Crack patterns in heterogenous rocks using a combined phase field-cohesive interface modeling approach: A numerical study

Rock fracture in geo-materials is a complex phenomenon due to its intrinsic characteristics and the potential external loading conditions. As a result, these materials can experience intricate fracture patterns endowing various cracking phenomena such as: Branching, coalescence, shielding, and amplification, among many others. In this article, we present a numerical investigation concerning the applicability of an original bulk-interface fracture simulation technique to trigger such phenomena within the context of the phase field approach for fracture. In particular, the prediction of failure patterns in heterogenous rock masses with brittle response is accomplished through the current methodology by combining the phase field approach for intact rock failure and the cohesive interface-like modeling approach for its application in joint fracture. Predictions from the present technique are first validated against Brazilian test results, which were developed using alternative phase field methods, and with respect to specimens subjected to different loading case and whose corresponding definitions are characterized by the presence of single and multiple flaws. Subsequently, the numerical study is extended to the analysis of heterogeneous rock masses including joints that separate different potential lithologies, leading to tortuous crack paths, which are observed in many practical situations.Ministerio de Economía y Competitividad MAT2015-71036-

A deterministic seismic risk macrozonation of Seville

The seismicity of the southwestern Iberian Peninsula is moderate but large events with long return periods occur (≈ 200 years). This exceeds the life of various generations, making the population unacquainted with the seismic hazard. On the one hand, this results in a low demanding seismic code which increases the seismic vulnerability and, therefore, the seismic risk. On the other hand, the local emergency services must be properly prepared to face a destructive seismic event, with emergency plans and mitigation strategies. This assumption enhances the need of assessing the seismic risk of Seville in a civil protection context. For all the aforementioned and for the lack of instrumental data of relevant earthquakes, the assessment of the seismic hazard in this area is challenging. To do this, seismogenic zones of the new seismic hazard map of Spain have been used as sources. The peak ground acceleration (PGA) for each scenario has been calculated by means of ground motion prediction equations (GMPE). To estimate the site efects, in a 1D model environment, a shear wave velocity (Vs) map of the top 5 m has been depicted based on the standard penetration test (SPT). Seville’s building stock has been classifed in agreement with the previous works in Lorca and Barcelona to determine its vulnerability. The main goal of this work was to investigate the infuence of the soil amplifcation on the seismic behaviour of diferent building typologies. Therefore, the fnal target was to plot the damage scenarios expected in Seville under a maximum credible earthquake by means of a deterministic seismic hazard assessment (DSHA). As outputs, the scenario modelled showed that around 27 000 buildings would experience a moderate damage and that 26 000 would sufer pre-collapse or even collapse. Thus, approximately 10% of the population would lose their dwellings. Regarding the human loses, around 22 000 people would sufer serious injuries and approximately 5 000 people would die. Owing to these conclusions, this research evidences the crucial need by civil protection services to implement a local emergency plan as a tool to mitigate the probable consequences that arise from this threat

Estudio del enfriamiento pasivo por fachadas ventiladas en el sur de España

En este trabajo, se estudia el efecto de enfriamiento pasivo por fachadas ventiladas, en edificios bajo las condiciones climáticas habituales del sur de España. En dichas condiciones climáticas, conseguir confort en el interior de las viviendas supone generalmente un fuerte consumo energético en los periodos de verano. El uso de fachadas ventiladas, cuando su diseño es correcto, puede reducir considerablemente dicho consumo en verano, especialmente en situaciones de fuerte irradiación solar. Las fachadas ventiladas presentan generalmente una capa exterior unida al muro interior del edificio por medio de estructuras especiales. De esta forma entre las dos capas se crea una cámara de aire, ventilada de forma natural. En nuestro contexto, la función más relevante de la capa exterior es proteger el muro interno de la radiación solar, así como dar carácter y definir la estética del edificio. Por otro lado, la radiación solar al calentar la hoja externa provoca en el interior de la cámara ventilada un flujo de aire ascendente, debido a la convección natural, que produce un fenómeno de ventilación transportando el calor desde las caras de dicha cámara al exterior. Algunos autores señalan la disminución de rendimiento energético de estas fachadas cuando la temperatura ambiental es alta. Fenómeno que puede agravarse cuando la presencia de viento hace aumentar el flujo de aire caliente hacia el interior de la cámara ventilada. El objetivo del presente trabajo consiste en determinar si en las condiciones climáticas habituales del sur de España, donde se pueden dar ambos fenómenos, las fachadas ventiladas aportan algún tipo de ahorro energético respecto las fachadas no ventiladas y deducir sus patrones de comportamiento en cuanto a su eficiencia energética. Para simular el flujo en el canal de aire, se utilizan las ecuaciones de Navier-Stokes para flujos termodinámicos. Se modeliza la fachada como un canal con dos planos verticales calentados de forma asimétrica mediante una aproximación por Elementos Finitos bidimensionales (2D). Los resultados obtenidos por la computación CFD, muestran que el efecto combinado de sombra de la capa externa y de ventilación producido en el interior de la cámara de aire, consiguen un significativo efecto de enfriamiento del edificio, que ha sido evaluado comparando el comportamiento térmico de las fachada ventiladas con otra no ventilada. Por último, se analiza el comportamiento de dichas fachadas bajo diversas condiciones atmosféricas como viento variable, y diferentes niveles de irradiación solar y temperatura ambiente

