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Rene Tinawi - One of the best experts on this subject based on the ideXlab platform.
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seismic structural stability of concrete gravity dams considering transient uplift pressures in Cracks
Engineering Structures, 2005Co-Authors: Farrokh Javanmardi, Pierre Leger, Rene TinawiAbstract:Abstract A theoretical model is developed for transient water pressure variations along a tensile seismic concrete Crack with known Crack Wall motion history. Experimental tests are performed to validate the proposed model. Experimental and numerical results show that water can penetrate into new seismic Cracks making them partially saturated over a length L sat . The magnitude of L sat and the total water uplift force acting on a Crack Wall are decreased by Crack opening and increased by Crack closing. The model is then implemented in a nonlinear discrete Crack finite element program for seismic analysis of concrete dams. A 90 m high gravity dam subjected to two different ground accelerations is analysed. The magnitude of uplift force in the opening mode of the Crack is small such that the downstream sliding safety factor (SSF) during Crack opening is similar to the SSF assuming zero uplift force in the Crack. Although the transient uplift force during Crack closing reduces the upstream SSF, compared to a similar value assuming zero uplift force in the Crack, its magnitude still remains larger than the minimum downstream SSF corresponding to the Crack opening mode.
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seismic water pressure in Cracked concrete gravity dams experimental study and theoretical modeling
Journal of Structural Engineering-asce, 2005Co-Authors: Farrokh Javanmardi, Pierre Leger, Rene TinawiAbstract:Water pressure variations along concrete Cracks with moving Walls are investigated experimentally and theoretically. Displacement control tests were conducted to measure water pressure on 0.4 m long concrete Cracks during harmonic motion of Crack Walls. The effects of key parameters including frequency of excitation, minimum and amplitude of Crack mouth opening displacement, and initial static uplift pressure on the magnitude of developed pressure is also studied. The experimental results show the possibility of cavitation in a new or existing Crack opening mode. A theoretical dynamic water–Crack interaction model is developed, considering the effect of cavitation phenomenon, to compute water pressure in Cracks as a function of Crack Wall motion history, Crack length, Crack roughness, and Crack mouth pressure. The validity of the developed method is verified by the test results and it is used to study the pressure variations in longer Cracks likely to develop in the concrete gravity dams. The computed upl...
Farrokh Javanmardi - One of the best experts on this subject based on the ideXlab platform.
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seismic structural stability of concrete gravity dams considering transient uplift pressures in Cracks
Engineering Structures, 2005Co-Authors: Farrokh Javanmardi, Pierre Leger, Rene TinawiAbstract:Abstract A theoretical model is developed for transient water pressure variations along a tensile seismic concrete Crack with known Crack Wall motion history. Experimental tests are performed to validate the proposed model. Experimental and numerical results show that water can penetrate into new seismic Cracks making them partially saturated over a length L sat . The magnitude of L sat and the total water uplift force acting on a Crack Wall are decreased by Crack opening and increased by Crack closing. The model is then implemented in a nonlinear discrete Crack finite element program for seismic analysis of concrete dams. A 90 m high gravity dam subjected to two different ground accelerations is analysed. The magnitude of uplift force in the opening mode of the Crack is small such that the downstream sliding safety factor (SSF) during Crack opening is similar to the SSF assuming zero uplift force in the Crack. Although the transient uplift force during Crack closing reduces the upstream SSF, compared to a similar value assuming zero uplift force in the Crack, its magnitude still remains larger than the minimum downstream SSF corresponding to the Crack opening mode.
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seismic water pressure in Cracked concrete gravity dams experimental study and theoretical modeling
Journal of Structural Engineering-asce, 2005Co-Authors: Farrokh Javanmardi, Pierre Leger, Rene TinawiAbstract:Water pressure variations along concrete Cracks with moving Walls are investigated experimentally and theoretically. Displacement control tests were conducted to measure water pressure on 0.4 m long concrete Cracks during harmonic motion of Crack Walls. The effects of key parameters including frequency of excitation, minimum and amplitude of Crack mouth opening displacement, and initial static uplift pressure on the magnitude of developed pressure is also studied. The experimental results show the possibility of cavitation in a new or existing Crack opening mode. A theoretical dynamic water–Crack interaction model is developed, considering the effect of cavitation phenomenon, to compute water pressure in Cracks as a function of Crack Wall motion history, Crack length, Crack roughness, and Crack mouth pressure. The validity of the developed method is verified by the test results and it is used to study the pressure variations in longer Cracks likely to develop in the concrete gravity dams. The computed upl...
