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Soil site studies are crucial in the analysis of seismic hazard in populated areas. This study focusses on the use of the Ground Penetrating Radar as a non-destructive geophysical method to analysis the water content of a sedimentary basin of a local urban area in Cervantes Parks in Barcelona city. Main objective of this work is to understand further the local seismic soil site, and analysis the background clutter amplitude and frequency of the GPR signal applied on the seasonal changes of the underground water content. Changes produces in the GPR signal could be associated to the changes of the ground material due to the existence of water content and water flow, which influence the grain size distribution of the soil characterisation. Previously, several methodologies have been applied to determine the changes of the ground material due to the existence of water content and most importantly effect of the seasonal changes on the soil characterisation. GPR has been applied as a new technology and non-invasive to further analysis water content in shallow geology. Methodology applied on this study compromised in four different phases; Two seasonal data collection using 100 MHz centre frequency shielded antenna in both dry and wet season, radar images are proceeded with common post-processing approaches, following more innovative processing approach based on the Fast Fourier Transform (FFT) method in order to analysis background clutter amplitude and frequency spectrum to achieve an accurate interpretation of underground water content activities, in conclusion a comparative study of the results driven from radar images are elaborated considering historical knowledge. Results show that GPR is an efficient technique to analysis water content invasively considering low frequency antennas to achieve deeper penetration depth in sedimentary deposits, and predict shifting and increasing of the underground streams due to changes in weather conditions. Results could contribute, Peer Reviewed, Postprint (author's final draft)

Structural damage detection is an important issue in conservation. In this research, principal component analysis (PCA) has been applied to the temporal variation of modal frequencies obtained from a dynamic test of a scaled steel structure subjected to different damages and different temperatures. PCA has been applied in order to reduce, as much as possible, the number of variables involved in the problem of structural damage detection. The aim of the PCA study is to determine the minimum number of principal components necessary to explain all the modal frequency variation. Three estimators have been studied: T2 (the square of the vector norm of the projection in the principal component plan), Q (the square of the norm of the residual vector), and the variance explained. In the study, the results related to the undamaged structure needed one principal component to explain the modal frequency variation. However, the high damage configurations need five principal components to explain the modal frequency. The T2 and Q estimators have been arranged in order of increasing damage for all the performed experimental tests. The results indicate that these estimators could be useful to detect damage and to distinguish among a range of intensities of structural damage., This research has been partially funded by the Spanish Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICIN) through project with reference: PID2020-117374RB-I00/AEI/10.13039/501100011033., Peer Reviewed, Postprint (published version)

Cultural heritage buildings are prone to failures when subjected to seismic events, and recent earthquakes worldwide resulted in many losses of these buildings. Therefore, there is a need for methodologies for assessing their seismic safety that should be based on enough knowledge of the building. Here, dynamic investigation by dynamic identification testing and dynamic monitoring increase significantly the level of knowledge about the assessed building. The dynamic identification tests give global information about the dynamic properties like natural frequencies that are useful in calibrating and updating a numerical model of the building that could be used in the seismic safety evaluation. Dynamic monitoring gives the dynamic properties’ evolution in time and may be used as an early warning tool able to send alarms when meaningful changes in dynamic properties are observed. This chapter gives some considerations on the different investigation activities of dynamic identification, dynamic monitoring, numerical model updating, and seismic safety assessment of cultural heritage buildings. As an application, the case study of the historic Mallorca cathedral is discussed., This study has been carried out within the context of the project “New Integrated Knowledge-based Approaches to the Protection of Cultural Heritage from Earthquake-Induced Risk-NIKER” sponsored by the European Commission (Grant Agreement No. 244123), which is gratefully acknowledged., Peer Reviewed, Postprint (published version)