Simplified 1D Empirical Model for Volumetric Behavior of High-Carbonate Clay

The Guadalquivir blue marl is a high plasticity overconsolidated carbonate clay. This soil presents an elevated fragility and high susceptibility to moisture changes. These characteristics have caused many geotechnical accidents, such as the Aznalcollar dam failure, in Seville (Spain). A comprehensive test campaign has been conducted to determine the physical and chemical properties of the blue marl. Analysis by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) allowed characterising its internal structure, revealing clear differences between the macro and the microstructure. A novel model for predicting the volumetric deformation (under oedometric conditions) of the Guadalquivir blue marl with suction and vertical pressure changes has been proposed. The model, based on data from shrink-swell tests, provides an acceptable estimation of the volumetric behaviour of the soil with a relatively simple set of parameters. The results were experimentally verified by suction-controlled oedometer tests and showed an acceptable agreement with the data measured. It has been specified when swelling. shrinkage or collapse occur

Optimal ductility enhancement of RC framed buildings considering different non-invasive retrofitting techniques

Existing RC framed buildings lack significant ductility, especially when they have been built with pre-code criteria. Improving their ductile capacity can help to prevent them from the brittle collapse mechanism and to reduce the seismic damage expected. This paper aims to investigate the enhancement of the ductile response behaviour of RC framed buildings considering different non-invasive retrofitting techniques. To do so, a pre-code RC framed school located in the Spanish province of Huelva has been selected as a case study. Five non-invasive retrofitting techniques have been tested: FRP wraps and steel jackets in columns, steel beams and plates under RC beams and single steel braces. They have been selected so that they can be easily implemented in the building. Some of them have been studied in detail in previous works and others have been included for further research in this paper. In order to compare the results obtained, the most typical technique in the seismic retrofitting of RC framed buildings, the addition of X-bracings in bays, has also been tested. Most previous studies on the seismic retrofitting of RC buildings are focused on validating a method based on artificial models. This paper compares the different techniques in terms of the capacity improvement and the damage reduction, performing analyses in detail and adding them in an existing RC building. A sensitivity analysis has been carried out to determine the influence of each technique in the building’s ductile capacity considering the finite element method. Nonlinear static analyses have been performed to obtain the capacity, the displacement ductility factor (μ) and the behaviour factor (q) of each model defined. The damage expected has been determined considering the ductile and fragile failure of the elements according to the Eurocode-8 (EC8) requirements. To analyse the suitability and the efficiency of each solution, a benefit/cost ratio has been obtained taking into account the ductility improvement and the damage reduction with regards to the retrofitting costs. The results have shown that the best benefit has been obtained with the addition of steel braces. However, the optimal solutions have been single braces and steel jackets due to their combination between benefit and cost. It has been observed that the solutions that increase the stiffness of the joints have had a higher improvement due to the key role that joints have in the resistant capacity of RC structurers. Also, it has been obtained that the values of the fundamental periods have been reduced, when adding the retrofitting elements and materials, up to 30% owing to the increase of the stiffness of the system. Finally, it must be highlighted that a detailed analysis of the behaviour of the whole building must be conducted in order to avoid additional rotation effects and shear forces that could worsen the building’s seismic behaviour

Assessment of specific structural and ground-improvement seismic retrofitting techniques for a case study RC building by means of a multi-criteria evaluation

Existing reinforced concrete (RC) structures might not comply with current seismic codes due to their aseismic design and construction date. By seismically retrofitting them, it is possible to improve their seismic performance to resist the expected seismic loads. However, selecting the best solution is challenging since social and economic issues can affect the choice. Multi-criteria decision making (MCDM) provides an opportunity to overcome the challenge but there are some drawbacks in the available MCDM techniques. This paper reports an improved MCDM-based seismic retrofit: Additional criteria have been included and weighted according to their importance (ductility improvement and damage reduction); Finite element modelling of the case study building has been carried out instead of following methods based on different simplifications; iii) Structural performances have been assessed by determining the damage in local elements instead of following global assessment procedures; Effects of soil-structure interaction (SSI) have been taken into account to ultimately compare different structural and ground-improvement techniques. Consistency and sensitivity analyses have proved the stability of the results and the robustness of the method. It is shown that SSI can increase the seismic damage up to 17%, and regarding the seismic safety verification, the building needs to be retrofitted. Adding fibre reinforcement polymers and steel bracings are the best solutions due to the minimum architectural impact and the outstanding structural improvement, respectively. Nevertheless, the solution preferred is the addition of single steel braces in beam- column joints despite its high maintenance costs. The sensitivity analysis indicates that the most sensitive criteria are the functional compatibility and the reduction of the collapse risk

Diseño y cálculo de mallas de alambre postesadas para la estabilización y refuerzo de taludes.

