La fisuración discreta: una alternativa a los modelos análisis no-lineal de estructuras de hormigón

En este trabajo se presenta un modelo de elementos finitos con fisuración discreta para el análisis no lineal de estructuras planas de hormigón cargadas en su plano. Mediante la utilización de cinco tipos de elementos finitos diferentes se incluyen en el análisis, no sólo el comportamiento no lineal del acero y el hormigón, sino también los efectos de la adherencia, encajamiento de áridos y pasador de las armaduras que cruzan una fisura. Se ha desarrollado un algoritmo que resuelve de manera automática los problemas derivados de la regeneración de la m d a propios de la técnica de la fisuración discreta. Por último, algunos de los resultados obtenidos con el modelo son comparados con los obtenidos experimentalmente en vigas con roturas por cortante y flexión.This paper presents a discrete-crack finite element model for the nonlinear analysis of concrete structures under plane-stress conditions. The model incorporates five types of finite elements in order to take into account the different mechanisms of stress transmission in concrete structures: concrete and steel finite elements, and special finite elements for the modelling of bond, aggregate interlock and dowel-action. The modifications of the finite element mesh, typical of the discret-crack approach, are carried out using a fully automatic strategy. Finally, the model is applied to the analysis of beams failing in flexure and in shear and the analytical predictions compared with the experimental data.Peer Reviewe

La fisuración discreta: una alternativa a los modelos análisis no-lineal de estructuras de hormigón

En este trabajo se presenta un modelo de elementos finitos con fisuración discreta para el análisis no lineal de estructuras planas de hormigón cargadas en su plano. Mediante la utilización de cinco tipos de elementos finitos diferentes se incluyen en el análisis, no sólo el comportamiento no lineal del acero y el hormigón, sino también los efectos de la adherencia, encajamiento de áridos y pasador de las armaduras que cruzan una fisura. Se ha desarrollado un algoritmo que resuelve de manera automática los problemas derivados de la regeneración de la m d a propios de la técnica de la fisuración discreta. Por último, algunos de los resultados obtenidos con el modelo son comparados con los obtenidos experimentalmente en vigas con roturas por cortante y flexión.This paper presents a discrete-crack finite element model for the nonlinear analysis of concrete structures under plane-stress conditions. The model incorporates five types of finite elements in order to take into account the different mechanisms of stress transmission in concrete structures: concrete and steel finite elements, and special finite elements for the modelling of bond, aggregate interlock and dowel-action. The modifications of the finite element mesh, typical of the discret-crack approach, are carried out using a fully automatic strategy. Finally, the model is applied to the analysis of beams failing in flexure and in shear and the analytical predictions compared with the experimental data.Peer Reviewe

Fractional reaction-diffusion problems

Cette thèse porte sur deux problèmes différents : dans le premier, nous étudions le comportement en temps long des solutions des équations de réaction diffusion 1d-fractionnaire de type Fisher-KPP lorsque la condition initiale est asymptotiquement de type front et décroît à l'infini plus lentement que, où et est l'indice du laplacien fractionnaire (Chapitre 2). Dans le second problème, nous étudions la propagation asymptotique en temps des solutions de systèmes coopératifs de réaction-diffusion (Chapitre 3). Dans le premier problème, nous démontrons que les ensembles de niveau des solutions se déplacent exponentiellement vite en temps quand t tend vers l'infini. De plus, une estimation quantitative du mouvement de ces ensembles est obtenue en fonction de la décroissance à l'infini de la condition initiale. Dans le second problème, nous montrons que la vitesse de propagation est exponentielle en temps et nous trouvons un exposant précis qui dépend du plus petit ordre des laplaciens fractionnaires considérés et de la non-linéarité. Nous notons aussi que cet indice ne dépend pas de la direction spatiale de propagation.This thesis deals with two different problems: in the first one, we study the large-time behavior of solutions of one-dimensional fractional Fisher-KPP reaction diffusion equations, when the initial condition is asymptotically front-like and it decays at infinity more slowly than a power , where and is the order of the fractional Laplacian (Chapter 2); in the second problem, we study the time asymptotic propagation of solutions to the fractional reaction diffusion cooperative systems (Chapter 3). For the first problem, we prove that the level sets of the solutions move exponentially fast as time goes to infinity. Moreover, a quantitative estimate of motion of the level sets is obtained in terms of the decay of the initial condition. In the second problem, we prove that the propagation speed is exponential in time, and we find a precise exponent depending on the smallest index of the fractional laplacians and of the nonlinearity, also we note that it does not depend on the space direction

