Uncertainties in the modal estimation from output-only data in civil structures

Cualquier estructura vibra según unas frecuencias propias definidas por sus parámetros modales (frecuencias naturales, amortiguamientos y formas modales). A través de las mediciones de la vibración en puntos clave de la estructura, los parámetros modales pueden ser estimados. En estructuras civiles, es difícil excitar una estructura de manera controlada, por lo tanto, las técnicas que implican la estimación de los parámetros modales sólo registrando su respuesta son de vital importancia para este tipo de estructuras. Esta técnica se conoce como Análisis Modal Operacional (OMA). La técnica del OMA no necesita excitar artificialmente la estructura, atendiendo únicamente a su comportamiento en servicio. La motivación para llevar a cabo pruebas de OMA surge en el campo de la Ingeniería Civil, debido a que excitar artificialmente con éxito grandes estructuras no sólo resulta difícil y costoso, sino que puede incluso dañarse la estructura. Su importancia reside en que el comportamiento global de una estructura está directamente relacionado con sus parámetros modales, y cualquier variación de rigidez, masa o condiciones de apoyo, aunque sean locales, quedan reflejadas en los parámetros modales. Por lo tanto, esta identificación puede integrarse en un sistema de vigilancia de la integridad estructural. La principal dificultad para el uso de los parámetros modales estimados mediante OMA son las incertidumbres asociadas a este proceso de estimación. Existen incertidumbres en el valor de los parámetros modales asociadas al proceso de cálculo (internos) y también asociadas a la influencia de los factores ambientales (externas), como es la temperatura. Este Trabajo Fin de Máster analiza estas dos fuentes de incertidumbre. Es decir, en primer lugar, para una estructura de laboratorio, se estudian y cuantifican las incertidumbres asociadas al programa de OMA utilizado. En segundo lugar, para una estructura en servicio (una pasarela de banda tesa), se estudian tanto el efecto del programa OMA como la influencia del factor ambiental en la estimación de los parámetros modales. Más concretamente, se ha propuesto un método para hacer un seguimiento de las frecuencias naturales de un mismo modo. Este método incluye un modelo de regresión lineal múltiple que permite eliminar la influencia de estos agentes externos. A structure vibrates according to some of its vibration modes, defined by their modal parameters (natural frequencies, damping ratios and modal shapes). Through the measurements of the vibration at key points of the structure, the modal parameters can be estimated. In civil engineering structures, it is difficult to excite structures in a controlled manner, thus, techniques involving output-only modal estimation are of vital importance for these structure. This techniques are known as Operational Modal Analysis (OMA). The OMA technique does not need to excite artificially the structure, this considers its behavior in service only. The motivation for carrying out OMA tests arises in the area of Civil Engineering, because successfully artificially excite large structures is difficult and expensive. It also may even damage the structure. The main goal is that the global behavior of a structure is directly related to their modal parameters, and any variation of stiffness, mass or support conditions, although it is local, is also reflected in the modal parameters. Therefore, this identification may be within a Structural Health Monitoring system. The main difficulty for using the modal parameters estimated by an OMA is the uncertainties associated to this estimation process. Thus, there are uncertainties in the value of the modal parameters associated to the computing process (internal) and the influence of environmental factors (external), such as the temperature. This Master’s Thesis analyzes these two sources of uncertainties. That is, firstly, for a lab structure, the uncertainties associated to the OMA program used are studied and quantified. Secondly, for an in-service structure (a stress-ribbon footbridge), both the effect of the OMA program and the influence of environmental factor on the modal parameters estimation are studied. More concretely, a method to track natural frequencies of the same mode has been proposed. This method includes a multiple linear regression model that allows to remove the influence of these external agents.

Active learning and generic competences in an operating systems course

The Bologna Declaration and the implementation of the European Higher Education Area are promoting the use of active learning methodologies. The aim of this study is to evaluate the effects obtained after applying active learning methodologies to the achievement of generic competences as well as to the academic performance. This study has been carried out at the Universidad Politécnica de Madrid, where these methodologies have been applied to the Operating Systems I subject of the degree in Technical Engineering in Computer Systems. The fundamental hypothesis tested was whether the implementation of active learning methodologies (cooperative learning and problem based learning) favours the achievement of certain generic competences (‘teamwork’ and ‘planning and time management’) and also whether this fact improved the academic performance of our students. The original approach of this work consists in using psychometric tests to measure the degree of acquired student’s generic competences instead of using opinion surveys, as usual. Results indicated that active learning methodologies improve the academic performance when compared to the traditional lecture/discussion method, according to the success rate obtained. These methods seem to have as well an effect on the teamwork competence (the perception of the behaviour of the other members in the group) but not on the perception of each students’ behaviour. Active learning does not produce any significant change in the generic competence ‘planning and time management'.

