Scipedia: Alex Barbat's articles in WoS/Scopus journals

Análisis sísmico de edificios con dispositivos de aislamiento de base elastoméricos

Scipedia content — Fri, 16 Jun 2017 10:16:52 +0200

Los sistemas de aislamiento sísmico de base desacoplan parcialmente una estructura de los movimientos del terreno por medio de dispositivos colocados entre la estructura y su cimentación. De los diversos tipos de dispositivos desarrollados, los más utilizados son lo de elastómero laminado que están constituidos por capas alternadas de elastómero y acero. Este artículo es una contribución al tratamiento numérico conjunto de las estructuras con sus dispositivos de aislamiento de base de elastómeros laminados.

Simulación numérica de elastómeros multi-fase en estiramientos principales

Scipedia content — Fri, 16 Jun 2017 10:17:13 +0200

En este trabajo se propone un modelo hiperelástico generalizado para el análisis de elastómeros milti-fase. El modelo se desarrolla en grandes deformaciones en función de los estiramientos principales. Debido a la cuasi-incomprensibilidad de los elastómeros, se supone un comportamiento diferente para las partes volumétrica y desviadora de la deformación. Se utiliza teoría de mezclas para incorporar las expresiones constitutivas básicas propuestas para cadqa material, viscoelasticidad para el caucho y elastoplasticidad para las partículas agregadas, en un formulación de sólido compuesto.

Evaluación probabilista del riesgo sísmico en zonas urbanas

Scipedia content — Fri, 16 Jun 2017 10:45:05 +0200

A methodology to evaluate the vulnerability and seismic risk of existing building structures in an urban area developed within a probabilistic scheme. It uses numerical procedures for the analysis of the non-linear seismic behaviour of structures and optimized sampling method and probabilistic models for the description of the obtained results. Occurrence probabilities for different damage levels of the structures in risk, corresponding to a giiven exposure period are thus obtained. From ail economical point of view, annual losses and minimum earthquake insurance taxes are evaluated. The proposed method is applied td the assessment of the seismic risk of a complete urban are a, located in the central part bf Barcelona, Spain, in which mostly unreiilforced masonry buildings and non-ductile reinforced concrete buildings are the most common building types. The method has been implemented, in a modular format in a Geographical Inforinatioil System, with the objetive of obtaining seismic risk scenarios.

Simulacion de escenarios de daño sísmico en zonas urbanas

Scipedia content — Fri, 16 Jun 2017 11:15:17 +0200

A methodology to perform a damage simulation procedure for existing non-reinforced masonry buildings in an urban zone is presented in this paper. By simulating the behaviour of thousands of hypothetical buildings and performing probabilistic studies of the computed results, damage probability matrices and vulnerability functions are obtained, which are the bases for vulnerability and seimic risk evaluations. The fundamentals of the presented methodology are the italian vulnerability index and the results of a post-earthquake survey damage study. As an example, an urban zone of Barcelona is examinated and probable damage scenarios are developped.

Un método de evaluación del daño sísmico en estructuras de hormigón armado

Scipedia content — Fri, 16 Jun 2017 11:15:42 +0200

En este artículo se presenta un método que permite evaluar el daño sísmico global en estructuras de barras de hormigón armado. Se denomina estado dañado de un punto del sólido a aquel estado termodinámico resultante de la entrada del material en estado de comportamiento no lineal. A partir del concepto de daño local en un punto del sólido, se deduce por extensión el índice de daño global estructural. Se utiliza la técnica de elementos finitos para aproximar el campo de desplazamientos. Se trabaja con un elemento de barra Timoshenko en 3-D subdividido en capas entrecruzadas (fibras), donde en cada una de ellas se aplica un modelo constitutivo general formulado en tensión-deformación. Esto último permite incluir cualquier fenómeno que acerque más la simulación numérica a la realidad del problema (plasticidad, degradación de rigidez, problemas viscosos, etc.). Al final se incluyen ejemplos de cálculo que demuestran la capacidad del método numérico que se presenta, para la obtensión del nivel de daño global en las estructuras.

Simulación de acelerogramas compatibles con espectros de energía sísmica inducida

Scipedia content — Fri, 16 Jun 2017 11:15:57 +0200

En este artículo se presenta un estudio sobre el espectro de energía inducida en las estructuras sometidas a acciones sísmicas. En primer lugar se discuten las variables que influyen en dicho espectro, con base en las relaciones que guarda el mismo con otras medidas de la acción sísmica. En segundo lugar, se presenta un procedimiento que permite estimar un espectro suavizado de diseño, basado en la regresión sobre los registros de las dos componentes horizontales de 56 sismos diferentes. Finalmente, se describe un método para simular acelerogramas compatibles con un espectro de energía prescrito y se presenta un ejemplo que ilustra la utilidad del método para la evaluación del daño sísmico.

