ABSTRACT This work deals with the damage due to the simultaneous presence of hydrogen in atomic form and stress – straining. The aim of this work is twofold: to better understand the hydrogen embrittlement mechanisms and to translate the acquired knowledge into a more appropriate qualification test. The phenomena of hydrogen entry and transport inside the metals, together with the different types of damages due to the presence of hydrogen, are presented. The analysis of the most important models proposed up to now for hydrogen embrittlement (HE) indicated that the slow dynamic plastic straining is a key factor for the embritteling process. There is a synergistic effect of hydrogen – dislocations interactions: on one hand hydrogen facilitates the dislocations movement (according to the HELP mechanism) and on the other hand dislocations transport hydrogen during their movement when their velocity is lower than a critical value. This work is focused on supermartensitic stainless steels, base and welded materials. The interest on these materials is due to their broad use in offshore oil production. First, the material’s characterisation with regards to hydrogen content and localisation was performed. This was conducted in charging conditions that are representative of industrial applications. Because of previous industrial experience it was necessary to find a more appropriate qualification test method to asses the risk of HE. In this work we proposed the stepwise repeated slow strain rate test (SW R – SSRT) as a qualification test method for supermartensitic stainless steels. This test method combines hydrogen charging, test duration, plastic, dynamic and slow strains. Thus, this test method is coherent with both the model HELP proposed for hydrogen embrittlement and the observations of industrial failures. The stepwise repeated slow strain rate test (SW RSSRT) is interesting not only as a qualification test of martensitic stainless steels, but also as a qualification test of conditions for using these materials (type of straining, range of strain and stress, strain rate, hydrogen charging conditions, etc.). RESUME Ce travail se rapporte à l’endommagement provoqué par la présence simultanée de l’hydrogène sous forme atomique et une contrainte (appliquée où résiduelle). Ce travail a comme but une meilleure compréhension du mécanisme de la fragilisation par l’hydrogène (FPH) et la recherche d’un essai de qualification qui soit cohérent avec ce mécanisme. Les phénomènes liés à l’entrée et au transport de l’hydrogène au sein des métaux, ensemble avec les différents types d’endommagements dus à la présence de l’hydrogène, sont présentés. L’analyse des modèles proposés jusqu’au présent pour la fragilisation par l’hydrogène (FPH) suggère que la déformation lente plastique dynamique est le facteur clé pour le processus de la fragilisation. Il y a un effet synergétique des interactions entre l’hydrogène et les dislocations: d’un coté l’hydrogène facilite le mouvement des dislocations (d’après le modèle HELP) et d’un autre coté les dislocations transportent l’hydrogène pendant leur mouvement, pourvu que leur vitesse soit en dessous d’une valeur critique. Le travail a été conduit sur des aciers supermartensitiques, matériau de base et soudé. L’intérêt pour ces matériaux réside de leur large utilisation dans la production du pétrole en offshore. D’abord, le matériau a été caractérisé du point de vu de la teneur et de la localisation de l’hydrogène. Les essais ont été conduits dans des conditions représentatives pour les cas industriels. L’expérience industrielle d’auparavant indique qu’il est nécessaire de trouver un test de qualification plus approprié pour estimer la susceptibilité à la fragilisation par l’hydrogène. Dans ce travail on propose un essai de traction lente incrémentée (SW R – SSRT) comme méthode de qualification pour les aciers supermartensitiques. L’essai combine le chargement en hydrogène, la durée d’essai, la déformation lente, plastique et dynamique. Donc, cette méthode d’essai est cohérente avec le modèle HELP proposé pour FPH et les observations des accidents industriels. Cet essai est intéressant pas seulement comme essai de qualification pour les aciers supermartensitiques, mais aussi comme essai de qualification pour les conditions d’utilisation des ces matériaux (type de déformation, niveau de déformation et contrainte, vitesse de déformation, conditions de chargement en hydrogène, etc.).

