This paper studies the cross-sectional behaviour of austenitic, ferritic and duplex stainless steel hollow sections subjected to several loading conditions and presents a full slenderness range DSM approach for the prediction of cross-sectional strengths. Pure compression, pure bending moment and combined uniaxial bending and compression loading resistances are predicted using the same strength curve, which is based on experimental data gathered from the literature and ultimate strengths generated through parametric studies. The proposed approach is applicable to slender and stocky cross-sections leading to an accurate full slenderness range DSM design approach since the resistance reduction due to local buckling and the effect of strain hardening are taken into account, as is the effect of partial yielding of the cross-section in bending. A new method based on the actual stress distribution of the cross-section is also presented for combined loading conditions, where the cross-sectional behaviour is directly tackled through the same strength curve, providing more accurate results than the methods considering the uncoupled problem. Finally, a statistical analysis is presented to demonstrate the reliability of the proposed DSM approach.
In contrast to terrestrial environment, the harsh lunar environment conditions include lower gravity acceleration, ultra-high vacuum and high (low) temperature in the daytime (night-time). This paper focuses on the effects of those mentioned features on soil cutting tests, a simplified excavation test, to reduce the risk of lunar excavation missions. Soil behavior and blade performance were analyzed under different environmental conditions. The results show that: (1) the cutting resistance and the energy consumption increase linearly with the gravity. The bending moment has a bigger increasing rate in low gravity fields due to a decreasing moment arm; (2) the cutting resistance, energy consumption and bending moment increase significantly because of the raised soil strength on the lunar environment, especially in low gravity fields. Under the lunar environment, the proportions of cutting resistance, bending moment and energy consumption due to the effect of the van der Waals forces are significant. Thus, they should be taken into consideration when planning excavations on the Moon. Therefore, considering that the maximum frictional force between the excavator and the lunar surface is proportional to the gravity acceleration, the same excavator that works efficiently on the Earth may not be able to work properly on the Moon.
The Campo de Cartagena (Eastern Spain) is one of Europe’s driest areas with a mean precipitation of around 300 mm. One of the main challengesin the region is to secure a reliable water supply in both quantity and quality terms, to provide a water supply and agricultural irrigation, while water desalination has become an extensively applied solution, and one of the most sustainable solutions to the water scarcity problem. As water availability is lacking and groundwater quality is poor, the agricultural sector in Campo de Cartagena has developed small private brackish groundwater desalination plants (15-20 m3/h) through already existing agricultural wells. Costs and benefits (C-B) for citrus cultivation (1 ha) in three such plants have been assessed. The results indicate that for the studied cases, current agricultural management is feasible and costs outweigh benefits, with a positive NPV and a cost/benefit ratio higher than 1. The internal rate of return is also positive and higher than 11%. The results evidence practical and theoretical implications as to how to increase water resources in areas where water is scarce by closing the loop, ensuring farmers’ profitability and encouraging private sector investments.
La presente invención se refiere, en estructuras flotantes de soporte de turbinas eólicas, a la materialización mediante una lámina de hormigón pretensado de la zona de transición entre la torre, de menor diámetro, y el flotador de hormigón de mayor diámetro, tanto si la torre es metálica como de hormigón. Dicha lámina de revolución presenta una geometría óptima para la correcta transmisión de esfuerzos entre ambas partes, torre y flotador, con un espesor reducido y sin necesidad de elementos de rigidización y refuerzo exteriores a sus superficies que aumentarían el peso y el coste de la estructura.
Perez, F.; Botella, R.; López-Montero, T.; Miro, R.; Martinez, A. International journal of fatigue num. 98, p. 111-120 DOI: 10.1016/j.ijfatigue.2017.01.026 Data de publicació: 2017-05 Article en revista
This paper compares the results obtained in two types of cyclic tension-compression tests, a time sweep test, constant strain amplitude, and a strain sweep test, increasing strain amplitude every 5000 cycles, called EBADE (standing for the Spanish words for strain sweep test). This comparison has shown that the rapid loss of stiffness during the initial part of cyclic testing is recoverable in bituminous materials. It has been found that reversible phenomena dominate in asphalt binders, while in mixtures are as important as damage. A damage equation has been proposed to describe the evolution of the material distress during the phase II in time sweep tests. In addition, a new methodology to estimate the fatigue law of bituminous mixtures is proposed.
Montero-Chacón, F.; Zaghi, S.; Rossi, R.; García-Pérez, E.; Heras, I.; Martinez, X.; Oller, S.; Doblaré, M. Finite elements in analysis and design Vol. 127, p. 31-43 DOI: 10.1016/j.finel.2016.12.006 Data de publicació: 2017-05 Article en revista
Solar selective coatings can be multi-layered materials that optimize the solar absorption while reducing thermal radiation losses, granting the material long-term stability. These layers are deposited on structural materials (e.g., stainless steel, Inconel) in order to enhance the optical and thermal properties of the heat transfer system. However, interesting questions regarding their mechanical stability arise when operating at high temperatures. In this work, a full thermo-mechanical multiscale methodology is presented, covering the nano-, micro-, and macroscopic scales. In such methodology, fundamental material properties are determined by means of molecular dynamics simulations that are consequently implemented at the microstructural level by means of finite element analyses. On the other hand, the macroscale problem is solved while taking into account the effect of the microstructure via thermo-mechanical homogenization on a representative volume element (RVE). The methodology presented herein has been successfully implemented in a reference problem in concentrating solar power plants, namely the characterization of a carbon-based nanocomposite and the obtained results are in agreement with the expected theoretical values, demonstrating that it is now possible to apply successfully the concepts behind Integrated Computational Materials Engineering to design new coatings for complex realistic thermo-mechanical applications.
Sole, M.; Cucina, M.; Folch, M.; Tapias, J.; Gigliotti, G.; Marianna Garfi'; Ferrer, I. Science of the total environment Vol. 586, p. 1-9 DOI: 10.1016/j.scitotenv.2017.02.006 Data de publicació: 2017-05 Article en revista
Microalgae anaerobic digestion produces biogas along with a digestate that may be reused in agriculture. However, the properties of this digestate for agricultural reuse have yet to be determined. The aim of this study was to characterise digestates from different microalgae anaerobic digestion processes (i.e. digestion of untreated microalgae, thermally pretreated microalgae and thermally pretreated microalgae in co-digestion with primary sludge). The main parameters evaluated were organic matter, macronutrients and heavy metals content, hygenisation, potential phytotoxicity and organic matter stabilisation. According to the results, all microalgae digestates presented suitable organic matter and macronutrients, especially organic and ammonium nitrogen, for agricultural soils amendment. However, the thermally pretreated microalgae digestate was the least stabilised digestate in comparison with untreated microalgae and co-digestion digestates. In vivo bioassays demonstrated that the digestates did not show residual phytotoxicity when properly diluted, being the co-digestion digestate the one which presented less phytotoxicity. Heavy metals contents resulted far below the threshold established by the European legislation on sludge spreading. Moreover, low presence of E. coli was observed in all digestates. Therefore, agricultural reuse of thermally pretreated microalgae and primary sludge co-digestate through irrigation emerges a suitable strategy to recycle nutrients from wastewater.
