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With the proliferation of sensor-enabled smartphones, significant attention has been attracted to develop sensing-driven mobile systems. Current research on sensing-driven mobile systems can be classified into two categories, based on the purpose of sensing. In the first category, smartphones are used to sense personal context information, such as locations, activities, and daily habits to enable applications such as location-aware systems and virtual reality systems. In the second category, smartphones are exploited to collect sensing data of the physical world and enable applications including traffic monitoring, environmental monitoring, and others. As smartphones become blossomed in popularity and ubiquity, new problems have emerged in both categories of mobile sensing systems. In this thesis, we investigate three core challenges by answering the following fundamental questions: first, how can we utilize user context to improve the operating system performance? Second, how can we process sensing data, especially images, with high accuracy? Third, how can we enable distributed sensing while satisfy resource constraints of smartphones? The first part of this thesis studies how to exploit user context to improve the responsiveness of mobile operating systems. We propose a context-aware application-preloading engine named FALCON. The core of FALCON is a decision engine that learns application usage patterns of mobile users and preloads applications ahead of time to improve the responsiveness of mobile OS. Compared with other approaches such as caching schemes like Least Recently Used (LRU), Falcon improves the application responsiveness by two times. The second part of this thesis focuses on image search for mobile phones. We first explore how to improve image search accuracy on centralized servers, and propose an image search engine named CrowdSearch. The core idea of CrowdSearch is to incorporate crowdsourced human validation into the system for removing erroneous results from automated image search engines, while still provide realtime response for mobile users. Compared with existing automated image search engines, CrowdSearch achieves over 95% accuracy consistently across multiple categories of images with response time in a minute. We then extend image search to distributed mobile phones, and emphasis resource constraint problems, especially on energy and bandwidth. We propose a distributed image search system named SenSearch, which turns smartphones into micro image search engines. Images are collected, indexed, and transmitted using compact features that are two magnitudes smaller than their raw format. SenSearch improves the energy and bandwidth cost by five times compared with centralized image search engines.

Apesar dos avanços tecnológicos e do conhecimento disponível sobre o concreto e suas propriedades, muitas estruturas apresentam-se degradadas prematuramente. Assim, são necessárias frequentes intervenções para reparo havendo, em consequência, consumo de quantidades expressivas de materiais, com importantes impactos financeiros e ambientais. A preocupação crescente com o desempenho das estruturas de concreto tem incentivado vários segmentos da sociedade a buscarem soluções que assegurem sua durabilidade. Nesse sentido, muitas pesquisas acadêmicas vêm sendo desenvolvidas para melhor entender o comportamento do concreto frente a diferentes condições de uso, considerando-se suas propriedades mecânicas e de durabilidade. Esta pesquisa teve por objetivo analisar o desempenho de concretos frente à retração por secagem, após terem sido submetidos ao pré-carregamento. Foram utilizados os cimentos CP V ARI e CP IV, nas relações a/c 0,35, 0,50 e 0,70, e adotadas as idades de cura de 7 e 28 dias. Nas idades 1, 3 e 7 dias, os concretos foram submetidos a carregamentos de 25%, 50% e 75% da carga média de ruptura à tração na flexão (NBR 12142, ABNT, 2010). Realizou-se o ensaio para determinação da retração por secagem (ASTM C157/C157M-08, 2014e1), em concretos de referência e nos pré-carregados. Foram também realizadas análises complementares, como determinação da velocidade da onda ultrassônica (NBR 8802, ABNT, 2013), porosimetria por intrusão de mercúrio e microtomografia de raios X. Comparando-se o desempenho dos concretos pré-carregados ao dos concretos de referência, o cimento CP V ARI apresentou redução da retração média, exceto para a relação a/c 0,35 com cura de 7 dias. Nos concretos com cimento CP IV, a retração média diminuiu para a relação a/c 0,70, com ambas as idades de cura. O pré-carregamento provocou, em maior ou menor grau, a associação de dois diferentes efeitos. Por um lado, a compactação ocasionou a quebra dos compostos menos resistentes da matriz, havendo um efeito físico de redução dos vazios capilares, além da exposição de grãos anidros. Em paralelo, ocorreu a microfissuração do concreto, favorecendo, também, a exposição de grãos anidros. A cura por imersão possibilitou a continuidade da hidratação, com a formação de novos produtos resistentes na matriz, reduzindo as porosidades total e efetiva e, portanto, a taxa da retração do concreto. Além da densificação da matriz, a cura prolongada possibilitou a hidratação dos grãos anidros de cimento expostos nas paredes das microfissuras, favorecendo a sua autocicatrização (self-healing), o que contribuiu com a recuperação da capacidade resistente dos concretos, frente aos esforços da secagem. Assim, a associação destes fatores promoveu a redução da retração por secagem nos concretos estudados, principalmente nos mais porosos. / The growing concern with the performance of structures has encouraged several segments of society to find solutions to improve concrete durability. Several