Pierre Leger - One of the best experts on this subject based on the ideXlab platform.
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seismic structural stability of concrete gravity dams considering transient uplift pressures in Cracks
Engineering Structures, 2005Co-Authors: Farrokh Javanmardi, Pierre Leger, Rene TinawiAbstract:Abstract A theoretical model is developed for transient water pressure variations along a tensile seismic concrete Crack with known Crack Wall motion history. Experimental tests are performed to validate the proposed model. Experimental and numerical results show that water can penetrate into new seismic Cracks making them partially saturated over a length L sat . The magnitude of L sat and the total water uplift force acting on a Crack Wall are decreased by Crack opening and increased by Crack closing. The model is then implemented in a nonlinear discrete Crack finite element program for seismic analysis of concrete dams. A 90 m high gravity dam subjected to two different ground accelerations is analysed. The magnitude of uplift force in the opening mode of the Crack is small such that the downstream sliding safety factor (SSF) during Crack opening is similar to the SSF assuming zero uplift force in the Crack. Although the transient uplift force during Crack closing reduces the upstream SSF, compared to a similar value assuming zero uplift force in the Crack, its magnitude still remains larger than the minimum downstream SSF corresponding to the Crack opening mode.
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seismic water pressure in Cracked concrete gravity dams experimental study and theoretical modeling
Journal of Structural Engineering-asce, 2005Co-Authors: Farrokh Javanmardi, Pierre Leger, Rene TinawiAbstract:Water pressure variations along concrete Cracks with moving Walls are investigated experimentally and theoretically. Displacement control tests were conducted to measure water pressure on 0.4 m long concrete Cracks during harmonic motion of Crack Walls. The effects of key parameters including frequency of excitation, minimum and amplitude of Crack mouth opening displacement, and initial static uplift pressure on the magnitude of developed pressure is also studied. The experimental results show the possibility of cavitation in a new or existing Crack opening mode. A theoretical dynamic water–Crack interaction model is developed, considering the effect of cavitation phenomenon, to compute water pressure in Cracks as a function of Crack Wall motion history, Crack length, Crack roughness, and Crack mouth pressure. The validity of the developed method is verified by the test results and it is used to study the pressure variations in longer Cracks likely to develop in the concrete gravity dams. The computed upl...
Kathleen M. Dorgan - One of the best experts on this subject based on the ideXlab platform.
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burrow extension with a proboscis mechanics of burrowing by the glycerid hemipodus simplex
The Journal of Experimental Biology, 2011Co-Authors: Elizabeth Murphy, Kathleen M. DorganAbstract:Burrowing marine infauna are morphologically diverse and ecologically important as ecosystem engineers. The polychaetes Nereis virens and Cirriformia moorei extend their burrows by Crack propagation. Nereis virens does so by everting its pharynx and C. moorei , lacking an eversible pharynx or proboscis, uses its hydrostatic skeleton to expand its anterior. Both behaviors apply stress to the burrow Wall that is amplified at the tip of the Crack, which extends by fracture. That two species with such distinct morphologies and life histories both burrow by fracturing sediment suggests that this mechanism may be widespread among burrowers. We tested this hypothesis with the glycerid polychaete Hemipodus simplex , which has an eversible proboscis that is much longer and everts more rapidly than the pharynx of N. virens . When the proboscis is fully everted, the tip flares out wider than the rest of the proboscis, creating a shape and applying a stress distribution similar to that of N. virens and resulting in relatively large forces near the tip of the Crack. These forces are larger than necessary to extend the Crack by fracture and are surprisingly uncorrelated with the resulting stress amplification at the Crack tip, which is also larger than necessary to extend the burrow by fracture. These large forces may plastically deform the mud, allowing the worm to build a semi-permanent burrow. Our results illustrate that similar mechanisms of burrowing are used by morphologically different burrowers. * a : distance from the tip of the Crack to the point of contact between the anterior end of the worm and the Crack Wall b : distance between the anterior end of the worm and the tip of the Crack B : body stress C : compressional stress around the proboscis E : modulus of elasticity (Pa) h : half-thickness of a worm at a point far away from the anterior end K I : stress intensity (Pa m0.5) K Ic : critical stress intensity factor (Pa m0.5) T : tensile stress at Crack tip ν : Poisson's ratio (dimensionless)
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it s tough to be small dependence of burrowing kinematics on body size
