Cette thèse porte sur l’optimisation en termes de microstructure et de composition des propriétés électrochimiques du composé Ca3Co4O9+δ pour une application comme cathode pour Pile à Combustible à Oxyde. En utilisant la sérigraphie comme technique de dépôt, la Résistance Surfacique Spécifique a été diminuée jusqu’à 0.5 Ωcm² à 700°C pour un matériau composé de 50% en masse d’oxyde de cérium dopé au gadolinium et Ca3Co4O9+δ. Par ailleurs, des techniques telles que le spin-coating et l’électro-spray apparaissent comme prometteuse pour l’amélioration des performances. Nous avons tenté d’étudié l’impact de la substitution partielle sur le site calcium sur les performances électrochimiques pour différents dopants (Sr, Pb, Bi, La). Du fait que les performances électrochimiques dépendent fortement de la préparation et de la faible concentration en dopant contrainte par la faible solubilité du plomb en site calcium, il n’a pas été possible de tirer des conclusions claires sur l’impact d’un tel dopage, de même pour les propriétés de transport de l’oxygène. Par contre, l’analyse par échange Isotopique Pulsé de la composition (Ca0.90Sr0.10)3Co4O9+δ a permis de confirmer les très bonnes cinétiques d’échange de l’oxygène pour les composés partiellement substitués par du strontium, montrant par ailleurs que ni l’adsorption en surface de l’oxygène ni son incorporation dans le solide sont des étapes limitantes dans le mécanisme d’échange en surface. / In this PhD thesis, the electrochemical performances of the misfit layered oxide Ca3Co4O9+δ used as a cathode for Solid Oxide Fuel Cell were tentatively optimised by optimisation of the electrode microstructure and composition. Using screen printing as a deposition technique, the Area Specific Resistance was decreased to 0.5 Ωcm2 at 700°C for a composite made of 50% in weight of cerium gadolinium doped oxide and Ca3Co4O9+δ. Spin coating and electro-spray deposition were also tested as promising technique to improve the performances. The impact of partial substitution of the calcium site on the electrochemical performances was tentatively studied with a wide range of dopant (Sr, Pb, Bi, La). It was difficult to draw conclusions since their performances depend strongly on the sample preparation. Moreover, due to the low amount of the dopant, imposed by the low solubility of lead in the calcium site, it was not possible to derive a clear tendency of the substituent’s impact on the oxygen transport properties. However, by pulse isotopic exchange, high surface exchange kinetics were confirmed for the (Ca0.90Sr0.10)3Co4O9+δ composition and it was shown that neither the oxygen adsorption of the surface nor the oxygen incorporation in the solid were the limiting step in the oxygen transfer.

<p> The base and shaft resistance of steel pipe piles installed in silica sand is affected by several factors; these include but are not limited to: shaft resistance degradation, shaft surface roughness, installation method, pile geometry, soil density and particle size, and setup.  This thesis focuses on the first four factors, while also considering the effect of soil density within each factor. Several of the pile design formulas available do not consider the effects of shaft resistance degradation due to load cycles during installation of jacked and driven closed-ended pipe piles, plug formation and evolution during driving of open-ended pipe piles, the degree of corrosion or pitting corrosion on the shaft surface of a pile and its potential impact on setup, and the geometry of the tip of the pile. To assess the impact on pile capacity of some of these factors, a series of static compression load tests were performed in a controlled environment in a calibration chamber with a scaled down instrumented model pile. The air-pluviation technique with different combination of sieves assembled in a large-scale pluviator was used to prepare F-55 sand samples of different density in the calibration chamber. Slight changes were made to the experimental setup to study each factor: sand sample density, driving energy, mode of installation, and geometry and shaft roughness of the model pile.