No description available.

Seismic tomography is a promising tool to help understand and evaluate the stability of a rock mass in mining excavations. Lab measurements give evidence that velocities of seismic wave propagations increase in high stress areas of rock samples. It is well known that closing effects of cracks under compressive pressures tend to increase the effective elastic moduli of rocks. Tomography can map stress transfer and redistribution and further forecast rock burst potential and other seismic hazards, which are influenced by mining. Recorded by seismic networks in multiple underground mines, arrival time of seismic waves and locations of seismic events are used as sources of tomographic imaging survey. An initial velocity model is established according to properties of a rock mass, then velocity structure is reconstructed by velocity inversion to reflect the anomalies of the rock mass. Mining-induced seismicity and double-difference tomographic images of rock mass in mining areas are coupled to show how stress changes with microseismic activities. Especially, comparisons between velocity structures of different periods (before and after rock burst) are performed to analyze effects of rock burst on stress distribution. Tomographic results show that high velocity anomalies form in the vicinity of rock burst before the occurrence, and velocity subsequently experiences a significant drop after the occurrence of rock burst. In addition, regression analysis of travel time and distance indicates that the average velocity of all the monitored region appears to increase before rock burst and reduce after them. A reasonable explanation is that rock bursts tend to be triggered in highly stressed rock masses. After the energy release of rock bursts, stress relief is expected to exhibit within rock mass. Average velocity significantly decreases because of lower stresses and as a result of fractures in the rock mass that are generated by shaking-induced damage from nearby rock burst zones. Mining-induced microseismic rate is positively correlated with stress level. The fact that highly concentrated seismicity is more likely to be located in margins between high-velocity and low-velocity regions manifests that high seismic rates appear to be along with high stress in rock masses. Statistical analyses were performed on the aftershock sequence in order to generate an aftershock decay model to detect potential hazards and evaluate stability of aftershock activities. / Ph. D.

To manage China’s growing demands of electricity, more and larger dams could be a part of the solution. It is important to evaluate and perform safety analysis for existing dams, in order to improve our understanding and knowledge about future dams. In this master thesis, a safety research of Longtan Dam on the Hongshui River in China was analysed. The main objectives in this research were to construct a 3D model and determine the critical points of large stress, strain and yield area in the dam for different cases.The factor of safety for sliding when primary loads were acting on the dam was calculated to be 0.50 for the non-overflow section of the dam and 0.48 for the overflow section. A safety factor against overturning was also calculated for the non-overflow and overflow section to 2.24 and 1.96 respectively. The results showed that the dam was safe from both sliding and overturning. The numerical results for distribution of stress, strain and yield area were simulated in 3D models by using ANSYS, a finite element program. Several cases for non-overflow and overflow sections of Longtan Dam were analysed for different heights and load combinations. For the first three cases where only self-weight was applied on the dam, high impacts of stress and strain were located at the dam heel, toe and at the largest maintenance tunnel of the dam. Appearance of plastic strain was also found around these areas. However, when primary loads were applied to the dam sections, the values of stress and strain became larger, especially in the toe area. In the last case when the dam was subjected to seismic activity, the distribution of stress and strain along the z-direction (along the dam) showed an uneven distribution, hence showing the importance of simulation in 3D.

Apesar dos pesquisadores afirmarem que os materiais odontológicos restauradores, devido às suas diferentes propriedades mecânicas, influenciam na transmissão da carga para os tecidos de suporte, não foi encontrada comprovação científica concludente. Os trabalhos de análise da distribuição da carga oclusal com diferentes materiais de reconstrução protética não são concordantes em seus resultados. Assim, diante da importância da seleção de materiais restauradores protéticos no prognóstico da reabilitação oral, este trabalho se propôs a estudar a influência de coroas protéticas metalo-cerâmica e de resina, cimentadas no canino, na transmissão de tensões para o tecido ósseo em mandíbulas frescas de cães, utilizando o método de interferometria holográfica de dupla exposição. Seis hemi-mandíbulas frescas de cães da espécie Canis familiares foram fixadas em um dispositivo para garantir a invariabilidade da força aplicada durante o experimento. Uma carga de 0,98 N foi aplicada sobre as coroas, seguindo o longo eixo do dente. Pelo método de interferometria holográfica, foram obtidos 12 hologramas, 6 para cada grupo de amostras. As coroas metalo-cerâmicas apresentaram maior deslocamento, com movimento de intrusão no alvéolo, em relação às de resina. Os microdeslocamentos resultantes nas hemimandíbulas demonstraram comportamentos semelhantes de deflexão, porém, não foram encontradas diferenças estatisticamente significantes na distribuição das tensões ao osso, com relação aos dois tipos de coroas consideradas, demonstrando a influência da presença do ligamento periodontal. / Although researches assert that restoring dental material, due to their different mechanical properties, influences at load transmission to support tissues, it was not find any conclusive scientific evidence. Researches with finite element, implants and different prosthetic reconstruction material do not have an agreement in terms of results. So, considering the importance of prosthetic restoring material selection on oral rehabilitate prognosis, this assignment studied the influence of metaloceramic and resin prosthetics crowns, cemented on canine, during stress transmission to bony tissue of post-mortem dog mandibles, using double exposure holographic interferometry method. Three fresh mandibles were split into 6 hemi-mandibles, which were fixed in a proper device in order to assure the same applied force during the whole experiment. A 0,98 N load was applied to the crowns, following the long axis of the tooth. It was collect 12 holograms, 6 for each sample group. Metaloceramic crowns presented larger intrusion micromovement in the alveolus, comparing that of resin ones. The resulting micromovings in the hemimandibles presented similar deflecting behaviour. However, significant statistical differences on bone tension distribution have not been found, concerning the two types of previously referred crowns, demonstrating the influence of periodontal ligament.