Evaluacion de la presión de fallo del edificio de contencion de una central nuclear tipo PWR-W tres lazos. Parte II: Simulacion numérica

Scipedia content — Mon, 19 Jun 2017 13:10:24 +0200

En este articulo se presentan los resultados de la simulación numérica efectuada para evaluar la presión de fallo debida a un accidente del edificio de contención de una central nuclear PWR- W tres lazos. El modelo computacional tridimensional de elementos finitos utilizado ha sido descrito en la primera parte del artículo1. En esta segunda parte se analiza la influencia que tiene sobre la presión de fallo de la contención tanto la inclusión en el modelo estructural de la losa de cimentación como los efectos térmicos. El estudio numérico demuestra que puede llevarse a cabo la simulación del proceso de fallo utilizando un modelo estructural que no incluya la losa de cimentación y la carga de temperatura. Finalmente, se presentan y se discuten los resultados de un estudio probabilista de simulación de la presión de fallo y se resumen las conclusiones.

Evaluacion de la presión de fallo del edificio de contencion de una central nuclear tipo PWR-W tres lazos. Parte I: Metodología

Scipedia content — Mon, 19 Jun 2017 13:10:55 +0200

Se presenta en este artículo la metodología seguida para la evaluación de la presión de fallo del edificio de contención de una central nuclear PWR-W tres lazos. El análisis debe ser totalmente tridimensional para permitir la consideración de los elementos estructurales más significativos, tener en cuenta el comportamiento no lineal de los materiales y estudiar la sensibilidad de los resultados ante ciertas incertidumbres asociadas a algunos parámetros. El modelo computacional incluye las ecuaciones constitutivas para el hormigón y las armaduras de acero, la discretización espacial (elementos isoparamétricos con armado) y la resolución del problema estructural no lineal mediante algoritmos incrementales-iterativos con aceleradores de convergencia. Se describen los modelos estructurales utilizados y los análisis llevados a cabo para su calibración.

Una formulación matricial generalizada. Parte 2: Analisis dinamico

Scipedia content — Mon, 19 Jun 2017 13:11:04 +0200

Se describe una formulación para el análisis dinámico de estructuras formadas por entramados espaciales de elementos de directriz curva y sección variable, cuyo desarrollo se basa en la Formulación Matricial Generalizada (FGM) presentada en una comunicación anterior. El aspecto más notable de la extensión de la FMG al análisis dinámico reside en la construcción de una matriz de masa elemental que, por una parte, no requiere ninguna hipótesis complementaria sobre el campo de movimientos y, por otra parte, permite considerar de forma exacta la distribución de rigidez y masa interior de los elementos. Ello parte de la previa definición de una matriz de masa seccional. Se ha realizado una comparación, para algunas estructuras sencillas, de los resultados obtenidos mediante la formulación presentada y los obtenidos por otros autores a través de distintas formulaciones. De ésta se desprenden la eficiencia y exactitud del método propuesto y, en particular, de la formulación que se realiza de la matriz de masa.

Comportamiento sísmico de edificios con un sistema no lineal de control híbrido

Scipedia content — Mon, 19 Jun 2017 14:55:03 +0200

En el artículo se propone una clase de sistema hibrido de control antisísmico de edificios que combina un sistema pasivo de aislamiento de base con comportamiento no lineal con uno , activo. La componente pasiva del sistema está constituida por un aparato de apoyo que puede ser de tipo histerético, de tipo friccional, o una combinación de los dos. Las fuerzas de control activo se aplican sobre la base y tienen como objetivo la reducción de su desplazamiento. Se desarrolla una ley de control adaptativo que garantiza una forma de comportamiento estable del sistema frente a las incertidumbres tanto en las características del edificio como en las de la excitación sismica así como frente a las no linealidades. La reducción del desplazamiento de la base estructural puede provocar un ligero empeoramiento del comportamiento dinámico del edificio con respecto al del caso puramente pasivo. Sin embargo, su comportamiento global mejora cuando se considera el sistema híbrido, especialmente para excitaciones con frecuencias predominantes para las cuales la respuesta de la estructura con control pasivo es máxima. La eficacia del procedimiento propuesto en solucionar el problema formulado se ilustra mediante estudios numéricos.

Cálculo de la respuesta dinámica de estructuras mediante un procedimiento de estado

Scipedia content — Mon, 19 Jun 2017 15:56:33 +0200

A procedure for computing the dynamic response of elastic linear structure is developed. The method is based on the state representation the equations of motion. The algorithm stability and accuracy compare favourably with those of step-by-step integration procedures. The proposed approach does not require any restriction on the type of dampingmatrix. The methodology isillustrated by two examples: seismic response of a dam and calculation of a building structure.