The use of Mechanically Stabilized Earth (MSE) wall structures has increased dramatically in recent years. Traffic barriers are frequently placed on top of the MSE wall to resist vehicular impact loads. The barrier systems are anchored to the concrete in case of rigid pavement. Nevertheless, in case of flexible pavement, the barriers are constructed in an L shape so that the impact load on the vertical part of the L can be resisted by the inertia force required to uplift the horizontal part of the L. The barrier must be designed to resist the full dynamic load but the size of the horizontal part of the L (moment slab) is determined using an equivalent static load. Current design practice of barriers mounted on top of MSE retaining wall is well defined for passenger cars and light trucks. However, the information of this impact level is extrapolated to heavy vehicle impact. Therefore, the bases of this research is to develop design procedure and to help understand the dynamic behavior of a barrier-moment slab system on top of an MSE wall when subjected to heavy vehicle impact loads. In a first part, numerical analyses were conducted to better understand the behavior of the barrier-moment slab system when subjected to heavy vehicle impact loads. The full-scale impact simulations were used to develop the recommendation for designing and sizing the barrier-moment slab system. In a second part, the barrier-moment slab systems defined to contain heavy vehicle impact loads were placed on top of an MSE wall model to study the kinematic behavior of the system. Loads in the soil reinforcing strips and displacements on the barriers and wall components are evaluated to define recommendation for design of strip reinforcements against pullout and yielding. In a third part, a full-scale crash test on a barrier-moment slab system on top of an instrumented 9.8 ft. (3 m) high MSE wall is described and analyzed. The MSE wall and barrier system were adequate to contain and redirected the vehicle and, therefore, it served as verification of the proposed recommendation. Finally, conclusions are drawn on the basis of the information presented herein.

The advent of multi-core processors, particularly with projections that numbers of cores will continue to increase, has focused attention on parallel programming. It is widely recognized that current programming techniques, including those that are used for scientific parallel programming, will not allow the easy formulation of general purpose applications. An area which is receiving interest is the use of programming styles which do not have side-effects. Previous work on parallel functional programming demonstrated the potential of this to permit the easy exploitation of parallelism. This thesis investigates a dynamic load balancing system for shared memory Chip Multiprocessors. This system is based on a parallel computing model called SLAM (Spreading Load with Active Messages), which makes use of functional language evaluation techniques. A novel hardware/software mechanism for exploiting fine grain parallelism is presented. This mechanism comprises a runtime system which performs dynamic scheduling and synchronization automatically when executing parallel applications. Additionally the interface for using this mechanism is provided in the form of an API. The proposed system is evaluated using cycle-level models and multithreaded applications running in a full system simulation environment.

Currently systems of virtual machines are load balanced statically which can create load imbalances for systems where the load changes dynamically over time. For throughput and response time of a system to be maximized it is necessary for load to be evenly distributed among each part of the system. We implement a prototype policy engine for the Xen virtual machine monitor which can dynamically load balance virtual machines. We compare the throughput and response time of our system using the cpu2000 and the WEB2005 benchmarks from SPEC. Under the loads we tested, dynamic load balancing had 5%-8% higher throughput than static load balancing.

Studies have shown that over 30 percent of the bridges in the United States are structurally deficient, and/or over 50 years old. The majority of the highway bridges have reinforced concrete decks supported on steel or concrete girders. Over the years, weathering and deicing chemicals have caused spalling of the concrete surrounding the reinforcing steel, deteriorating many bridges to levels that often result in closure. Repairing or reconstructing the reinforced concrete deck to meet current design specifications is often not possible or feasible, and at times seems illogical due to the possibility of reoccurrence. Because of reinforced concrete's downfalls, there is a move toward alternative materials and designs for bridge deck replacements. In particular, Reynolds Metals Company has lead the movement toward the use of a shop-extruded aluminum deck system known as ALUMADECKTM. The purpose of this research is to evaluate data collected from full-scale testing under test truck loading of an in-service ALUMADECK bridge system. The bridge is known as the Little Buffalo Creek Bridge and is located in Mecklenburg County, VA. The topics researched from the load tests are the composite action amongst the deck and supporting members, the load distribution amongst supporting members, the dynamic load allowance for supporting members, and the developed deck stresses due to test truck loads. Evaluations of the research topics include comparisons to the methods employed in the design calculations provided by VDOT and to those of the American Association of State Highway and Transportation Officials (AASHTO) design specifications. / Master of Science