Understanding a Version of Multivariate Symmetric Uncertainty to assist in Feature Selection

In this paper, we analyze the behavior of the multivariate symmetric uncertainty (MSU) measure through the use of statistical simulation techniques under various mixes of informative and non-informative randomly generated features. Experiments show how the number of attributes, their cardinalities, and the sample size affect the MSU. We discovered a condition that preserves good quality in the MSU under different combinations of these three factors, providing a new useful criterion to help drive the process of dimension reduction

Predicción y análisis de interacciones de usuarios en plataformas de enseñanza online

Las plataformas de enseñanza online generan gran cantidad de metadatos sobre las interacciones entre los estudiantes y con la plataforma. Esta información puede ser aprovechada por los profesores de los cursos para mejorar el curso y la experiencia docente de los estudiantes. En este contexto el objetivo de este TFG es el análisis de las interacciones realizadas por los estudiantes en cursos online y la predicción del comportamiento del estudiante utilizando su patrón de acceso a la plataforma. Debido al volumen de datos que se maneja se hará uso herramientas de computación en paralelo como Apache Spark para preprocesar los datos generados por la plataforma. Mediante Apache Spark se creará una aplicación que extraiga el patrón de acceso de los estudiantes a la plataforma y disminuya la gran cantidad de metadatos generada en un curso online. Por último, se aplicarán algoritmos de aprendizaje automático para predecir variables de interés sobre la interacción de los estudiantes con el curso como la probabilidad de abandono o el rendimiento académico. Esto también se realizará con la herramienta Apache Spark. En concreto, se utilizará el algoritmo Random Forest de la librería MLlib de Spark con la finalidad de obtener el mejor resultado a la hora de predecir las variables de interés del curso.Online education platforms generate a lot of metadata about interactions among students and with the platform. This information can be harnessed by teachers to improve the course and student’s teaching experience. In this context the aim of this study is the analysis of interactions performed by students and the prediction of student’s behavior using his access patterns to platform. Due to the volume of data handled, we use a tool for parallel computing such as Apache Spark for preprocessing the data generated by the platform. We create an application that extracts the access patterns to platform and decreases the volume of the metadata generated in this online course. Finally, we apply machine learning algorithms to predict target variables related to the interactions of students enrolled in the course, for example the dropout rate or the academic performance. We also use the tool Apache Spark for this task. Specifically, we apply the algorithm Random Forest from the library MLlib in order to get the best result in predicting the course’s target variables

Sekcijas “Mārketings un loģistika” Ekonomikas un vadības fakultātē (1. februāris, 2016): Referātu tēzes

In recent years, there has been a significant increase of mobile devices usage (e.g. phones, tablets), consequently the demand of network capacity is higher than ever before. In large crowd events (such as football matches, concerts, accidents, etc), current content distribution is done in a host-centric manner where users have to retrieve content from external servers using the 3G-Uplink. This result in problems like Up-link congestion when there is an unexpected boost in data traffic. The prototype developed within this master thesis project, implements a new control layer in mobile devices, which can be used in events with large crowds as an alternative solution for optimizing content distribution. The usage of this solution decreases the amount of data sent over the 3G-uplink to retrieve similar contents, since they can be obtained from nearby peers using short range transport technologies. The alternative solution is based on information-centric networking paradigm. Using this approach in Large Crowd events, popular content could be cached in users’ devices creating new sources of content within the crowd. Afterwards, these copies could be shared between users using P2P-like communication over short range transport technologies available in nowadays’ mobile devices. In this new content distribution scheme, the more popular the content gets the more chances it could be retrieved from a cached copy within the crowd and, this could lead to a less amount of data transferred over the 3G uplin

