Dissertations / Theses on the topic 'Openseespy'

Questa tesi presenta i risultati di una campagna sperimentale incentrata sulla caratterizzazione della trazione dei basalt e glass FRCM e della caratterizzazione del legame di aderenza composito-Calcarenite. Il lavoro sperimentale è completato dalla proposta di due modelli numerici sia per prove di trazione che per quelle di aderenza. L'indagine sperimentale è stata condotta considerando l'influenza di diversi rinforzi, matrici e metodi di prova. I risultati sperimentali consentono di valutare l'effetto della malta sulle curve sforzo-deformazione, la resistenza, la duttilità e le modalità di crisi. Inoltre, la tesi fornisce un importante contributo per valutare l'influenza di diversi metodi di prova (es. clamping e clevis come riportato da diversi standard e linee guida) sulle prestazioni dei sistemi FRCM testati a trazione. Inoltre, la correlazione dell'immagine digitale è stata utilizzata per misurare le tensioni di trazione e per analizzare le modalità di crisi offrendo una caratterizzazione meccanica accurata. L'elemento di principale novità è l'adozione di un set-up per le prove di aderenza modificato e progettato per analizzare l'influenza della dimensione del composito sulla lunghezza e la resistenza del legame. Un'analisi approfondita dei risultati conferma l'efficacia di questo innovativo set-up. Infine, vengono presentati due modelli numerici che tentano di fornire un semplice strumento numerico per valutare il comportamento costitutivo dei sistemi FRCM. I modelli sono stati calibrati sulla base delle curve sperimentali sforzo-deformazione e carico-slittamento dimostrando di essere uno strumento efficace per prevedere il comportamento meccanico dei materiali compositi FRCM.
This thesis presents the results of an experimental campaign focused on the tensile characterization of basalt and glass FRCM and composite-calcarenite bond characterization. The experimental work is complemented by the proposal of two numerical models both for tensile and bond tests. The experimental investigation was carried out considering the influence of different reinforcements, matrices and testing methods. Experimental results provide for assessing the effect of mortar grade on the stress-strain curves, strength, ductility and failure modes. Moreover, the thesis provides an important contribution to assess the influence of different testing methods (i.e. clamping and clevis as reported by different standard and guidelines) on the performance of the FRCM systems tested in tension. Moreover, the Digital image correlation was used to measure the tensile strains and to analyse the failure modes offering an accurate mechanical characterization. The main element of novelty is the adoption of a modified bond test set-up designed to analyse the influence of the composite size on bond length and strength. A deep analysis of the results confirms the effectiveness of this innovative set-up. Finally, two numerical models are presented attempt at providing a simple numerical tool for capturing the constitutive behaviour of the FRCM systems. The models were calibrated on the basis of the experimental stress-strain and load-slip curves showing to be an effective tool for predicting the mechanical behaviour of the FRCM composites.

The behaviour of heated structures is strongly governed by thermal induced deformation and degradation of material properties. This thesis presents an augmentation of the software framework OpenSees to enable thermomechanical analysis of structures. The developments contributed to OpenSees are tested by series of benchmark cases and experimental results. OpenSees is an object-oriented, open source software framework developed at UC Berekeley for providing an advanced computational tool to simulate non-linear response of structural frames to earthquakes. OpenSees was chosen to be extended to enable the modelling of structures in fire. The development of this capability involved creating new thermal load classes to define the temperature distribution in structural members and modifying existing material classes to include temperature dependent properties according to Eurocodes. New functions were also added into the existing corotational beam/column element (2D and 3D) to apply temperature related loads. A new geometrically nonlinear shell element was created (based on the existing linear MITC4 shell element in OpenSees) using total Lagrangian formulation. Appropriate thermal load, material and section classes were also developed for enabling thermomechanical analysis using the nonlinear shell element. A number of benchmark tests were carried out to verify the performance of the new developments implemented in OpenSees. The benchmark tests involved subjecting beams and plates to a range of through depth temperature gradients with OpenSees results compared against closed form solutions. Further verification was also carried out by comparing OpenSees results with ABAQUS results. The extended OpenSees framework was also used to model experiments such as two plane steel frames at elevated temperatures, the Cardington Restrained Beam Test and the Cardington Corner Test and an earthquake damaged reinforced concrete (RC) frame subjected to a subsequent fire. The existing DruckerPrager material class in OpenSees was used to the model concrete in the composite floor in the Cardington tests and in the RC frame. The pinching material available in OpenSees was used to model the beams and columns in the RC frame to consider the cyclic degradation of strength and stiffness during the increasing cyclic displacements imposed on the RC frame before the fire. In all cases the results from OpenSees show good agreement with test data.