This is an Accepted Manuscript of an article published by Taylor & Francis Group in International Journal of Architectural Heritage on 2020, available online at: http://www.tandfonline.com/10.1080/15583058.2020.1831101., Detection of structural damage is an important issue. Some techniques require knowledge of the undamaged state or in-depth knowledge of the construction materials used. The application of principal component analysis to the temporal variation in natural frequencies is a promising technique. With an undamaged structure a single principal component will suffice to explain the change in modal frequencies with weather variables, whereas more components are needed in the case of damaged structures. Like all other detection techniques, it has advantages and drawbacks. The main advantages are the ability to work without knowledge of the previous state of the structure, the relatively short monitoring time required (about 10 days), low cost, and low number of instrumentations. The main drawback is the need for more studies to correlate degree of damage with the number of principal components. This paper presents the results obtained for six structures: Mallorca Cathedral, four university buildings in Barcelona, and a reduced model structure in a laboratory. We also propose a semiautomatic algorithm to track modal frequencies over time and add a discussion of operational modal analysis in real buildings., This research was partially funded by the Ministry of Economy and Competitiveness (MINECO) of the Spanish Government and by the European Regional Development Fund of the European Union through the project referenced as CGL2015-65913-P (MINECO/FEDER, UE). We also want to acknowledge the management and maintenance services of the UPC schools of Industrial Engineering (ETSEIB) and Architecture (ETSAB) for their readiness and help, and the Department of Quantum Physics and Astrophysics of the University of Barcelona for the meteorological data., Peer Reviewed, Postprint (author's final draft)

This is an Accepted Manuscript of an article published by Taylor & Francis Group in International Journal of Architectural Heritage on 2019, available online at: http://www.tandfonline.com/10.1080/15583058.2019.1643947, The study of structural safety when it is covered by important paintings requires a careful analysis without affecting the paintings. Therefore, non-destructive surveys are the only feasible method to obtain data about its state. In Cueva Pintada case, the problem requires a detailed but noninvasive analysis because this cave was dug in volcanic tuff. The tuff presents poor consolidation. This geological material is very sensitive to vibration. Furthermore, the proximity to the city downtown increases vibrations due to traffic. Recently, a small rockfall produces damage and alerted of the cave state of conservation. The painting walls constraint many of the NDT surveys. Two methodologies have been applied: ground-penetrating radar (GPR) and passive seismic. GPR analysis allowed determining the inner structure of the tuff cave, and results were used to determine the zones that required a wider and dense vibration study. Radar images show important anomalies at depths of about 0.2 m to 0.8 m and from 1.5 m to the top of the roof, almost horizontal. Amplification factor measured by passive seismic survey ranges from 0.03 to 93, with near half of the ceil with amplifications higher than 5 and about 10% with amplifications over 50 times., This research was partially funded by the Ministry of Economy and Competitiveness (MINECO) of the Spanish Government and by the European Regional Development Fund (FEDER) of the European Union (UE) through the project referenced as CGL2015-65913-P (MINECO/ FEDER, UE)., Peer Reviewed, Postprint (author's final draft)

Combined non-destructive techniques are applied in the study of a historical building in Barcelona. Santa Maria del Mar is a magnificent Mediterranean gothic church built between 1329 and 1383. Two of the most important characteristics of this building are the slender columns and the almost flat rooftop. This structure, used to create a visual impression of a unique space, transmits high loads to the tall columns. Previous to restoration, vaults, roofs, and columns were extensively assessed with non-destructive tests, in order to improve the knowledge of those structures. This information will be used in further simulations to analyse load distributions at each part of the structure. Ground and floor were also studied. The analysis of the columns was based on ground- penetrating radar (GPR) surveys and on seismic tomography. Finally, the dynamic behaviour of the structure was determined by seismic monitoring of the main nave and the bell tower. Results obtained at the radar survey highlight the existence of unexpected anomalies in homogeneous materials, supporting the hypothesis of an inner structure between arches and roof composed by hollow elements. Seismic tomography defined the inner geometry of the columns and detected some damage or lower quality stone in various zones. Seismic monitoring established the perfect junction between the bell tower and the main nave. GPR survey on the floor allowed detecting a large number of graves, and some images suggest the existence of large underground walls and some of the foundations of the main façade., Peer Reviewed, Postprint (published version)