The influence of transverse reinforcement and yielding of flexural reinforcement on the shear-transfer actions of RC members

[EN] The assessment of the shear strength of reinforced concrete beams with and without shear reinforcement is investigated in this paper on the basis of the contribution of the various potential shear-transfer actions. To that aim, a comprehensive experimental programme is presented, aimed at representing realistic conditions in reinforced concrete members. The programme comprised 15 cantilevers and 15 continuous beams with and without stirrups. In addition, some of the tests were designed to fail in shear after yielding of the flexural reinforcement, allowing to investigate on the structural implications of this phenomenon. The tests were instrumented by means of surface measurements using Digital Image Correlation (DIC), tracking in a detailed manner the development and kinematics of the critical shear crack leading to failure. Based on these mea-surements, and by accounting for suitable constitutive models, the contribution of the shear-transfer actions is estimated at different levels of load. The comparison of the experimental results with the calculated shear strength (sum of the contribution of the various shear-transfer actions at failure) shows consistent agreement for the various cases investigated. On this basis, several conclusions about the dominant shear-transfer actions at shear failure are presented, particularly on the role of the shear reinforcement and on the implications of the flexural reinforcement yielding on the overall response.This research was funded by grants from the Spanish Ministry of Economy and Competitiveness to Research Project BIA2015-64672-C4-4-R. The experimental programme was developed in the Laboratory of Concrete at the Institute of Concrete Science and Technology (ICITECH) of the Universitat Politecnica de Valencia (UPV), with concrete supplied by Caplansa. Andrea Monserrat was supported by the Conselleria d'Educacio, Investigacio, Cultura i Esport of the Generalitat Valenciana (Order 6/2015, DOGV no. 7615 15.09.2015) with European Regional Development Funds (ERDF) allocated by the EU. VIC2D software was employed during the research stay of Andrea Monserrat at the EPFL (Lausanne, Switzerland).Monserrat López, A.; Fernánez Ruiz, M.; Miguel Sosa, P. (2021). The influence of transverse reinforcement and yielding of flexural reinforcement on the shear-transfer actions of RC members. Engineering Structures. 234:1-17. https://doi.org/10.1016/j.engstruct.2021.111949S11723

Punching shear failure in three-pile caps: Influence of the shear span-depth ratio and secondary reinforcement

[EN] The strut-and-tie model (STM) is currently established as the best approach for pile cap design. This model leads to efficient estimations of the main reinforcement placed in strips between piles. However, good practices and some international Concrete Design Standards recommend some secondary distributed reinforcement, and even vertical stirrups that are not considered by the STM. An experimental campaign with nine three-pile caps tested by a centered load is presented to show the influence of both secondary reinforcement and the shear span-depth ratio on pile cap strength. The experimental results show a potential redistribution of internal forces in pile caps after yielding of main reinforcement, finally collapsed due to punching. Secondary reinforcement proves efficient to enhance pile cap strength since it takes part in complementary resistance mechanisms. As expected, the failure load increases with shear span-depth ratio reduction. The STM neither captures the effect of this ratio nor considers punching failure. Checking this failure mode is also required for pile caps. The punching formulation of Eurocode 2 allows considering the influence of this ratio, but some interpretation is required whether one deals with pile caps, regarding the effective width of the shear enhancement factor and the definition of the basic control perimeter. A proper definition would prevent unsafe or very conservative results. Therefore, some recommendations for the verification of deep pile caps following the Eurocode 2 are presented. The contribution of vertical stirrups as punching reinforcement is also investigated. The proposed approach is applied to the existing experimental database of three- and four-pile caps to check formulation validity, and conservative predictions with low coefficient of variation are reached.The authors would like to acknowledge the funding received from the Spanish Ministry of Economy and Competitiveness for basic non oriented research projects (BIA2012-32300), which also included a PhD fellowship (BES-2013-063409).Miguel-Tortola, L.; Pallarés Rubio, L.; Miguel Sosa, P. (2018). Punching shear failure in three-pile caps: Influence of the shear span-depth ratio and secondary reinforcement. Engineering Structures. 155:127-142. https://doi.org/10.1016/j.engstruct.2017.10.077S12714215