Fire following an earthquake (FFE) is a hazard that is not usually accounted for in either earthquake or fire resistant design of structures. There have however been many instances in the past of FFE events causing even greater damage and even loss of life than the original earthquake. The potential damage associate with this hazard is increasing considerably with increasing urbanisation in seismically vulnerable regions. It is reasonable for users to expect that structures should maintain their integrity for a long enough period in an FFE event allowing emergency crews to assist the most vulnerable occupants to evacuate the building safely. Because of the lack of regulatory requirements there is naturally very little research on the response of structural frames under FFE events so far, but given the reasons discussed earlier, it is clearly a matter of increasing importance that engineers should develop a better understanding of the behaviour of seismically damaged structural frames in fire. This thesis project was fortunate to have occurred at a time when a set of full-scale fire tests were taking place at IIT Roorkee in India, in collaboration with the University of Edinburgh to address exactly this topic. This thesis research was undertaken to model these experiments (to determine the fire resistance of a reinforced concrete frame first subjected to simulated seismic damage). The open source software framework OpenSees was chosen for the modelling work as it was considered to be the best software tool for modelling structures under earthquake loading. The first part of this thesis reports the development work done on OpenSees for adding thermomechanical analysis modules to enable the modelling of FFE events using this software framework. The code developed for OpenSees has been allowed the introduction of features not available in commercial software such as ABAQUS. Many new classes were developed, such as ThermalAction, ThermalElement, ThermalSeciton, TheramalMaterial, etc. The newly developed code was tested using a number of benchmark problems and modelling of real fire experiments on steel and composite framed structures. The results from these tests showed that the new developments were successful. The second part of the thesis describes the modelling of the reinforced concrete (RC) frame tested at IIT Roorkee, which was first subjected to cyclic displacement loading (to introduce damage in the frame similar to that of a seismic event) and then to a one hour kerosene fire. The modelling was first used to provide predictions of the performance of the test frame under the proposed loading, to fine tune the design of the experiment. The modelling subsequent to the tests was gradually improved to achieve better comparisons with the test results and to develop a detailed understanding of the behaviour of seismically damaged RC frames in fire, which was also compared to the behaviour in fire of undamaged frames.

Dissertação para obtenção do Grau de Mestre em Engenharia Civil – Perfil de Estruturas
Os sismos são fenómenos que podem ter consequências socioeconómicas elevadas, pelo que é necessário estudar os seus efeitos nas estruturas. Assim, nos últimos anos têm sido estudados e desenvolvidos, matematicamente e numericamente, modelos capazes de reproduzir fielmente o comportamento de estruturas em aço sujeitas a sismos, o que permitiu uma evolução da modelação dessas estruturas. Neste trabalho, são apresentadas várias técnicas de modelação não-linear de estruturas em aço, tendo sido aplicadas, com o programa de elementos finitos Open System for Earthquake Engineering Simulation (OpenSees), a vários exemplos e a dois casos de estudo de forma a serem avaliadas. No primeiro caso de estudo, estudou-se o comportamento sísmico da estrutura de betão armado com parede de alvenaria de enchimento, descrita em Hashemi e Mosalam (2007), com o objetivo de validar o modelo de fibras, que simula o comportamento de paredes de enchimento. Através dos resultados obtidos, e comparando com os resultados experimentais, foi possível validar o comportamento desse modelo no plano, após a calibração de alguns parâmetros. No segundo caso de estudo, foi estudado o comportamento sísmico do edifício de quatro pisos com estrutura em aço testado no E-Defense (2007). O edifício foi modelado tridimensionalmente no OpenSees com elementos de plasticidade concentrada, zonas painel de ligação viga-pilar e paredes exteriores. Neste modelo teve-se em conta os efeitos P-Delta, a influência das lajes na flexão das vigas e o comportamento de diafragma rígido das lajes. De forma a modelar a estrutura, com um comportamento mais próximo do verificado experimentalmente, foi desenvolvido um novo modelo de comportamento das zonas de painel, através de uma análise de sensibilidade. Para além disso, o modelo de fibras das paredes, apresentado inicialmente neste trabalho, foi calibrado de forma a simular o comportamento verificado experimentalmente. Através dos resultados obtidos, e comparando-os com os resultados experimentais, verificou-se que é possível, com recurso às ferramentas apresentadas neste trabalho, reproduzir com precisão a resposta sísmica de estruturas de aço.