This thesis presents the results of an investigation into the evaluation of a selected test bridge using instrumentation to obtain site-specific factors contributing to the evaluation, with the ultimate objective of improving the estimate of the bridges reliability in order to assess allowable loading more accurately. The experimental portion of the research program involved instrumenting the test bridge with strain gauges, and recording field measurements using two forms of loading. The analytical portion of the research program involved the analysis of the bridge in the as-designed state, based on the design drawings and specification, followed by a re-analysis of the bridge using the site-specific factors measured on-site. The bridge was evaluated using methods outlined in the Canadian Highway Bridge Design Code CAN/CSA-S6-00 (CSA 2000). <p>The test bridge is located near the community of Hudson Bay, Saskatchewan. The bridge is constructed of steel-reinforced concrete, and there are three, three-span arch-shaped girders. There are also external steel bars added after initial construction to increase the midspan bending moment resistance. In total, 45 strain gauges were placed on the middle spans of the three girders to record strain induced by two forms of loading: controlled loading, in which a truck of known weight and dimensions was driven over the bridge in a number of pre-determined configurations, and in-situ loading, in which normal truck traffic was used. The current allowable loading on the bridge is a gross vehicle weight of 62.5 t, although increasing the allowable loading to 110 t has been proposed, along with two strengthening alternatives to make this increased loading feasible. <p>To provide a base-line analysis for comparison purposes, the bridge was first evaluated based strictly on information taken from the design drawings and specifications. The evaluation was performed using the load and resistance factor method, in which load and resistance factors were used to account for uncertainty, as well as by the mean load method, in which statistical properties of the variables parameters included in the design were used to account for uncertainty. The result of the load and resistance factor method was a live load capacity factor, indicating the overall rating of the bridge. In addition to the live load capacity factor, the mean load method was also used to determine the reliability index. The results of the as-designed analysis showed that the mean load method gave more conservative estimates of the bridge capacity. Furthermore, it was determined that, based on these assessments, the bridge would not have sufficient capacity to carry the proposed 110 t truck loads.<p>The bridge was re-evaluated using site-specific factors with the mean load method. Using the measured strains, statistical parameters were determined for live load effects, distribution factors, dynamic load allowance, and resistance. Statistical parameters that could not be obtained readily through testing were obtained from the literature. The results indicated that code-predicted estimates of a number of factors were highly conservative. Flexural and shear load effects in the girders were found to be less than 15% of the theoretical predictions, as a result of apparent arching action in the girders, generating significant axial forces. For this arching action to occur, horizontal restraint was required at the supports, either through unanticipated restraint in the bearings, or tension tie action of the tensile girder reinforcement. Furthermore, the dynamic amplification was found to be less than 1.0. The resulting reliability indices indicated that the bridge would be safe under the proposed increased allowable loading (110 t). <p>Finite element models were used to confirm the dynamic amplification observations and examine the effects of different degrees of bearing restraint. The model showed results similar to those measured for dynamic amplification. It was found that if the bearings were to become completely fixed against horizontal translation, the bridge would become overloaded as a result of increased shear effects, demonstrating the need for proper bearing maintenance. <p>An analysis of relative costs was completed to determine the most cost-effective solution for hauling logs. Assumptions were made regarding truck and maintenance and operating costs. The results indicated that the most economic solution was to use the method outlined in the research to increase the allowable loading on the bridge to 110 t, over the strengthening alternatives and simply leaving the bridge in the current state.

