Long-term static and dynamic monitoring to failure scenarios assessment in steel truss railway bridges: A case study

The latest studies on failures in steel truss-type bridge found that they are highly vulnerable to damage and thus prone to potential local or total collapse. Many authors recommend monitoring the critical elements in the existing steel truss-type bridges in real time to anticipate any failures in local members. Although mechanical strain is the most frequently used variable for this purpose, this method also happens to be the most expensive monitoring strategy. This paper describes a case study of failure scenarios assessment in a steel truss-type railway bridge after extensive long-term monitoring conducted by the authors, based on measuring vertical deflections and modal frequencies. The structure has both an isostatic and a hyperstatic configuration, and was assessed by means of a combination of: (i) long-term monitoring results, and (ii) a finite element analysis to simulate several failure scenarios. A sensitivity study of the different failure scenarios has been carried out, identifying those that can be detected. The results are used to define practical recommendations for failure detection by measuring vertical deflections and modal frequencies

Una plataforma para facilitar el aprendizaje en ingeniería acústica

En este trabajo se presenta una plataforma que facilita la realización de diversas actividades y prácticas asociadas a contenidos en el ámbito de lo que se viene denominando “ingeniería acústica”. El sistema central de esta plataforma es una tarjeta de adquisición de datos para la que se han programado diversas aplicaciones en Labview. Se pueden distinguir distintas áreas entre las que destacamos: el estudio de los transductores (con emisión audible y ultrasónicos) y la acústica de salas. También se han implementado aplicaciones concretas para la realización de medidas con técnicas ultrasónicas (emisor-receptor y eco-impulso). A lo largo del documento se explican, en primer lugar los fundamentos teóricos de las aplicaciones. A continuación se indica la estrategia a seguir por el profesor tanto en una sesión de prácticas presencial como en una lección magistral demostrativa. La utilización de plataformas como las que se presentan en este documento es un elemento de motivación para el alumnado, ya que puede comprobar que es capaz de desarrollar herramientas que compiten (y a veces aventajan) con las comerciales

Use of Higher-Harmonic and Intermodulation Generation of Ultrasonic Waves to Detecting Cracks due to Steel Corrosion in Reinforced Cement Mortar

The aim of this work was to provide further confirmation of the possible use of non-linear ultrasonic techniques for detecting the cracking due to corrosion of steel reinforcements in concrete. To this end accelerated steel corrosion tests have been conducted on model reinforced cement mortar specimens, while monitoring the appearance and width evolution of visible surface cracks, and performing non-linear ultrasonic measurements based on the phenomena of harmonic distortion and intermodulation. A new parameter, based on the difference between the amplitude of the fundamental frequency and the sum of the amplitudes of all the first-order and second-order intermodulation products, has been proposed in this work. The results confirm that the appearance of visible surface micro-cracks are preceded and accompanied by the observation of strong non-linear features in the received signal. Furthermore, the new parameter proposed in this work is as efficient as the relative non-linearity parameters, classically used in harmonic distortion non-linear ultrasonic studies, for detecting the non-linear features associated with the critical events of the cracking of cement mortar due to embedded steel corrosion. A hypothesis has been developed considering the possible effect of the filling of the void space by liquid containing rust products after the formation of new cracks or the enlargement of its width. This filling process, which might be particularly enhanced by net convective transport of liquid, would explain the evolution of the values of all the parameters used for putting in evidence the non-linear elastic features after the critical events of the cracking process.This research was funded by the Spanish Agencia Estatal de Investigación (Grant code BIA2016-80982-R) and by the European Regional Development Fund (Grant code BIA2016-80982-R)

Uso de señales pseudoaleatorias en aplicaciones para el estudio de la dinámica de vibraciones

El estudio de la propagación de una perturbación en un medio elástico es un contenido de relevancia en una carrera técnica. En los laboratorios docentes no es fácil llevar a cabo experimentos en los que el alumnado visualice fácilmente la dinámica de vibraciones. Además, la ejecución de prácticas demostrativas de análisis modal exige la utilización de configuraciones en las que son necesarios dispositivos excitadores como los Shaker o los martillos de impacto. En este trabajo se presenta una metodología experimental basada en la utilización de señales pseudoaleatorias tipo MLS (Maximum Length Sequence) y actuadores de tipo electrodinámico, de fácil acceso al profesorado, en aplicaciones para el estudio de la dinámica de vibraciones y que ha sido ensayada con éxito en diferentes titulaciones. La base experimental sobre la que se proponen las aplicaciones consiste en barras y estructuras tipo “L” construidas a partir de piedra arenisca tipo Bateig

Guidelines for the design of efficient sono-microreactors

Possible drawbacks of microreactors are inefficient reactant mixing and the clogging of microchannels when solid-forming reactions are carried out or solid (catalysts) suspensions are used. Ultrasonic irradiation has been successfully implemented for solving these problems in microreactor configurations ranging from capillaries immersed in ultrasonic baths to devices with miniaturized piezoelectric transducers. Moving forward in process intensification and sustainable development, the acoustic energy implementation requires a strategy to optimize the microreactor from an ultrasound viewpoint during its design. In this work, we present a simple analytical model that can be used as a guide to achieving a proper acoustic design of stacked microreactors. An example of this methodology was demonstrated through finite element analysis and it was compared with an experimental study found in the literature.This research is funded by the EU project MAPSYN: Microwave, Acoustic and Plasma SYNtheses, under grant agreement No. CP-IP 309376 of the European Union Seventh Framework Program

Underwater Anthropogenic Noise Pollution Assessment in Shallow Waters on the South-Eastern Coast of Spain

