this study was to advance our understanding of AAA evolution using a rabbit model. AAAs were developed in rabbits using a periaortic incubation of CaCl2 and elastase. Rabbits were imaged using 3D angiography at 0 (healthy), 2, 4, and 6 weeks. Material properties and histological analyses were obtained for each stage. Results showed an increase in maximum diameter and wall thickness with aneurysmal tissue. The healthy aorta was stronger than all aneurysmal tissue. Tissue at 6 weeks had the stiffest and strongest properties compared to aneurysmal tissue. Elastin degradation and separation between wall layers was observed in all aneurysmal tissue with the highest collagen remodeling at 6 weeks. Because human aneurysms are diagnosed at an unknown time after initial formation, control animal experiments are necessary to understand the evolution of the mechanical and histological properties of the aortic tissue.
- ItemOpen AccessAn Instrumented Spatial Linkage to Measure In-Vivo Kinematics and Motion Reproduction with a Robotic Test System(2014-05-14) Rosvold, Joshua; Shrive, NigelDetermination of the mechanical environment of the knee joint is essential in order to understand the normal and pathological states of the tissues in that joint, mechanisms of injuries, and in developing and evaluating surgical interventions. A 6 degree of freedom Instrumented Spatial Linkage (ISL) was developed to record ovine stifle joint kinematics during normal treadmill gait, and reproduce those same motions in-vitro on a robotic testing platform in order to provide an in-vitro environment in which to examine the effects of in-vivo displacement on the soft tissues of the joint. The ISL was designed to provide increased accuracy, reduced processing time, and ease of use when compared to traditional motion capture methods. The ISL was evaluated dynamically to ensure that accurate results were maintained. The ISL and robotic test platform allow determination of the loads on the four major ligaments and the two menisci in the joint. Structural loads for 4 animals were determined for 20 representative strides beginning at hoof strike. Results showed similar loading patterns between animals but with some quantitative differences. With respect to the gait cycle beginning at hoof strike, the PCL reached a peak load just after hoof strike (5%) followed by rapid unloading. The ACL was loaded immediately thereafter with a peak at about 10% of gait. The MCL tended to follow the PCL but with a much reduced force magnitude. The LCL was largely unloaded throughout, suggesting that this ligament must play a more prominent role in other motions. For three of the four animals the average meniscal load was nearly even between the lateral and medial menisci, the fourth animal carried an average of 46.9 N more load in the lateral meniscus. Linear correlations between joint structures and kinematics were attempted but no strong correlations existed. Additionally, ligament length was also shown to be a poor predictor of ACL load. A method is proposed whereby an Artificial Neural Network can be constructed as to accurately predict ACL load given relative joint position and orientation. This study shows for the first time the loads experienced by all 4 major ligaments of the knee, and the minimum loads in the menisci in response to in-vivo motions. The load in each structure has been shown throughout gait and future studies can look at a variety of different motions and loading situations.
- ItemOpen AccessBehaviour and design of slender masonry walls at full- and half-scale subject to axial eccentric loads(2023-08) Iskander, George Sami Aziz Salama; Shrive, Nigel; Wong, Ron; Duncan, NeilThe behaviour of slender concrete masonry walls is poorly understood. This is particularly evident by the treatment of such walls in the Canadian masonry design standard, CSA S304-14. Many researchers have noted the poor accuracy of CSA S304-14’s provisions and the need for more experimental data. A major limiting factor to building and testing walls is their size and the quantity of materials used. This limitation can be overcome by using half-scale walls – however, it must first be proven that scale effects do not influence the results obtained. Of further utility would be a verified finite-element model to predict wall failure loads and modes with a high degree of confidence. Towards these ends, twelve masonry walls, six at full-scale and six corresponding half-scale walls, were built and tested under an axial load with an eccentricity of 1/3 of the wall thickness; single curvature moment was applied. Digital image correlation (DIC) was used to acquire lateral displacement data; its implementation in this study is presented. Specimen handling procedures are also presented. Wall strengths, lateral displacement profiles and behaviour were recorded and are presented. Experimental results show that size effect does not influence the behaviour and strength of slender concrete masonry walls at half-scale. Experimental results are used to discuss shortcomings in CSA S304-14’s treatment of wall effective stiffness. A verified finite element model was also used to investigate the failure load and mode of 80 hollow masonry walls, with varying effective height to thickness ratio, eccentricity, and inclusion of initial geometric imperfection. Numerical results are used to determine when the inclusion of geometric imperfections impacts numerical predictions, and to determine wall failure modes for various parametric combinations. The model is also used to discuss adjustments to clauses in CSA S304-14 related to minimum primary moment and hollow masonry wall axial strength.
