Coleções gerais - Comunicações em conferências e congressos internacionais
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- Retargeting 4K Video for Mobile Access Using Visual Attention and Temporal StabilizationPublication . Kumar, Rohit; Ferreira, Lino; Assunção, Pedro; Navarro, AntónioThis paper presents different methods of retargeting 4K resolution videos for the smaller resolutions of mobile devices. Several methods are investigated using image cropping based on visual attention maps with removal of temporal jitter. Visual comparison between video sequences obtained from the retargeting methods is presented and evaluated through subjective testing. Based on subjective scores, the proposed algorithm shows the best performance for 480p target resolution.
- Measurements and Modelling of Spatial Diversity using 2D TransmitarrayPublication . Reis, Joao R.; Hammoudeh, Akram; Copner, Nigel; Caldeirinha, RafaelThis paper disseminates the results of the first experimental trials on Spatial Diversity (SD) with beamsteering capabilities by the means of 2D transmitarray and thus reduced RF chains. The SD arrangement is composed of a dual antenna configuration in which beamsteering is activated by using electronically reconfigurable transmitarray (eRT) in front of the two single directive antennas. The experimental radiation patterns obtained at 5.2 GHz proves the usefulness of the concept.
- Modelling Issues on Seismic Assessment of Irregular RC StructuresPublication . Sousa, Romain; Bianchi, Federica; Pinho, Rui; Nascimbene, Roberto; Kazantzidou, DanaiMany 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 (Italian code), 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 nonstructural 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 procedures, 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Using Nonlinear Static Procedures for the Seismic Assessment of Irregular RC BuildingsPublication . Sousa, Romain; Eroglu, T; Kazantzidou, D.; Kohrangi, M.; Sousa, L.; Nascimbene, Roberto; Pinho, R.The application of Nonlinear Static Procedures (NSPs) to assess the seismic vulnerability of existing structures has become widely accepted and extensively used in the literature as well as in engineering practice. Nevertheless, their success in predicting the response of irregular buildings is not yet fully verified. The main goal of the present study is to evaluate the capability and accuracy of some of the existing nonlinear static procedures (N2 and ACSM, in this case) to estimate the seismic performance of irregular structures. In order to accomplish this objective, four existing buildings, irregular in plan and elevation, were subjected to an extensive number of nonlinear static and dynamic analyses. The comparisons, focused on both global and local response parameters provide first indications on the reliability of static procedures to estimate the actual response of irregular RC buildings.
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