Control digital predictivo de la respuesta sísmica de estructuras

Scipedia content — Mon, 19 Jun 2017 16:02:48 +0200

En este artículo se desarrolla un controlador digital predictivo con aplicación en la reducción de la respuesta sísmica de estructuras. Su eficacia se comprueba controlando la respuesta de un modelo de reactor nuclear.

Seismic and structural response of a framed four level building with RC and steel structure designed according to current Venezuelan codes

Alex Barbat — Sat, 07 Apr 2018 09:49:02 +0200

This study determines the structural behavior of a four level framed building with composite RC and steel structure designed according Venezuelan seismic codes. The structural system consists of RC frames in the first three levels and steel frames in the fourth. It was performed linear analysis to design all structural elements. Capacity curves and performance points were obtained with pushover
analysis. Results showed greater ductility in the X frames’ direction and greater resistance reserve in the external frames. Performing points showed adequate resistance values but low stiffness in two Y frames’ directions. Seismic action is carried on through synthetic accelerograms defined by the seismic codes used in this study. Dynamic analysis is used to compute parameters of ductility, over
strength and displacements. In one case the collapse Limit State was reached, implying a general collapse of the building. Incremental dynamic analysis was performed to obtain fragility curves and damage probability matrix; a very high probability of significant lateral displacement and damage was evidenced from this despite a normative design of structural elements.

Seismic response and torsional effects of RC structure with irregular plant and variations in diaphragms, designed with Venezuelan codes

Alex Barbat — Sat, 07 Apr 2018 09:39:58 +0200

The objective of this study is to determine the seismic response and torsional effects of an existing Reinforced Concrete building with irregular plant and five levels projected according to an older version of Venezuelan seismic design code. Two structures were analysed: the original building and a redesigned version. Nonlinear static analysis and nonlinear 3D dynamic analysis were applied, based on registers of three synthetic accelerograms compatible with the elastic design spectrum for the used code. In 3D analysis, four structures were simulated, with and without rigid diaphragms so as to compare the seismic behaviour of the buildings. Through this nonlinear analysis parameters were determined that define the behaviour of the structure, torsional moments and rotations in columns reached for simulated buildings. Also, to obtain damage fragility curves for five states damage were generated. Results show that the
original structure has an inadequate resistant behaviour and a high probability of exceeding the moderate damage state, while the redesigned structure presents good performance under seismic events according to the existing code. It was also observed that maximum torsional effects occur in the entrant corners of the irregular plant, which are reduced in mid-rise buildings by using a rigid
diaphragm.

Probabilistic Seismic Damage Assessment of RC Buildings Based on Nonlinear Dynamic Analysis

Alex Barbat — Sat, 07 Apr 2018 09:30:40 +0200

The incremental dynamic analysis is a powerful tool for evaluating the seismic vulnerability and risk of buildings. It allows calculating the global damage of structures for different PGAs and representing this result by means of damage curves. Such curves are used by many methods to obtain seismic risk scenarios at urban level. Even if the use of this method in a probabilistic environment requires a relevant computational effort, it should be the reference method for seismic risk evaluation. In this article we propose to assess the seismic expected damage by using nonlinear dynamic analysis. We will obtain damage curves by means of the incremental dynamic analysis combined with the damage index of Park & Ang. The uncertainties related to the mechanical properties of the materials and the seismic action will be considered. The probabilistic damage curves obtained can be used to calculate not only seismic risk scenarios at urban level, but also to estimate economic losses.

Vulnerability Assessment of Reinforced Concrete Framed Structures Considering the Effect of Structural Characteristics

Alex Barbat — Sat, 07 Apr 2018 09:21:24 +0200

Considering the effects of earthquakes occurred during the last 15 years, this article focusses on finding solutions to minimize the human and economic losses. Several methodologies were developed in order to assess the vulnerability of the built environment with special reference to one of the most suitable structural systems in seismic areas for dwellings, offices or other functionalities, which is the reinforced concrete framed structure. Thus, the present article studies the influence on the vulnerability of reinforced concrete framed structures of geometric structural characteristics like the slab thickness, the building height and the plan configuration. Referring to the slab, it adds supplementary stiffness to the structure that can significantly influence upon its overall failure mechanism. 3D static nonlinear analyses are conducted by means of the SAP2000 computer program. The results are capacity curves which are used to develop the vulnerability curves. Three thicknesses are considered for the slab: 0.1 cm, 0.12 cm and 0.15 m. Medium and high rise structures are considered, with 4, and 8 levels, respectively, in order to determine the influence of the building height on the
vulnerability index. Three plan configurations of the buildings are compared: a square one, a rectangular one and an L shaped one. For all the analyzed cases, the corresponding vulnerability curves are compared. The obtained results reveal that more realistic results for the behavior of the structure can be obtained if special attention is given to the structural characteristics, especially during the conceptual design process.