The paper discusses the seismic assessment of Mallorca cathedral in Spain. This cathedral is an audacious Gothic structure built on the island of Mallorca during 14th-16th centuries, characterized by its large dimensions and slender structural members. For that purpose, different analysis methods were used. A 3D Finite Element (FE) model of the cathedral was created and then updated based on in-situ dynamic identification tests. Nonlinear static (pushover) analysis was firstly carried out applying the seismic loads in the longitudinal and transversal directions of the cathedral considering both positive and negative signs. The pushover results were compared with the results of the kinematic limit analysis as a way to cross check the seismic safety assessment. Although for such a large historical structure, the nonlinear time-history (dynamic) analysis requires a very high computer effort, an attempt to perform this type of advanced analysis was carried out., Peer Reviewed, Postprint (published version)

For preserving existing structures to the extent possible, vibration-based damage detection techniques are gaining more attention. In specific, tracking the changes in a structure’s natural frequencies employing the Principal Component Analysis (PCA) seems to be a promising technique. This paper presents an on-going research for developing an approach for damage detection based on identifying the natural frequencies of the structure (via dynamic identification or monitoring) followed by applying PCA on the temporal variation of the identified natural frequencies. The processing of the dynamic monitoring data was carried out using a proposed semiautomatic algorithm able to identify and track the natural frequencies of the monitored structures and their changes over time. The algorithm was applied on one historical structure and two modern ones. PCA will to be carried out. The so far developed approach as a whole was applied on a steel structure model tested in lab. It was subjected to dynamic identification tests with and without damage. It was found that PCA applied to frequency variation seems to be a possible tool to know damages in structures. Nevertheless, the simplified point of view correlating directly the number of PCs with the damage importance seems to be not accurate. First results seem to indicate that the variance percentage explained by each of the principal components could be correlated with the kind of damages and the shake used to excite the structure., Postprint (published version)

An integrated investigation of engineering archaeometry was carried out using dynamic identification, dynamic monitoring and Infra-Red (IR) thermography for the study of the dynamic behavior of Mallorca cathedral in Spain. The cathedral is a large historical masonry structure built during 14-16th c. Dynamic identification and monitoring allowed the capturing of eight natural frequencies of the cathedral. IR thermography was used as a complementary inspection technique in the context of a continuous monitoring. Usually, IR thermography is used punctually for the inspection of a part of an inspected structure. Here an alternative was tried as the IR camera was installed for two two-weeks periods in the winter and in the summer of 2011 to monitor the stone surface temperature of a large portion of the cathedral. The correlation between the cathedral natural frequencies and the stone surface temperature of some selected structural elements was investigated and compared with the correlation with the external and the internal temperatures. It was found that the correlation with stone surface temperature was lower than that with external temperature. The study allowed a better understanding of the influence of temperature changes on the structure’s dynamic behavior., Peer Reviewed, Postprint (published version)

The collapse of a tunnel and the damage in a second tunnel during the construction works, forced to the assessment of the ground in the front tunnel of the second structure, in order to avoid additional problems. The first evaluation was carried out with a borehole radar, because the structure was in a populated zone of a dense city. The uncertainty associated to the near surface studies is, in this case, greater because the unshielded antennas produce a rotational ambiguity. The imprecision in the location of the targets was reduced using seven non-parallel boreholes. The results shows the anomalies that could be associated to faults and also an irregular area of the B-scans that could be related to heterogeneous materials and the existence of a large number of voids., Postprint (author's final draft)

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., Peer Reviewed, Postprint (author's final draft)