Many studies of the fire induced thermal and structural behaviour in large compartments, carried out over the past two decades, show a great deal of non-uniformity, unlike the homogeneous compartment temperature assumption in the current fire safety engineering practice. Furthermore, some large compartment fires may burn locally and they tend to move across entire floor plates over a period of time as the fuel is consumed. This kind of fire scenario is beginning to be idealized as 'travelling fires' in the context of performance‐based structural and fire safety engineering. However, the previous research of travelling fires still relies on highly simplified travelling fire models (i.e. Clifton's model and Rein's model); and no equivalent numerical tools can perform such simulations, which involves analysis of realistic fire, heat transfer and thermo-mechanical response in one single software package with an automatic coupled manner. Both of these hinder the advance of the research on performance‐based structural fire engineering. The author develops an extended travelling fire method (ETFM) framework and an integrated comprehensive tool with high computational expediency in this research, to address the above‐mentioned issues. The experiments conducted for characterizing travelling fires over the past two decades are reviewed, in conjunction with the current available travelling fire models. It is found that no performed travelling fire experiment records both the structural response and the mass loss rate of the fuel (to estimate the fire heat release rate) in a single test, which further implies closer collaboration between the structural and the fire engineers' teams are needed, especially for the travelling fire research topic. In addition, an overview of the development of OpenSees software framework for modelling structures in fire is presented, addressing its theoretical background, fundamental assumptions, and inherent limitations. After a decade of development, OpenSees has modules including fire, heat transfer, and thermo‐mechanical analysis. Meanwhile, it is one of the few structural fire modelling software which is open source and free to the entire community, allowing interested researchers to use and contribute with no expense. An OpenSees‐based integrated tool called SIFBuilder is developed by the author and co‐workers, which can perform fire modelling, heat transfer analysis, and thermo-mechanical analysis in one single software with an automatic coupled manner. This manner would facilitate structural engineers to apply fire loading on their design structures like other mechanical loading types (e.g. seismic loading, gravity loading, etc.), without transferring the fire and heat transfer modelling results to each structural element manually and further assemble them to the entire structure. This feature would largely free the structural engineers' efforts to focus on the structural response for performance-based design under different fire scenarios, without investigating the modelling details of fire and heat transfer analysis. Moreover, the efficiency due to this automatic coupled manner would become more superior, for modelling larger structures under more realistic fire scenarios (e.g. travelling fires). This advantage has been confirmed by the studies carried out in this research, including 29 travelling fire scenarios containing total number of 696 heat transfer analysis for the structural members, which were undertaken at very modest computational costs. In addition, a set of benchmark problems for verification and validation of OpenSees/SIFBuilder are investigated, which demonstrates good agreement against analytical solutions, ABAQUS, SAFIR, and the experimental data. These benchmark problems can also be used for interested researchers to verify their own numerical or analytical models for other purposes, and can be also used as an induction guide of OpenSees/SIFBuilder. Significantly, an extended travelling fire method (ETFM) framework is put forward in this research, which can predict the fire severity considering a travelling fire concept with an upper bound. This framework considers the energy and mass conservation, rather than simply forcing other independent models to 'travel' in the compartment (i.e. modified parametric fire curves in Clifton's model, 800°C‐1200°C temperature block and the Alpert's ceiling jet in Rein's model). It is developed based on combining Hasemi's localized fire model for the fire plume, and a simple smoke layer calculation by utilising the FIRM zone model for the areas of the compartment away from the fire. Different from mainly investigating the thermal impact due to various ratios of the fire size to the compartment size (e.g. 5%, 10%, 25%, 75%, etc.), as in Rein's model, this research investigates the travelling fire thermal impact through explicit representation of the various fire spread rates and fuel load densities, which are the key input parameters in the ETFM framework. To represent the far field thermal exposures, two zone models (i.e. ASET zone model & FIRM zone model) and the ETFM framework are implemented in SIFBuilder, in order to provide the community a 'vehicle' to try, test, and further improve this ETFM framework, and also the SIFBuilder itself. It is found that for 'slow' travelling fires (i.e. low fire spread rates), the near‐field fire plume brings more dominant thermal impact compared with the impact from far‐field smoke. In contrast, for 'fast' travelling fires (i.e. high fire spread rates), the far‐field smoke brings more dominant thermal impact. Furthermore, the through depth thermal gradients due to different travelling fire scenarios were explored, especially with regards to the 'thermal gradient reversal' due to the near‐field fire plume approaching and leaving the design structural member. This 'thermal gradient reversal' would fundamentally reverse the thermally‐induced bending moment from hogging to sagging. The modelling results suggest that the peak thermal gradient due to near‐field approaching is more sensitive to the fuel load density than fire spread rate, where larger peak values are captured with lower fuel load densities. Moreover, the reverse peak thermal gradient due to near‐field leaving is also sensitive to the fuel load density rather than the fire spread rate, but this reverse peak value is inversely proportional to the fuel load densities. Finally, the key assumptions of the ETFM framework are rationalised and its limitations are emphasized. Design instructions with relevant information which can be readily used by the structural fire engineers for the ETFM framework are also included. Hence more optimised and robust structural design under such fire threat can be generated and guaranteed, where we believe these efforts will advance the performance‐based structural and fire safety engineering.