This research project has investigated the mechanical behaviour of artificial turf surface systems used for sports under a range of real player movements, and the contribution of component layers to the overall system response by developing advanced measurement systems and methods. Artificial turf surface systems are comprised of a number of different materials and commonly with several layers, all of which contribute to their composite behaviour. During sports movements a player loads the surface, resulting in deformation that can change the surface behaviour, which in turn modifies the player biomechanical response. Improving the understanding of surface response to actual player loading is important for developing enhanced products for improving play performance. Likewise, by improving knowledge of surface effects on players, the understanding of injury risk can be improved. However, there is currently no published research to measure and analyse the behaviour of artificial turf system during real player locomotion. This research was undertaken to address this current lack of knowledge within the interaction between player and sports surface regarding the effects of player loading on the mechanical behaviour of artificial turf systems. In addition to support player loading regime, mechanical behaviour of hockey and third generation artificial turf surface systems and their component shockpad layers (a rubber shreds bonded shockpad and a polyurethane foam shockpad) was examined through dynamic cyclic compressive loading using an advanced material testing machine in laboratory environment. Each layer and carpet-shockpad system was subjected to controlled loading designed with previous biomechanical data at various loading frequencies (0.9 Hz, 3.3 Hz and 10 Hz) and under two different contact areas (50 mm and 125 mm diameter) to simulate aspects of player walking, running and sprinting. All layers and surface systems tested showed nonlinear stress-strain behaviour with hysteresis. Increasing the contact area resulted in reduced surface vertical deflection and more linear response. Increasing the loading frequency led to stiffer response in the lower stress range (< 400 kPa) for all surface systems. The third generation artificial turf systems showed also an increase in stiffness at higher stress range ( > 600 kPa) and a decrease in maximum strain as the loading frequency increased. Hysteresis loops obtained at different loading frequencies indicated that the amount of energy lost at the same peak load of 1900 N in each surface system decreased with an increase in loading rate. Player loading regime was performed to quantify the load/stress and the resulting surface deformation/strain under subject loading. Measurement systems including motion capture system, force plate and high speed were developed to characterise the response behaviour in a novel way. The mechanical behaviour of artificial turf surface systems under three player movement patterns (heel-toe walking, forefoot running and forefoot single leg landing) was measured. Boot-surface contact area of each movement varied during the stance. The heel-toe walking results indicated that the maximum applied stress and surface strain occurred in very early stance (first 10%) when the boot-surface contact area was small. For forefoot running and landing, the peak surface strain occurred around mid-stance concurrent with the time of peak applied stress. The maximum strain measured under running was smaller than under landing. A thin-film pressure sensing mat was used in both mechanical and player loading regimes and proved to be a useful tool for evaluating the pressure distributions and contact areas at different interfaces of the surface system. The applied stress on surface was observed to greatly reduce with depth over increasing contact area through the surface systems. Although the average pressure was reduced, pressure distribution contour showed directly under the surface load area the pressure at depth was still relatively large and that outside of this area the pressure was much lower. A comparison of the mechanical behaviour of artificial turf systems in terms of compressive strain, modulus of elasticity, stress distribution and energy loss under mechanical and player loading was evaluated. Key loading parameters in different loading regimes and their influence on surface system response were determined. The structure and material intrinsic properties of shockpad were considered to further explain the observed surface system behaviour. Two mathematical models were used to fit through the experimental data and found to be able to describe the loading behaviour. A breakthrough in understanding of the effects of real player loading on the mechanical behaviour response of artificial turf systems, and the contribution of the components to the whole system response has been achieved through the development of advanced measurement techniques.