Integrating Generic Competences into Engineering Curricula

The new degrees in Spanish universities generated as a result of the Bologna process, stress a new dimension: the generic competencies to be acquired by university students (leadership, problem solving, respect for the environment, etc.). At Universidad Polite¿cnica de Madrid a teaching model was defined for two degrees: Graduate in Computer Engineering and Graduate in Software Engineering. Such model incorporates the training, development and assessment of generic competencies planned in these curricula. The aim of this paper is to describe how this model was implemented in both degrees. The model has three components. The first refers to a set of seven activities for introducing mechanisms for training, development and assessment of generic competencies. The second component aims to coordinate actions that implement the competencies across courses (in space and time). The third component consists of a series of activities to perform quality control. The implementation of generic competencies was carried out in first year courses (first and second semesters), together with the planning for second year courses (third and fourth semesters). We managed to involve a high percentage of first-year courses (80%) and the contacts that have been initiated suggest a high percentage in the second year as well.

Replications of software engineering experiments

There are many open issues that must be addressed before the replication process can be successfully formalized in empirical software engineering research. We define replication as the deliberate repetition of the same empirical study for the purpose of determining whether the results of the first experiment can be reproduced. This definition would appear at first glance to be good. However, it needs several clarifications that have not yet been forthcoming in software engineering: – What is the exact meaning of the same empirical study? Namely how similar should an experiment be to the baseline study for it to be considered a replication? What is the exact meaning of a result being reproduced? Namely how similar does a result have to be to the result of the baseline study for it to be considered reproduced? These and other methodological questions need to be researched and tailored for empirical software engineering.

In memoriam of Professor J. Munro

In memoriam of Professor John Munro was born in Glasgow the 8th of July 1925 and died on Wednesday 27th February 1985. He graduated in Civil Engineering at Glasgow University in 1951

Evidence of the presence of bias in subjective metrics: analysis within a family of experiments

Context: Measurement is crucial and important to empirical software engineering. Although reliability and validity are two important properties warranting consideration in measurement processes, they may be influenced by random or systematic error (bias) depending on which metric is used. Aim: Check whether, the simple subjective metrics used in empirical software engineering studies are prone to bias. Method: Comparison of the reliability of a family of empirical studies on requirements elicitation that explore the same phenomenon using different design types and objective and subjective metrics. Results: The objectively measured variables (experience and knowledge) tend to achieve more reliable results, whereas subjective metrics using Likert scales (expertise and familiarity) tend to be influenced by systematic error or bias. Conclusions: Studies that predominantly use variables measured subjectively, like opinion polls or expert opinion acquisition.

Análisis del rendimiento académico del alumnado de último curso de ingeniería mediante nuevas tecnologías en el proceso de enseñanza‐aprendizaje