</p> <p><br></p> <p>The results from the experiments confirmed that each of these factors affects the pile resistance. Some of the important conclusions were:</p> <p><br></p> <p>i. The shaft resistance of the model pile is about 2.4 times greater for jacked piles than for driven piles in dense sand, due to the greater shaft resistance degradation in driven piles. </p> <p>ii. Despite the effect of degradation, the shaft resistance of the non-displacement model pile which had no loading cycles was a ratio of 0.37 to that of the driven model pile in medium dense sand and 0.60 in dense sand, due to the absence of displacement.</p> <p>iii. An increase in the surface roughness of the jacked model piles from smooth to medium-rough resulted in an increase of the shaft resistance, which had a ratio of 7.75 to the smooth pile in dense sand and 3.05 in medium dense sand. An increase from smooth to rough resulted in an increase of the shaft resistance, which had a ratio of 8.00 to the smooth pile in dense sand and 4.26 in medium dense sand.</p> <p>iv. Although rougher interfaces produce greater interface friction angles than smooth interfaces with sand, once a limiting value of surface roughness is reached, shearing occurs in a narrow band in the sand in the immediate vicinity of the model pile, with the shaft resistance depending on the critical-state friction angle of the sand. This means the shaft resistance will not increase further with changes in pile surface roughness, due to the fact that the internal critical-state friction angle of the sand has been reached in the shear band during loading.  </p> <p>v. During installation, the conical-based pile had a higher penetration per blow compared to the flat based pile from 0 to 25.6<em>B</em> in medium dense sand and 0 to 20<em>B</em> in dense sand (<em>B</em> = base diameter). After the pile was installed beyond 25.6<em>B</em> in medium dense and 20<em>B</em> in dense sand, the penetration per blow was identical. </p> <p>vi. The base resistance of a conical-based model pile was about 0.76 times that of a flat-based model pile in dense sand and 0.56 in medium dense sand. </p> <p>vii. Jacked piles had similar base resistance ratio of about 0.93 to 0.95 of driven piles in dense sand and 0.98 to 1.05 in medium dense sand. However, they had a much higher shaft resistance ratio of about 1.67 to 2.07 in dense sand and 1.44 to 1.50 in medium dense sand. </p>

There is presently considerable uncertainty regarding appropriate connection details between driven piles and pile caps. Prior research on the subject suggests that given a proper embedment length, a specialized reinforced connection may not be necessary. Eliminating these costly connection details could save thousands of dollars on both labor and materials. This research study focuses on the importance of the pile-to-cap connection detail with respect to the reinforcement connection and pile embedment length. Four pile caps were constructed, each with two 40 foot-long steel pipe piles, and were tested with different connection details. Two caps included a reinforced connection detail while the other two relied on their respective embedment lengths. A hydraulic ram was used to apply a cyclic lateral force to each of these pile caps until failure occurred. Load-displacement curves were developed for each pile cap and strain gauge measurements were used to evaluate tension and bending moments in the pile caps. Comparisons are presented regarding the effect of the connection on pile cap response. An analysis has been conducted to best understand possible failure modes; two computer modeling programs were used and their respective results have been presented and compared to the observed readings. This thesis provides test data supporting the theory that a proper embedment length acts as an adequate connection in place of a specialized reinforced detail. A pile cap with piles embedded two diameters into the cap performed successfully. In contrast, a cap with piles embedded only one diameter failed after developing a large crack through the entire cap. For the two pile caps with a reinforcing cage connection; the performance was essentially the same for the piles embedded either six inches (.5 diameter) or twelve inches (one diameter) into the cap. The data produced was found to be very similar to what was estimated by the two programs used for analysis (GROUP 4.0 and LPILE 4.0).