- ItemOpen AccessBond Strength of Adhered Manufactured Thin Stone/Brick Masonry Veneer Units to Setting Bed Mortar at Different Temperatures and Different Cycles of Freeze-Thaw(2021-05-14) Rizaee, Samira; Shrive, Nigel; Duncan, Neil; Khoshnazar, Rahil; Husein, Maen; Feldman, LisaClose to no study has been conducted to identify the possible influential physical and mechanical characteristics of adhered thin masonry units and mortars on the bond strength in adhered thin masonry veneer (ATMV) applications. There have been numerous cases of bond failures in ATMV applications probably due to lack of knowledge and the lack of any standards for the design and installation of ATMV. In the Canadian climate, exposure to extreme weather conditions like very low temperatures and freeze-thaw cycles are common and may be a cause of bond deterioration and failures. Therefore, it is important to study the effects of exposure to extreme weather conditions on the bond strength. This research first measures and evaluates the physical and mechanical properties of thin masonry units and mortars. Then shear and tensile bond strengths are studied considering different age and environmental factors. At least three different ages, two different curing temperatures, three testing temperatures and four cycles of freeze-thaw were considered. Subsequently, any possible relationship between these characteristics and bond strengths were evaluated and proper practices were recommended.
- ItemOpen AccessDiagonal Shear Of Partially Grouted Concrete Masonry Panels(2013-04-29) Oan, Ahmed; Shrive, NigelMasonry shear walls are the main structural elements that resist in-plane lateral loads applied to a masonry building. The current Canadian Code assumes the shear resistance of a masonry wall to be the sum of two components: the shear resistance of the masonry and the shear resistance of horizontal reinforcement. This assumption is a point of debate with respect to other codes and design expressions. The results of estimating the shear resistance with the Canadian Code design formula are very conservative as they significantly underestimate the shear resistance of walls. In the current study, the behaviour of sixty six concrete masonry walls with the same aspect ratio but with different methods of reinforcement, axial stress, methods of construction and grouting was investigated. The aim of the study was to understand the shear behaviour of concrete masonry walls better and to investigate the influence of changing each variable on the shear strength of the walls. In this study, the results were analyzed using different statistical methods to identify the significance of the variation between the results obtained. Finally, based on the results, a new formula for predicting the shear strength of concrete masonry walls with aspect ratios less than 2 is proposed. The formula was examined against test results reported in literature and the results of the tests described in the thesis. The formula proved on average to estimate the shear resistance of all the walls better than other code and design expressions and with less variability.
- ItemOpen AccessDifferences in Bone and Cartilage Between Women with Anterior Cruciate Ligament Tears and Healthy Controls(2017) Bhatla, Jennifer; Boyd, Steven; Dunn, Jeffrey; Shrive, NigelAnterior cruciate ligament (ACL) tears increase the risk of osteoarthritis (OA) leading to degradation of cartilage and bone. While the contribution of bone in OA development is unclear, evidence suggests that bone changes accompany cartilage degradation. This study aims to explore the relationship between subchondral compact bone thickness and cartilage thickness by comparing women with ACL reconstructions (ACLR) 5 years post-injury to uninjured controls using magnetic resonance imaging (MRI) and high resolution peripheral quantitative computed tomography (HR-pQCT). We found that ACLR knees had thicker subchondral compact bone in the lateral femur than contralateral knees (12.9% thicker, p=0.013) and injured participants had more subchondral compact bone thickness side-to-side variation than controls (>6.4 times increase, p<0.004). We did not detect cartilage thickness differences (p>0.06). This study demonstrates that subchondral compact bone thickness differences are prominent following injury, as measured by HR-pQCT, which may provide novel insight into OA pathogenesis.