studies have been made to provide a better understanding of the mechanical properties and concrete durability in different conditions. This study assessed the drying shrinkage performance of preloaded concrete. Cement types CP V ARI, equivalent to Portland type III (ASTM C150/C150M-16e1) and CP IV, equivalent to Portland type IP (ASTM C595/C595M-16) were used with w/b = 0.35, 0.50 and 0.70 and curing ages of 7 and 28 days. At the ages of 1, 3 and 7 days, concrete mixes were subject to loads of 25%, 50% and 75% of their mean ultimate flexural strength (Brazilian Standard NBR 12142, ABNT, 2010). Drying shrinkage in reference and preloaded concrete was determined according to ASTM C157/C157M-14e1. Additional tests included ultrasound pulse velocity (NBR 8802, ABNT, 2013), mercury intrusion porosimetry (MIP) and X-ray microtomography. Preloaded CP V ARI cement concrete showed a drop in mean shrinkage when compared with the reference mix, except for the mix with w/b = 0.35 cured for 7 days. For CP IV cement, mean shrinkage dropped with w/b =0.70 for both curing ages. Early loading caused a compaction effect, promoting the weakest compounds of the matrix to be broken, filling the capillary voids. In this process some unhydrous grains probably were exposed. On the other hand, microcracking also occurred, lefting unhydrated grains exposed in the microcracks walls. Due to immersion curing, the availability of water promoted the hydration continuity. New resistant hydrates filled the large voids and reduced the total and effective porosities in the cement matrix. The hydration of anhydrous grains in the microcracks walls had led to self-healing, with partial resistance capacity recovery. The combined effect of these factors promoted the drying shrinkage reducing, mainly for the more porous concrets.

Mobile jack-up rigs are widely used in offshore oil and gas exploration and increasingly in temporary production and maintenance work. There is a steadily increasing demand for their use in deeper water and harsher environments. A typical modem jack-up has three independent legs, each equipped with a footing known as ‘spudcan’. This thesis is concerned with the performance of spudcan foundation subjected to vertical loading correspondent to preloading during its installation into uniform clay. The chief aim of this study is to investigate the bearing behaviour with the corresponding soil failure mechanisms during spudcan penetration. Centrifuge model test and Finite Element (FE) analysis are carried out extensively. In centrifuge modelling, a half-spudcan model and a full spudcan model are used. In the half- spudcan model test, a novel system for revealing soil failure mechanisms and measuring soil deformation has been adopted, in which the half-spudcan model is placed against a transparent window and a subsequent Particle Image Velocimetry (PIV) analysis is performed. The full-spudcan model test is conducted to measure the load-penetration response. In numerical simulation, both small strain and large deformation analyses are carried out with smooth and rough soil-spudcan interfaces considered. At the initial stage of penetration, it is observed that a cavity is formed above the spudcan as it is penetrating into a uniform clay. Meanwhile, soil flows towards the surface and thus soil heave forms close to the spudcan shoulders. With further penetration, the soil underneath the spudcan starts to flow back into the cavity on the exposed top of the spudcan. This backflow causes the spudcan to be embedded while the initially formed cavity remains open. / Eventually, the spudcan becomes fully embedded and the soil flow mechanism reaches a fully localised failure mechanism with deep embedment. The lateral extent of visible distortion due to soil flow is confined well within 1.5-1.6 D (D: spudcan diameter). From both centrifuge and numerical investigations, it is found that in uniform clay, it is inevitable to form a cavity above the spudcan foundation. Thus, the stable cavity depth and soil back flow mechanisms are studied. It is clear that the back flow is caused by a Flow Failure, where it is due to the downward penetration of the spudcan. This is contrary to the Wall Failure that is the mechanism recommended by the current offshore design guidelines to estimate the stable cavity depth. In wall failure, the soil back flow is due to the cavity wall too high to stand. The stable cavity depth is estimated up to 4 times higher by the wall failure mechanism than the one by the flow failure. This explains that the wall failure is never observed in model test. Therefore, a new design chart with design formula is developed for design engineers in the stable cavity depth calculation. The spudcan bearing response is strongly correspondent with the variation of soil failure mechanisms during penetration. At the initial stage of the penetration, the spudcan bearing capacity increases with penetration, which is due to the increase of overburden pressure from cavity formation. At the second stage of the penetration, soil back flow embeds the spudcan, and the spudcan bearing capacity is increasing as the soil flow mechanism transits from its shallow failure mechanism to its deep failure mechanism. / At the final stage of the penetration, the spudcan bearing capacity reaches its ultimate value, where the deep/localised failure mechanism remains. A rough spudcan shows 14 % higher bearing capacity than a smooth spudcan. And a flat-plate shows 8 % higher capacity than a spudcan with a same surface roughness. The ultimate bearing capacity factor N, = 10.5 in uniform soil is recommended as a conservative value when the deep failure mechanism is reached. A correspondent N, = 10.1 in NC clay is suggested for a deeply embedded spudcan.