A geotechnical composite foundation system that has become increasingly popular over the years is a column-supported, geosynthetic-reinforced embankment. This system consists of strong columns or piles placed in soft clay, a bridging layer of sand or sand and gravel, and one or more layers of geosynthetic reinforcement. It is often used in soft ground situations where there is a need for faster construction and/or where there are adjacent structures that would be affected by settlement caused by the new embankment. The geosynthetic reinforcement is placed in the bridging layer to help transfer the load to the columns and decrease the total and differential settlements. Current methods of analysis for this material are extremely simplified, and do not thoroughly model the behavior of the system. Therefore, a more comprehensive analysis needs to be conducted that will better predict the true effect of the geosynthetic layer or layers. In this thesis, one geosynthetic layer was considered. Models were developed using two different computer programs: Mathematica and ABAQUS. In Mathematica, the Rayleigh-Ritz method was used to approximate the deflections and tensile forces in the membrane. This method considered the geosynthetic reinforcement as a plate and minimized the total energy of the system. In ABAQUS, a finite element modeling program, the membrane was analyzed as a shell, and results were compared with some results from Mathematica. A parametric study was completed in Mathematica to determine the effects of different parameters. The parameters varied involved the geogrid properties (Poisson's ratio, modulus of elasticity, and thickness), the vertical load, the soil stiffness above the piles, the soil stiffness between the piles, the size of the piles, and the distance between the piles. / Master of Science

This degree project compares piling methods with respect to technical and economic aspects, all affecting factors are measured as realistic as possible. The aim was to get a better understanding for piling methods used in Sweden and to work as an information tool for structural engineers. In order to get the technical aspects on piling methods literature study and interviews with structural engineers from Kadesjös Ingenjörsbyrå AB have been conducted. The case study on a residential building in Västerås was also performed. In this case study calculations for a quantity of piling methods have been made and sent for RFQs for various entrepreneurs. Subsequently piling methods have been analyzed and compared with respect to their prices. By calculating the costs of various piling methods it has been analyzed why some piling methods are more expensive than others. In a layer from soil that is free from rocks and other obstacles the concrete pile is the economically effective piling method for a residential building for both five and thirty meters. The magnificent steel pile is only 5% more expensive than the concrete pile. Note that this degree project is not a cheat sheet for the most economical pile.

Thèse doctorat : Energétique et Thermique : Nancy 1 : 2006. / Titre provenant de l'écran-titre.

Pile foundations are extensively used to support various structures that are constructed in soft/loose soils, where shallow foundations would be considered ineffective due to low bearing capacities and large settlements. The design of these structures to accommodate lateral applied loads in particular, usually imposed by winds, water and earth pressures, has gained popularity over the past few decades. The behaviour of horizontally loaded piled foundations is a complex soil-structure interaction problem and is usually concerned with the relative stiffness between the pile and the surrounding soil, where the relative stiffness is a function of both the stiffness and properties of the pile and the stiffness of the soil. Many design assumptions and methods used for pile foundations are based on the principles observed from metal piles. This raises the question of the validity and accuracy of assumptions and methods for the use of analysing and designing reinforced concrete piles, that exhibits highly non-linear material behaviour and changing pile properties after cracking. Due to the elastic behaviour of metal sections, these methods typically only focus on the soil component of the soil-structure interaction problem, only allowing changes and non-linear behaviour of the soil surrounding the pile to take place upon load application, mostly disregarding the behaviour and response of the pile itself. The main purpose and objective of the study was to determine whether aluminium sections in a centrifuge could be used to realistically and sufficiently accurately model the monotonic and cyclic response of reinforced concrete piles subjected to lateral loading. This was observed though a number of tests conducted in a geotechnical centrifuge on scaled aluminium and reinforced concrete