This is the peer reviewed version of the following article: [Elyamani, A., Caselles, O., Roca, P., and Clapes, J. ( 2017) Dynamic investigation of a large historical cathedral, Struct. Control Health Monit., 24: e1885. doi: 10.1002/stc.1885. ], which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1002/stc.1885. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving., The presented research aimed at studying the dynamic behavior of Mallorca cathedral (Mallorca Island, Spain) under ambient sources of vibration and seismic events. The cathedral is one of the greatest built masonry structures worldwide. It is characterized for its audacious dimensions and slender structural members. Because of it, the study of its dynamic behavior is a clear concern. The cathedral dynamic properties were firstly identified using ambient vibration testing. Afterwards, a dynamic monitoring system was implemented to continuously measure, record, and wirelessly transfer the acceleration records without having to set up an activating threshold. This monitoring type was implemented because of the low seismic intensity of Mallorca Island with a basic ground acceleration of only 0.04 g according to the Spanish seismic standard. The continuous monitoring allowed for capturing some seismic events and some drops in the natural frequencies were noticed because of a breathing crack effect. Using both ambient vibration testing and continuous monitoring system, global modes could be more accurately identified than more local ones. The identification of the global modes was more attainable than in the case of more local ones. The temperature was a more influential environmental parameter than humidity and wind for all of the identified modes except for one more directly depended on wind., Peer Reviewed, Postprint (author's final draft)

Santa Maria del Mar is a magnificent gothic church built between 1329 and 1383 in a neighbourhood outside the city walls, over the remains of a more ancient church. The inhabitants of this district (merchants, downloaders of the port, ship-owners artisans and craftsmen) contributed and took part in the construction of this building. Nowadays it is one of the most representative gothic buildings of Barcelona. The structure was completely studied with GPR in order to obtain useful information for a further restoration. Some of the most interesting results were obtained during the evaluation of the vaults and roofs of the building. Radar images demonstrate that the inner structure was designed in order to diminish the load on the arches and walls. Hollow elements were used to support partly the roof in some areas. Moreover, walls, floors and columns were also assessed, and also the ground outside the building. A large number of graves were located under the church floor, but also some of the radar images suggest the existence of large underground walls. The GPR study of the columns and walls was completed with a seismic survey that demonstrates the existence of zones of non-consolidated materials and defined the joints of the ashlars., Postprint (author's final draft)

The GPR assessment of buildings depends on the structure or part of the building studied. In this paper, three different case study are presented, all of them about old buildings that need to be restored or modified. The radar study objective was, in all cases, the detection of hidden targets or structural elements. The first case presents the study of some terraces in buildings in order to determine the structural elements and also to determine approximately the materials, previous to an important modification. The second case is based in the study of the ground underneath the building. Several structures that could affect to the further restoration were detected. The last case presents the study of floors in the different levels of a building, showing the changes in the structural elements that support the floors. All the examples demonstrate the ability of the method applied previous to the restoration projects., Postprint (published version)

Cultural heritage buildings are irreplaceable vestiges of the civilizations. The knowledge about ancient civilizations and the past of the contemporary societies is based in most cases in the study of these structures and remains. Some magnificent constructions are the cathedrals, the Christian churches that become the most representative buildings in the Middle Age European cities. These unique structures present usually a wide representation of styles and constructive techniques, being clear examples of the development and history of the societies. Unfortunately, the age and weather affect the cathedrals because all materials deteriorate due to these factors. In addition, natural or fortuitous hazards as earthquakes or fires can cause damage in their structures. As a result, restorations and conservation are usual tasks. However, maintenance of those huge and impressive monuments can only be done when the architects and engineers have enough information about the structure of the building and the possible damage. Therefore, the previous and careful structural assessment of the building becomes a decisive task for their preservation. Furthermore, in most cases, the cathedrals are built over most ancient remains. Sometimes over the most important buildings of previous civilizations, and some structures could remain hidden under the present construction. Other times, Roman or Greek temples, or Arabian mosques were partially demolished or enlarged to be transformed into cathedrals. Even older Visigothic churches were also transformed in more important structures, being hidden under it, or used partially in the construction of the new cathedral. Geophysical surveys are carried out in many cases to provide information related to these two aspects: existence of older remains under the Cathedral and definition of structural health, detection of possible damage or even, evaluating possible causes of the damage. This paper present three case study in different Cathedrals, d, Postprint (author's final draft)