Una solución barata para la protección de taludes es la utilización de mallas de alambre. Este trabajo muestra el diseño de una malla de alambre de alto límite elástico, postesada con anclajes, para la estabilización y refuerzo de taludes. Es una solución económica que permite actuar en terrenos muy altos y empinados. El impacto visual de la malla y los anclajes, una vez colocados, es moderado debido a que la malla es muy flexible, lo que permite su adaptación a las irregularidades del terreno. Además, se puede colorear lo que favorece su camuflaje y ayuda a evitar la erosión del terreno lo que ayuda a la revegetación. También se presenta un modelo de cálculo para la malla. Para ello se han realizado ensayos de laboratorio sobre mallas normalizadas con el objetivo de obtener sus parámetros en condiciones de campo simuladas. Por último, los resultados de los ensayos se han introducido en las ecuaciones teóricas

Analysis of the soil structure-interaction effects on the seismic vulnerability of mid-rise RC buildings in Lisbon

Soil-structure interaction (SSI) effects are usually omitted in the seismic vulnerability analyses of buildings. However, it has been proved that they might notably affect their seismic performance. In fact, European seismic codes establish that they should be included in the analyses of certain structures: with considerable second order (p-Δ) effects or mid/high-rise buildings. These characteristics are shared by reinforced concrete (RC) buildings in Portugal, which represent a considerable amount of its building stock. Moreover, a significant percentage (50%) have been constructed prior to restrictive seismic codes, i.e., without adequate seismic design. To obtain reliable results when including the SSI effects, the state-of-the-art reveals that a proper modelling of soil and foundations should be carried out. Nevertheless, most of the related studies are based on ideal structural and soil configu- rations. In addition, it has been found that there is a lack of studies and guidance, even in codes, on the quantification of the SSI effects. Therefore, this paper focuses on quantifying the SSI effects in RC buildings seismic vulnerability analyses by means of two approaches: the Beam on Nonlinear Winker method (BNWM) and the direct modelling of soil. The aim is to propose a method to practically include the SSI effects and to thor- oughly characterise the soil behaviour. The method has been applied to a case study RC mid-rise building of Lisbon. A clay-type soil commonly found in Lisbon has been characterised, carrying the analyses out under undrained conditions. 3D finite elements procedures have been proposed to reproduce the complex soil nonlinear constitutive law to represent the behaviour of the entire system (soil + foundation + structure) as realistically as possible. The results have been compared in terms of the seismic safety verification and the fragility assessment. The results have shown that the modal behaviour and the deformed shape of the building are the same with and without the SSI. Nonetheless, it has been demonstrated that increasing the soil flexibility leads to higher periods and higher seismic damage. For this case study, the maximum capacity of the models can be reduced by up to 15% if the SSI effects are considere

Un modelo tridimensional para el estudio de la fluencia en presas de materiales sueltos

En este artículo se recoge el estudio realizado para la presa zonada de Beliche, de 54 m de altura y 106 m3 de volumen, considerando en los cálculos el fenómeno de la fluencia de los materiales que la componen. Se formula un modelo de elementos finitos en tres dimensiones basado en la disminución del módulo de deformación con el tiempo (esta relación también es dependiente de la presión) con el objeto de interpretar los movimientos de fluencia hasta 3.506 días después del final de la construcción de la presa. Se ha obtenido un buen acuerdo entre los asientos medidos y calculados.Peer Reviewe

Innovación docente en estructuras mediante aprendizaje activo con proyectos de estructuras y técnicas complementarias

En un grupo de la asignatura Estructuras 2 de la titulación de Arquitecto se ha realizado una experiencia piloto de innovación docente en el segundo cuatrimestre del curso 2008/2009. El centro de la experiencia es el empleo del aprendizaje activo para obtener la competencia específica del proyecto de estructuras de acero y las competencias transversales de aprendizaje cooperativo y aprendizaje autónomo. Se emplea una metodología multitarea, tanto en las actividades del profesor como de los alumnos. La actividad principal es el desarrollo de un proyecto de estructura de acero a partir de edificios de un arquitecto relevante en el panorama internacional (Louis Kahn). Se utilizan diversas técnicas complementarias. Los resultados indican un alto grado de compromiso de los alumnos con la experiencia docente, y un elevado nivel de satisfacción con los resultados de su aprendizaje y con las metodologías empleadas