- ItemOpen AccessDirect Measurement of the Change in In-vivo Stresses in Ovine Stifle Joints following Trauma Using Fiber Optic Sensors(2019-04-30) Vakiel, Paris; Shrive, Nigel; Dennison, Christopher; Hart, David; Bertram, John Edward Arthur; Sadak, Leszek Jozef; Fleming, BradenUnderstanding stresses within the joint is central to understanding the etiology and progression of osteoarthritis (OA), as well as the effects of clinical interventions meant to slow or halt OA progression. It’s been hypothesized that a change in stress is a significant factor in the initiation and progression of post-traumatic osteoarthritis. Without a reliable method for measuring stress this hypothesis has largely gone untested. This study was aimed at testing this hypothesis by developing and implementing an alternative stress sensing technology. Currently the most widely used method for measuring contact stresses is stress sensitive films. Their use requires a significant amount of dissection and removal of biomechanically relevant structures. Their presence in the joint alters the natural mechanics and the lubrication properties of the joint. There are also significant errors associated with the thickness and curvature, and modulus dependency resulting in large errors and unreliable data. To address the existing knowledge gap small fibre optic sensors capable of measuring normal stress between contact surfaces in diarthrodial joints were developed. The small size of these sensors (diameter of 125-300 μm and sensing length of 1 mm) allows these sensors to be inserted into the joint space without the removal of biomechanically relevant structures. Fibre optic sensors specifically designed to be inserted into ovine knee joints were used to measure in-vivo stresses on the surface of the cartilage for both healthy and surgically damaged joints. Undeniably the most important finding of this study was the correlation iii between changes in average and peak stress values following trauma and the likelihood of the development of focal damage at each position signaling the onset of post-traumatic osteoarthritis. Another important result in the non-uniformity of stress under the meniscus. This study successfully addressed many of the challenges associated with the use of fibre optic sensors to obtain repeatable in vivo stress measurements, validating an innovative technique for measuring stresses in the knee joint. Along with our capability to reproduce invivo motions accurately and the improvements of fibre optic technology, this study is the first accurate, direct measurement of stress in a joint during in-vivo gait replication.
- ItemOpen AccessEffect of aging on tibiofemoral cartilage and meniscal stiffness(2017) Ritchie, Brodie; Ronsky, Janet; Shrive, Nigel; Edwards, BrentKnee osteoarthritis (OA) is a prevalent degenerative cartilage disease characterized by degradation and loss of articular cartilage. Current OA diagnosis methods are ineffective at detecting and monitoring early signs of degeneration in the joint. Changes in mechanical properties of the tissue such as stiffness, or ability to resist compressive load, could present a more sensitive measure for the detection of early OA. This study has developed a novel methodology for the in-vivo measurement of tibiofemoral cartilage and meniscal stiffness using dual fluoroscopy (DF) and magnetic resonance (MR) imaging. This study further aimed to advance understanding of changes in cartilage and meniscal stiffness with normal aging, as age is generally believed to be a leading risk factor for OA. Two groups of five normal males (20-30 and 50-60 years of age) were tested to determine median cartilage and meniscal stiffness over a 5-minute static loading trial. Cartilage and meniscal stiffness was found to significantly increase by 12.51 N/mm (p=0.009) with age. The 20-30 year old group median was 3.39 N/mm (interquartile range (IQR)=2.01-7.29 N/mm) while the 50-60 year old group median was 15.90 N/mm (IQR=11.35-21.17 N/mm). This study contributes toward advancement of early OA clinical diagnostics by demonstrating the presence of significant changes in cartilage and meniscal stiffness with normal aging.