En el marco del Espacio Europeo de Educación Superior los estudios deben de estar orientados a facilitar la movilidad de los futuros egresados para que su inclusión en mundo laboral sea global y en este contexto, los sistemas educativos deben introducir cambios en el proceso de enseñanza – aprendizaje y en la gestión. Como uno de los elementos básicos de la creación del EEES es el aprendizaje a lo largo de la vida, se deben adoptar metodologías que doten al estudiante de capacidades para poder enfrentarse a todos los retos de la vida laboral. A través de la presente investigación se trata de aportar una visión real de la aplicación efectiva de un modelo de Aprendizaje Basado en Problemas y el Método del Caso acompañados de una fuerte Acción Tutorial y el uso de la Tecnología de la Información y Comunicación en la Universidad (TIC). Se considera asimismo de gran interés para la mejora del aprendizaje conocer cuál es la opinión real de los estudiantes universitarios, ya que son los principales implicados en relación a un modelo formativo apoyado en el Aprendizaje Basado en Problemas, el Método del Caso, la Acción Tutorial y utilización de las TIC. A través de este estudio se pretende comprobar y valorar cual es la visión real que los alumnos tienen de estas aplicaciones y como las utilizan. Para ello durante los últimos cursos se ha trabajado con alumnos de los últimos cursos de la Escuela Técnica Superior de Ingeniería Civil de la Universidad Politécnica de Madrid aplicando técnicas de Aprendizaje Basado en Problemas y el Método del Caso conjuntamente con la utilización de un Modelo de Acción Tutorial y el uso de la TIC. La tarea se ha centrado en desarrollar, a lo largo de los cursos 2009-10, 2010-11, 2011-12 y 2013-14, un modelo de Acción Tutorial con los alumnos matriculados en las asignaturas de Caminos I, Caminos II, Aforos y Ordenación del Tráfico, asignaturas de la titulación de Ingeniería Técnica de Obras Públicas, y por otro lado, en la asignatura de Caminos, perteneciente a la titulación de Ingeniería Civil. Mediante cuestionarios al inicio y final del curso, se ha conocido cuál es la opinión que poseen los alumnos sobre esta acción. A continuación, durante los cursos 2010-11, 2011-12 y 2013-14 se desarrolla un modelo experimental para evaluar las mejoras, tanto de rendimiento como de adquisición de competencias, utilizando el Aprendizaje Basado en Problemas y el Método del Caso acompañados de las TIC en el proceso de enseñanza–aprendizaje como modelo de Acción Tutorial con alumnos. ABSTRACT Abstract In the frame of the European Higher Education Area, the studies must be faced to facilitate mobility of future graduates for inclusion in the workplace is global and in this context, educational systems must introduce changes in the process of education-learning and management. Since one of the basic elements of the creation of the EHEA is learning throughout life, there must be adopted methodologies that provide the student of aptitudes to be able to face all the challenges of the labor life. Through this research it is provided a real vision of the effective application of a Model of Learning Based on Problems and the Case Method accompanied by a strong Tutorial Action and the use of ITC in the University. It is also considered of great interest for the improvement of learning to know what the real opinion of the college students is, as they are the main players in relation in a training model based on Problem-Based Learning, the Case Method, the Tutorial Action and Use of ICT. Through this study it is expected to verify and assess which is the real vision that students have about these applications and how they use them. In order to achieve the goal of this research project, during the last three years I have been working with students of last courses of the Civil Engineering School of the Technical University of Madrid applying with them techniques of Problem-Based Learning and the Case Method together with the use of a Model Action Tutorial and the Use of Information Technology and Communication (ICT). The task has focused on developing, over the 2009-10, 2010-11, 2011-12 and 2013-14 courses, a model of Tutorial Action with students enrolled in the subjects of Roads I, Roads II, Traffic Gauging and Traffic Management, all of them of the old degree in Civil Engineering (1971 Study Plan), and secondly, on the subject of Roads which belong to the current degree of Civil Engineering. Using questionnaires at the beginning and end of the course the perception that students have on this action.. Then, during the 2010-11, 2011-12 and 2013-14 courses an experimental model is developed to evaluate improvements in both performance and skills acquisition, using Problem-Based Learning and the Case Method together with the ICT in Teaching-Learning Pprocess as a model of Tutorial Action with students.

Two-dimensional isostatic meshes in the finite element method

In a Finite Element (FE) analysis of elastic solids several items are usually considered, namely, type and shape of the elements, number of nodes per element, node positions, FE mesh, total number of degrees of freedom (dot) among others. In this paper a method to improve a given FE mesh used for a particular analysis is described. For the improvement criterion different objective functions have been chosen (Total potential energy and Average quadratic error) and the number of nodes and dof's of the new mesh remain constant and equal to the initial FE mesh. In order to find the mesh producing the minimum of the selected objective function the steepest descent gradient technique has been applied as optimization algorithm. However this efficient technique has the drawback that demands a large computation power. Extensive application of this methodology to different 2-D elasticity problems leads to the conclusion that isometric isostatic meshes (ii-meshes) produce better results than the standard reasonably initial regular meshes used in practice. This conclusion seems to be independent on the objective function used for comparison. These ii-meshes are obtained by placing FE nodes along the isostatic lines, i.e. curves tangent at each point to the principal direction lines of the elastic problem to be solved and they should be regularly spaced in order to build regular elements. That means ii-meshes are usually obtained by iteration, i.e. with the initial FE mesh the elastic analysis is carried out. By using the obtained results of this analysis the net of isostatic lines can be drawn and in a first trial an ii-mesh can be built. This first ii-mesh can be improved, if it necessary, by analyzing again the problem and generate after the FE analysis the new and improved ii-mesh. Typically, after two first tentative ii-meshes it is sufficient to produce good FE results from the elastic analysis. Several example of this procedure are presented.