Structures in high seismic risk areas may be susceptible to severe damage in a major earthquake. Structures designed to meet older code requirements may be at even greater risk. When these structures are evaluated with respect to current code criteria, it is observed that they lack of lateral strength and/or ductility. Since safety and economic considerations are major problems, these structures become viable candidates for retrofit and seismic strengthening. For the variety of structures and possible deficiencies that arise, several retrofitting techniques can be considered. Diagonal bracing system is one of the retrofitting techniques and it provides an excellent approach for strengthening and stiffening existing building for lateral forces. Also, another potential advantage of this system is the comparatively small increase in mass associated with the retrofitting scheme since this is a great problem for several retrofitting techniques. In this study, the use of steel bracing for the strengthening of low, intermediate, and relatively high rise reinforced concrete frames are investigated analytically. The ultimate lateral load capacities of the strengthened frames are determined by a load controlled push-over analysis. The post-tensioning effect of preloading is also investigated.

Apesar dos avanços tecnológicos e do conhecimento disponível sobre o concreto e suas propriedades, muitas estruturas apresentam-se degradadas prematuramente. Assim, são necessárias frequentes intervenções para reparo havendo, em consequência, consumo de quantidades expressivas de materiais, com importantes impactos financeiros e ambientais. A preocupação crescente com o desempenho das estruturas de concreto tem incentivado vários segmentos da sociedade a buscarem soluções que assegurem sua durabilidade. Nesse sentido, muitas pesquisas acadêmicas vêm sendo desenvolvidas para melhor entender o comportamento do concreto frente a diferentes condições de uso, considerando-se suas propriedades mecânicas e de durabilidade. Esta pesquisa teve por objetivo analisar o desempenho de concretos frente à retração por secagem, após terem sido submetidos ao pré-carregamento. Foram utilizados os cimentos CP V ARI e CP IV, nas relações a/c 0,35, 0,50 e 0,70, e adotadas as idades de cura de 7 e 28 dias. Nas idades 1, 3 e 7 dias, os concretos foram submetidos a carregamentos de 25%, 50% e 75% da carga média de ruptura à tração na flexão (NBR 12142, ABNT, 2010). Realizou-se o ensaio para determinação da retração por secagem (ASTM C157/C157M-08, 2014e1), em concretos de referência e nos pré-carregados. Foram também realizadas análises complementares, como determinação da velocidade da onda ultrassônica (NBR 8802, ABNT, 2013), porosimetria por intrusão de mercúrio e microtomografia de raios X. Comparando-se o desempenho dos concretos pré-carregados ao dos concretos de referência, o cimento CP V ARI apresentou redução da retração média, exceto para a relação a/c 0,35 com cura de 7 dias. Nos concretos com cimento CP IV, a retração média diminuiu para a relação a/c 0,70, com ambas as idades de cura. O pré-carregamento provocou, em maior ou menor grau, a associação de dois diferentes efeitos. Por um lado, a compactação ocasionou a quebra dos compostos menos resistentes da matriz, havendo um efeito físico de redução dos vazios capilares, além da exposição de grãos anidros. Em paralelo, ocorreu a microfissuração do concreto, favorecendo, também, a exposição de grãos anidros. A cura por imersão possibilitou a continuidade da hidratação, com a formação de novos produtos resistentes na matriz, reduzindo as porosidades total e efetiva e, portanto, a taxa da retração do concreto. Além da densificação da matriz, a cura prolongada possibilitou a hidratação dos grãos anidros de cimento expostos nas paredes das microfissuras, favorecendo a sua autocicatrização (self-healing), o que contribuiu com a recuperação da capacidade resistente dos concretos, frente aos esforços da secagem. Assim, a associação destes fatores promoveu a redução da retração por secagem nos concretos estudados, principalmente nos mais porosos. / The growing concern with the performance of structures has encouraged several segments of society to find solutions to improve concrete durability. Several studies have been made to provide a better understanding of the mechanical properties and concrete durability in different conditions. This study assessed the drying shrinkage performance of preloaded concrete. Cement types CP V ARI, equivalent to Portland type III (ASTM C150/C150M-16e1) and