- ItemOpen AccessEnabling Resilient Structures with Repeated Post-Tensioning Using Novel Iron Shape Memory Alloy System(2023-09-19) Forrest, Benjamin Thorne; El-Hacha, Raafat; Shrive, Nigel; Duncan, Neil; Federico, Salvatore; Billah, Muntasir; Alam, ShahriaThe degradation of reinforced concrete (RC) structures like bridge girders is concerning and emphasizes the need to invest in sustainable design practices. A proactive maintenance program employing an incremental post-tensioning (IP) technique should increase the service life of structures by inhibiting the ingress of moisture and harmful environmental agents which contribute to their degradation. IP is achieved using the shape memory effect of iron shape memory alloy (Fe-SMA) which recovers deformations (representing a period of degradation) from preloaded beams. Eight beams were tested in a four-point bending configuration to validate the Fe-SMA prestress-strengthening system (FPSS). The deformation from varying preload amounts and subsequent recovery of those deformations from activating the FPSS were investigated to validate the capability of the system and demonstrate how the proactive maintenance approach enables structural resiliency. The beams were constructed of carbon nanofiber-infused, ultra-high-performance, fibre-reinforced concrete (CNF-UHPFRC), which couples the benefits of IP with the exceptional mechanical properties and contribution from the steel fibres and CNF. The IP beam had comparable flexural performance as that of the beam preloaded to 45% (beam ID PS30) of the reference load (68 kN, yield load of the beam strengthened with a non-activated Fe-SMA strip), even though it experienced a larger preload (75% of the reference load). Also, the results of beam IP showed structural resiliency in terms of crack widths and deflections. The midspan deflection at 45% of the reference load (representing a service load on the girder) for PS30 and beam PS60 (preloaded to 90% of the reference load) was 7.20 and 5.09 mm, respectively while it was 4.93 mm for the IP Beam. The bottom crack widths at 90% of the reference load (60 kN) for PS30 and PS60 were 0.61 and 0.79 mm, respectively while it was 0.5 mm for the IP beam. The yield loads for PS30 and PS60 were 70.85 and 76.11 kN, respectively, while it was 71.98 kN for the IP beam. The ultimate loads for PS30 and PS60 were 72.78 and 77.64 kN, respectively, while it was 72.75 kN for the IP beam. IP experienced a less ductile failure than PS60.
- ItemOpen AccessExperimental Investigation on the Shear Strength of Masonry Prisms(2024-05-13) Farjad, Sahar; Shrive, Nigel; Sudak, Les Jozef; Wong, Ron Chik-KwongMasonry structures are used ubiquitisly all over the world from many years ago till today. However, there are still lots of unknowns in terms of their behavior. These ambiguities become even more significant when the structure is exposed to the shear loads. In addition, the Canadian masonry standard has been the focus of numerous studies, and it was shown that this standard might be improved in many aspects regarding the shear strength of masonry. In this study, first the variability of the mortar joint thickness in both brick and concrete block masonry was explored. Then, considering these variation, experimental tests were conducted to investigate the effect of mortar joint thickness on the shear strength of triplet masonry prisms made with concrete blocks. With regard to the conflict that exist in the literature about the effect of mortar type on the shear strength, it was another parameter investigated by a series of experiments. As evidenced by the results of this study, mortar type in fully grouted (FG) and partially grouted (PG) prisms was not an influencing parameter on the shear strength, as well as mortar joint thickness of fully-grouted prisms. It was shown that joint thickness did affect the shear stiffness though. In fact it was argued that mason experience and proficiency affect the shear stiffness and not the shear strength of FG prisms in this study. However, this study showed that mortar joint thickness does have some effect on the shear strength in hollow masonry prisms. According to the results the higher joint thickness showed less shear strength. Although to conclude this as a general rule, more experiments are required.
- ItemOpen AccessFlat Arch Masonry Retaining Wall(2020-08-21) Kurukulasuriya, Maithree Chiranthya; Shrive, Nigel; Wong, Ron Chik Kwong; Dann, Markus R.; Federico, SalvatoreThe inherent strength and durability of masonry arches is eminent through many historical structures still existing to this day. Amidst a wide range of retaining wall types and applications available, the concept of utilizing masonry arches as earth retaining structures is surprisingly unprecedented in the recent past. In this research, a novel masonry low-rise arch retaining wall is introduced. An experimental programme was implemented to explore the feasibility of the proposed earth retaining system, where a full-scale, concrete block arch wall was constructed between two rigid abutments and backfilled with soil. Surcharge loading was also applied to the backfill soil to explore the stability of the wall under additional dead loads. The concept is that the blockwork wall will resist the lateral pressure through arch action, avoiding “snap-through” of the wall. The response of the wall to the soil pressure, compaction and surcharge loading was monitored by observing deflections and strains in the wall. Furthermore, one half of the wall was fully grouted, while the other half was left hollow to compare the behaviour of the grouted and un-grouted masonry. Retaining walls are typically constructed using concrete, steel, masonry or timber. The use of concrete blocks in this instance was desirable due to its strength, ease of construction, cost effectiveness and aesthetic appearance. This makes such a wall ideal for low-rise retention, opening a new market in which masonry can compete. From the results of the experimental study, the efficacy of the proposed masonry arch retaining wall was substantiated with deflections less than 1.3% of the least dimension of the wall, compressive stresses well within the elastic range of masonry and no cracks observed in the visible region of the wall.