This paper deals with the Middle Triassic-to-earliest Jurassic evaporite sedimentation in the epicontinental, eastern Iberian platform. This deposition occurred under extensional regime during the westwards migration of the Neotethys Ocean at the start of the Pangea break-up. Although attention is focused on the evaporitic episodes recorded in the Epicontinental (Germanic) Triassic of the platform, the evaporite units in the carbonatic Alpine Triassic are also considered. In the Epicontinental Triassic, up to six evaporitic episodes, which alternated with three carbonatic episodes and a siliciclastic one, occurred between the Anisian and the Lower Hettangian. The evaporitic episodes may be divided into two groups. The stratigraphic units of the older group have similar characteristics in salinity and facies, and were formed in chloride-rich, evaporitic mudflats. In the younger group, the salinity and depositional features display considerable differences and the environments evolved from evaporitic mudflats to extensive salterns. The different evolutive trends in the evaporites of the two groups suggest major re-structuration of the platform after the sedimentation of the siliciclastic units of the middle Keuper (Carnian Humide Episode). Progressive marine influence in the assemblage of the six evaporitic episodes is deduced from the changing nature of the evaporites and their host sediment. All the evaporite units accumulated as transgressive and highstand systems tracts. The close relationship between evaporite units and thick accumulation suggests that the structural control played a major role in the sedimentation. In the Alpine Triassic, the presence of evaporites interbedded in the allochthonous carbonate units is documented. Lateral correlation of the evaporite units of the Epicontinental and the Alpine types of Triassic allows us to reconstruct the facies continuum across the original Iberian platform. Such a west-to-east transect illustrates the palaeogeography, structural evolution, and major depositional controls in the platform during the period under study. The deduced evaporitic pattern could be applied to other Triassic platforms which acted as epeiric seaways for the westward advance of the Neotethys.
Soriguera, F.; Martínez, I.; Sala, M.; Menéndez, M. Transportation research. Part C, emerging technologies Vol. 77, p. 257-274 DOI: 10.1016/j.trc.2017.01.024 Data de publicació: 2017-04 Article en revista
Recent years have seen a renewed interest in Variable Speed Limit (VSL) strategies. New opportunities for VSL as a freeway metering mechanism or a homogenization scheme to reduce speed differences and lane changing maneuvers are being explored. This paper examines both the macroscopic and microscopic effects of different speed limits on a traffic stream, especially when adopting low speed limits. To that end, data from a VSL experiment carried out on a freeway in Spain are used. Data include vehicle counts, speeds and occupancy per lane, as well as lane changing rates for three days, each with a different fixed speed limit (80 km/h, 60 km/h, and 40km/h). Results reveal some of the mechanisms through which VSL affects traffic performance, specifically the flow and speed distribution across lanes, as well as the ensuing lane changing maneuvers. It is confirmed that the lower the speed limit, the higher the occupancy to achieve a given flow. This result has been observed even for relatively high flows and low speed limits. For instance, a stable flow of 1942 veh/h/lane has been measured with the 40 km/h speed limit in force. The corresponding occupancy was 33%, doubling the typical occupancy for this flow in the absence of speed limits. This means that VSL strategies aiming to restrict the mainline flow on a freeway by using low speed limits will need to be applied carefully, avoiding conditions as the ones presented here, where speed limits have a reduced ability to limit flows. On the other hand, VSL strategies trying to get the most from the increased vehicle storage capacity of freeways under low speed limits might be rather promising. Additionally, results show that lower speed limits increase the speed differences across lanes for moderate demands. This, in turn, also increases the lane changing rate. This means that VSL strategies aiming to homogenize traffic and reduce lane changing activity might not be successful when adopting such low speed limits. In contrast, lower speed limits widen the range of flows under uniform lane flow distributions, so that, even for moderate to low demands, the under-utilization of any lane is avoided. These findings are useful for the development of better traffic models that are able to emulate these effects. Moreover, they are crucial for the implementation and assessment of VSL strategies and other traffic control algorithms.
The purpose of this paper is to determine the Recreational Carrying Capacity of three estuarine beaches (Colares, Marudá and Murubira) on the Amazon coast of Brazil, based on the combined assessment of natural conditions and visitor facilities. In the final analysis, the carrying capacity of Colares beach was estimated to be 1089 visitors per day, and that of Murubira beach, 238 visitors per day. At Marudá beach, however, the inadequate quality of the water resulted in an RCC of zero, indicating that the beach should not be visited for recreational use. The results of this study may provide a valuable diagnostic tool for the development of future state and municipal coastal management programs. We believe that the procedures adopted in this study are applicable to other estuarine beaches on the Amazon coast, as well as in other estuarine beaches elsewhere with similar natural characteristics.
In this work we prove that weak solutions constructed by a variational multiscale method are suitable in the sense of Scheffer. In order to prove this result, we consider a subgrid model that enforces orthogonality between subgrid and finite element components. Further, the subgrid component must be tracked in time. Since this type of schemes introduce pressure stabilization, we have proved the result for equal-order velocity and pressure finite element spaces that do not satisfy a discrete inf-sup condition.
This paper presents the results of an experimental program carried out in the laboratory to evaluate the shear strength of aerial lime mortar brickwork. Masonry triplets and walls were tested after one year from their construction by adopting two different testing methods. The first approach consisted in the shear tests of masonry triplets, whereas the second technique was based on core drilling from walls of 90 mm diameter cylindrical specimens to be subjected to Brazilian tests with varying inclination of the diametric mortar joint. The first method is more adequate to characterize new masonry, whilst the second one is a suitable MDT procedure for the analysis of existing structures. The experimental results from standard and non-standard tests were properly investigated in order to obtain the shear failure envelope of the bond interface and mortar joint. The comparisons between the different tests and their interpretative theories show the possibilities of the novel non-standard testing method for the evaluation of the shear strength of structures of the built cultural heritage.
The paper presents an integrated approach aimed at assessing the seismic safety of Mallorca cathedral. This cathedral is an extraordinary historical construction dating back to the middle-ages. The experimental modal parameters of the cathedral were identified using Ambient Vibration Testing (AVT). The cathedral numerical model was updated using the identified modal parameters. This updated model was then used to study the seismic response of the cathedral using non-linear static (pushover) analysis. A sensitively analysis was carried out to reveal the dependency of the seismic capacity on the input materials properties. To assess the seismic performance and the safety of the cathedral, the N2 method was employed. It was found that the cathedral is safe when subjected to the earthquakes expected in Mallorca Island.
