Browsing by Author "Pinho, Rui"
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- Analysis Issues on Seismic Assessment of Existing StructuresPublication . Sousa, Romain; Biachi, Federica; Nascimbene, Roberto; Pinho, RuiMany existing RC structures worldwide were designed for gravity loads only, with inadequate lateral load resistance, lateral stiffness and poor detailing of the reinforcement. Moreover, the concept of regularity both in plan and elevation that characterise a good conceptual design was, in most cases, not taken into account. The introduction in Europe of the regulations for seismic assessment of existing structures imposed stricter performance requirements for building structures. In order to take into account the poor seismic behaviour of such buildings, recent seismic codes – namely EC8 and NTC08, introduce a number of prescriptions regarding issues such as analysis type, load distribution, accidental eccentricity, etc. At the same time, these codes give room for engineering judgment to be used with reference to the definition of structural and non-structural elements such as slabs or infill walls, and obviously leave it up to the analyst decisions regarding Finite Elements typology, meshing, mass modelling, etc. The main goal of this work is thus to provide an extensive and wide evaluation on the influence of each of the abovementioned parameter on the seismic assessment of structures. For this purpose, nonlinear static analysis, as well as nonlinear dynamic analysis are performed on a real building that has also been experimentally tested in the past. The results will hopefully provide indications on the relative importance of each modelling parameter or decision.
- Avaliação de Modelos Numéricos com Elementos de Fibra Recorrendo a Ensaios em Mesa SísmicaPublication . Sousa, Romain; Correia, António A.; Almeida, João P.; Pinho, RuiO comportamento sísmico de estruturas de betão armado envolve uma série de fenómenos físicos que, em última análise, são impossíveis de modelar exaustivamente. No presente estudo, a resposta de três estruturas porticadas submetidas a ensaios dinâmicos em mesas sísmicas foi comparada com resultados de análises numéricas considerando diferentes opções de modelação. A interpretação dos resultados associados a cada um dos modelos considerados permite avaliar a importância relativa de cada solução, bem como fornecer indicações relativas ao desenvolvimento de simulações numéricas optimizadas. As conclusões fornecem indicações para engenheiros e investigadores desenvolverem análises não-lineares mais fiáveis com elementos de fibra.
- Blind Prediction of a Full-Scale RC Bridge Column Tested Under Dynamic ConditionsPublication . Bianchi, Federica; Sousa, Romain; Pinho, RuiThe definition of appropriate modelling approaches combined with a consistent software framework is a topic of major importance in the present days for structural engineering in general and, particularly, for earthquake engineering. The accuracy of the results obtained in the recent “Concrete Column Blind Prediction Contest 2010” for a full-scale reinforced concrete bridge column tested on the NEES Large High-Performance Outdoor Shake Table, seems to indicate that current modelling strategies are on the right track. The 1.2 m diameter cantilevered column spans 7.2 m from the footing. A massive 230 tonne reinforced concrete block supported by the column generates the inertial forces to mobilize the column capacity. Seismic performance was investigated under 6 ground motions, starting with lowintensity shaking and bringing the column progressively to near-collapse conditions. Based on the obtained results from the pre-contest simulation, as well with the post-contest analysis, it was possible to extract some important conclusions regarding the application of several strategies, namely the use of different type elements, element discretization, constitutive laws for materials.
- Blind Prediction Tests as a Benchmark to Improve the Seismic Response of Fibre ModelsPublication . Sousa, Romain; Correia, António A.; Almeida, João P.; Pinho, RuiThe seismic behaviour of reinforced concrete framed structures involves a number of nonlinear material and geometrical phenomena that are impossible to model exhaustively in a single model. Furthermore, past studies showed that the most correct modelling options from the scientific viewpoint are sometimes challenged by experimental results. Over the years, attempts have been made to identify and measure the importance of different modelling options. This work intends to consolidate some of these findings and further extend them in order to progressively bridge the gap between solidly established theoretical principles and shaking table test results. The response of three different structures used in international blind prediction test challenges serves as benchmark to assess the goodness-of-fit of alternative numerical solutions. The interpretation of the results highlights the sensitivity of the response with respect to the modelling choices and provides indications towards the development of optimized numerical analyses.
- Effect of Different Modelling Assumptions on the Seismic Response of RC StructuresPublication . Sousa, Romain; Eroglu, T; Kazantzidou, D.; Kohrangi, M.; Sousa, Luís; Nascimbene, Roberto; Pinho, RuiThe introduction of new regulations for seismic assessment of structures established stricter performance requirements for existing buildings. In order to account for the poor seismic behaviour of such buildings, recent seismic codes, namely Eurocode 8 (EC8), introduce a number of prescriptions regarding issues such as analysis type, load distribution, accidental eccentricity, etc. At the same time, these codes give room for engineering judgment to be used with reference to the definition of structural and non-structural elements such as slabs or infill walls, and obviously leave the modelling assumptions, such as Finite Elements typology, meshing, mass modelling, etc. to the analyst decision. As such, four existing RC buildings, representative of traditional Mediterranean construction, considering different modelling assumptions, were subjected to an extensive number of nonlinear static analyses. The interpretation of possible deviations in the results will hopefully provide indications on the relative importance of each modelling parameter or decision.