piles, subjected to both monotonic and cyclic loading. After conducting the tests on both the scaled aluminium and reinforced concrete piles in the centrifuge it was concluded that aluminium sections cannot be used to accurately model and predict the lateral behaviour of reinforced concrete piles. Both the scaled aluminium and reinforced concrete piles proved to model the concept of laterally loaded piles quite well regarding bending at low loads. However, even at low lateral loads, the observed response of the scaled reinforced concrete was significantly different than that observed from the scaled aluminium pile. Furthermore, as the magnitude of the applied load and bending increased, the scaled reinforced concrete pile cracked, resulting in non-linear behaviour of the section under loading, which was not the case for the scaled aluminium pile that remained uncracked. This contributed to the difference in behaviour between the piles studied, therefore, the true material behaviour and failure mechanisms involved with reinforced concrete piles were not replicated by using a scaled aluminium pile section. The non-linear behaviour of the scaled reinforced concrete pile after cracking affected both the behaviour of the pile, as well as the response of the soil surrounding the pile, in contrast with the behaviour observed from the scaled aluminium pile. / Dissertation (MEng)--University of Pretoria, 2020. / The Concrete Institute / Concrete Society of Southern Africa / WindAfrica project / Civil Engineering / MEng (Structural Engineering) / Unrestricted

A team from Brigham Young University and I performed full-scale lateral load tests on individual and grouped 12.75x0.375 inch pipe piles spaced at varying distances behind an MSE wall. The individually loaded pile which acted as a control was spaced at 4.0 pile diameters from the wall face, and the three grouped piles which were loaded in unison were spaced at 3.0, 2.8, and 1.8 pile diameters from the wall face and transversely spaced at 4.7 pile diameters center-to-center. The purpose of these tests was to determine the extent of group effects on lateral pile resistance, induced loads in soil reinforcements, and MSE wall panel deflections compared to those previously observed in individually laterally loaded piles behind MSE walls. The computer model LPILE was used in my analysis of the measured test data. The p-multipliers back-calculated with LPILE for the grouped piles were 0.25, 0.60, and 0.25 for the grouped piles spaced at 3.0, 2.8, and 1.8 pile diameters from the wall, respectively. These values are lower than that predicted for piles at the same pile-to-wall spacings using the most recent equation for computing p-multipliers. I propose the use of an additional p-multiplier for grouped piles near an MSE wall, a group-effect p-multiplier, to account for discrepancies between individual and grouped pile behaviors. The group effect p-multipliers were 0.35, 0.91, and 0.74 for the grouped piles spaced at 3.0, 2.8, and 1.8 pile diameters from the wall, respectively. The average group-effect p-multiplier was 0.66. Additionally, I used LPILE to analyze test data from Pierson et al. (2009), who had previously performed full-scale lateral load tests of individual and grouped shafts. In said analysis, the group of three 3-foot diameter concrete shafts spaced at 2.0 shaft diameters from the wall face and transversely spaced at 5.0 shaft diameters center-to-center had an average group effect p-multiplier of 0.78. As in previous studies, the induced forces in soil reinforcements in this study were greatest either near the locations of the test piles or at the MSE wall face. The most recent equation for calculating the maximum induced force in a soil reinforcement strip was reasonably effective in predicting the measured maximum loads when superimposed between the test piles, with 65% and 85% of the data points falling within the one and two standard deviation boundaries, respectively, of the original data used to develop the equation. Deflection of the MSE wall panels was greater during the grouped pile test than was previously observed for individually loaded piles under similar pile head deflections--with a maximum wall deflection of 0.31 inch compared to the previous average of 0.10 inch for pile head deflections of about 1.25 inches.