Probabilistic seismic risk evaluation of reinforced concrete buildings

Alex Barbat — Sat, 07 Apr 2018 09:12:20 +0200

The main objective of this article is to propose a simplified methodology to assess the expected seismic damage in reinforced concrete buildings from a probabilistic point of view by using Monte Carlo simulation. In order to do so, the seismic behaviour of the building was studied by using random capacity obtained by considering the mechanical properties of the materials as random variables. From the capacity curves, the damage states and fragility curves can be obtained, and curves describing the expected seismic damage to the structure as a function of a seismic hazard characteristic can be developed. The latter can be calculated using the capacity spectrum and the demand spectrum according to the methodology proposed by the Risk-UE project. In order to define the seismic demand as a random variable, a set of real accelerograms were obtained from European and Spanish databases in such a way that the mean of their elastic response spectra was similar to an elastic response spectrum selected from Eurocode 8. In order to combine the uncertainties associated with the seismic action and the mechanical properties of materials, two procedures are considered to obtain functions relating the peak ground acceleration to the maximum spectral displacements. The first method is based on a series of non-linear dynamic analyses, while the second is based on the well-known ATC-40 procedure called equal displacement approximation. After applying both procedures, the probability density functions of the maximum displacement at the roof of the building are gathered and compared. The expected structural damage is finally obtained by replacing the spectral displacement calculated using ATC-40
and the incremental dynamic procedure. In the damage functions, the results obtained from incremental static and dynamic analyses are compared and discussed from a probabilistic point of view.

Seismic performance of waffled-slab floor buildings

Alex Barbat — Sat, 07 Apr 2018 09:00:55 +0200

The codes used in seismic design of waffled-slab floors buildings (WSFB), such as the Spanish NCSE-02 earthquake-resistant design code, assign them restricted ductility, utilise linear structural analysis based on modal analysis, but also consider the structural ductility
concept. Uncertainties arise whenever these codes are applied to the special case of buildings with waffled-slab floors, the ductility of which is doubtful. In many cases, during earthquakes, buildings with restricted ductility are unable to reach the ductility values assumed in the design process, although they may exhibit adequate values of overstrength. This paper therefore studies typical WSFB by applying static incremental non-linear analysis procedures (pushover analysis) in order to calculate their actual structural ductility and overstrength values. Fragility curves corresponding to different damage states and damage probability matrices are also calculated and compared with those of moment-resisting frame buildings (MRFB) in order to obtain useful conclusions for earthquake resistant design. One of the most relevant conclusions of this article is that the use of a better confinement and of ductile steel can only improve the seismic behaviour of MRFB but not that of WSFB.

Probabilistic seismic damage assessment of reinforced concrete buildings considering directionality effects

Alex Barbat — Fri, 06 Apr 2018 15:49:22 +0200

Most of buildings and structures are usually projected according to two main axes. However, the geographical position of these buildings varies randomly. Such random distributions of the azimuthal positions of structures, in most of the cities, generally, are not accounted for when assessing their seismic risk; certainly, the direction of the seismic loads is another highly random variable. Moreover, an additional important source of uncertainty is related to the structural response, mainly due to the random character of the mechanical properties. There is a consensus that uncertainties must be considered for adequately assessing the seismic risk of structures, but these directionality effects have not been deeply explored so far. In this article, the influence of the high uncertainty involved in these input variables on the expected seismic damage is analysed. Thus, an actual earthquake, which affected the southern part of Spain, is studied. Notably, damages on a group of affected buildings, located close to the epicentre, are analysed and discussed in detail. The results show that the influence of the random azimuthal position of structures is an important source of uncertainty and that it should be taken into account when estimating the expected seismic risk in urban areas.

Seismic vulnerability and risk evaluation methods for urban areas. A review with application to a pilot area

Alex Barbat — Fri, 06 Apr 2018 15:40:57 +0200

The most relevant seismic vulnerability and risk analysis methods are discussed and compared in this article using, as a pilot urban area, the city of Barcelona, Spain, where risk studies have been carried out over the last 15 years in the framework of different research projects. Most of the buildings in Barcelona, which have unreinforced masonry structure or reinforced concrete structure with waffled slab floors, show a high degree of vulnerability to earthquakes. The physical seismic risk but also the socio-economic implications of risk are considered in the article. The robustness of the innovative holistic approach, based on indicators related to the physical exposure, the social fragilities and the lack of resilience of urban area, is also proved. Using a geographic information system (GIS), the seismic risk results are described by means of scenarios of expected losses, but also as scenarios of probabilities of occurrence of predefined damage states.