Cateura, J.; Sospedra, J.; González-Marco, D.; Sanchez-Arcilla, A. HydroSenSoft - Simposio Internacional de Sensores y Software Hidro-Ambiental con Exposición p. 37-38 Data de presentació: 2017-03-01 Presentació treball a congrés
The pressure on coastal seas keeps on increasing (navigation, fisheries, tourism, etc.) and this requires robust observations with adequate coverage. The deployment of wind turbines in shallow waters offers a good example demanding high resolution data in the air column, from the free surface to a height of order 200m. The corresponding structural assessment (loads for fixed towers and loads/motions for floating structures) needs also waves/current/sea level data in the upper part of the water column.
To address this challenge a prototype buoy, equipped to measure airflow with a LIDAR and water flow with an acoustic Doppler profiler, has been developed and is here presented. The paper shows the conceptual design and performance of this new buoy as a platform for efficient multi-variable observations. The operation of the buoy is based on batteries and solar cells. The resulting observations have been calibrated with data from an instrumented coastal pier during a pilot deployment off the Badalona coast and a meteo mast off the Dutch coast, covering a number of representative met-ocean events.
This paper reviews the simplified procedure proposed by Ghosn and Sivakumar to model the maximum expected traffic load effect on highway bridges and illustrates the methodology using a set of Weigh-In-Motion (WIM) data collected on one site in the U.S.A. The paper compares different approaches for implementing the procedure and explores the effects of limitations in the site-specific data on the projected maximum live load effect for different bridge service lives. A sensitivity analysis is carried out to study changes in the final results due to variations in the parameters that define the characteristics of the WIM data and those used in the calculation of the maximum load effect. The procedure is also implemented on a set of WIM data collected in Slovenia to study the maximum load effect on existing Slovenian highway bridges and how the projected results compare to the values obtained using advanced simulation algorithms and those specified in the Eurocode of actions.
Petracca, M.; Pela, L.; Rossi, R.; Oller, S.; Camata, G.; Spacone, E. Computer methods in applied mechanics and engineering Vol. 315, p. 273-301 DOI: 10.1016/j.cma.2016.10.046 Data de publicació: 2017-03 Article en revista
This work presents a multiscale method based on computational homogenization for the analysis of general heterogeneous thick shell structures, with special focus on periodic brick-masonry walls. The proposed method is designed for the analysis of shells whose micro-structure is heterogeneous in the in-plane directions, but initially homogeneous in the shell-thickness direction, a structural topology that can be found in single-leaf brick masonry walls. Under this assumption, this work proposes an efficient homogenization scheme where both the macro-scale and the micro-scale are described by the same shell theory. The proposed method is then applied to the analysis of out-of-plane loaded brick-masonry walls, and compared to experimental and micro-modeling results.
This paper describes the capabilities of a novel technique to investigate crack formation and propagation in drying soils. The technique is a relatively simple, non-destructive indirect technique using a ground-penetrating-radar (GPR) system to detect cracks that form and propagate inside a soil specimen during desiccation. Although GPR devices have been used for multiple applications, their use in soils for the detection of small desiccation cracks has not been demonstrated yet. The experiment and the methodology used to test the accuracy of a small compact commercial GPR device for crack identification are described. The main objective was to identify what type of signals and what crack width and separation between them can be detected using the GPR device. The results indicate that cracks of 1 or 2mm wide can be detected depending on its position and shape, whereas sub-millimeter cracks are undetectable with the currently existing devices in the market. Regardless of this limitation, the GPR method can be useful to find time-related bounds of when the cracks appear, to point at their location and sometimes at the separation between two of them. Detection of cracks with origin at the bottom or within the specimen was accomplished with this system. Distances of 5 cm or more between cracks can be detected and measured, as well, with accuracy.
Angrill, S.; Segura, L.; Petit-Boix, A.; Rieradevall, J.; Gabarrell, X.; Josa, A. International journal of life cycle assessment Vol. 22, num. 3, p. 1-12 DOI: 10.1007/s11367-016-1174-x Data de publicació: 2017-03 Article en revista
Purpose: The rapid urbanization and the constant expansion of urban areas during the last decades have locally led to increasing water shortage. Rainwater harvesting (RWH) systems have the potential to be an important contributor to urban water self-sufficiency. The goal of this study was to select an environmentally optimal RWH strategy in newly constructed residential buildings linked to rainwater demand for laundry under Mediterranean climatic conditions, without accounting for water from the mains.
Methods: Different strategies were environmentally assessed for the design and use of RWH infrastructures in residential apartment blocks in Mediterranean climates. The harvested rainwater was used for laundry in all strategies. These strategies accounted for (i) tank location (i.e., tank distributed over the roof and underground tank), (ii) building height considering the number of stories (i.e., 6, 9, 12, and 15), and (iii) distribution strategy (i.e., shared laundry, supply to the nearest apartments, and distribution throughout the building). The RWH systems consisted of the catchment, storage, and distribution stages, and the structural and hydraulic calculations were based on Mediterranean conditions. The quantification of the environmental performance of each strategy (e.g., CO2eq. emissions) was performed in accordance with the life cycle assessment methodology.
Results and discussion: According to the environmental assessment, the tank location and distribution strategy chosen were the most important variables in the optimization of RWH systems. Roof tank strategies present fewer impacts than their underground tank equivalents because they enhance energy and material savings, and their reinforcement requirements can be accounted for within the safety factors of the building structure without the tank. Among roof tanks and depending on the height, a distribution strategy that concentrates demand in a laundry room was the preferable option, resulting in reductions from 25 to 54 % in most of the selected impact categories compared to distribution throughout the building.
Conclusions: These results may set new urban planning standards for the design and construction of buildings from the perspective of sustainable water management. In this sense, a behavioral change regarding demand should be promoted in compact, dense urban settlements.
In this work a kinematics for laminated beams enriched with a refined formulation ZigZag (RZT), originally presented by Tessler et al. in 2007, introduced in a hierarchical one dimensional type “p” finite element is presented. The finite element employs Lagrange polynomials for the approximation of the degrees of freedom of the ends (nodes) and orthogonal Gram-Schmidt polynomials to the internal degrees of freedoms. This finite element allows a very low discretization, is free of shear locking and behaves very well when the analysis of laminated composites with accurate determination of local stresses and strains at laminar level is necessary.
This element has been validated in the analysis of laminated beams with various sequences of symmetric and asymmetric stacking, studying in each case its accuracy and stability.