In Sweden as well as other countries the trend of building higher is more and more popular. The global stability of tall buildings is a very important aspect that has to be taken into account while designing. Foundation on piles, that is common in Sweden, reduces the global stability compared to foundation directly on bedrock. Using inclined piles in the foundation is inevitable for high-rise buildings, because they are essential for transferring the horizontal loads into the bedrock. The aim of this paper is to look into the influence that foundation on piles has on global stability and investigate two simple methods to asses global stability. In this thesis the influence of the stiffness of the substructure (foundation), length and inclination of the piles on the global stability were investigated. It was also looked into how does the pile center affect the rotation and thus global stability. One method that was presented was based on the equivalent stiffness. Displacement at the top of the wall is used in order to calculate the bending stiffness that is reduced due to foundation on piles and further calculate buckling load on the basis of Euler buckling. In the other method that was proposed rotation at the foundation level was taken into account so as to calculate rotational spring stiffness and later buckling load due to combined flexural and rotational buckling. The analysis was conducted on a simple two dimensional problem, namely stabilizing wall as well as a building stabilized by two towers. Three different configurations of piles were investigated for single wall as well as for the structure. The investigation showed that the position of pile center has its effect on the global stability. The closer the pile center is to the foundation on piles the better the global stability of a  structure. The length of the piles plays a role in stability as well. The longer the piles are the worse the stability is. With longer piles the overall stiffness of a structure decreases and thus the global stability. The analysis showed that the foundation of piles significantly lowers the stability of high rise building. The investigated methods showed that the one based on rotation at the base gave better results compared to the method based on the equivalent bending stiffness. But to use this first method, the position of the pile center is required to be known in order to get correct results which in a complex structure is hard to estimate. In an analysis of a building stabilized by two towers it was seen that when the inclined piles that are inclined opposite to each other in a pile group and are positioned far from rotation center of a structure it increases the global safety and rotational stiffness as well. It is recommended to use such configuration of piles that the pile center is at the foundation level in order to increase global stability. / I Sverige och andra länder är trenden att bygga högre alltmer populärt. Den globala stabiliteten hos höga byggnader är en viktig aspekt som måste beaktas vid byggnadens utformning. Den vanligaste grundläggningsmetoden i Sverige är grundläggning med pålar. Denna typ av grundläggning minskar den globala stabiliteten jämfört med grundläggning direkt på berggrunden. Att använda sneda pålar i grundläggningen är oundviklig för höghus, eftersom de är nödvändiga för att överföra horisontella laster till berggrunden. Syftet med detta examensarbete är att se hur grundläggning på pålar påverkar den globala stabiliteten och undersöka två enkla metoder för global stabilitet. I detta examensarbete undersöktes hur styvheten påverkar grundläggning med pålar med olika längder och lutningar, med hänseende på den globala stabiliteten. Pålcentrumets påverkan av rotation och den globala stabiliteten har även studerats. En metod som presenterades i examensarbetet är baserades på ekvivalent styvhet. Där utböjning på toppen av väggen togs för att beräkna böjstyvheten som reduceras på grund av grundläggning med pålar och ytterligare beräknades knäcklasten baserat på Eulers knäckning. I den andra metoden som föreslogs togs rotationen vid grundläggningsnivån med i beräkningen för att beräkna rotationsfjäderns styvhet och senare knäckningslasten på grund av kombinerad böjnings- och rotationsknäckning. Analysen genomfördes på en enkel tvådimensionell vägg och en tredimensionell byggnad som är stabiliserad av två torn. Tre olika konfigurationer av pålar undersöktes för enkel vägg och även för byggnaden Utredningen av examensarbetet visade att positionen av pålcentrum har en stor påverkan på den globala stabiliteten. Ju närmare pålcentrumet är till grundläggningsnivån desto bättre är den globala stabiliteten hos en konstruktion. Längden på pålarna har även en betydelse när det gäller stabiliteten. Ju längre pålarna är desto värre blir stabiliteten. Med längre pålar minskar den totala styvheten hos hela konstruktionen och därmed minskar även den globala stabiliteten. Utredningen visade även att metoden med rotation vid grundläggningsnivån gav mer noggrannare resultat än metoden för ekvivalent styvhet. Men för att kunna använda den förstnämnda metoden behöver man ha kännedom om vart pålcentrum ligger för konstruktionen och detta kan vara svårt att uppskatta. I en analys av en byggnad stabiliserad av två torn visades det att när pålarna är placerade långt från rotationscentrum av en konstruktion ökar den globala säkerheten och rotationsstyvheten. Det rekommenderas att använda sådan konfiguration av pålar att pålcentrum ligger på grundnivå för att öka den globala stabiliteten.