CP IV, equivalent to Portland type IP (ASTM C595/C595M-16) were used with w/b = 0.35, 0.50 and 0.70 and curing ages of 7 and 28 days. At the ages of 1, 3 and 7 days, concrete mixes were subject to loads of 25%, 50% and 75% of their mean ultimate flexural strength (Brazilian Standard NBR 12142, ABNT, 2010). Drying shrinkage in reference and preloaded concrete was determined according to ASTM C157/C157M-14e1. Additional tests included ultrasound pulse velocity (NBR 8802, ABNT, 2013), mercury intrusion porosimetry (MIP) and X-ray microtomography. Preloaded CP V ARI cement concrete showed a drop in mean shrinkage when compared with the reference mix, except for the mix with w/b = 0.35 cured for 7 days. For CP IV cement, mean shrinkage dropped with w/b =0.70 for both curing ages. Early loading caused a compaction effect, promoting the weakest compounds of the matrix to be broken, filling the capillary voids. In this process some unhydrous grains probably were exposed. On the other hand, microcracking also occurred, lefting unhydrated grains exposed in the microcracks walls. Due to immersion curing, the availability of water promoted the hydration continuity. New resistant hydrates filled the large voids and reduced the total and effective porosities in the cement matrix. The hydration of anhydrous grains in the microcracks walls had led to self-healing, with partial resistance capacity recovery. The combined effect of these factors promoted the drying shrinkage reducing, mainly for the more porous concrets.

Apesar dos avanços tecnológicos e do conhecimento disponível sobre o concreto e suas propriedades, muitas estruturas apresentam-se degradadas prematuramente. Assim, são necessárias frequentes intervenções para reparo havendo, em consequência, consumo de quantidades expressivas de materiais, com importantes impactos financeiros e ambientais. A preocupação crescente com o desempenho das estruturas de concreto tem incentivado vários segmentos da sociedade a buscarem soluções que assegurem sua durabilidade. Nesse sentido, muitas pesquisas acadêmicas vêm sendo desenvolvidas para melhor entender o comportamento do concreto frente a diferentes condições de uso, considerando-se suas propriedades mecânicas e de durabilidade. Esta pesquisa teve por objetivo analisar o desempenho de concretos frente à retração por secagem, após terem sido submetidos ao pré-carregamento. Foram utilizados os cimentos CP V ARI e CP IV, nas relações a/c 0,35, 0,50 e 0,70, e adotadas as idades de cura de 7 e 28 dias. Nas idades 1, 3 e 7 dias, os concretos foram submetidos a carregamentos de 25%, 50% e 75% da carga média de ruptura à tração na flexão (NBR 12142, ABNT, 2010). Realizou-se o ensaio para determinação da retração por secagem (ASTM C157/C157M-08, 2014e1), em concretos de referência e nos pré-carregados. Foram também realizadas análises complementares, como determinação da velocidade da onda ultrassônica (NBR 8802, ABNT, 2013), porosimetria por intrusão de mercúrio e microtomografia de raios X. Comparando-se o desempenho dos concretos pré-carregados ao dos concretos de referência, o cimento CP V ARI apresentou redução da retração média, exceto para a relação a/c 0,35 com cura de 7 dias. Nos concretos com cimento CP IV, a retração média diminuiu para a relação a/c 0,70, com ambas as idades de cura. O pré-carregamento provocou, em maior ou menor grau, a associação de dois diferentes efeitos. Por um lado, a compactação ocasionou a quebra dos compostos menos resistentes da matriz, havendo um efeito físico de redução dos vazios capilares, além da exposição de grãos anidros. Em paralelo, ocorreu a microfissuração do concreto, favorecendo, também, a exposição de grãos anidros. A cura por imersão possibilitou a continuidade da hidratação, com a formação de novos produtos resistentes na matriz, reduzindo as porosidades total e efetiva e, portanto, a taxa da retração do concreto. Além da densificação da matriz, a cura prolongada possibilitou a hidratação dos grãos anidros de cimento expostos nas paredes das microfissuras, favorecendo a sua autocicatrização (self-healing), o que contribuiu com a recuperação da capacidade resistente dos concretos, frente aos esforços da secagem. Assim, a associação destes fatores promoveu a redução da retração por secagem nos concretos estudados, principalmente nos mais porosos. / The growing concern with the performance of structures has encouraged several segments of society to find solutions to improve concrete durability. Several studies have been made to provide a better understanding of the