Angrill, S.; Petit-Boix, A.; Morales, T.; Josa, A.; Rieradevall, J.; Gabarrell, X. Journal of environmental management Vol. 189, p. 14-21 DOI: 10.1016/j.jenvman.2016.12.027 Data de publicació: 2017-03 Article en revista
Rainwater harvesting might help to achieve self-sufficiency, but it must comply with health standards. We studied the runoff quantity and quality harvested from seven urban surfaces in a university campus in Barcelona according to their use (pedestrian or motorized mobility) and materials (concrete, asphalt and slabs). An experimental rainwater harvesting system was used to collect the runoff resulting from a set of rainfall events. We estimated the runoff coefficient and initial abstraction of each surface and analyzed the physicochemical and microbiological properties, and hydrocarbon and metal content of the samples. Rainfall intensity, surface material and state of conservation were essential parameters. Because of low rainfall intensity and surface degradation, the runoff coefficient was variable, with a minimum of 0.41. Concrete had the best quality, whereas weathering and particulate matter deposition led to worse quality in asphalt areas. Physicochemical runoff quality was outstanding when compared to superficial and underground water. Microorganisms were identified in the samples (>1 CFU/100 mL) and treatment is required to meet human consumption standards. Motorized traffic mostly affects the presence of metals such as zinc (31.7 µg/L). In the future, sustainable mobility patterns might result in improved rainwater quality standards.
Fatigue cracking of bituminous mixtures is closely related to the loss of ductility produced by the stiffening of the bituminous binder. The main two factors that cause the asphalt binder to lose its ductility are aging and exposure to low temperatures. However, most of the tests designed to evaluate the fatigue behavior of bituminous mixtures are very time consuming, and make unpractical those studies that try to evaluate the influence of many variables. In this research project a strain sweep test was used to analyze the influence of aging, test temperature and bituminous binder type on the fatigue behavior of a continuously graded mixture. As expected, the mixture with SBS polymer modified binder retained more ductility at low temperatures, while the mixture with crumb rubber modified binder had the highest stiffness modulus. All mixtures exhibited the worst fatigue behavior at low temperatures and aging was equivalent to testing an unaged mixture at a lower temperature. The main result of this paper was the implementation of a new methodology to estimate the fatigue law of the material using a strain sweep test, which allowed this fatigue analysis to be carried out in nearly 10 times less testing time than that required by the procedure described in the EN 12697-24 standard.
This paper presents advanced computer simulation of rock cutting process typical for excavation works in civil engineering. Theoretical formulation of the hybrid discrete/finite element model has been presented. The discrete and finite element methods have been used in different subdomains of a rock sample according to expected material behaviour, the part which is fractured and damaged during cutting is discretized with the discrete elements while the other part is treated as a continuous body and it is modelled using the finite element method. In this way, an optimum model is created, enabling a proper representation of the physical phenomena during cutting and efficient numerical computation. The model has been applied to simulation of the laboratory test of rock cutting with a single TBM (tunnel boring machine) disc cutter. The micromechanical parameters have been determined using the dimensionless relationships between micro- and macroscopic parameters. A number of numerical simulations of the LCM test in the unrelieved and relieved cutting modes have been performed. Numerical results have been compared with available data from in-situ measurements in a real TBM as well as with the theoretical predictions showing quite a good agreement. The numerical model has provided a new insight into the cutting mechanism enabling us to investigate the stress and pressure distribution at the tool–rock interaction. Sensitivity analysis of rock cutting performed for different parameters including disc geometry, cutting velocity, disc penetration and spacing has shown that the presented numerical model is a suitable tool for the design and optimization of rock cutting process.
Scenario-based risk assessment for rockfalls, requires assumptions for different scenarios of magnitude (volume). The magnitude of such instabilities is related to the properties of the jointed rock mass, with the characteristics of the existing unfavourably dipping joint sets playing a major role. The critical factors for the determination of the maximum credible rockfall volume in a study site, the Forat Negre in Andorra, are investigated. The results from two previous analyses for the rockfall size distribution at this site are discussed. The first analysis provides the observed size distribution of the rockfall scars, and it is an empirical evidence of past rockfalls. The second one, calculates the kinematically detachable rock masses, indicating hypothetical rockfalls that might occur in the future. The later gives a maximum rockfall volume, which is one order of magnitude higher, because the persistence of the basal planes is overestimated. The tension cracks and lateral planes interrupt systematically the basal planes, exerting a control over their persistence, and restricting the formation of extensive planes and large rockfall failures. Nonetheless, the formation of basal planes across more than one spacings of tension cracks is possible and small step-path failures have been observed too. Concluding, the key factor for the determination of the maximum credible volume at the study-site is the maximum realistic length of the basal planes, penetrating into the rock mass, their spacing, and, if applied, the contribution of the rock bridges to the overall rock mass resistance.
