Unreinforced masonry buildings prevail in many old historical centres and urban areas worldwide. These structures may present inadequate seismic performance because they were often designed without considering any seismic resistance requirements. Therefore, they may be highly vulnerable and susceptible to damage caused by earthquakes, even of low intensity.This work investigates the seismic vulnerability of typical unreinforced masonry buildings situated in the Eixample district of Barcelona, Spain. Most of the buildings of the district were designed only for vertical static loads with slender load-bearing masonry walls and flexible diaphragms. A typical characteristic is the presence of openings with considerable size on the facades. The identification of the main parameters affecting the structural behaviour under lateral loading is necessary to evaluate the seismic vulnerability.As a first step, a building taxonomy for the Eixample district has been prepared in order to classify the different building typologies by taking into account the influence of the structural features in the overall response. This typology classification serves two aims. The first aim is to empirically evaluate the vulnerability of each category. The second one is to provide the basis for creating a numerical model of a representative building and analyse its seismic performance.The main objective of this paper is to assess the seismic behaviour of a typical unreinforced masonry structure by means of nonlinear static analysis. For this purpose, a three-dimensional Finite Element model of a representative building has been prepared. Pushover analyses have been performed in two directions (parallel and perpendicular to the façades) aiming to identify the typical failure mechanisms and the seismic capacity.The performance of the representative building typology, with its typical heterogeneities and irregularities, is compared with that of a reference regular unreinforced masonry structure. Additionally, a parametric analysis is carried out to evaluate the different seismic response by adding more storeys in height. This work is the basis for future analyses devoted to large scale seismic vulnerability assessment of the most representative building typologies of the Eixample district.

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This paper presents the historical development of the vertical extensions of unreinforced masonry buildings in the Eixample district of Barcelona and their impact on the seismic behaviour. Existing masonry buildings of Eixample present significant seismic risk because, despite the low to moderate seismic hazard of Barcelona, they show a marked vulnerability given their average height of six storeys and the substantial slenderness of the walls. Between the end of the 19 th century and the beginning of the 20 th century, the vertical extensions, known as remuntes in Catalan, were a common solution to the increasing demographic demand of the city. In their majority, these vertical extensions add a structural irregularity that represents a potential vulnerability factor not yet investigated. The present study focuses on Eixample's remuntes, including their historical development, the description of their structural features and the identification of their most representative configurations in the existing building stock. A seismic analysis based on the Finite Element Method is presented on a reference model without extensions and three others with the most recurrent configurations of remuntes. The seismic response is investigated through pushover analysis. The results provide a better understanding of the negative impact of the vertical extensions on the seismic performance.

(English) Unreinforced masonry buildings (URM), which prevail in many historic and urban centres, can be considered to be significantly vulnerable to seismic actions due to their peculiar constructive and structural features that could influence their seismic performance, even in low to moderate seismic hazard areas. These existing structures were usually designed considering only gravity loads without any seismic design requirements. Hence, they may endure severe consequences in the event of an earthquake due to the presence of many specific sources of structural vulnerability, such as the material's limited resistant capacity and ductility, the buildings’ height, very slender load-bearing walls, semi-flexible horizontal diaphragms, irregular plan configurations, presence of vertical extensions, large façade openings, among other structural features.The scientific literature currently offers a variety of methods for assessing seismic vulnerability of existing buildings on a large scale, as it is considered a challenging task. The selection of the appropriate approach is determined by several factors, including the purpose and nature of the study, the amount of data and resources available, the investigated building typologies, the level of analysis effort, and the cost required for the studies.The aim of this research is to contribute to the seismic vulnerability assessment of existing masonry buildings of the Eixample district of Barcelona, though the derivation of a general methodology, intensively based on numerical simulation due to lack of seismic damage observations from past earthquakes. This approach could be applied to similar problems involving the vulnerability assessment of historic urban centres in low to moderate seismic regions, by applying the necessary modifications. The first step of the proposed methodology