- ItemOpen AccessA framework for pipeline corrosion growth modeling tailored to mass in-line inspection data(2019-08-30) Birkland, Monica; Dann, Markus R.; Shrive, Nigel; Hugo, Ronald J.The integrity management of existing oil and gas pipelines is vital to avoid failures with potentially severe consequences. As many existing pipelines are constructed of steel, corrosion poses a significant threat to the integrity of these pipelines, in-line inspections are periodically performed, and a corrosion growth analysis is used to predict the future state of the pipeline. Currently, there is no standard or guideline for a corrosion growth analysis; and since there are many uncertainties surrounding corrosion, it is difficult to navigate. Additionally, in-line inspections, particularly for upstream and subsea pipelines, often lead to large datasets and the reported data is subject to measurement error. This framework proposed in this thesis is a generalized, step-by-step approach for performing a corrosion growth analysis designed to accommodate for a mass dataset with measurement uncertainty while also allowing for other scenarios. The objectives of this research are primarily to provide consistency of the corrosion growth analysis process, while also improving the efficiency and to provide guidance and advice throughout. An example is carried out from start to finish and the results presented to demonstrate how the framework can be used in practice.
- ItemOpen AccessGait Entrainment in Coupled Oscillator Systems: Clarifying the Role of Energy Optimization in Human Walking(2020-01-13) Schroeder, Ryan T.; Bertram, John E. A.; Croft, James L.; Sawicki, Gregory S.; von Tscharner, Vinzenz; Shrive, Nigel; Cluff, Tyler; Rubenson, JonasEmpirical evidence suggests that parameters of human gait (e.g. step frequency, step length) tend to minimize energy expenditure. However, it is unclear if individuals can adapt to dynamic environments in real time, i.e. continuously optimize energy expenditure, and to what extent. Two coupled oscillator systems were used to test the learned interactions of individuals within dynamic environments: (1) experienced farmworkers carrying oscillating loads on a flexible bamboo pole and (2) individuals walking on a treadmill while strapped to a mechatronics oscillator system providing periodic forces to the body. Reductionist trajectory optimization models predicted energy-minimizing gait interactions within the coupled oscillator systems and were compared to experimental data assessed with linear mixed models. On average, pole carriers significantly adjusted step frequency by 3.3% (0.067 Hz, p=0.014) to accommodate the bamboo pole – consistent with model predictions of energy savings. Novice subjects entrained (i.e. synchronized) their step frequency with machine oscillations up to ±10% of preferred step frequency and at amplitudes as low as 5% body weight (or ~33 N). Still, some subjects rarely entrained at all, and many exhibited transient entrainment, i.e. they drifted in and out of step frequencies matching the machine oscillations. Overall, subject entrainment was more robust and consistent with lower frequencies and higher amplitudes (20-30% of body weight). Although no systematic difference was found between the metabolic consumption of subjects during and not during entrainment, the net mechanical work done on subjects by the force oscillations had a strong effect on metabolic output (p<0.0001). Net work was largely determined by the alignment of oscillation forces within the gait cycle. Both the optimization model and subjects aligned force oscillations with their body velocity to increase positive power. All in all, it seems that subjects prefer entrainment with environmental oscillations under certain circumstances. However, entrainment does not appear to be motivated by energetic cost, at least not directly and not as a first priority. It is possible that individuals stabilize interactions with the environment (e.g. entrainment) as a prerequisite for effective feedforward and/or feedback gait control.