Esta tesis presenta un estudio de la reducción de modelos (MOR) para redes de transmisión y distribución de electricidad. El enfoque principal utilizado ha sido la dinámica transitoria y para la reducción de modelos se ha adoptado un punto de vista matemático. Las redes eléctricas son complejas y tienen un tamaño importante. Por lo tanto, el análisis y diseño de este tipo de redes mediante la simulación numérica, requiere la resolución de modelos no-lineales complejos. En el contexto del desarrollo de redes inteligentes, el objetivo es un análisis en tiempo real de sistemas complejos, por lo que son necesarios modelos rápidos, fiables y precisos. En el presente estudio se proponen diferentes métodos de reducción de modelos, tanto a priori como a posteriori, adecuados para modelos dinámicos de redes eléctricas. La dinámica transitoria de redes eléctricas, se describe mediante modelos dinámicos oscilatorios no-lineales. Esta no-linearidad del modelo necesita ser bien tratada para obtener el máximo beneficio de las técnicas de reducción de modelos. Métodos como la POD y la LATIN han sido inicialmente utilizados en esta problemática con diferentes grados de éxito. El método de TPWL, que combina la POD con múltiples aproximaciones lineales, ha resultado ser el mas adecuado para sistemas dinámicos oscilatorios.En el caso de las redes de transmisión eléctrica, se utiliza un modelo de parámetros distribuidos en el dominio de la frecuencia. Se propone reducir este modelo basándose en la PGD, donde los parámetros eléctricos de la red de transmisión son incluidos como coordenadas de la representación separada del modelo paramétrico. Este método es ampliado para representar la solución de modelos con parámetros dependientes de la frecuencia para las redes de transmisión eléctrica.Palabras claves Redes Inteligentes, Dinámicas Transitorias, Ecuaciones de MovimientoOscilatorio, Líneas de Transmisión, Reducción de Modelos, Descomposición OrtogonalPropia, Método de Incremento de Gran Tiempo, Método Lineal en TrayectoriaPiece-wise, Descomposición Generalizada Propia, Parámetros Dependientes de laFrecuencia
Esta Tesis se enfoca en el modelamiento numérico de la fractura y su propagación en materiales heterogéneos sujetos a degradación, mediante modelos multiescala jerárquicos basados en la técnica FE2, abordando a su vez la problemática del coste computacional excesivo mediante el desarrollo, la implementación y validación de un conjunto de herramientas computacionales basadas en técnicas de modelos reducidos.Para la modelización de problemas de fractura, se desarrolló, implementó y validó, un modelo multiescala de fallo con las siguientes características:- En la macroescala, se adaptaron los últimos avances de la Aproximación de Discontinuidades Fuertes del Continuo (CSDA), hasta el momento desarrollados para modelos monoescala. Se formula un nuevo elemento finito con alta capacidad de capturar y modelar localización de deformaciones en bandas que pueden interceptar al elemento finito en direcciones arbitrarias. Para evaluar la dirección de propagación de falla se utiliza la técnica del crack-path (oliver/2014).- En la microescala, en aras de usar mecanismos de fallo que sean simples de implementar y calcular, y de cara al posterior desarrollo de una formulación de modelos reducidos, se propone el uso de elementos cohesivos tipo banda, equipados con un modelo constitutivo de daño isótropo regularizado, capaz de representar la decohesión del material. Estos elementos cohesivos son distribuidos entre los diferentes componentes de la microestructura, y en sus fronteras.Se verificó la objetividad de los resultados del modelo con respecto al tamaño de la celda de fallo, y al tamaño del elemento finito de la macroestructura. De igual forma, también se verificó la consistencia del modelo multiescala por medio de la comparación de resultados obtenidos con el mismo, y soluciones obtenidas mediante Simulaciones Numéricas Directas (DNS).En cuanto a la reducción del coste computacional en los modelos multiescala jerárquicos del tipo FE2. Se propone reformular el problema de valores de contorno de la microescala, mediante el uso de dos técnicas sucesivas de reducción, definidas como Modelo de Orden Reducido MOR y Modelo de Orden Hiper-reducido (HROM ó HPROM), respectivamente.En primer lugar, para el Modelo de Orden Reducido, el problema de elementos finitos estándar (de alta fidelidad) de la microestructura, es proyectado y resuelto en un subespacio de menor dimensión mediante el método de la Descomposición Ortogonal Propia (POD). En segundo lugar, para el desarrollo del Modelo de Orden Hiper-reducido, dos técnicas han sido estudiadas y desarrolladas, a saber: los métodos de interpolación y los métodos de Cuadratura de Orden Reducido ROQ (An/2009). Las bases reducidas para la proyección de las variables primales, son calculadas por medio de la Descomposición en Valores Singulares SVD de snapshots captados de trayectorias de entrenamiento previamente definidas.Teniendo en cuenta el caracter discontinuo de las deformaciones en la microescala en problemas de fractura. Se propone la descomposición de la celda de fallo en dos partes, un dominio cohesivo que contiene la totalidad de bandas cohesivas, y un dominio regular compuesto por el dominio disjunto remanente de la microcelda. Cada uno de estos dominios tiene un tratamiento individual. El modelo de la microescala, es reformulado como un problema de punto de silla en el cual se busca minimizar el potencial de energía libre.Para la validar los modelos reducidos desarrollados en esta Tesis, se realizaron múltiples pruebas variando la cantidad de bases para ambas reducciones incrementando la cantidad de modos y puntos de integración. Se puede concluir que, para errores admisibles (inferiores al 5%), las aceleraciones del costo computacional involucrado respecto al tiempo requerido por el modelo de alta fidelidad (speed-up) son del orden de 110 veces. Lo que constituye aceleraciones considerablemente superiores a lo reportado por la literatura.
El comportamiento estructural de las presas de embalse es difícil de predecir con precisión. Los modelos numéricos para el cálculo estructural resuelven las ecuaciones de la mecánica de medios continuos, pero están sujetos a una gran incertidumbre en cuanto a la caracterización de los materiales, especialmente en lo que respecta a la cimentación. Como consecuencia, frecuentemente estos modelos no son capaces de calcular el comportamiento de las presas con suficiente precisión. Así, es difícil discernir si un estado que se aleja en cierta medida de la normalidad supone o no una situación de riesgo estructural.Por el contrario, muchas de las presas en operación cuentan con un gran número de aparatos de auscultación, que registran la evolución de diversos indicadores como los movimientos, el caudal de filtración, o la presión intersticial, entre otros. Aunque hoy en día hay muchas presas con pocos datos observados, hay una tendencia clara hacia la instalación de un mayor número de aparatos que registran el comportamiento con mayor frecuencia.Como consecuencia, se tiende a disponer de un volumen creciente de datos que reflejan el comportamiento de la presa, lo cual hace interesante estudiar la capacidad de herramientas desarrolladas en otros campos para extraer información útil a partir de variables observadas.En particular, en el ámbito del Aprendizaje Automático (Machine Learning), se han desarrollado algoritmos muy potentes para entender fenómenos cuyo mecanismo es poco conocido, acerca de los cuales se dispone de grandes volúmenes de datos.En la tesis se ha hecho un análisis de las posibilidades de las técnicas más recientes de aprendizaje automático para su aplicación al análisis estructural de presas basado en los datos de auscultación. Para ello se han tenido en cuenta las características habituales de las series de datos disponibles en las presas, en cuanto a su naturaleza, calidad y cantidad.Se ha realizado una revisión crítica de la bibliografía existente, a partir de la cual se han identificado los aspectos clave a tener en cuenta para implementación de estos algoritmos en la seguridad de presas.Se ha realizado un estudio comparativo de la precisión de un conjunto de algoritmos para la predicción del comportamiento de presas considerando desplazamientos radiales, tangenciales y filtraciones. Para ello se han utilizado datos reales de una presa bóveda. Los resultados sugieren que el algoritmo denominado ``Boosted Regression Trees'' (BRTs) es el más adecuado, por ser más preciso en general, además de flexible y relativamente fácil de implementar.En una etapa posterior, se han identificado las posibilidades de interpretación del citado algoritmo para extraer la forma e intensidad de la asociación entre las variables exteriores y la respuesta de la presa, así como el efecto del tiempo. Las herramientas empleadas se han aplicado al mismo caso piloto, y han permitido identificar el efecto del tiempo con más precisión que el método estadístico tradicional.Finalmente, se ha desarrollado una metodología para la aplicación de modelos de predicción basados en BRTs en la detección de anomalías en tiempo real. Esta metodología se ha implementado en una herramienta informática interactiva que ofrece información sobre el comportamiento de la presa, a través de un conjunto de aparatos seleccionados. Permite comprobar a simple vista si los datos reales de cada uno de estos aparatos se encuentran dentro del rango de funcionamiento normal de la presa.