Anthropogenic noise is a growing threat to marine life due to the incrementation of human activity in the marine environment. In Europe, the Directive 2008/56/EC of the European Parliament and of the Council was published with the aim of establishing a framework for community action in the field of marine environmental policy. The directive introduces underwater acoustic energy, as detailed in Descriptor 11, and stipulates that the member states should set the threshold levels at which a good environmental status can be achieved by means of long-term monitoring campaigns. This research presents the results of a long-term underwater noise monitoring campaign with a duration of three years in the port of Cartagena located on the south-eastern coast of Spain, focusing on the monthly and annual variation patterns of low-frequency continuous noise. The acquired data are classified according to the source of the acoustic noise into shipping, other anthropogenic, and natural noise measurements. These three groups of measurements are processed in order to obtain one-third octave band levels centered at 63 and 125 Hz, as well as the overall bandwidth of unweighted Sound Pressure Level (SPL). The analysis of the measurements shows an increase in the annual average overall band of 4 and 3 dB of the natural and shipping noise, respectively, from 2013 to 2015. This monitoring campaign provides accurate acoustic values to establish threshold levels to achieve good environmental status and recommendations to conduct monitoring programs and regulations to control underwater noise pollution

Strain-based autoregressive modelling for system identification of railway bridges

Vehicular traffic represents the most influential loads on the structural integrity of railway bridges, therefore the design on dynamic criteria. This work explores the use of strain dynamic measurements to characterize the health condition of railway bridges under moving train loads. Specifically, the approach proposed in this work exploits the implementation of auto-regressive (AR) time series analysis for continuous damage detection. In this light, continuously extracted AR coefficients are used as damage-sensitive features. To automate the definition of the order of the AR model, the methodology implements a model selection approach based on the Bayesian information criterion (BIC), Akaike Information Criterion (AIC) and Mean Squared Error (MSE). In this exploratory investigation, the suitability and effectiveness of strain measurements against acceleration-based systems are appraised through a case study of a simply supported Euler-Bernoulli beam under moving loads. The moving loads problem in terms of vertical accelerations and normal strains is solved through modal decomposition in closed form. The presented numerical results and discussion evidence the effectiveness of the proposed approach, laying the basis for its implementation to real-world instrumented bridges

Caracterización vibroacústica de ruedas no neumáticas

Los estudios realizados sobre ruedas suelen tener en cuenta muestras de grandes dimensiones: ruedas de coches (neumáticas) o trenes (no neumáticas). No obstante, con relación a estructuras más reducidas no existen demasiados estudios. En el presente trabajo se propone una metodología experimental no destructiva y de bajo presupuesto para la caracterización de ruedas no neumáticas empleadas habitualmente en patines y patinetes. Estos elementos son de tamaño reducido y por norma general se encuentran compuestos por elastómeros como el poliuretano, lo que les confiere un comportamiento hiperelástico. Mediante el uso de instrumental de reducido tamaño, diseñado y fabricado a medida, se logra excitar la estructura de forma impulsiva. A partir de la respuesta del sistema, obtenida a partir de un micrófono de medida, se realiza un análisis modal operacional de la estructura. La repetición sistemática de medidas en campo cercano, en un plano paralelo a la superficie de la muestra, permite la identificación de las formas modales del sistema sin afectar al comportamiento del mismo. A partir de los resultados, se lleva a cabo el ajuste de un modelo numérico en FEM con el fin de establecer las propiedades mecánicas aparentes de cada uno de los componentes principales de la rueda.The studies about wheels only take in account the samples of big size: car (pneumatic - wheel) or train (non - pneumatic - wheel). However, there is a lack of effort about small structure in this field. In this work is proposed an experimental, low-cost methodology for the characterization of non-pneumatical wheels of small size, typical of roller-skates. Which are usually composed by hyperelastic polymers as PU (Polyurethane). By using a set of small-size 3D printed tools it could be done an impulsive excitation over the structure for an OMA (Operational Modal Analysis) study of the structure. The systematic near-filed measurements in a plane parallel to the wheel can be used to reconstruct and identify the different vibration modes of the structure. Finally, the results have been used to fit a numerical method has been in FEM, with the aim of obtain the apparent physical properties of the different elements of the wheel

Percepción Sonora de Vehículos Eléctricos

Los vehículos eléctricos e híbridos (EVs y HEVs) están llamados a ser el futuro del transporte en ciudades inteligentes y la clave para la reducción total del ruido y la polución en áreas urbanas. Sin embargo, para garantizar la seguridad vial deben solucionarse diversos problemas asociados a este tipo de vehículos. Hasta el momento, el uso de HEVs ha puesto de manifiesto el incremento del riesgo en entornos urbanos debido a la presencia de un sistema de transporte completamente silencioso. Las distintas administraciones están analizando el problema, siendo la medida más significativa hasta ahora el uso de Sistemas Acústicos de Alerta de Vehículos (AVAS). El objetivo de este artículo es analizar el comportamiento acústico de los vehículos híbridos y eléctricos a partir de las principales contribuciones científicas.Electric and hybrid Electric vehicles (EVs and HEVs) seem to be the future of transport in smart cities and the key for the total reduction of noise disturbance and pollution in urban areas. However, several problems have to be solved in order to guarantee the safety of these types of vehicles. So far, the use of HEVs has shown the danger of a «quiet» transport system in urban environments. The Competent Authorities are addressing the problem and the most significant proposal up to now is the use of Acoustic Vehicles Alerting Systems (AVAS). The aim of this chapter is to collect the main contributions regarding the acoustic behaviour of hybrid electric vehicles and electric vehicles