is elaborating a detailed building taxonomy of the masonry buildings of the Eixample district according to their structural, material and geometrical characteristics, relevant to their seismic behaviour and possible sources of vulnerability. The most representative building typologies are selected based on the aforementioned building taxonomy, by using available statistical data of structural features of the analysed building stock. The next step is developing sophisticated numerical models of the previously identified representative masonry buildings, by using an efficient and realistic simulation of their seismic response based on the Finite Element Method (FEM). Non-linear static (pushover) analysis are performed for both main directions (parallel and perpendicular to the façade) in order to better understand their global seismic behaviour in terms of capacity and failure mechanisms. Moreover, parametric analyses are carried out to investigate the influence of different structural parameters on the building’s seismic performance. The N2 method is applied for the evaluation of the buildings’ seismic performance for the seismic hazard scenarios in Barcelona. The final step is the proposal of new forms of the Vulnerability Index Method (VIM) for both main directions, by defining the classes and calibrating the weights of the specific vulnerability parameters. The methodology is applied eventually to the Eixample district of Barcelona’s urban centre, by including two cases: a large number of existing masonry buildings and a typical urban block. (Español) Los edificios de obra de fábrica no armada (URM), abundantes en muchos centros urbanos históricos, resultan frecuentemente vulnerables ante las acciones sísmicas, incluso en zonas de baja o moderada peligrosidad sísmica, debido a sus características constructivas y estructurales. Por lo general, estas estructuras fueron diseñadas teniendo en cuenta únicamente las cargas gravitatorias y sin verificar su comportamiento sísmico. Ante un terremoto, dichas estructuras pueden sufrir graves consecuencias debido a varias fuentes específicas de vulnerabilidad estructural, como son la limitada capacidad resistente y limitada ductilidad del material, la altura de los edificios, los presencia de muros de carga muy esbeltos, forjados flexibles o semiflexible, las configuraciones de planta, frecuentemente irregulares, la presencia de extensiones verticales (remontas) y la frecuente presencia de grandes aberturas de fachada, entre otras.Como consecuencia del desafío que supone la evaluación de la vulnerabilidad sísmica de los edificios existentes a gran escala, en la literatura científica actual se han propuesto una gran variedad de métodos orientados hacia su caracterización. La selección del método más adecuado viene determinada por varios factores, entre los cuales se hallan el propósito y la naturaleza del estudio, la cantidad de datos y de recursos disponibles, las tipologías de los edificios investigados, el esfuerzo computacional requerido para el análisis y el coste de la investigación.El objetivo del presente trabajo reside en contribuir a la evaluación de la vulnerabilidad sísmica de los edificios de obra de fábrica existentes en el distrito del Eixample de Barcelona. Ello se lleva a cabo mediante la elaboración de una metodología general basada principalmente en la simulación numérica debido a la ausencia de observaciones, en el caso investigado, relativas a daños sísmicos producidos terremotos ocurridos en el pasado. Esta metodología podría aplicarse, con las modificaciones necesarias, a casos similares relativos a la evaluación de la vulnerabilidad de centros urbanos históricos en regiones de sismicidad baja a moderada. El primer paso de la metodología propuesta consiste en elaborar una taxonomía detallada de los edificios de obra de fábrica del distrito del Eixample en función de las características estructurales, materiales y geométricas que resultan relevantes para la caracterización de comportamiento sísmico. Los tipos de edificios más representativos se han seleccionado en base a dicha taxonomía, utilizando para ello datos estadísticos disponibles sobre sus características estructurales. El siguiente paso ha consistido en desarrollar modelos numéricos avanzados de los edificios seleccionados. Para este fin se ha utilizado el Método de los Elementos Finitos (MEF) por su simulación eficiente y realista de la respuesta sísmica. Se han realizado análisis estáticos no lineales (pushover) para las dos direcciones principales (paralela y perpendicular a la fachada) de los edificios, con el fin caracterizar su comportamiento sísmico global en términos de capacidad y mecanismos de fallo. Además, se han realizado análisis paramétricos con la finalidad de investigar la influencia de diferentes parámetros estructurales en el comportamiento sísmico. Se ha aplica el método N2 para la evaluación del comportamiento sísmico de los edificios para distintos escenarios de peligrosidad sísmica en Barcelona. Finalmente, se han propuesto unos formularios modificados para la aplicación del Método del Índice de Vulnerabilidad (VIM) según las dos direcciones principales, de los edificios. Ello ha comportado una definición de las clases de vulnerabilidad y la calibración de los pesos de los parámetros específicos de vulnerabilidad consistentes en (1) un conjunto amplio de edificios de obra de fábrica existentes y (2) el caso específico de un bloque de edificios típico del entorno urbano investigado. Finite Element Model, Pushover Analysis, N2 method, Vulnerability Index Method.