mechanical properties and concrete durability in different conditions. This study assessed the drying shrinkage performance of preloaded concrete. Cement types CP V ARI, equivalent to Portland type III (ASTM C150/C150M-16e1) and CP IV, equivalent to Portland type IP (ASTM C595/C595M-16) were used with w/b = 0.35, 0.50 and 0.70 and curing ages of 7 and 28 days. At the ages of 1, 3 and 7 days, concrete mixes were subject to loads of 25%, 50% and 75% of their mean ultimate flexural strength (Brazilian Standard NBR 12142, ABNT, 2010). Drying shrinkage in reference and preloaded concrete was determined according to ASTM C157/C157M-14e1. Additional tests included ultrasound pulse velocity (NBR 8802, ABNT, 2013), mercury intrusion porosimetry (MIP) and X-ray microtomography. Preloaded CP V ARI cement concrete showed a drop in mean shrinkage when compared with the reference mix, except for the mix with w/b = 0.35 cured for 7 days. For CP IV cement, mean shrinkage dropped with w/b =0.70 for both curing ages. Early loading caused a compaction effect, promoting the weakest compounds of the matrix to be broken, filling the capillary voids. In this process some unhydrous grains probably were exposed. On the other hand, microcracking also occurred, lefting unhydrated grains exposed in the microcracks walls. Due to immersion curing, the availability of water promoted the hydration continuity. New resistant hydrates filled the large voids and reduced the total and effective porosities in the cement matrix. The hydration of anhydrous grains in the microcracks walls had led to self-healing, with partial resistance capacity recovery. The combined effect of these factors promoted the drying shrinkage reducing, mainly for the more porous concrets.

The master thesis is focused on an evaluation of a preload lost in a tappered joint. The analyzed bolts are preloaded by a hydraulic tensioner. When the tensioner is removed, the joint is established and the preload in bolt is decreased. The analysisis carried out on axisymmetry model of joint in ANSYS Workbench 15, a finite element method is implemented in that software. The evaluation of the preload lost is made for a used range of ratio of clamped length to a nominal diameter of bolt. Geometry and material assumptions are defined. Before preloading of bolts to a desired value the process of stabilization preloading must be done otherwise outlines of the analysis are not applicable. On the base of the outlines of the analysis, the method for analytical computing of the desired pretension is done. The method involves the preload lost, which occurs due to establishment of the joint. The strength assesment of the hydraulic tensioner for bolts M72x4 is done. A 3D model of the tensioner with one plane of symmetry was used. Strength criteria for maximum allowed linear-elastic stress are in accordance with ČSN EN 13 445-3.

Preloading without a surcharge is a common method for ground improvement. Thereare however uncertainties related to the number of site investigations and the partialfactor method has been identified as a problem. This thesis proposes a probabilisticdesign approach, using a Monte Carlo simulation to calculate the failure probabilityin the serviceability limit state for preloading without a surcharge. The methodwas applied to a case where the possibility of using preloading without a surchargewas determined. A parameter influence and sensitivity analysis were performed todetermine what parameters were most important for the calculation. Problems withthe generation of random samples for the parameters; preconsolidation pressure andlimit pressure were identified, and four different methods of generating the randomsamples were tested, and discussed.The failure probability was calculated as a function of preloading time which wasused to determine what preloading time is needed to fall below the acceptable failureprobability of 5%. The required preloading time was found to be 580 days. Themost important parameters were found to be preconsolidation pressure, the modulusM0 and the coefficient of vertical consolidation.The proposed method is working and has several advantages, among them are theability to calculate the failure probability and the compatibility with the observationalmethod. The model uncertainty has been discussed, and a general commentis that with more research can the model uncertainty be decreased. Only 1D consolidationis considered in the method, this simplification is very practical as 2D and3D effects often can be neglected.

No description available.