The Journal of Experimental Biology, 2010Co-Authors: Kathleen M. DorganAbstract:Burrowing marine infauna are morphologically diverse and range in size over several orders of magnitude. Whilst effects of ontogenetic and morphological differences on running, flying and swimming are relatively well understood, similar analyses of burrowing mechanics and kinematics are lacking. The polychaete Nereis virens Sars extends its burrow by fracture, using an eversible pharynx to exert force on the Walls of the burrow. The resulting stress is amplified at the anterior tip of the burrow, which extends when the stress exceeds the fracture toughness of the material. Here we show that the polychaete Cirriformia moorei extends its burrow by a similar mechanism, but by using its hydrostatic skeleton rather than an eversible pharynx. Based on the dimensionless wedge number, which relates work of fracture to work to maintain body shape against the elasticity of sediment, we predicted that smaller worms would exhibit behaviors characteristic of tougher sediments and that scaling of kinematics would reflect decreasing difficulty in fracturing sediment with increasing body size. We found that smaller worms were relatively blunter and thicker, and had a greater variation of thickness than larger worms as they burrowed. Although these kinematic differences increase the stress amplification at the Crack tip, smaller worms still generate lower stress intensity factors. The greater relative body thickness and shape changes of smaller worms are consistent with ontogenetic changes in forces exerted by earthworms, and are likely driven by the challenge of exerting enough stress to extend a Crack with a small body size. * a : distance from the tip of the Crack to the point of contact between the anterior end of the worm and the Crack Wall a c : half-width of a bubble in a medium a max : average maximum value of a achieved for each cycle a min : average minimum value of a achieved for each cycle b : distance between the anterior end of the worm and the tip of the Crack E : modulus of elasticity (Pa) G c : Crack resistance, critical energy release rate (J m−2) h : half-thickness of a worm at a point far away from the anterior end K I : stress intensity (Pa m0.5) K Ic : critical stress intensity factor (Pa m0.5) ma : slope of the worm body at its point of contact a p r : point on a regression line through the midpoints of a worm contour w Crack : width of a Crack in a medium (m) W cr : work to extend Crack by fracture w worm : width of a worm body in a medium (m) W El : work to deform elastic material Wg : ‘wedge’ number (dimensionless) z : the distance from the anterior of the worm δc : the half-thickness of a bubble Δ x : distance of Crack growth ν : Poisson's ratio (dimensionless)
Francis Rebillat - One of the best experts on this subject based on the ideXlab platform.
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Modeling of Simultaneous Oxidation and Volatilization Phenomena along a Crack in a Self-healing Multi- constituent Material
Oxidation of Metals, 2017Co-Authors: Coraline Simon, Florent Bouillon, Gerald Camus, Francis RebillatAbstract:Multi-layer Ceramic Matrix Composites with self-healing capacities have been developed for high-temperature aeronautical applications. However, the use of these sophisticated materials lead to complex thermo-chemical behavior which requires a proper analysis. Previous models have allowed to determine the quantity of oxygen reaching the fiber at the end of a Crack, in a dry atmosphere. The focus of this study was to extend this model to the case of humid atmospheres, for the presence of moisture can lead to the volatilization of the healing oxide. Applications of the model have been performed on a material composed of successive layers of SiC and B 4 C. Changes of the Crack Wall surface could then be evaluated, as well as the healing or recession behavior, and the evolution of the oxygen concentration. Moreover, the introduction of a uniform equivalent averaged material allowed estimations of the consumption of all constituents, and in particular of carbon interphase, over durations representative of aeronautical service lives.
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Modeling of Simultaneous Oxidation and Volatilization Phenomena Along a Crack in a Self-Healing Multi-constituent Material
Oxidation of Metals, 2017Co-Authors: Coraline Simon, Florent Bouillon, Gerald Camus, Francis RebillatAbstract:Multilayer ceramic matrix composites with self-healing capacities have been developed for high-temperature aeronautical applications. However, the use of these sophisticated materials leads to complex thermo-chemical behavior which requires a proper analysis. Previous models have allowed to determine the quantity of oxygen reaching the fiber at the end of a Crack, in a dry atmosphere. The focus of this study was to extend this model to the case of humid atmospheres, for the presence of moisture can lead to the volatilization of the healing oxide. Applications of the model were conducted on a material composed of successive layers of SiC and B4C. Changes of the Crack Wall surface could then be evaluated, as well as the healing or recession behavior, and the evolution of the oxygen concentration. Moreover, the introduction of a uniform equivalent averaged material allowed estimations of the consumption of all constituents, and in particular of carbon interphase, over durations representative of aeronautical service lives.