Bond in a reinforced concrete (RC) structure is the interaction force that transfers force between the steel and concrete. It influences the structural performance and serviceability of a structure under both static and cyclic loading. Corrosion of reinforcing steel in RC structures is the primary reason behind bond loss in RC elements. A loss of bond in concrete results in a decrease in the serviceability strength and eventually causes a brittle and sudden failure. Structures, such as bridges, are vulnerable to corrosion and at the same time are subjected to repeated loading rather than static loading. Nevertheless, little experimental or analytical studies that address the problem of corroded steel-concrete bond under repeated loading exist. This study was aimed at increasing the understanding of the behaviour of bond between corroded reinforcing steel bars and concrete for structures subjected to repeated loading. In addition, the effect of fibre reinforced polymers (FRP) as a rehabilitation method was assessed. Fibre reinforced polymers is considered to be a state-of-the art rehabilitation material due to its advantages, such as high strength, light weight and ease of handling and application. Forty-seven anchorage-beam specimens were cast and tested. The specimens’ dimensions were 152 x 254 x 2000 mm reinforced with two 20M bars. The steel reinforcement in a specimen was unbonded except for 250 mm from each end. This bonded length was selected to ensure a bond failure. The corrosion was induced using an accelerated corrosion process. The parameters investigated were the corrosion level (0, 5 and 9% measured mass loss), whether the specimen was wrapped in the anchorage zone with a U-shaped carbon fibre reinforced polymer (CFRP) sheets or not, and the load range applied. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to give the desired range of fatigue lives (103 to 106 cycles). The test frequency for all repeated tests was 1.5 Hz. Results showed that the repeated loading either pushed the bottom concrete cover away from the steel bar by wedge action for unwrapped beams or cracked and crushed the CFRP confined bottom concrete cover for wrapped beams. The concrete damage caused the bond stress to undergo a gradual redistribution, moving the peak bond stress from the loaded end towards the free end, resulting in failure of the specimens by fatigue of bond. Corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. The rate of slip of the steel bar increased as the corrosion level increased. CFRP sheets changed the mechanism by which the concrete resist the bond forces by engaging the bottom cover. This in turn increased the fatigue bond strength at all corrosion levels on average by 31% compared to unwrapped specimens. Based on the test results and observations, a hypothesis of the mechanics of bond under repeated loading was postulated and a fatigue slip-growth analysis (similar to the fracture mechanics crack growth approach) was proposed to calculate the fatigue life of a specimen that fail in bond. The proposed analysis was in reasonable agreement with the experimental results.

Bond in a reinforced concrete (RC) structure is the interaction force that transfers force between the steel and concrete. It influences the structural performance and serviceability of a structure under both static and cyclic loading. Corrosion of reinforcing steel in RC structures is the primary reason behind bond loss in RC elements. A loss of bond in concrete results in a decrease in the serviceability strength and eventually causes a brittle and sudden failure. Structures, such as bridges, are vulnerable to corrosion and at the same time are subjected to repeated loading rather than static loading. Nevertheless, little experimental or analytical studies that address the problem of corroded steel-concrete bond under repeated loading exist. This study was aimed at increasing the understanding of the behaviour of bond between corroded reinforcing steel bars and concrete for structures subjected to repeated loading. In addition, the effect of fibre reinforced polymers (FRP) as a rehabilitation method was assessed. Fibre reinforced polymers is considered to be a state-of-the art rehabilitation material due to its advantages, such as high strength, light weight and ease of handling and application. Forty-seven anchorage-beam specimens were cast and tested. The specimens’ dimensions were 152 x 254 x 2000 mm reinforced with two 20M bars. The steel reinforcement in a specimen was unbonded except for 250 mm from each end. This bonded length was selected to ensure a bond failure. The corrosion was induced using an accelerated corrosion process. The parameters investigated were the corrosion level (0, 5 and 9% measured mass loss), whether the specimen was wrapped in the anchorage zone with a U-shaped carbon fibre reinforced polymer (CFRP) sheets or not, and the load range applied. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to give the desired range of fatigue lives (103 to 106 cycles). The test frequency for all repeated tests was 1.5 Hz. Results showed that the repeated loading either pushed the bottom concrete cover away from the steel bar by wedge action for unwrapped beams or cracked and crushed the CFRP confined bottom concrete cover for wrapped beams. The concrete damage caused the bond stress to undergo a gradual redistribution, moving the peak bond stress from the loaded end towards the free end, resulting in failure of the specimens by fatigue of bond. Corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. The rate of slip of the steel bar increased as the corrosion level increased. CFRP sheets changed the mechanism by which the concrete resist the bond forces by engaging the bottom cover. This in turn increased the fatigue bond strength at all corrosion levels on average by 31% compared to unwrapped specimens. Based on the test results and observations, a hypothesis of the mechanics of bond under repeated loading was postulated and a fatigue slip-growth analysis (similar to the fracture mechanics crack growth approach) was proposed to calculate the fatigue life of a specimen that fail in bond. The proposed analysis was in reasonable agreement with the experimental results.