Strength of pile caps under eccentric loads: Experimental study and review of code provisions

[EN] Pile caps are rigid reinforced concrete structures that transfer column loads, generally consisting of a combination of an axial load and bending moments in one or two directions, to the piles. The design formulations of pile caps for more than two piles were derived from the results of experimental tests under a centered load. The practice of checking both punching and shear failure modes is common as described in the literature review, even though these formulations were developed for more slender elements. Currently, Codes ACI 318-14 and EC2 allow designing pile caps with strut-and-tie models or sectional approaches (shear, punching and flexural designs). In this study, 21 full-scale pile caps with different shear span-depth ratios and reinforcement layouts were studied to investigate the effect of eccentric loading on the strength and accuracy of the code formulations. The results show that in eccentrically loaded pile caps, the ultimate load is reduced but the maximum pile reaction increases and the secondary reinforcement proves effective to enhance the pile cap strength. Although the strut-and-tie models (STM) allow eccentric loads to be taken into consideration, they predict a much lower peak load than that observed at the experimental results and do not adequately reflect either the influence of slenderness or the failure mode. In general the sectional approach provided by Codes ACI-318-14, EC2 and MC-2010 (Level I of Approximation) lead to safe predictions of the peak load but do not always correctly predict the failure mode. The ultimate load predicted by EC-2 formulation comes closest to the experimental peak load, accurately reflects the influence of slenderness and the effect of secondary reinforcement, however, additional assumptions need to be made for its application. The ACI formulation complemented by the CRSI-2008 Special Investigation for deep pile caps is the safest but does not adequately capture the effect of horizontal and vertical secondary reinforcement. The MC2010 LoAI formulation is also conservative but does not detect the influence of slenderness or the contribution of secondary reinforcement.The authors wish to express their gratitude for the financial support (BIA2012-32300 and BIA2015-64672-C4-4-R) received from the Spanish Ministry of Economy and Competitiveness, which enabled the experimental campaign to be carried out, also for the PhD fellowship (BES-2013-063409).Miguel-Tortola, L.; Miguel Sosa, P.; Pallarés Rubio, L. (2019). Strength of pile caps under eccentric loads: Experimental study and review of code provisions. Engineering Structures. 182:251-267. https://doi.org/10.1016/j.engstruct.2018.12.064S25126718

Impacto del tratado de libre comercio Perú - Estados Unidos en las exportaciones no tradicionales (periodo 2001 – 2016)

El objetivo de este trabajo es identificar el impacto del Tratado de Libre Comercio Perú – Estados Unidos en las exportaciones no tradicionales. En tal sentido se ha empleado una muestra de datos Trimestrales de los años 2000 y 2016 de las exportaciones no tradicionales del Perú a Estados Unidos, del PBI real norteamericano y del Tipo de cambio real bilateral. Para la prueba de hipótesis se empleó métodos econométricos con datos cuantitativos, empleándose el método de los mínimos cuadrados y estimadores MELI (mejores estimadores lineales insesgados). Los resultados obtenidos nos permitirán evaluar si el TLC ha tenido un impacto positivo en el crecimiento de nuestras exportaciones no tradicionales. Del análisis gráfico y del test de la raíz unitaria para las variables exportaciones no tradicionales, PBIreal delos Estados Unidos, tipo de cambio real y la vigencia del acuerdo comercial se puede concluir que el PBI de Estados Unidos afecta significativa y directamente a las exportaciones no tradicionales del Perú, El tipo de cambio real influye en relación directa a las exportaciones no tradicionales del Perú durante el período de estudio. La investigación es cuantitativa y longitudinal, longitudinal porque estamos investigando el comportamiento de las variables desde 2000 hasta el 2016. Por último el acuerdo ha sido beneficioso para las exportaciones no tradicionales peruanas durante el período 2009-2016