This thesis presents the results of an investigation into the evaluation of a selected test bridge using instrumentation to obtain site-specific factors contributing to the evaluation, with the ultimate objective of improving the estimate of the bridges reliability in order to assess allowable loading more accurately. The experimental portion of the research program involved instrumenting the test bridge with strain gauges, and recording field measurements using two forms of loading. The analytical portion of the research program involved the analysis of the bridge in the as-designed state, based on the design drawings and specification, followed by a re-analysis of the bridge using the site-specific factors measured on-site. The bridge was evaluated using methods outlined in the Canadian Highway Bridge Design Code CAN/CSA-S6-00 (CSA 2000). <p>The test bridge is located near the community of Hudson Bay, Saskatchewan. The bridge is constructed of steel-reinforced concrete, and there are three, three-span arch-shaped girders. There are also external steel bars added after initial construction to increase the midspan bending moment resistance. In total, 45 strain gauges were placed on the middle spans of the three girders to record strain induced by two forms of loading: controlled loading, in which a truck of known weight and dimensions was driven over the bridge in a number of pre-determined configurations, and in-situ loading, in which normal truck traffic was used. The current allowable loading on the bridge is a gross vehicle weight of 62.5 t, although increasing the allowable loading to 110 t has been proposed, along with two strengthening alternatives to make this increased loading feasible. <p>To provide a base-line analysis for comparison purposes, the bridge was first evaluated based strictly on information taken from the design drawings and specifications. The evaluation was performed using the load and resistance factor method, in which load and resistance factors were used to account for uncertainty, as well as by the mean load method, in which statistical properties of the variables parameters included in the design were used to account for uncertainty. The result of the load and resistance factor method was a live load capacity factor, indicating the overall rating of the bridge. In addition to the live load capacity factor, the mean load method was also used to determine the reliability index. The results of the as-designed analysis showed that the mean load method gave more conservative estimates of the bridge capacity. Furthermore, it was determined that, based on these assessments, the bridge would not have sufficient capacity to carry the proposed 110 t truck loads.<p>The bridge was re-evaluated using site-specific factors with the mean load method. Using the measured strains, statistical parameters were determined for live load effects, distribution factors, dynamic load allowance, and resistance. Statistical parameters that could not be obtained readily through testing were obtained from the literature. The results indicated that code-predicted estimates of a number of factors were highly conservative. Flexural and shear load effects in the girders were found to be less than 15% of the theoretical predictions, as a result of apparent arching action in the girders, generating significant axial forces. For this arching action to occur, horizontal restraint was required at the supports, either through unanticipated restraint in the bearings, or tension tie action of the tensile girder reinforcement. Furthermore, the dynamic amplification was found to be less than 1.0. The resulting reliability indices indicated that the bridge would be safe under the proposed increased allowable loading (110 t). <p>Finite element models were used to confirm the dynamic amplification observations and examine the effects of different degrees of bearing restraint. The model showed results similar to those measured for dynamic amplification. It was found that if the bearings were to become completely fixed against horizontal translation, the bridge would become overloaded as a result of increased shear effects, demonstrating the need for proper bearing maintenance. <p>An analysis of relative costs was completed to determine the most cost-effective solution for hauling logs. Assumptions were made regarding truck and maintenance and operating costs. The results indicated that the most economic solution was to use the method outlined in the research to increase the allowable loading on the bridge to 110 t, over the strengthening alternatives and simply leaving the bridge in the current state.

The development in society means that infrastructure like ballasted railway systems are facing challenges due to request for increased number of high-speed trains and heavier freight trains. This implies that ballasted railways get an increased impact from larger dynamic loads. The question is how the ballasted railways are today affected by dynamic loading and how will an increase in train speed and weight change the soil behaviour within the railway embankment.  A method of investigating dynamic soil behaviour is via geophysical measurements. Accelerometers are commonly used for vibration measurements and by installing them on trains are measurements possible to perform for complete railway sections. The knowledge of expected natural frequencies for various track components and soil layers are essential when considering frequency based analysis of vibration measurements. Thus, a frequency based analysis of accelerometer measurements from track recording coaches enables a possible method for analysing the impact of dynamic loads on underlying soil materials with means of a knowledge of expected natural frequencies for various track components and soil layers. Importance to study frequency content of ground motions became more relevant after the Mexico City earthquake 1985 i.e. studies on this specific earthquake revealed amplification of ground motions due to a long duration of shaking and resonance of soil deposits and furthermore causing damage to buildings whose natural period was the same as the period of ground motion. Thus, if we consider a railway with long train sets running along the railway line. Long durations of shaking of the ground can occur as well as a possible resonance of various soil layers leading to changes in material properties. An interesting finding regarding vibration measurements conducted on a track recording coach show that after Fast Fourier Transformation of the measured vibration data, a frequency spectrum analysis indicate possibilities to detect resonance of the ballast layer in the railway embankment. Therefore, this thesis focus on frequency based analysis of the ballast layer were indications of changes in shear modulus of ballast is seen with means of frequency spectrum and theoretical knowledge of the change in shear modulus in ballast material under cyclic loading and increased shear strain. The thesis consists of two main parts, first is the construction of the so-called frequency-based analysis method of track alignment measurements in a geodynamic perspective and the second part is application of the frequency-based method on a case study. Thus, the scientific contribution of this thesis is to increase knowledge of track alignment measurements in the geotechnical field and to provide a frequency based analysis method of track alignment measurements in a geodynamic perspective for evaluation of soil properties. For the actual case study two different railway sections in Sweden is chosen to enable a comparison, especially when these sections differ with respect to one having only a ballast layer and subgrade and one having ballast, sub ballast and subgrade. Thus, the section with only ballast and subgrade enable a clearer analysis since these layers have large difference in natural frequency. First section is located at Tolikberget in the north part of Sweden and second one between Stenkumla and Dunsjö in south of Sweden. From the analysis of the selected sections it is possible to see indications from the frequency spectrum that the vibration measurements capture the natural frequencies of ballast material associated to the maximum shear modulus and to varying degrees of reduced shear modulus due to increased shear strain. Thus, it can be concluded that vibration measurements conducted on track recording coaches have potential to be used for studies of changes in ballast materials dynamic properties.