The last two decades have witnessed the shift of structural fire design from prescriptive approaches to performance-based approaches in order to build more advanced structures while reducing costs. However, it is recognised that the implementation of performance-based approaches requires several key elements that are currently not fully developed or understood. This research set out to address some of these issues by focusing on the development, validation and application of methodologies for accurate predictions of thermal responses of structures in fire using numerical methods. This research firstly proposed a numerical approach with the finite element and the discrete ordinates method to quantify the fire imposed radiative heat fluxes to structural members with cavity geometry. With satisfactory results from the verification and validation tests, it is used to simulate heat transfer to unprotected steel I-sections with symmetrical cavities exposed to post-flashover fires. Results show that the cavity geometry could strongly attenuate the radiative energy, while the presence of hot smoke enhances radiative transfer by emission. Average radiative fluxes for the inner surfaces of the I-sections are seen to increase with smoke opacity. In addition, the net radiative fluxes are observed to decrease faster for I-sections with higher section factors. This work also shows that the self-radiating mechanism of I-sections is important in the optically thin region, and existing methodologies neglecting these physics could significantly underpredict steel temperatures. The next focus of this work is to develop a thermal analysis framework dedicated to structures-in-fire modelling in the OpenSees (Open System for Earthquake Engineering Simulation) platform which has been developed towards a highly robust, extensible and flexible numerical analysis framework for the structural fire engineering community. The thermal analysis framework, which is developed with object-oriented programming paradigm, consists of a fire module which has incorporated a range of conventional empirical models as well as the travelling fire model recently developed elsewhere to quantify the fire imposed boundary conditions, and a heat transfer module which addresses non-linear heat conduction in structural members with the finite element method. The developed work has demonstrated good performance from benchmark problems where analytical solutions are available and from full scale tests with measured data. With the thermal analysis capability developed in this work together with the work by other colleagues to quantify the mechanical response at elevated temperatures, the extended OpenSees framework can be used to predict structural performances subjected to a wide range of re scenarios. This work uses OpenSees for a case study of a generic composite structure subjected to travelling fires. The latest work on travelling fire methodology for structural fire design has been implemented in the OpenSees framework. The work presented in this thesis is the first effort to examine both the thermal and structural responses of a composite tall building in travelling fires using OpenSees. Results from the thermal analysis show that travelling fires of larger sizes (e.g. burning area equal to 50% of the floor area) are more detrimental to steel beams in terms of more rapid heating rate, while those of smaller sizes (e.g. burning area equal to 4% of the floor area) burn for longer duration and thus are more detrimental to concrete slabs in light of higher peak temperatures. The results also show that fires of large sizes tends to produce higher through-depth thermal gradients in the steel beam sections particularly in neighbouring regions with the concrete slab. Due to less rapid heating rates but prolonged burning durations, smaller fires produce lower thermal gradients but with higher temperatures in the concrete slab particularly at locations far from the fire origin. The subsequent structural analysis suggests that travelling fires produce higher deflections and higher plastic deformations in comparison with the uniform parametric fires, particularly with smaller fire sizes producing more onerous results. The results seem to be more physically convincing and they challenge the conventional assumption that the post-flashover fires are always more conservative for structural performance.