Determining the behavior of a structure estimated by means of finite elements analysis requires not only an in-depth knowledge of its geometry and dynamic properties but also an experimental validation to corroborate the adequacy of the characteristics of the structure. Most of the current structural identification techniques are based on linear methods that call for many measurement points and/or a relative simple structure. Complex structures are somewhat still an unexplored field due to the difficulties with the finite element method and the experimental corroboration of its results. This study presents the use of particle motion computation applied to each structural vibration mode to improve the identification of its dynamic properties, and its application to the Gothic Cathedral of Palma de Majorca (Spain)., Postprint (author’s final draft)

Microzonation is widely used in seismic risk evaluations to define the predominant period values, which are usually associated with extended areas of a few hundred meters. However, the representative values corresponding to these areas are obtained from few measurements in each area. Thereby, results are accurate only in the case of depth-dependent soils. However, not detected narrow and sharp lateral changes in soil are potentially the cause of imprecision and could be a source of specific errors. This article aims to present several tests conducted in order to emphasise the importance of accurate selection of points, to underscore the necessity of more precise and detailed evaluations, and to suggest a possible methodology to select the most appropriate data acquisition points. Results highlight the need to divide microzonation areas into smaller zones for a precise evaluation in locations where sudden changes in soil characteristics exist. Therefore, in such sites the requirement of nanozonation appears; defining zones with the same soil response. Distance between vibration measurements could be the main problem for nanozonation; data acquisition in areas with irregular geology can be time consuming when a precise analysis is required. In the most complicated environments or in dense cities, it could even be unfeasible. Consequently, it is necessary to establish a functional methodology to adequately distribute the measurement points throughout the area. On this occasion, three sites in Barcelona city were studied. This city is surrounded by mountains at NW, W, and S, and by the Mediterranean Sea at N and E. As a consequence, the shallow geology is characterized by many paleochannels and streams that are currently buried. These geological structures most likely affect the soil response maps, including nanozonation., Peer Reviewed, Postprint (author’s final draft)

This work describes two mid-height RC base isolated buildings recently erected in Barcelona. Both buildings are located near the main railway station in Barcelona (Barcelona-Sants), thus undergoing dynamic excitations due to intensive railway traffic. The base isolation system consists of spring-dashpot devices located at the ground level. The isolators were designed after the expected input according to extensive field measurements. The moderate levels of vibrations detected from numerical simulations (dynamic analyses) and from present observations confirm the efficiency of the base isolation systems., Postprint (published version)

This paper describes an integrated near-surface geophysical study carried out in order to obtain high-resolution images of the shallow subsurface under and around the Cathedral of Mallorca. The study was a part of a global project focused on determining the state of the building structure and on evaluating the Cathedral's dynamical behaviour (natural frequencies and vibration modes). Ground-penetrating radar (GPR) and the capacitively coupled resistivity method were used to obtain 2D images of the shallow subsurface. Refraction microtremor array measurements (ReMi) were also used to characterize the rock and soil properties and several invasive boreholes provided detailed and exact information on the stratigraphy. The information from the geophysical data was used to determine a final model of the ground, with indications of the most likely vulnerable zones. As a part of this final model, GPR profiles enabled us to delineate the superficial ground structure and to detect some archaeological features. Electrical resistivity imaging data were in good agreement with the GPR results, and showed shallow major changes in the soil and rock under the filling materials. The refraction microtremor array (ReMi) results indicate the existence of compacted soils in different areas, probably corresponding to old filled zones, in good correlation with GPR and resistivity profiles in the most superficial part of the ground., Postprint (published version)