Expressed protein ligation: A general method for protein engineering

A protein semisynthesis method—expressed protein ligation—is described that involves the chemoselective addition of a peptide to a recombinant protein. This method was used to ligate a phosphotyrosine peptide to the C terminus of the protein tyrosine kinase C-terminal Src kinase (Csk). By intercepting a thioester generated in the recombinant protein with an N-terminal cysteine containing synthetic peptide, near quantitative chemical ligation of the peptide to the protein was achieved. The semisynthetic tail-phosphorylated Csk showed evidence of an intramolecular phosphotyrosine-Src homology 2 interaction and an unexpected increase in catalytic phosphoryl transfer efficiency toward a physiologically relevant substrate compared with the non-tail-phosphorylated control. This work illustrates that expressed protein ligation is a simple and powerful new method in protein engineering to introduce sequences of unnatural amino acids, posttranslational modifications, and biophysical probes into proteins of any size.

Use of subpixel techniques in pocket cameras to measure vibrations and displacements

Presentación oral SPIE Photonics Europe, Brussels, 16-19 April 2012.

Chloride Penetration Prediction in Concrete through an Empirical Model Based on Constant Flux Diffusion

An empirical model based on constant flux is presented for chloride transport through concrete in atmospherical exposure conditions. A continuous supply of chlorides is assumed as a constant mass flux at the exposed concrete surface. The model is applied to experimental chloride profiles obtained from a real marine structure, and results are compared with the classical error-function model. The proposed model shows some advantages. It yields a better predictive capacity than the classical error-function model. The previously observed chloride surface concentration increases are compatible with the proposed model. Nevertheless, the predictive capacity of the model can fail if the concrete microstructure changes with time. The model seems to be appropriate for well-maturated concretes exposed to a marine environment in atmospherical conditions.

Using Sewage-Sludge Ash as Filler in Bituminous Mixes

In this study, the behavior of bituminous mixes made with sewage sludge ash (SSA) as mineral filler was investigated. The behavior of these mixes was evaluated with the Cantabro, indirect tensile strength, water sensitivity, permanent deformation, and resilient modulus tests. The results show that SSA waste may be used in bituminous mixes at approximately 2–3% weight percent, maintaining adequate levels of cohesion and adhesion in the mixtures, which is comparable to mixtures made with active fillers such as hydrated lime and cement. Moreover, its use does not increase permanent deformations. However, the resilient modulus test gave slightly lower results for mixes made with SSA than for mixtures made with other fillers. It may be concluded that SSA waste may be used as a filler for bituminous mixes with better results than for mixes made with limestone fillers and with similar results for mixes made with other fillers such as hydrated lime and cement.

Modelling and control of refrigeration systems: an account of a pedagogic experiment in a post-secondary technical course

Comunicação apresentada no CYTEF 2016/VIII Congresso Ibérico | VI Congresso Ibero-Americano de Ciências e Técnicas do Frio, 3-6 maio 2016, Coimbra, Portugal

Numerical and experimental investigation of structural stiffness influence on ratcheting convection cell in granular soils under cyclic loading

Lateral cyclic loaded structures in granular soils can lead to an accumulation of irreversible strains by changing their mechanical response (densification) and forming a closed convective cell in the upper layer of the bedding. In the present thesis the convective cell dimension, formation and grain migration inside this closed volume have been studied and presented in relation to structural stiffness and different loads. This relation was experimentally investigated by applying a cyclic lateral force to a scaled flexible vertical element embedded in dry granular soil. The model was monitored with a camera in order to derive the displacement field by means of the PIV technique. Modelling large soil deformation turns out to be difficult, using mesh-based methods. Consequently, a mesh-free approach (DEM) was chosen in order to investigate the granular flow with the aim of extracting interesting micromechanical information. In both the numerical and experimental analyses the effect of different loading magnitudes and different dimensions of the vertical element were considered. The main results regarded the different development, shape and dimensions of the convection cell and the surface settlements. Moreover, the Discrete Element Method has proven to give satisfactory results in the modelling of large deformation phenomena such as the ratcheting convective cell.

Selection of vehicle rear lighting systems. Final report.

National Highway Safety Bureau, Washington, D.C.