The aim of this study is to develop a process to produce high-performance cement-based
composites reinforced with flax nonwoven fabrics, analyzing the influence of the fabric
structure—thickness and entanglement—on mechanical behavior under flexural and tensile loadings.
For this purpose, composite with flax nonwoven fabrics with different thicknesses were first prepared
and their cement infiltration was evaluated with backscattered electron (BSE) images
En términos generales, el ensayo del Ground Penetrating Radar (GPR) aplicado a la ingeniería de carreteras, suele circunscribirse a la determinación geométrica de la estructura del firme mediante el análisis de la onda en el dominio del tiempo.En muchas ocasiones, suele utilizarse para apoyar el cálculo del módulo de rigidez de las capas de la estructura mediante el método conocido como retro-cálculo, según indican las principales guías de diseño empírico-mecanicistas de firmes asfálticos.Sin embargo, los principios geofísicos que sustentan el ensayo permiten, de forma indirecta y mediante la interpretación de variables asociadas a la respuesta física de los materiales frente a una onda electromagnética, obtener datos relacionados con el estado estructural de un firme. Dichas variables pueden asociarse a patologías estructurales relacionadas, por ejemplo, con la presencia de humedad o la falta de adherencia entre las capas del firme.En este trabajo se aborda las posibilidades que tiene el ensayo de GPR mediante el análisis de la onda en sus dimensiones temporal y frecuencial, con el propósito de permitir el diseño de futuros indicadores de estado, asociados al deterioro estructural de un firme. Los indicadores de estado basados en la respuesta de la señal de GPR permitirán reducir considerablemente el número de ensayos destructivos practicados hoy día en los firmes tales como la extracción de testigos, u otros ensayos no destructivos pero igualmente caros y de elevada complejidad logística, como son los ensayos de deflexión.
We prove that the solution of any linear mechanical system can be expressed as a linear combination of signal transmission paths. This is done in the framework of the Global Transfer Direct Transfer (GTDT) formulation for vibroacoustic problems. Transmission paths are expressed as powers of the transfer matrix. The key idea of the proof is to generalise the Neumann series of the transfer matrix --which is convergent only if its spectral radius is smaller than one-- into a modified Neumann series that is convergent regardless of the eigenvalues of the transfer matrix. The modification consists in choosing the appropriate combination coefficients for the powers of the transfer matrix in the series. A recursive formula for the computation of these factors is derived. The theoretical results are illustrated by means of numerical examples. Finally, we show that the generalised Neumann series can be understood as an acceleration (i.e. convergence speedup) of the Jacobi iterative method.
El modelo de flujo de potencias se usa para predecir el comportamiento de redes eléctricas y desemboca en la resolución de un sistema de ecuaciones algebraicas no lineales. Modelar una red es esencial para optimizar su diseño y control. Ambas aplicaciones requieren una respuesta rápida a las múltiples peticiones de una familia paramétrica de problemas de flujo de potencias. Diversos métodos de resolución se diseñaron especialmente para resolver la versión algebraica de las ecuaciones de flujo de potencias. Sin embargo, no existe ninguna metodología que proporcione una solución explícita al problema paramétrico de flujo de potencias (esto quiere decir, un vademecum computacional explícito en términos de los parámetros).Esta tesis tiene como objetivo diseñar algoritmos que produzcan vademecums para el problema paramétrico de flujo de potencias. Una vez que las soluciones están disponibles, resolver problemas para diferentes valores de los parámetros es un posproceso extremadamente rápido (en tiempo real) y por lo tanto los problemas de diseño óptimo y control se pueden resolver inmediatamente.En la primera fase, una nueva familia de métodos de resolución iterativos para la versión algebraica del problema se construye. El método se basa en una formulación híbrida del problema combinado con un esquema de direcciones alternadas. Estos métodos se han diseñado para generalizarlos de forma que puedan resolver la versión paramétrica del problema siguiendo una estrategia llamada Descomposición Propia Generalizada (PGD).El método de resolución para el problema paramétrico calcula las incógnitas paramétricas usando la técnica PGD. El algoritmo sigue los mismo pasos que el algoritmo algebraico, pero algunas operaciones se llevan a cabo en el ambiente PGD, esto requiere algoritmos iterativos anidados. El método de resolución PGD se acompaña con una evaluación del error cometido permitiendo monitorizar la convergencia de los procesos iterativos y decidir el número de términos que requiere la solución para alcanzar la precisión preescrita. Diferentes ejemplos de redes reales y tests estándar se usan para demostrar el funcionamiento de las metodologías propuestas.
This study elucidates the origin of the multiplicity of stable oscillatory flows detected by time integration in tall rectangular cavities heated from the side. By using continuation techniques for periodic orbits, it is shown that initially unstable branches, arising at Hopf bifurcations of the basic steady flow, become stable after crossing Neimark-Sacker points. There are no saddle-node or pitchfork bifurcations of periodic orbits, which could have been alternative mechanisms of stabilization. According to the symmetries of the system, the orbits are either fixed cycles, which retain at any time the center symmetry of the steady flow, or symmetric cycles involving a time shift in the global invariance of the orbit. The bifurcation points along the branches of periodic flows are determined. By using time integrations, with unstable periodic solutions as initial conditions, we determine which of the bifurcations at the limits of the intervals of stable periodic orbits are sub- or supercritical.
de la Fuente, A.; Armengou, J.; Pons-Valladares, O.; Aguado, A. Journal of civil engineering and management (Spausdinta) Vol. 23, num. 2, p. 194-203 DOI: 10.3846/13923730.2015.1023347 Data de publicació: 2017-02 Article en revista
A multi-criteria decision-making system based on the MIVES method is presented as a model for assessing the global sustainability index scores of existing wind-turbine support systems. This model is specifically designed to discriminate between tower systems in order to minimize the subjectivity of the decision and, thus, facilitate the task of deciding which system is best for a given set of boundary conditions (e.g., height, turbine power, soil conditions) and economic, social and environmental requirements. The model’s versatility is proven by assessing the sustainability index of an innovative new precast concrete tower alternative also described in this paper. As a result of this analysis, some points of improvement in the new system have been detected.