In terms of developing knowledge to enable more effective use of performance based engineering (PBE), one of the key limitations is the lack of an easy to use integrated computational tool that is also robust and comprehensive enough to enable automated modelling of more realistic fire scenarios, i.e., the structural response to localised or travelling fires. The main objective of this thesis is to establish such an integrated computational tool, which shall be based on the OpenSees software framework and facilitated by specially developed approaches to achieve higher efficiency of the integrated analysis. This includes the analysis of heat transfer from the fire to structural members, as well as the analysis of structural response to elevated temperatures during the fire. In this thesis, the research begins with the investigation of the feasibility of dimensional reduction for heat transfer analyses of structural members subjected to localised fire action (SFPE and Eurocode 1 fire models), which can be numerically represented by a linear or exponential correlation between incident heat flux and radial distance. Accurate estimates of the error induced by dimensional reduction are presented under strongly varying localised heat fluxes that represent the most non-uniform fire conditions in a building compartment. It is shown that beams and slabs can be adequately modelled with a lower dimensional heat transfer analysis for ordinary building fires. Using this approach, the complexity of heat transfer modelling and the required computing resource and user effort can both be significantly reduced, especially in cases where structural members are subjected to localised fire action. Thermo-mechanical simulations are presented to address the behaviour of structural members subjected to localised fire action, for which a ThermalAction- Wrapper is developed to approximate the temperature distribution from a mixed-order interpolation between sections (beam) or locations (slab). For concrete slabs subjected to localised fire, MITC4 based shell elements are used to account for material and geometric nonlinearities. An integrated simulation environment is developed, which is designed to be a computational tool that requires limited input but provides a comprehensive solution to the problem of simulating large structural frame and sub-frame response under realistic fire scenarios. A considerable amount of code has been written to create and operate the building model, and to process the heat fluxes from the design fires to the structure and the consequential structural response to the evolution of temperatures within it. Parametric studies have been performed to investigate the computational performance of the newly developed elements in modelling beams and slabs subjected to different cases of localised fire action. The results suggest that 3 to 6 force-based beam elements can adequately describe the localised response however more elements are required for quadratic distribution of incident heat flux and higher temperatures, which is due to the degradation of material strength that governs the accuracy especially when the members are heavily loaded. For slabs exposed to localised fires, centre fires are found to produce greater deflections than corner fires, while lateral restraints applied to the slabs may also lead to higher deflections. A small-scale three dimensional structural frame is modelled as a demonstration of the tool, tested against a number of localised fire scenarios. The global behaviour of the structure with the local effects induced by the fire action and partially damaged fire protection are investigated. Severe damage can be found in the members exposed to a single whole compartment fire, in contrast with the relatively small deflections that are observed when a fully protected column is engulfed by a localised fire. However if the passive fire protection is partially damaged, collapse may occur in the column as a result of load magnification because of the redistribution. To the author's knowledge this is the first piece of research that has been able to develop a practically feasible approach to enable efficient coupled computation of the response of structural frames to realistic fire scenarios on a freely available open source software platform. Currently this kind of analysis can only be carried out by just two or three large consulting firms because of the prohibitive commitment of analyst time and effort and to a lesser extent the need for significant computing resources. The work of this thesis will contribute enormously towards making high-end performance based engineering of structural fire resistance a much more practical proposition for small and medium size structural consultancies. Furthermore, the choice of OpenSees, which is a very well respected software framework for simulating structural response to earthquakes naturally enables this work to be extended to the simulating the multi-hazard structural resistance, such as in the event of a fire following an earthquake which may have locally damaged passive fire protection.