No description available.

Em obras de fundações por estacas cravadas, os diferentes comprimentos finais das estacas refletem a variabilidade natural do terreno, e variam de acordo com o critério de paralização da cravação, normalmente baseado em medidas de nega e repique elástico. Pouco se tem aproveitado desses registros para o controle da resistência mobilizada na fundação ao final da cravação, devido à limitação da aplicação das fórmulas dinâmicas e ao desconhecimento de alguns parâmetros. Em muitos casos de controle de capacidade de carga, apenas é realizada a aferição de um fator de segurança pontual, obtido via prova de carga. Neste trabalho, é apresentado um procedimento de controle de capacidade de carga de fundações por estacas cravadas, baseado em registros de nega e repique elástico, a partir de fórmulas dinâmicas, que possibilitam a estimativa da resistência mobilizada ao final da cravação em todo o universo de estacas de uma obra. Este procedimento proposto foi aplicado em um estudo de caso de uma obra em um porto em Santa Catarina. Nesta obra foram cravadas 2506 estacas pré-moldadas de concreto, controladas por nega e repique elástico, registrados em todas as estacas no final da cravação. Neste conjunto de estacas foram executadas 74 provas de carga dinâmica, com energia crescente, e quatro provas de carga estática. Neste caso de obra controlada, os resultados mostraram que o procedimento adotado, baseado na utilização de fórmulas dinâmicas, com parâmetros calibrados a partir dos resultados das provas de carga dinâmica, permitiu estimar valores de resistência mobilizada ao final da cravação das 2506 estacas da obra, que apresentaram um valor médio próximo ao valor médio encontrado nas 74 estacas ensaiadas. Além disso, o coeficiente de variação dos valores de resistência mobilizada de todas as estacas da obra foi da ordem de 16,0%, similar ao coeficiente de variação de 14,7%, obtido nos resultados das provas de carga dinâmica. / The different final lengths of driven piles reflect the natural variability of the soil, and are dependent of the driving controls based in the measurements of the final set and elastic rebound. Normally these measurements are not used to predict the ultimate capacity of pile foundations, at the end of driving, due to the limitation of the dynamic formulas and the lack of some parameters. In many cases, the pile capacity control is based on a determination of a single safety factor, obtained from pile load tests. In this work, it is proposed a procedure to control the ultimate capacity of driven piles, based on the results of the final set and the elastic rebound, and dynamic formulas, which allow the estimation of the mobilized resistance at the end of driving of all piles driven in a particular project. This procedure was applied in a case study of a port in Santa Catarina. In this case, 2506 precast concrete piles were driven, and controlled by the elastic rebound, recorded at the end of driving. Also, dynamic load tests, with increasing energy, were performed on 74 piles, and static load tests were carried out on four piles. The results showed that this procedure adopted, based on the use of dynamic formulas calibrated using the results of dynamic load tests, is capable to estimate the values of mobilized resistance along all piles at the end of driving. The average result of the mobilized resistance of the 2506 piles was close to the average value found by the results of the 74 pile dynamic load tests. Also, the coefficient of variation of the mobilized resistance of all piles was around 16.0%, similar to the coefficient of variation of 14.7%, obtained by the dynamic load tests.