This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Civil Engineering and Management on 2017, available online at: http://www.tandfonline.com/10.3846/13923730.2015.1023347
Nadal, A.; Llorach, P.; Cuerva, E.; López-Capel, E.; Montero, J.; Josa, A.; Rieradevall, J.; Royapoor, M. Applied energy Vol. 187, p. 338-351 DOI: 10.1016/j.apenergy.2016.11.051 Data de publicació: 2017-02 Article en revista
A sustainable and secure food supply within a low-carbon and resilient infrastructure is encapsulated in several of The United Nations’ 17 sustainable development goals. The integration of urban agriculture in buildings can offer improved efficiencies; in recognition of this, the first south European example of a fully integrated rooftop greenhouse (iRTG) was designed and incorporated into the ICTA-ICP building by the Autonomous University of Barcelona. This design seeks to interchange heat, CO2 and rainwater between the building and its rooftop greenhouse. Average air temperatures for 2015 in the iRTG were 16.5 °C (winter) and 25.79 °C (summer), making the iRTG an ideal growing environment. Using detailed thermophysical fabric properties, 2015 site-specific weather data, exact control strategies and dynamic soil temperatures, the iRTG was modelled in EnergyPlus to assess the performance of an equivalent ‘freestanding’ greenhouse. The validated result shows that the thermal interchange between the iRTG and the ICTA-ICP building has considerable moderating effects on the iRTG’s indoor climate; since average hourly temperatures in an equivalent freestanding greenhouse would have been 4.1 °C colder in winter and 4.4 °C warmer in summer under the 2015 climatic conditions. The simulation results demonstrate that the iRTG case study recycled 43.78 MWh of thermal energy (or 341.93 kWh/m2/yr) from the main building in 2015. Assuming 100% energy conversion efficiency, compared to freestanding greenhouses heated with oil, gas or biomass systems, the iRTG delivered an equivalent carbon savings of 113.8, 82.4 or 5.5 kg CO2(eq)/m2/yr, respectively, and economic savings of 19.63, 15.88 or 17.33 €/m2/yr, respectively. Under similar climatic conditions, this symbiosis between buildings and urban agriculture makes an iRTG an efficient resource-management model and supports the promotion of a new typology or concept of buildings with a nexus or symbiosis between energy efficiency and food production.
The behavior of reinforced concrete (RC) structures under severe demands, as strong ground motions, is highly complex; this is mainly due to joint operation of concrete and steel, with several coupled failure modes. Furthermore, given the increasing awareness and concern for the important seismic worldwide risk, new developments have arisen in earthquake engineering. Nonetheless, simplified numerical models are widely used (given their moderate computational cost), and many developments rely mainly on them. The authors have started a long-term research whose final objective is to provide, by using advanced numerical models, solid basis for these developments. Those models are based on continuum mechanics, and consider Plastic Damage Model to simulate concrete behavior. Within this context, this paper presents a new methodology to calculate damage variables evolution; the proposed approach is based in the Lubliner/Lee/Fenves formulation and provides closed-form expressions of the compressive and tensile damage variables in terms of the corresponding strains. This methodology does not require calibration with experimental results and incorporates a strategy to avoid mesh-sensitivity. A particular algorithm, suitable for implementation in Abaqus, is described. Mesh-insensitivity is validated in a simple tension example. Accuracy and reliability are verified by simulating a cyclic experiment on a plain concrete specimen. Two laboratory experiments consisting in pushing until failure two 2-D RC frames are simulated with the proposed approach to investigate its ability to reproduce actual monotonic behavior of RC structures; the obtained results are also compared with the aforementioned simplified models that are commonly employed in earthquake engineering.
The role of the filler in asphalt mixtures is particularly important because of its influence on mastic behaviour. The filler improves the resistance properties of bitumen against the action of traffic loads and temperature. However, the filler can also adversely affect bitumen in mastics excessively brittle and stiff due to inappropriate design. For these reasons, it is interesting to investigate the effect of filler type and content on mastic composition. This paper presents results from a strain sweep test applied to bituminous mastics prepared with different filler types and contents at several temperatures. The obtained stiffness modulus and failure strain results provide information to assess the fatigue behaviour of the analysed mastics.
Petit-Boix, A.; Arahuetes, A.; Josa, A.; Rieradevall, J.; Gabarrell, X. Science of the total environment Vol. 580, p. 873-881 DOI: 10.1016/j.scitotenv.2016.12.034 Data de publicació: 2017-02 Article en revista
Flood damage results in economic and environmental losses in the society, but flood prevention also entails an initial investment in infrastructure. This study presents an integrated eco-efficiency approach for assessing flood prevention and avoided damage. We focused on ephemeral streams in the Maresme region (Catalonia, Spain) to determine the feasibility of post-disaster emergency actions implemented after a major event in hydrologic, environmental and economic terms. Life cycle assessment (LCA) and costing (LCC) were used to determine the eco-efficiency of these actions, and their net impact and payback were calculated by integrating avoided flood damage. Results showed that the actions effectively reduced damage generation when compared to the water flows and rainfall intensities registered. The eco-efficiency of the emergency actions resulted in 1.2 kg CO2eq. per invested euro. When integrating the avoided damage into the initial investment, negative net impacts were obtained (e.g., -5.2E+05 € and -2.9E+04 kg CO2 eq. per event), which suggests that these interventions contributed with environmental and economic benefits to the society. The economic investment was recovered in two years, whereas the design could be improved to reduce their environmental footprint, which is recovered in 25 years. Our method and results highlight the effects of integrating the environmental and economic consequences of decisions at an urban scale and might help the administration and insurance companies in the design of prevention plans and climate change adaptation.
This paper presents the results of morphodynamic modelling and analysis of onshore and offshore sandbar migration based on a depth-integrated approach. The coastal flow was modeled using the Boussinesq equation and the morphological evolution was modeled using the suspended sediment transport equation and bed load formulae based on the instantaneous velocity and acceleration. The proposed model was applied to the accretive and erosive conditions and the model reproduced the onshore and offshore sandbar migration and the formation of a berm around the shoreline reasonably. An analysis of the computed results revealed the following. (i) The vertical flow velocity can affect the suspension time of the sediments considerably and the bottom evolution. (ii) The suspended load is the main contributor to the morphological changes in terms of the quantity and quality, regardless of the accretive or erosive conditions. (iii) Regardless of accretive or erosive conditions, in terms of the time-average, the instantaneous flow velocity and acceleration-based bed load models always yielded an offshore and onshore direction sediment flux, respectively, except in the swash zone. On the other hand, the suspended sediment flux calculated by the advection-diffusion equation results in the sediment transport in either direction depending on the flow field.