- ItemOpen AccessHistoric Reinforced Concrete in Alberta: Analysis and Conservation of Two Structures(2018-09-14) Rouhi, Alireza; Shrive, Nigel; Vera, Jacqueline; Ingham, Jason Maxwell; Lissel, Shelley L.; Duncan, Neil A.The Brooks Aqueduct and the Greenhill mine tipple structure were built in the turn of the twentieth century in southern Alberta. They were among the first reinforced concrete structures to be built in that region and are considered great engineering and construction achievements for their time. They were both built at a time when there was no standard for the design of reinforced concrete structures in North America and lots of issues about the concrete design and construction, especially from the durability point of view, were still unknown. Both structures had a great impact on the economy of their local regions and now are designated as national and provincial historic sites respectively. Frequent repair and maintenance became necessary from the early stages of operation of Brooks Aqueduct due to design and construction deficiencies. Both structures show significant signs of damage and deterioration and need to be evaluated and properly repaired and maintained. This research involves evaluation of the two structures through site inspections and laboratory tests on the samples taken from them. The work also involves numerical modelling of the structures to identify areas of possible over stress and find the main causes of damage and deterioration. Several similarities and differences are found between the concrete used in these structures and their deterioration mechanism. The main goal in evaluation and repair of Brooks Aqueduct is to maintain it as a monument and an engineering and construction achievement. In the case of the Greenhill mine tipple structure, two scenarios were studied: adaptive reuse as a restaurant and maintaining the structure as a monument. Results of the analyses show that although there was clear lack of understanding about the behaviour of concrete in the design of these structures, most of the damage and deterioration are non-structural and has happened due to durability issues mainly from exposure to freeze-thaw cycles and corrosion of the reinforcement. Service life analysis of the two structure is also performed based on theoretical models and test results. Recommendations for extending the remaining service life and conservation and retrofitting of the two structures and similar cases are provided based on the results of the tests and analyses. The research identifies common types of problems in historic reinforced concrete structures constructed in Alberta in the early twentieth century and ways to recognise and overcome these problems. The results also emphasize that in evaluation of concrete from the early twentieth century, one has to look for certain problems such as lack of resistance against durability issues (mainly freeze-thaw and carbonation), lack of precision in placement of the reinforcing steel (rebar), lack of rebar splice lengths, lack of proper cover of concrete and lack of proper grading and selection of aggregates.
- ItemOpen AccessIn-Plane Core Fill Strengthening of Concrete Block Masonry Shear Walls(2017) Harris, Ryan Timothy; Lissel, Shelley; El-Badry, Mamdouh; Shrive, Nigel; Sudak, Leszek; Sherwood, EdwardGiven the observed poor performance of unreinforced concrete block masonry walls in recent earthquakes, there is significant demand in Canada and internationally for economical methods to improve the seismic performance of such walls. Common retrofit methods such as the application of external fibre reinforced polymer sheets, installation of conventional steel reinforcement or post-tensioning are often expensive, and visually intrusive. The proposed retrofit method involves filling the internal void space of concrete block walls with grout or a similar material that hardens after installation. This approach has been examined in a few studies, but has yet to be studied comprehensively. Herein referred to as core fill strengthening, this method has the potential to be a simple, unobtrusive and cost effective retrofit. In the current study, two core fill types, steel fibre reinforced grout and two part polyurethanes, have been examined. This was done through tests at a material level, tests of small masonry assemblages and tests on full scale masonry walls. These tests were coupled with finite element analyses of the various core fill materials, and later finite element models of full scale walls. Experimental results were then used to develop equations to predict the strength of core filled walls under in-plane shear failing in flexure, diagonal shear and sliding. Results indicate that core fill materials can improve both the strength and ductility of masonry walls in diagonal shear and flexure, and that further investigation into both polyurethane and steel fibre reinforced grout retrofits is justified.
- ItemOpen AccessInnovative Near-Surface Mounted Iron-Based Shape Memory Alloy for Strengthening Structures(2017) Rojob, Hothifa; El-Hacha, Raafat; Shrive, Nigel; Duncan, Neil; Priest, Jeffrey; Sudak, Leszek; Al-Mahaidi, RiadhA recent development of smart materials called Iron-based Shape Memory Alloys (Fe-SMA) envisages a new perspective in the rehabilitation of structures. SMAs are metallic alloys that recover their original shape through heating. Utilizing this interesting feature of SMAs to retrofit reinforced concrete (RC) beams is the main objective of the current research project. An innovative active self-prestressing technique using Near Surface Mounted (NSM) Fe-SMA bars/strips for flexural strengthening of RC beams is proposed. The pre-strained (elongated) Fe-SMA bar/strip is anchored in a pre-cut groove in the tension side of the RC beam; heating the bar/strip will then trigger the recovery of the induced strain (i.e. the bar/strip tendency to shorten). However, due to the restrained ends of the bar/strip, a tensile force develops instead (i.e. prestressing force). In this case, no jacking tools or special anchorage systems are required. The main objective of this study is to examine the potential capability of the newly developed Fe-SMA as an active retrofitting material for RC beams. Consequently, its contribution to the flexural performance enhancement of the RC beam at service and ultimate load conditions was investigated. In addition, the long-term performance of the strengthened beams subjected to freeze-thaw cycles and fatigue loading was studied. In total, 11 RC beams were tested; 7 beams with a length of 2 meters and 4 large-scale beams with a length of 5 meters. The experimental test results revealed the effectiveness of the proposed technique in enhancing the flexural capacity of the RC beams at the service and ultimate load conditions, while maintaining a ductile failure mode similar to the under-reinforced beams. The strengthened beams tested under severe freeze-thaw cycles and fatigue loading showed a good performance except for the bonding between the Fe-SMA bars and the grout which experienced a rapid deterioration and resulted in a rupture of the Fe-SMA bar at the anchorage location under fatigue loading.
