Browsing by Author "Ferreira, Tiago Miguel"
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- An approach for the estimation of the magnitude of historical earthquakes: a sensitivity study of the 1980 and 1998 earthquakes in AzoresPublication . De Azevedo Charters Fuentes Morais, Eduardo José; Ferreira, Tiago Miguel; Estêvão, João M. C.; Oliveira, Carlos SousaIn regions with low-to-moderate seismicity, the return-period of seismic events with large magnitudes is relatively high. Nevertheless, historical seismic events are relevant for the evaluation of seismic hazard in those regions. Thus, seismologists study the records of the effects of historical earthquakes to map the distribution intensity points, using an Intensity Scale. Afterwards, the maximum intensity point is identified as well as the probable epicentral location and magnitude. Another method, introduced by earthquake engineers, incorporates the knowledge of the behaviour of structures into posterior distributions of magnitude using fragility functions and the damage reported in historical documents. The method uses the total probability theorem to combine the uncertainty in the structural behaviour, ground motion intensity, site-to-source distance. Then, the Bayes’s theorem is employed to update a prior magnitude model into a posterior magnitude distribution. Thus, the reduction of the uncertainty in the final estimates requires the preliminary application of the method to instrumental events in order to validate the appropriate framework to address historical seismicity, namely ground motion and structural response. This paper investigates the earthquakes of January 1st 1980 with Mw=6.8-7.2 and of July 9th 1998 with Mw=5.9-6.2 in Azores Islands (Portugal) as study cases to test the sensitivity to different attenuation models Ambraseys et al. (2005) and Akkar et al. (2014). A single set of fragility functions, derived from a detailed vulnerability assessment in Faial, is assumed to model the structural response in both events. The results show that, for both events, the attenuation model from Akkar et al. (2014) and the fault source model presented results closer to those of detailed methods. Discrepancies can also be explained by differences in the prior distance model resulting from source models assumptions. The intervals Mw=5.96±0.53 and Mw=6.91±0.42 have been estimated for the 1998 and the 1980 earthquake, respectively.
- Casting a new light on the seismic risk assessment of stone masonry buildings located within historic centresPublication . Maio, Rui; Estêvão, João M. C.; Ferreira, Tiago Miguel; Vicente, RomeuIn light of the new legal framework in force in Portugal, which defines the terms for reporting the seismic vulnerability assessment and the need for seismic strengthening of existing buildings, this paper aims at investigating the correlation between two well-known approaches for the seismic risk assessment of stone masonry buildings located within historic centres: the vulnerability index method and nonlinear static seismic analyses. The latter were carried out by using a new three-dimensional macroelement model to numerically represent the considered sample of prototype buildings, together with the application of the N2 Method. In this paper, the original purpose of the vulnerability index method, that of ranking the seismic vulnerability of existing urban cultural heritage (UCH) assets within the same building typology, was numerically validated. However, when reverting the use of the vulnerability index method by replacing the Macroseismic Intensity with a response spectrum, the results were not as interesting as envisaged, since the correlations between the vulnerability index and the main properties of the capacity curves derived from numerical models, presented, in general, a poor fitting. Finally, the possible causes for such poor fitting and future lines of investigation are discussed. Despite these results must be understood with due care and diligence, the authors believe that this exercise might encourage new investigations on this topic that could lead to the development of a new code-oriented methodology for the seismic risk assessment of UCH assets within historic centres.
- Cost-benefit analysis of traditional seismic retrofitting strategies integrated in the renovation of stone masonry buildingsPublication . Maio, Rui; Estêvão, João M. C.; Ferreira, Tiago Miguel; Vicente, RomeuThis study discusses the cost-benefit analysis resulting from the application of traditional seismic retrofitting strategies on four case studies considered representative of both rural and urban stone masonry building stock of Faial Island, in Azores (Portugal). The seismic performance-based assessment was carried out by applying the N2 Method procedure, and the global seismic capacity of each case study estimated by using a three-dimensional model based on the macroelement approach, which combines both the in-plane and out-of-plane response of masonry buildings, to perform nonlinear static analyses. Fragility and loss estimation was evaluated according to the HAZUS methodology. In general terms, the cost-benefit analysis has demonstrated that the studied retrofitting strategies are indeed capable of reducing substantially the seismic vulnerability of the considered case studies, and also that they represent, in fact, a limited amount of the total replacement cost, not compromising, therefore, their economic viability.