Dissertação para obtencão do Grau de Mestre em Engenharia Civil - Perfil Estruturas
Os sismos são um dos desastres naturais que mais impacto apresentam, não só pelos danos humanos e materiais causados, mas também pela sua imprevisibilidade. Deste modo, é essencial recorrer à regulamentação vigente anti-sísmica para o dimensionamento de novas estruturas e implementar sistemas de protecção sísmica em estruturas existentes, caso necessário, por forma a melhorar a sua resposta a esta acção. A presente dissertação pretende estudar o comportamento dinâmico de um passadiço pedonal localizado na Estrada Nacional 125-10, no distrito de Faro. A necessidade de avaliar a sua resposta à acção sísmica recai sobre a sua composição maioritária por elementos pré-fabricados de betão armado, dimensionados segundo a regulamentação RSA/REBAP, que já não se encontra vigente, e a sua localização sobre uma importante via de comunicação, pondo em causa o seu funcionamento para uma situação de colapso estrutural. Foi efectuada uma modelação numérica em elementos finitos, com recurso ao programa OpenSees, onde se modelaram os elementos de ligação tendo em conta o efeito de ferrolho. Posteriormente, foi efectuada a calibração manual do modelo, pela comparação das características dinâmicas obtidas por via numérica e experimental. Os ensaios de vibração ambiental efectuados, permitiram a obtenção das propriedades dinâmicas actuais da estrutura, pelo processamento do sinal através das técnicas de identificação modal estocástica. Avaliou-se a resposta estrutural dinâmica não-linear, física e geométrica, à acção sísmica, recorrendo-se a acelerogramas artificiais gerados a partir do espectro de resposta elástico apresentado pelo EC8. Tendo sido identificada uma deficiente resistência à acção sísmica, foram consideradas duas propostas de reforço sísmico de protecção passiva, baseadas em dispositivos de dissipação de energia, através de barras de aço de alta resistência e ligas com memória de forma. Evidenciou-se a eficiência de cada sistema de protecção sísmica através da avaliação da resposta dinâmica do passadiço pedonal.

Reinforced concrete frames infilled with unreinforced masonry are commonly used in structures worldwide. The interaction between the frame and the infill panel is usually ignored in engineering practice, and the masonry infill is not considered as a structural element. However, observations made after the occurrence of strong earthquakes have shown that the bare frame and infill-frame behave differently when subjected to in-plane lateral loads. Extensive research has been conducted on the behaviour of infill-frames when laterally loaded. This research focuses on the analysis of infill-frames using the equivalent strut modelling method, whereby an infill-frame is simplified, and the infill panel is replaced by one or more compressive strut elements. A large number of strut models have been proposed in the literature, but recent studies have demonstrated that it is not possible to apply one strut model to all infill-frame structures. It has been found that changing the properties of an infill-frame can also change the geometric properties of struts, namely width, location and number of struts in an equivalent strut model. For this reason, recent studies have proposed a case-specific strut modelling approach. In the current study, a macro script available in the literature that can be used to generate a detailed finite element (FE) model has been applied to construct and analyse a number of infill-frames with different material and geometric properties. Sensitivity analyses on some of these infill-frames have also been conducted by varying the material properties of the infill, and the amount and distribution of vertical loads on the frame. The results of detailed FE analyses, more specifically contours of the compressive principal stresses, have been used to define the geometric properties of the struts of case-specific strut models for each of the infill-frames. Equivalent strut models were then analysed and compared. Further, the proposed strut models were applied to other infill-frames selected for this study; two strut models from the literature were also applied to these infill-frames. It was concluded that the geometric properties of, and the vertical load on an infill-frame can be related to the geometric properties of its equivalent strut model. In contrast, a variation of up to 25% in the masonry material properties did not have a significant effect on the strut properties. It was shown that casespecific strut modelling is a versatile and generic technique that can adequately replicate the highly nonlinear behaviour of infill-frames regardless of their geometric or material properties. By expanding the current research, it is hoped that a rigorous classification of infill-frames and their relevant equivalent strut models can be developed to assist structural engineers in their everyday design tasks.

Nonlinear time history analysis is increasingly being used in the design of tall steel structures, but member sizes still must be determined by a designer before an analysis can be performed. Often the distribution of story strength is still based on an assumed first mode response as determined from the Equivalent Lateral Force (ELF) procedure. For tall buckling restrained braced frames (BRBFs), two questions remain unanswered: what brace distribution will minimize total brace area, while satisfying story drift and ductility limits, and is the ELF procedure an effective approximation of that distribution? In order to investigate these issues, an optimization algorithm was incorporated into the OpenSees dynamic analysis platform. The resulting program uses a genetic algorithm to determine optimum designs that satisfy prescribed drift/ductility limits during nonlinear time history analyses. The computer program was used to investigate the optimized distribution of brace strength in BRBFs with different heights. The results of the study provide insight into efficient design of tall buildings in high seismic areas and evaluate the effectiveness of the ELF procedure.