Se presenta la obtención de la vulnerabilidad sísmica para una catedral Gótica de grandes dimensiones mediante la aplicación del Método del Espectro de Capacidad, y la obtención de las probabilidades de daño asociadas., Peer Reviewed, Postprint (published version)

Dentro del proyecto de estudio de la vulnerabilidad sísmica de la Ciutat Vella de Valencia se ha estudiado la respuesta de suelo de esta y su afectación a los edificios de vivienda existentes. Debido a la baja sismicidad de la zona, las características urbanísticas y al bajo coste, la respuesta de suelo se ha calculado mediante el método del cociente espectral aplicado a ruido ambiente (técnica de Nakamura), que proporciona solamente los rangos de periodos, en los que se produce amplificación pero no su valor. Para una correcta aplicación de este método previamente se ha estudiado su aplicabilidad en diversas zonas de la ciudad de Barcelona, ciudad densamente poblada, y por tanto, con escasa proporción de zonas libres donde realizar las mediciones libres de ruidos perjudiciales. Por ello se ha estudiado la influencia, que el trafico de vehículos, paso de peatones y la presencia de árboles, mobiliario urbano, césped y edificios puede tener en los resultados obteniéndose una buena guía de aplicabilidad del método. Paralelamente se ha estudiado e implementado una ponderación de las señales medidas para mejorar los resultados y permitir condiciones de medida menos restrictivas. También se propone el uso de un ajuste gaussiano de los picos de amplificación para la asignación del valor máximo (periodo predominante) y distinguir mediante la desviación estándar de esta, cuando la variación lateral de dos medidas son significativas o no. Los resultados obtenidos en Valencia reflejan su complejidad geológica con tres rangos de periodos donde existe amplificación. También se ha calculado que el 36 % del total de los edificios de vivienda existentes presentan interacción suelo-estructura., Peer Reviewed

Several zones of the northern part of Barcelona City have old water mining galleries located in the upper part of the granite formation. These galleries are now out of use and their localization are unkown. This fact involves some problemes when foundations are built near or over them. Usually geothecnical or geophysical prospecting are only carried out to detect these underground galleries when foundation has been already built and, therefore, geophysical prospecting is more difficult and hard to carry out. The presence of parts of the totally of the building foundation makes very difficult to apply some of the geophysical prospecting techniques like some electromagnetic ones. GPR prospecting surveys are one of the few techniques that are little influenced by near undergound objects, only being affected by down metallic objects or water cables. In this work we present an example of a georradar survey made in Barcelona when building foundation was already made., Postprint (published version)

El ruido cultural o vibración ambiental se genera por el hombre debido a la maquinaria industrial, por el tráfico de vehículos, por el viento, por cambios en presión atmosférica, por actividad volcánica interna, etcétera, y se utiliza para determinar características dinámicas de suelos y estructuras entre otras aplicaciones. Las pruebas de víbración ambiental tienen la ventaja de ser eficientes, rápidas y de bajo coste. La información lograda permite mejorar el proceso de construcción de modelos matemáticos de sistemas dinámicos realizando un ajuste de sus parámetros de tal manera que se establezca la mejor correlación posible entre las respuestas predichas por el modelo y las obtenidas experimentalmente. La frecuencia natural o su inverso, el periodo propio, es de entre las características dinámicas, el parámetro más importante para la estimación de las condiciones físicas de las estructuras. En la ciudad de Barcelona se está realizando un estudio para determinar los periodos propios de los edificios utilizando vibración ambiental como fuente de excitación. En este trabajo se presentan los resultados obtenidos al realizar mediciones durante tres etapas de la construcción de un edificio mixto, de hormigón armado y acero, de ocho niveles. Se busca determinar la influencia de los elementos no estructurales analizando el comportamiento del periodo propio. Los resultados preliminares muestran que el periodo disminuye a medida que se incorporan elementos no estructurales al edificio, indicando un aumento de su rigidez., Postprint (published version)