- Displacement-based seismic performance evaluation and vulnerability assessment of buildings: the N2 method revisitedPublication . Lopes, Gonçalo Correia; Vicente, Romeu; Ferreira, Tiago Miguel; Azenha, Miguel; Estêvão, João M. C.The so-called N2 method is a widely used nonlinear static method for the seismic design and/or assessment of different building typologies. In this paper, the idea of reversing the so-called N2 method currently adopted in the Annex B of Eurocode 8 (the code on which the present paper is based) in a direct displacement-based procedure is presented in a simple alternative format. In this way, it is possible to obtain the percentage of the seismic action associated to any performance displacement. By doing so, it is also possible to determine the target displacement without the need for an iterative procedure. The proposed method presents several advantages for professional engineering practice in respect to the seismic vulnerability assessment of new and existing buildings. The comparison of the original N2 method with the proposed one is illustrated by means of a test structure example.
- A estabilidade estrutural e a vulnerabilidade dos edifícios em centros históricos face ao risco sísmicoPublication . Vicente, Romeu; Ferreira, Tiago Miguel; Maio, Rui; Estêvão, João M. C.; Rodrigues, HugoPresentemente os países europeus estão a despertar para uma cultura da gestão de risco integrado, quer a nível nacional quer em termos municipais. A gestão de risco é um processo que engloba uma série de ações que apoiam a implementação de medidas que reduzam o potencial de perda na ocorrência de um evento, por exemplo, de natureza sísmica. Porém, a avaliação do risco sísmico é apenas uma das tarefas da teia complexa da gestão de risco e definição de estratégias de intervenção e controlo de um sistema urbano. De entre muitos objetivos que se perspetivam no âmbito do planeamento e gestão urbana, com este artigo abordar a avaliação de risco no domínio específico da segurança estrutural, com enfoque na avaliação do risco sísmico, cujas graves consequências fazem parte da nossa memória coletiva e, infelizmente, em alguns casos, da memória viva de diversas comunidades. A gravidade dos danos que deles decorrem é motivo suficiente para uma forte valorização das estratégias de prevenção, planeamento e mitigação que diminuam a sua probabilidade, limitem as suas consequências e permitam uma ação continuada de melhoria, já que só utopicamente se poderá considerar a possibilidade de transformação integral e imediata das realidades urbanas em situações de risco “zero”.
- Implementation and validation of an approach for the estimation of the magnitude of historical earthquakes in Azores IslandsPublication . Fuentes Morais, Eduardo José de Azevedo Charters; Ferreira, Tiago Miguel; Estêvão, João M. C.; Oliveira, Carlos SousaIn many regions of the globe, the seismic data associated with higher magnitude seismic events usable in the characterization of the seismic hazard is scarce. Therefore, seismologists have been estimating the magnitude and probable epicentral location of historical earthquakes using the historical records and intensity scales to map the observed damage. Another method, employed by earthquake engineers, uses fragility functions, a ground motion model and the Bayes’ theorem to estimate the probable magnitude of historical seismic events. Nevertheless, this method requires assembling an approach consistent with the local seismicity and building stock of the period of reference. This paper implements and validates an approach for the estimation of the magnitude of historical seismic events in Azores Islands, Portugal, that uses fragility functions. In order to carry out this study, data from the damage surveys, a vulnerability distribution and approximate epicentral positions of the 1998 Faial earthquake Mw = 6.0–6.2, as well as a specific attenuation model, are utilized in a calibration phase. The vulnerability index methodology is employed to derive fragility functions from a detailed vulnerability assessment. Afterwards, the approach is validated using analogous data corresponding to the 1980 Terceira earthquake Mw = 6.8–7.2. The different assumptions and results are discussed and compared. The results show that this approach can model expected magnitude values with accuracy: Mw = 6.01–5.76 for the 1998 Faial and Mw = 6.90–6.55 for the 1980 Terceira earthquakes. Additionally, the real PGAs may have been in several locations lower than those predicted by the selected ground motion equation.
- Seismic performance-based assessment of urban cultural heritage assets through different macroelement approachesPublication . Maio, Rui; Ferreira, Tiago Miguel; Estêvão, João M. C.; Pantò, Bartolomeo; Caliò, Ivo; Vicente, RomeuThis paper aims at providing an insightful comparison between three of the most widely used commercially available macroelement models for assessing the global seismic performance of existing masonry structures: the equivalent frame model of 3Muri®, and the two- and three-dimensional discrete macroelements available in 3D-Macro®. To this aim, a stone masonry building, representative of the Urban Cultural Heritage (UCH) typology of the Azores archipelago (in Portugal), was considered as a case study. Firstly, sensitivity analyses were performed to investigate the impact of a few modelling aspects on the seismic performance of the case study building, and ultimately to define the reference model. Secondly, this reference model was analysed both linearly and nonlinearly. Finally, the seismic performance was evaluated by applying the N2 Method. With this comparative study, the authors aim at discussing, from the user viewpoint, the features that these software codes and corresponding macroelement models have in common and those where they most diverge, as well as their main advantages and drawbacks. Results demonstrate that these models should be applied to UCH assets with due diligence, bearing in mind both the particularities of the case study as well as features and limitations associated with the chosen modelling strategy and software.