Prior experimental research clearly reveals that the performance of reinforced concrete frame structures under earthquake loading is closely related to the behavior of beam-to-column connection regions. In order for a reinforced concrete building to have an adequate response under high lateral deformations, beam-to-column connections should be able to preserve their integrity. However, even today beam-to-column connections are assumed to be rigid or elastic, leading to an incorrect estimation of the structural response under earthquake loading. One of the basic reasons for the assumption of rigid joints is the lack of analytical models that adequately represent the seismic behavior of the connection region. In this thesis, an analytical model that realistically represents the beam-to-column connection response is developed, in the light of prior experimental data. The experimental subassemblies used in the generation of the analytical model are later modeled in OpenSees environment in order to verify the accuracy of the model. Throughout the research, utmost attention is paid for the model to be simple enough to be used practically and also to cover a wide range of beam to column connection properties.

This thesis presents the results of basically two separate studies. The first study involved identifying structural and earthquake parameters that influenced seismic structural collapse. The parameter study involved nonlinear dynamic analyses using single-degree-of-freedom (SDOF) bilinear models. Four parameters were associated with the SDOF models â the lateral stiffness, the post-yield stiffness ratio, the yield strength, and the stability ratio (P-Delta effects). Then, three parameters were associated with the ground motions â the records themselves, the lateral ground motion scales, and the vertical ground motion scales.

From the parameter study, it was found that the post-yield stiffness ratio augmented by P-Delta effects (rp) in conjunction with the ductility demand was the best predictor of collapse. These two quantities include all four structural parameters and the seismic displacement demands. It was also discovered in the parameter study that vertical accelerations did not significantly influence lateral displacements unless a given combination of model and earthquake parameters was altered such that the model was on the verge of collapsing.

The second study involved Incremental Dynamic Analysis (IDA) using bilinear SDOF models representative of low rise buildings in both the Western United States (WUS) and the Central and Eastern United States (CEUS). Models were created that represented three, five, seven, and nine story buildings. Five sites from both the WUS and CEUS were used. Four different damage measures were used to assess the performance of the buildings. The IDA study was primarily interested in the response of the structures between the earthquake intensities that have a 10 percent probability of occurring in 50 years (10/50) and 2 percent probability of occurring in 50 years (2/50).

The results showed that all structures could be in danger of severe damage and possible collapse, depending on which damage measure and which earthquake was used. It is important to note, though, that the aforementioned is based on a damage-based collapse rule. The damage-based rule results were highly variable.

Using an intensity-based collapse rule, proved to be more consistent. Due to the nature of the bilinear models, only those structures with negative rp values ever collapsed using an intensity-based collapse rule. Most of the WUS models had positive rp values and many of the CEUS models had negative rp values. While many of the CEUS structures had negative rp values, which made them prone to collapse, most of the CEUS structures analyzed did not collapse at the 2/50 intensity. The reason was that the periods of the CEUS models were much longer than the approximate periods that were required to determine the strengths. Consequently, the strength capacity of most of the CEUS models was much greater than the seismic strength demands. While many of the CEUS models did have sudden collapses due to the large negative rp values, the collapses happened at intensities that were generally much higher than the 2/50 event.

In the IDA, it was also shown that vertical accelerations can significantly affect the ductility demands of a model with a negative rp post-yield stiffness ratio as the earthquake intensity approaches the collapse intensity. Since IDA is concerned with establishing collapse limit states, it seems that the most accurate collapse assessments would include vertical accelerations.
Master of Science