Time-dependent strains, when restrained, can lead to important tensile forces and damage, affecting, among other aspects, the shear response and ultimate load carrying capacity of shear-critical RC frames. This paper presents a detailed study of this problematic by means of an extension of a shear-sensitive fibre beam model to time dependent behaviour of concrete. The model is firstly validated with experimental tests on diagonally pre-cracked beams under sustained loads. From these analyses, the contributions of shear distortions and bending curvatures to the total long-term deflection of the beams are discerned. Afterwards, the model is applied to study the influence of restraining strains due to long-term creep and shrinkage in the service and ultimate shear response of frames. In contrast with flexural resistant mechanisms, delayed strains may influence the latter shear resistance of integral structures by reducing the concrete contribution to shear resistance and leading to a sooner activation of the transversal reinforcement. These aspects can be relevant in assessing existing structures and this model, due to its relative simplicity, can be advantageous for practical applications.
The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0875-8
The aim of this paper was to analyse how changes in wave patterns, due to the effect of climate change, can affect wave energy power and yield around Menorca (NW Mediterranean Sea). The present and future wave energy conditions were derived from recently developed high-resolution wave projections in the NW Mediterranean. These wave projections were forced by surface wind fields obtained, respectively, by 5 different combinations of global and regional circulation models (GCMs and RCMs) for the A1B scenario. The results showed that the projected future spatial and directional distributions of wave energy are very similar to those of the present conditions. The multi-model ensemble average illustrated a slight general decrease in the annual and seasonal wave power (except for summer). However, the inter-model variability is large since two models showed opposite trends to the other 3 in most cases. Such inter-model variability is lower(higher) for winter(autumn). Another result is the reduction of the temporal variability in the future, considering both the multi-model mean and each single model projection. Such a decrease is consistent with the future seasonal redistribution of energy throughout the year. This would entail an increase in the efficiency of wave energy converters deployed in this area due to the more regular temporal distribution of the energy.
Overtime, bridge condition declines due to a number of degradation processes such as creep, corrosion, and cyclic loading, among others. Traditionally, vibration-based damage detection techniques in bridges have focused on monitoring changes to modal parameters. These techniques can often suffer to their sensitivity to changes in environmental and operational conditions, mistaking them as structural damage. Recent research has seen the emergence of more advanced computational techniques that not only allow the assessment of noisier and more complex data but also allow research to veer away from monitoring changes in modal parameters alone. This paper presents a review of the current state-of-the-art developments in vibration-based damage detection in small to medium span bridges with particular focus on the utilization of advanced computational methods that avoid traditional damage detection pitfalls. A case study based on the S101
bridge is also presented to test the damage sensitivity to a chosen methodology.
The identification of the geological structure from seismic data is formulated as an inverse problem. The properties and the shape of the rock formations in the subsoil are described by material and geometric parameters, which are taken as input data for a predictive model. Here, the model is based on the Helmholtz equation, describing the acoustic response of the system for a given wave length. Thus, the inverse problem consists in identifying the values of these parameters such that the output of the model agrees the best with observations. This optimization algorithm requires multiple queries to the model with different values of the parameters. Reduced order models are especially well suited to significantly reduce the computational overhead of the multiple evaluations of the model.
In particular, the proper generalized decomposition produces a solution explicitly stating the parametric dependence, where the parameters play the same role as the physical coordinates. A proper generalized decomposition solver is devised to inexpensively explore the parametric space along the iterative process. This exploration of the parametric space is in fact seen as a post-process of the generalized solution. The approach adopted demonstrates its viability when tested in two illustrative examples.
This is the peer reviewed version of the following article: [Signorini, M., Zlotnik, S., and Díez, P. (2017) Proper generalized decomposition solution of the parameterized Helmholtz problem: application to inverse geophysical problems. Int. J. Numer. Meth. Engng, 109: 1085–1102. doi: 10.1002/nme.5313], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.5313/full. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Tracking algorithms constitute an efficient numerical technique for modelling fracture in quasi-brittle materials. They succeed in representing localized cracks in the numerical model without mesh-induced directional bias. Currently available tracking algorithms have an important limitation: cracking originates either from the boundary of the discretized domain or from predefined “crack-root” elements and then propagates along one orientation. This paper aims to circumvent this drawback by proposing a novel tracking algorithm that can simulate cracking starting at any point of the mesh and propagating along one or two orientations. This enhancement allows the simulation of structural case-studies experiencing multiple cracking. The proposed approach is validated through the simulation of a benchmark example and an experimentally tested structural frame under in-plane loading. Mesh-bias independency of the numerical solution, computational cost and predicted collapse mechanisms with and without the tracking algorithm are discussed.
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-016-1351-6
The Catalan coast as most of the developed Mediterranean coastal zone is characterized by the coincidence of stresses and pressures on the natural system with a high exposure and low adaptive capacity. Due to this, climate change-induced effects will increase natural hazards and aggravate their associated impacts and, in consequence, it is necessary to assess their effects for proper long-term management. In this work, we assess the impact of sea-level rise (SLR)-induced shoreline retreat on the Catalan coast for three scenarios ranging from 0.53 to 1.75 m by the year 2100. Implications are analysed in terms of affectation of two main functions provided by beaches, i.e. recreation and protection. Obtained results show that CC will be a serious threat to analysed functions since the expected enhanced shoreline retreat will severely decrease the recreational carrying capacity and the capacity of protection in the near future under tested scenarios. The actual level of development along the coastal zone reduces the natural resilient capacity of beaches to SLR in such a way that the lack of accommodation space can be identified as a main factor for the estimated impacts.
The final publication is available at Springer via http://dx.doi.org/10.1007/s10113-016-1052-x
A comparative analysis of the structural behaviour of prestressed concrete sleepers made with high performance concrete (HPC) and high performance recycled aggregate concrete (HPRAC) is presented in this study. Two types of HPRAC sleepers were tested, using 50 and 100% of recycled concrete aggregate (RCA) in replacement of coarse natural aggregates. The RCA employed in this research was sourced from crushing rejected HPC sleepers. The aim of this study was to determine through analysis if the HPRAC sleepers’ behaviour fulfilled the European minimum requirements standards for prestressed concrete sleepers and compare their experimental behaviour with that of the HPC sleepers. The three types of prestressed concrete sleepers were subjected to static load tests at rail-seat and centre section (positive and negative load). In the centre section tests a comparative study between the experimental results and the proposed values of four assessment methods of ultimate capacity was carried out. Dynamic load and fatigue tests were also performed at the rail-seat section. The HPRACs and HPC sleepers met all the structural requirements for prestressed concrete sleepers. The experimental results determined the satisfactory performance of the HPRAC-50 and the HPRAC-100, which was very similar to that of the HPC sleepers. The load–strain behaviour recorded via the use of strain gauges on the prestressing bars revealed slightly higher stiffness of the HPC sleepers. The values obtained from the four assessment methods of ultimate capacity were also accurate when applied to HPRAC.
The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0966-6