- Evaluation of Analytical Methodologies to Derive Vulnerability FunctionsPublication . Silva, Vitor; Varum, Humberto; Crowley, Helen; Sousa, Romain; Pinho, RuiThe recognition of fragility functions as a fundamental tool in seismic risk assessment has led to the development of more and more complex and elaborate procedures for their computation. Although vulnerability functions have been traditionally produced using observed damage and loss data, more recent studies propose the employment of analytical methodologies as a way to overcome the frequent lack of post-earthquake data. The variation of the structural modelling approaches on the estimation of building capacity has been the target of many studies in the past, however, its influence in the resulting vulnerability model, impact in loss estimations or propagation of the uncertainty to the seismic risk calculations has so far been the object of restricted scrutiny. Hence, in this paper, an extensive study of static and dynamic procedures for estimating the nonlinear response of buildings has been carried out in order to evaluate the impact of the chosen methodology on the resulting vulnerability and risk outputs. Moreover, the computational effort and numerical stability provided by each approach were evaluated and conclusions were obtained regarding which one offers the optimal balance between accuracy and complexity.
- A fibre flexure-shear model for seismic analysis of RC-framed structuresPublication . Ceresa, Paola; Petrini, Lorenza; Pinho, Rui; Sousa, RomainWhilst currently existing modelling approaches of reinforced concrete behaviour allow a reasonably accurate prediction of flexural response, the determination of its shear counterpart needs further developments. There are various modelling strategies in literature able to predict the shear response and the shear-flexure coupling under monotonic loading conditions. However, very few are the reported models that have demonstrated successful results under cyclic loading, as in the seismic load case. These considerations lead to this research work focused on the development of a flexure-shear model for reinforced concrete beam-column elements. A reliable constitutive model for cracked reinforced concrete subjected to cyclic loading was implemented as bi-axial fibre constitutive model into a two-dimensional Timoshenko beam-column element. Aim of this research work is to arrive at the definition of a numerical model sufficiently accurate and, at the same time, computationally efficient, that will enable implementation within a Finite Element package for nonlinear dynamic analysis of existing non seismically designed RC structures that are prone to shear-induced damage and collapse.
- A Fibre-Based Frame Element with Explicit Consideration of Bond-Slip EffectsPublication . Sousa, Romain; Correia, António A.; Almeida, João P.; Pinho, RuiReinforced concrete (RC) frames subjected to seismic loading often depict localized member-end deformations due to strain penetration effects between adjacent members, such as beam-column and column-footing joints. Past experimental programs indicate that the bond-slip deformations occurring at the interface between the reinforcement and the surrounding concrete can contribute up to 40% of the lateral deformation of the RC members. The employment of advanced bond-slip models within detailed finite element formulations, capable of simulating continuous domains with highly discretized meshes, has witnessed great advances over the recent years with encouraging results. Nonetheless, this modelling approach is computationally heavy and hence inapplicable for practical seismic (nonlinear) analysis of structures. Alternatively, the use of beam-column elements with lumped or distributed plasticity is a more computationally efficient and engineering-friendly modelling approach. Unfortunately, the elements of this type available in conventional numerical packages did not yet consider an explicit simulation of the interface between the reinforcing bars and the surrounding concrete along their embedment length. The present study aimed at overcoming the foregoing limitation by developing an explicit bond-slip model applicable to general fibre-based beam-column elements. Using a state-of-the-art bond-slip constitutive model, the current paper introduces a zero-length element that computes the localized member-end deformations accounting for the bond-slip response at each reinforcing bar of a given RC section. Along with the material properties and anchorage conditions, the proposed nonlinear model also accounts for cyclic degradation and rebar yielding effects. Validation studies conducted with the proposed numerical formulation reveal a good agreement with past experimental tests, evidencing an important stability and accuracy at the expense of an acceptable additional computational effort.
- Modelação numérica do escorregamento de armaduras em elementos de betão armadoPublication . Sousa, Romain; Correia, António A.; Almeida, João P.; Pinho, RuiEstruturas porticadas de betão armado (BA) sujeitas à ação sísmica apresentam frequentemente deformações localizadas nas extremidades dos seus elementos devidas ao escorregamento das armaduras em relação ao betão, nomeadamente ao longo do seu comprimento de amarração. Apesar de as mesmas poderem representar 40% da deformação lateral total de elementos em BA, a modelação numérica deste comportamento apresenta ainda diversas limitações. O presente artigo introduz uma estratégia de simulação onde, pela primeira vez, um modelo explícito para o escorregamento de armaduras é associado a um elemento de viga, com discretização seccional por fibras, através de um elemento de ligação com comprimento nulo. O elemento proposto adota uma sofisticada relação constitutiva de aderência, representando os efeitos da degradação cíclica ou da cedência das armaduras, entre outros. O modelo é validado através da comparação entre resultados numéricos e experimentais, demonstrando uma eficiência, precisão e estabilidade numérica assinaláveis.
- Modellazione di una pila da ponte nell’ambito di un “Blind Prediction Contest"Publication . Biachi, Federica; Sousa, Romain; Pinho, RuiNel presente lavoro vengono descritte le strategie di modellazione impiegate per la previsione della risposta nonlineare dinamica di una pila da ponte a scala reale in cemento armato soggetta a sei accelerogrammi di crescente intensità. Il prototipo della struttura, una colonna a sezione circolare con diametro pari a 1.22 m, di altezza pari a 7.32 m misurata dal piano di fondazione e che sorregge all’estremità un blocco in cemento armato di 230 tonnellate, è stato testato sulla “NEES @ UC San Diego Large High Performance Outdoor Shake Table” in occasione del recente “Concrete Column Blind Prediction Contest 2010”. Al termine della competizione sono state messe a disposizione dei partecipanti le misurazioni sperimentali necessarie per procedere con il confronto con i risultati numerici della previsione. Da tale confronto è emerso che, grazie alle strategie adottate in fase di modellazione e grazie all’utilizzo di un appropriato software di calcolo agli elementi finiti (a plasticità diffusa, cioè con elementi a fibre), è stato possibile stimare in modo sufficientemente accurato il comportamento della struttura in esame.