Presently, fuel cell technology is one of the most exciting fields in the area of new energy development with high scientific and technological challenges. Progress made up to now in the field of Proton Exchange Membrane Fuel Cell, PEMFC, technology offers large perspectives of applications. The interest in this environmentally benign technology has grown during the last years due to the Kyoto protocol requirements. However, a drastic decrease in PEMFC cost is needed prior to the widespread acceptance of PEMFC as automotive power Systems. The main objective of this study was to develop a new concept of high performance and low-cost porous electrode gas diffusion layer for PEMFC. Novel and industrially viable processing techniques based on twin-screw extrusion, post-extrusion film stretching or selective dissolution treatment were used. Conventional materials presently used for PEMFC electrodes were replaced in this project by new formulations based on highly filled thermoplastic polymers. To create the porous structure of the gas diffusion layer, two different techniques were used. For the first technique, a thin film was made from low viscosity polypropylene, PP, filled with high specific surface area carbon black and synthetic flake graphite. Conductive blends were first prepared in a co-rotating twin-screw extruder and subsequently extruded through a sheet die to obtain films of around 500 microns in thickness. These films were then stretched in two successive steps to generate a film (100-200 microns) of controlled porous structure. However, for the second technique, the thin film was made from two immiscible polymers filled with a mixture of electronic conductive additives via twin-screw extrusion followed by selective extraction of one of the two polymers. The two polymers were a low viscosity PP and polystyrene, PS, and the conductive additives were the same as those used in the first technique. Conductive blends were first compounded in a co-rotating twin-screw extruder and subsequently extruded through a flexible film die to obtain a 500 microns film of high electronic conductivity. The PS phase was then extracted with tetrahydrofuran, THF, solvent and a film of controlled porosity was generated. The morphology of the porous structures was then analyzed by scanning electron microscopy, SEM, and by BET surface area measurements. The effects of PS concentration and extraction time with THF on film conductivity and porosity were also studied. / Actuellement, la technologie des piles à combustible représente l'un des champs les plus passionnants avec des défis scientifiques et technologiques élevés. Les progrès réalisé jusqu'à date dans le domaine des piles à combustibles à membrane échangeuse de proton, PEMFC, offre de grandes perspectives d'applications. L'intérêt pour cette technologie non polluante a fortement grandit durant les dernières années à cause des conditions exigeantes du protocole de Kyoto. Cependant, l'optimisation des coûts de production des piles de type PEMFC est nécessaire avant leur intégration en tant que systèmes d'alimentation des véhicules à moteur. L'objectif principal de cette étude était de mettre au point un nouveau design non coûteux de couche poreuse de diffusion de gaz pour électrodes de piles PEMFC. Des techniques pouvant être intégrées à l'échelle industrielle qui sont basées sur l'extrusion bi-vis, l'étirage postextrusion de film mince ou la dissolution sélective ont été utilisés. Les matériaux conventionnels présentement utilises pour fabriquer les électrodes ont été remplacés dans le cadre de ce projet par des nouvelles formulations basées sur les polymères thermoplastiques fortement chargés avec des additifs à conductivité électronique élevée. Pour créer la structure poreuse de la couche de diffusion de gaz, deux techniques différentes ont été employées. Pour la première technique, un film a été développé à partir d'une matrice en polypropylène, PP, de faible viscosité, chargé d'un grade spécial de noir de carbone possédant une surface spécifique élevée et de graphite synthétique en forme de feuillets. Les mélanges conducteurs ont d'abord été préparés dans une extrudeuse co-rotative bi-vis puis poussés à travers une filière plate. Cela a permis d'obtenir des films d'environ 500 microns d'épaisseur. Ces films ont ensuite été étirés en deux étapes successives afin de produire des films (de 100 à 200 microns) à structure poreuse contrôlée. En ce qui concerne la seconde technique, le film fin a été obtenu en mélangeant deux polymères immiscibles puis en y additionnant un mélange de charges électriquement conductrices. Cette opération a été menée en extrusion bi-vis. Elle a ensuite été suivie d'une extraction sélective de l'un des deux polymères. Les deux polymères dont il s'agit sont le PP à basse viscosité et le polystyrène, PS. Les charges conductrices sont les mêmes que celles utilisées à la première technique. Ces mélanges conducteurs ont été composés dans une extrudeuse co-rotative bi-vis puis poussés à travers une filière plate flexible afin d'obtenir un film de 500 microns à grande conductivité électrique. Le phase PS a été extraite par la suite grâce à un solvant : le tétrahydrofurane, THF. Des films à porosité contrôlée ont ainsi été générés. Les morphologies des structures poreuses ont été analysées par microscopie électronique à balayage, SEM, ainsi que par des mesures de surfaces spécifiques BET. Les effets de la concentration du PS et du temps d'extraction sélective par THF sur la conductivité et la porosité des films ont également été étudiés.