- Seismic vulnerability assessment of historical urban centres: case study of the old city centre of Faro, PortugalPublication . Maio, Rui; Ferreira, Tiago Miguel; Vicente, Romeu; Manuel Carvalho Estêvão, JoãoThe necessity of implementing seismic vulnerability assessment procedures to the Portuguese building stock has become urgent as recent predictions indicate the possibility of the occurrence of an earthquake similar to the well-known 1755 Lisbon earthquake within the next 50 years. Obviously, at first instance, large-scale procedures should be used rather than more extensive and accurate methodologies suited for individual buildings assessment. Moreover, it is fundamental to operate in the most vulnerable areas in our built environment, typically, the historical urban centres. As it is recognised, it is within these areas, that old masonry buildings are generally concentrated, being both the most representative and vulnerable constructive typology. Comprising 354 buildings, the case study of the old city centre of Faro is herein presented aiming at analysing and evaluating the seismic vulnerability of its old masonry building stock. In order to achieve these objectives, a vulnerability-index-based methodology was used for the assessment of the seismic vulnerability of the old masonry buildings belonging to the historical centre of Faro (Ribeirinha area) carried out through detailed inspection and survey. The results obtained were analysed using a geographical information system tool. The integration of such vulnerability and loss results represents a valuable tool for city councils and/or regional authorities to plan interventions, on the basis of a global view of the site under analysis, leading this way to more accurate and comprehensive risk mitigation strategies which comply with the requirements of safety and emergency planning. The application of this large-scale scoring methodology has confirmed moderate-to-high values for the vulnerability of this particular area, which combined with its high seismicity, may be quite alarming.
- The use of Artificial Neural Networks to estimate seismic damage and derive vulnerability functions for traditional masonryPublication . Ferreira, Tiago Miguel; Estêvão, João M. C.; Maio, Rui; Vicente, R.This paper discusses the adoption of Artificial Intelligence-based techniques to estimate seismic damage, not with the goal of replacing existing approaches, but as a mean to improve the precision of empirical methods. For such, damage data collected in the aftermath of the 1998 Azores earthquake (Portugal) is used to develop a comparative analysis between damage grades obtained resorting to a classic damage formulation and an innovative approach based on Artificial Neural Networks (ANNs). The analysis is carried out on the basis of a vulnerability index computed with a hybrid seismic vulnerability assessment methodology, which is subsequently used as input to both approaches. The results obtained are then compared with real post-earthquake damage observation and critically discussed taking into account the level of adjustment achieved by each approach. Finally, a computer routine that uses the ANN as an approximation function is developed and applied to derive a new vulnerability curve expression. In general terms, the ANN developed in this study allowed to obtain much better approximations than those achieved with the original vulnerability approach, which has revealed to be quite non-conservative. Similarly, the proposed vulnerability curve expression was found to provide a more accurate damage prediction than the traditional analytical expressions.
- The use of Artificial Neural Networks to estimate seismic damage and derive vulnerability functions for traditional masonryPublication . Ferreira, Tiago Miguel; Estêvão, João M. C.; Maio, Rui; Vicente, RomeuThis paper discusses the adoption of Artificial Intelligence-based techniques to estimate seismic damage, not with the goal of replacing existing approaches, but as a mean to improve the precision of empirical methods. For such, damage data collected in the aftermath of the 1998 Azores earthquake (Portugal) is used to develop a comparative analysis between damage grades obtained resorting to a classic damage formulation and an innovative approach based on Artificial Neural Networks (ANNs). The analysis is carried out on the basis of a vulnerability index computed with a hybrid seismic vulnerability assessment methodology, which is subsequently used as input to both approaches. The results obtained are then compared with real post-earthquake damage observation and critically discussed taking into account the level of adjustment achieved by each approach. Finally, a computer routine that uses the ANN as an approximation function is developed and applied to derive a new vulnerability curve expression. In general terms, the ANN developed in this study allowed to obtain much better approximations than those achieved with the original vulnerability approach, which has revealed to be quite non-conservative. Similarly, the proposed vulnerability curve expression was found to provide a more accurate damage prediction than the traditional analytical expressions.