Patch repairs are sometimes considered to be capable of contributing to the resisting of externally applied load when the repairs are applied to deteriorated concrete structural members, particularly when the repair is subj ected to compression. However, it is generally known that many patch repair materials shrink and creep significantly relative to the concrete substrate. This thesis presents an experimental and numerical study of the contribution of patch repairs to load carrying in reinforced concrete columns, its quantification and the effect of shrinkage and creep. Twelve reinforced concrete columns were cast with a cavity located halfway up one side of the column. Two control columns were cast without a cavity. The parameters varied in the experimental testing were the depth of the repair cavity, type of repair material (one polymeric and the other polymer-modified), and whether the repaired columns were monitored under load or without being loaded. Test results prior to repair indicate that the loss of concrete from the column induces bending in the loaded column. Both the polymer-modified and polymeric mortar contributed to the column's resistance of the applied load in the short term, but in the long term the contribution of the polymer-modified mortar decreased substantially while that of the polymeric mortar was sustained. Repaired columns which were monitored with no load showed that shrinkage of the polymer-modified mortar can induce bending in the repaired column; this bending increased with cavity depth. Bending strain distributions in the repaired area are close to a straight line, particularly for columns monitored under load. The finite element numerical simulations showed good qualitative agreement with the test results. The analyses also indicated that strain distributions outside but close to the repaired area are nonlinear. However, predictions of the engineer's theory of bending showed favourable quantitative agreement with the finite element analyses.

本論文研究探討了在IEEE 802.11無線區域網路下支援服務品質的負載控制方法。我們所提出的ELB方法用動態的調整AP之間的網路負載分佈以達到負載平衡的目標。我們根據每個客戶端的統計特性進行負載平衡，並以允入控制來避免流量雍塞的情況發生。透過將使用者區分為三個等級，並控制每個使用者的使用頻寬來達到維持服務品質的目的。而進行漫遊的使用者，在我們的機制下，經由在新的AP上的頻寬預先保留，也可以維持一定的服務品質。除此之外，我們的ELB不需要修改任何的硬體機制，就可以運作在現存的802.11b無線區域網路中。最後，我們也對我們的機制做了模擬與實作，並量測、比較了我們的機制的表現。結果指出我們的結果可以有效的平衡AP間的負載，讓頻寬達到更大的使用效率，也能維持令人滿意的服務品質。 / This thesis presents and evaluates a mechanism for the load control with QoS supported in IEEE 802.11b Wireless LANs. Our mechanism named Enhanced Load Balance (ELB) dynamically adapts load distribution over APs to achieve load balance. The ELB mechanism balances the load by STAs’ statistical traffic load. This mechanism also performs admission control to avoid congestion. The ELB mechanism maintains QoS by classifying STAs into three classes and control the traffic flow of every STA. The roaming STAs can get enough bandwidth to maintain the QoS in the new AP by the bandwidth reservation mechanism of ELB. ELB can be used on top of the standard 802.11b access mechanism without requiring any modification or additional hardware. The performance of the IEEE 802.11 protocol with or without the ELB mechanism is investigated in the paper via simulation and implementation. The results indicate that our mechanism can balance the load effectively and the bandwidth can be fully utilized. Therefore, QoS can also be maintained.

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.).

VISIR “Virtual Instrument Systems in Reality” is a remote laboratory that empowers students and researchers to design, implement, and measure on electronic circuits remotely. Users are able to connect to this system regardless of their location and use traditional lab resources online via JavaScript and HTML5 enabled web browser. The VISIR project is deployed to seven universities around the globe including Blekinge Institute of Technology (BTH) in Sweden. In this thesis work, the main aim is to introduce load-balancing Scenarios in VISIR network in order to enable and improve load balancing, stability, and scalability in this system. The participant universities will be connected in a grid topology, and they exchange capabilities, features, and data repository in order to share workload and resources. For this purpose, the behavior of VISIR network nodes were studied and simplified as simple servers. According to the VISIR characteristics, infrastructure, and requirement a set of design paradigms and guidelines were defined for selecting suitable load balancing mechanism to be used in VISIR system. Four different load-balancing methods described, were selected for comparison in an experimental setup. Moreover, an experimental test bed with utilizing virtual Linux machines was modeled, and chosen scenarios were implemented and tested under different circumstances i.e. various number of servers and clients.

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