- ItemOpen AccessKnee joint biomechanics in ovine models of post-traumatic osteoarthritis(2018-08-23) Shekarforoush, Seyed Mohammad Mehdi; Shrive, Nigel; Hart, David A.; Goldsmith, Peter B.Post-traumatic osteoarthritis (PTOA) is a sub-type of osteoarthritis, which can develop after injury to a joint and to date, many aspects of the etiology of the disease remain unclear. The main objective of this research was to quantify the subtle changes in the kinematic and the kinetic variables in the ovine stifle (knee) joint following different types of ligamentous and meniscal injury, and to investigate possible consequences of those biomechanical changes on gross morphological osteoarthritis-like damage in the joints. Overall, there was a high degree of inter-subject variability in the measured variables. We found different degrees of instabilities in the 6 degree-of-freedom kinematics and finite helical axis variables of the joints after ligamentous and meniscal injuries. Nevertheless, we did not detect correlations between the magnitudes of the changes in the kinematic variables with significant change and osteoarthritis-like damage in the joints. The kinematic analyses also suggest that the absolute change of the tibiofemoral translation vector could be an important risk factor for osteoarthritis development after ligament injuries. The magnitude of the joint angular velocities was decreased in extension during swing after different types of injury and the reduction was correlated with the morphological damage for two multiple ligament injury groups. We also found a weak correlation between the increase in some components of the tibiofemoral sliding velocity during stance after partial- anterior cruciate ligament (ACL) and medial collateral ligament (MCL) transection (p-ACL/MCL Tx) and the joint morphological damage in both the lateral and medial compartments of the joint. Kinetic analyses demonstrated a reduction in LCL load, slight increase in the PCL load and a consistent increase in the healed MCL load, especially during the stance stage of gait, after p-ACL/MCL Tx. Overall, the medial meniscus carried a higher magnitude of load than the lateral meniscus and the magnitude of the medial meniscus load was increased consistently in the animals through some parts of the gait cycle, 20 weeks after p-ACL/MCL Tx. No correlation was detected between variation in the meniscal loads and morphological damage in the joints, suggesting that the increase in the meniscal load after p-ACL/MCL Tx might not result in visible post-traumatic osteoarthritis damage in the short term after injury in an ovine model. Finally, we did not detect any consistent correlation between the changes in the ligament or meniscal loads and changes in analyzed kinematic variables, suggesting that ligamentous and meniscal loading regimes are not linear functions of different kinematic variables. The results improve our insight on how joint mechanical abnormalities can result in the development of post-traumatic osteoarthritis.