Apesar dos pesquisadores afirmarem que os materiais odontológicos restauradores, devido às suas diferentes propriedades mecânicas, influenciam na transmissão da carga para os tecidos de suporte, não foi encontrada comprovação científica concludente. Os trabalhos de análise da distribuição da carga oclusal com diferentes materiais de reconstrução protética não são concordantes em seus resultados. Assim, diante da importância da seleção de materiais restauradores protéticos no prognóstico da reabilitação oral, este trabalho se propôs a estudar a influência de coroas protéticas metalo-cerâmica e de resina, cimentadas no canino, na transmissão de tensões para o tecido ósseo em mandíbulas frescas de cães, utilizando o método de interferometria holográfica de dupla exposição. Seis hemi-mandíbulas frescas de cães da espécie Canis familiares foram fixadas em um dispositivo para garantir a invariabilidade da força aplicada durante o experimento. Uma carga de 0,98 N foi aplicada sobre as coroas, seguindo o longo eixo do dente. Pelo método de interferometria holográfica, foram obtidos 12 hologramas, 6 para cada grupo de amostras. As coroas metalo-cerâmicas apresentaram maior deslocamento, com movimento de intrusão no alvéolo, em relação às de resina. Os microdeslocamentos resultantes nas hemimandíbulas demonstraram comportamentos semelhantes de deflexão, porém, não foram encontradas diferenças estatisticamente significantes na distribuição das tensões ao osso, com relação aos dois tipos de coroas consideradas, demonstrando a influência da presença do ligamento periodontal. / Although researches assert that restoring dental material, due to their different mechanical properties, influences at load transmission to support tissues, it was not find any conclusive scientific evidence. Researches with finite element, implants and different prosthetic reconstruction material do not have an agreement in terms of results. So, considering the importance of prosthetic restoring material selection on oral rehabilitate prognosis, this assignment studied the influence of metaloceramic and resin prosthetics crowns, cemented on canine, during stress transmission to bony tissue of post-mortem dog mandibles, using double exposure holographic interferometry method. Three fresh mandibles were split into 6 hemi-mandibles, which were fixed in a proper device in order to assure the same applied force during the whole experiment. A 0,98 N load was applied to the crowns, following the long axis of the tooth. It was collect 12 holograms, 6 for each sample group. Metaloceramic crowns presented larger intrusion micromovement in the alveolus, comparing that of resin ones. The resulting micromovings in the hemimandibles presented similar deflecting behaviour. However, significant statistical differences on bone tension distribution have not been found, concerning the two types of previously referred crowns, demonstrating the influence of periodontal ligament.

No description available.

The application of dynamic wind load on photovoltaic (PV) solar systems mounted on flat roofs influenced their structural behavior significantly. It is implied that when the PV solar system is exposed to extreme weather characteristics such as low temperatures, these might influence the load distribution along each layer of the solar panel, which is composed by multiple layers of different materials. Therefore, the high record of weather characteristics as one scenario in addition to the field experiment were designed to describe parametric structural behavior of PV solar system help to increase the precision of study. According to the mentioned procedures different parameters of weather characteristics measured with instrumentation at the site of PV panel installation at the University of Ottawa where the low temperature equal to -24.3° C and wind speed of 11.8 recorded. The mechanical and thermal properties of full-scale specimen and load application that computed based on weather record for every two minutes of January and February from northern side of specimen, introduced to FEM software SAP 2000. Moreover, the support structure and connection used to assemble real specimen considered in modeling with respect to average temperature equal to -7° C that caused to simulate 36 different cases to compare with simultaneous experiment designed to measured strain within same period. The second investigation involved instrumenting a full-scale PV solar panel specimen with 13 half-bridge strain gauges on both surfaces of the PV solar panel, which were used to measure strain values in longitudinal and transversal directions of solar panel and also on the top and bottom edges of the same panel. According to an equivalent uniform Young’s modulus numerically determined for the five layers of the PV solar panel, and with respect to the Hook’s law, the stresses were found to be equal to 50 Mpa for strain gauges at the mid area of PV solar panel,. This value was used to calibrate boundary conditions of the FE model namely the Fix-Equal and the Pin-Equal conditions along the edges of the solar panel and along the mounting frame.