- ItemOpen AccessMechanisms of Early Filling in the Left Ventricle(2017) Burrowes, Lindsay; Shrive, Nigel; Tyberg, John; Sudak, Les; Thompson, Richard; Mehta, Sudarshan (Raj)Filling of the left ventricle (LV) occurs in two phases; early filling and late filling. Late filling, the mitral flow “A-wave”, is a result of the left atrial contraction. Early filling, manifest as the “E-wave”, is thought to be substantially due to diastolic suction (DS), a phenomenon whereby the LV aspirates blood and fills itself independent of atrial activity. The presence and importance of DS has been the source of much debate within the scientific literature, dating back to the early 20th century. It has been said that DS is important in order for the LV to fill efficiently as the heart adjusts to varying demands, for example, an increased heart rate due to exercise. The presence of a favourable pressure gradient (PG) that drives blood flow from the LA towards the LV has been well established. Additional studies have shown that, under abnormally small end-systolic volumes (ESV), or, with impeding LV inflow, a negative transmural pressure is recorded, which was considered evidence of suction. The purpose of this study was to vary the working conditions of the heart in a porcine model, and measure DS in two different ways and compare these measures of DS to ESV as well as ejection fraction (EF). By varying the working conditions of the heart using drug interventions (isoproterenol, phenylephrine & metoprolol), as well as volume loading, the amount of DS at different states was determined. The volume of filling due to suction, VDS, as well as the amount of energy resulting from suction (via a backwards decompression wave, BDW), are both indicative that ESV decreases as the amount of DS increases. As EF increased, both measures of DS also increased. Additionally, results for VDS display that DS is still present at ESV larger than baseline ESV. Finally, comparing the two measures of DS to each other showed good agreement. DS is often suggested to be a result of elastic recoil of the LV after contracting below an unstressed state. However, our findings that VDS exists at large ESV would contradict that DS is only a result of elastic recoil, suggesting that further studies must be conducted focusing on DS at large ESV.
- ItemOpen AccessMode I and Mode II Fracture Toughness of Montney Shale under Confining Pressure(2019-01-22) Chen, Qiang; Wong, Ron C. K.; Shrive, Nigel; Wan, Richard; Lines, Laurence R.; Martin, Charles DerekThis thesis investigated the geomechanical properties of Montney shale using uniaxial compression, triaxial compression, Brazilian, semi-circular bending (SCB), straight-notched disk-bending (SNDB) and double shear (DS) tests. The volumetric strain method (VSM), crack volumetric strain method (CVSM), axial strain response method (ASR), and lateral strain response method (LSR) along with the crack axial and lateral strain method (CALSM) were employed to determine the crack closure and crack initiation stresses under uniaxial and triaxial compression. The LSR and ASR methods depend heavily on the initial portion of the stress-strain curve. Thus, at least two or three methods should be used when determining the crack stress thresholds. The Mode I fracture toughness under confining pressure was measured using SNDB samples with crack length to thickness ratios of about 0.2 and 0.4, respectively. The application of confining stress might induce tensile crack at the top of the SNDB sample with crack length to thickness ratio around 0.4. The tensile stresses achieved around the crack tip in confined SNDB tests under crack initiation load are close to the tensile strength of the sample and not affected by confining pressure. The Mode I fracture toughness of Montney shale is independent of confining pressure. The Mode II fracture toughness and shear fracture energy of Montney shale were measured using DS tests. The shear fracture energy values determined from post-peak portion of the axial force-displacement curve are always higher than those converted from the Mode II fracture toughness. However, with increasing confining pressure, the amount of difference decreases. Under confining pressures ranging from 0 MPa to 30 MPa, the Mode II fracture toughness and shear fracture energy increase with confining pressure. For confining pressure greater than 30 MPa, the double shear sample tends to behave ductile, evidenced by the multiple shear fractures branched out from the main shear fracture. Consequently, the double shear test is only suitable for determination of the Mode II fracture toughness of rock with confining pressure below 30 MPa.
- ItemOpen AccessModelling In-plane Shear in Partially Reinforced Concrete Masonry(2018-06-25) Pan, Huina; Shrive, Nigel; Wong, Ron; Sudak, Leszek JozefDiagonal cracking is the most commonly reported mode of failure for masonry walls subject to in-plane shear loads. Finite element studies were therefore carried out to seek better understanding of this failure mode by attempting to capture the diagonal shear cracks in unreinforced concrete masonry and partially grouted/reinforced concrete masonry. Some key parameters (such as boundary and loading conditions, axial stress, and wall aspect ratio) were examined in the research. Interaction between axial stress and aspect ratio has been noticed. Diagonal compression “strut” was identified from contour plots of principal compressive stress, and therefore two distinct “strut” widths were proposed to account for strength and stiffness of the wall separately. Last but not least, effect of relative panel-to-“frame” stiffness ratio (represented by effective panel-to-frame modulus ratio in this study) has been observed through modelling in partially grouted/reinforced walls. This is rather an important step toward understanding the failure patterns of partially grouted masonry since this factor has not received much attention in the literature.