This doctoral dissertation aims to report on the research work carried out and to provide a contribution to the field of seismic base isolation. Since its introduction, the base isolation strategy proved to be an effective solution for the protection of structures and their components from the earthquake-induced damage, enhancing their resilience and implying a significative decrease in time and cost of repair compared to a conventional fixed-base structure. Sliding isolation devices feature some important characteristics, over other devices, that make them particularly suitable for the application in the existing buildings retrofit such as the high displacements capacity combined with limited plan dimensions. Even though these devices diffusion has gotten more popular worldwide in last years, a full understanding of their performances and limits as well as their behaviour under real seismic excitations has not been yet completely achieved. When Curved Surface Sliders reach their displacement capacity, they enter the so-called over-stroke sliding regime which is characterized by an increase in stiffness and friction coefficient. While in the over-stroke displacements regime, anyways, sliding isolators are still capable, until certain threshold values, of preserving their ability to support gravity loads. In this doctoral dissertation, the analysis of Curved Surface Sliding devices influence on different structures and under different configurations is presented and a tool for to help professionals in the design phase is provided. The research main focuses are: i) the numerical investigation of the over-stroke displacement influence on base isolated structures; ii) the numerical investigation of displacement retaining elements influence on base isolated structures; iii) the development of a mechanical model and an algebraic solution describing the over-stroke sliding regime and the associated limit displacements.

La presenza di tamponamenti in muratura all’interno delle maglie di strutture intelaiate induce, in presenza di azioni laterali, una sostanziale modificazione della risposta globale rispetto a quella dei telai nudi in termini di rigidezza, resistenza e capacità di spostamento. La tesi presenta i risultati di una campagna sperimentale su telai tamponati con diverse tipologie di muratura soggetti a prove di carico cicliche. Successivamente viene proposto un criterio per la modellazione semplificata del comportamento ciclico attraverso un macromodello a puntone diagonale equivalente. Una ulteriore indagine numerica è eseguita per valutare l'entità degli effetti locali dovuti all'interazione fra telaio a tamponamento proponendo un criterio per la loro inclusone nella modellazione a puntone concentrico. Infine viene eseguita una calibrazione del puntone diagonale attraverso un modello a fibre. Tale modellazione è utilizzata per studiare il comportamento nel piano e fuori piano dei pannelli in presenza di azioni sismiche provenienti da qualsiasi direzione.
The presence of infill masonry in RC framed structures substantially modifies of the overall response in presence of seismic actions with respect of bare frames in terms of stiffness, strength and displacement capacity . The thesis presents the results of an experimental campaign on infilled frames with different kinds of masonry subjected to cyclic loading tests. Subsequently, a criterion for the simplified modeling of the cyclic hysteretic behavior through a macromodel equivalent diagonal strut is proposed. A further numerical investigation is carried out to assess the influence of local effects due to the interaction between infill a frame and a criterion for their inclusion when concentric strut models are used is developed. Finally calibration of the equivalent strut by means of a fiber model is performed. This approach is also applied to study the in plane-out of plane behavior of masonry infill panels when in the presence of seismic actions acting in any direction .

Fires following earthquake (FFE) have historically produced enormous post-earthquake damage and losses in terms of lives, buildings and economic costs, like the San Francisco earthquake (1906), the Kobe earthquake (1995), the Turkey earthquake (2011), the Tohoku earthquake (2011) and the Christchurch earthquakes (2011). The structural fire performance can worsen significantly because the fire acts on a structure damaged by the seismic event. On these premises, the purpose of this work is the investigation of the experimental and numerical response of structural and non-structural components of steel structures subjected to fire following earthquake (FFE) to increase the knowledge and provide a robust framework for hybrid fire testing and hybrid fire following earthquake testing. A partitioned algorithm to test a real case study with substructuring techniques was developed. The framework is developed in MATLAB and it is also based on the implementation of nonlinear finite elements to model the effects of earthquake forces and post-earthquake effects such as fire and thermal loads on structures. These elements should be able to capture geometrical and mechanical non-linearities to deal with large displacements. Two numerical validation procedures of the partitioned algorithm simulating two virtual hybrid fire testing and one virtual hybrid seismic testing were carried out. Two sets of experimental tests in two different laboratories were performed to provide valuable data for the calibration and comparison of numerical finite element case studies reproducing the conditions used in the tests. Another goal of this thesis is to develop a fire following earthquake numerical framework based on a modified version of the OpenSees software and several scripts developed in MATLAB to perform probabilistic analyses of structures subjected to FFE. A new material class, namely SteelFFEThermal, was implemented to simulate the steel behaviour subjected to FFE events.

The aspiration of this thesis is to provide a tool for engineers in making rational decisions based on the balance between cost and safety. This objective is accomplished by merging the optimization and reliability analyses with sophisticated finite element models that predict structural response. In particular, two state-of-the-art reliability-based design optimization approaches are implemented in OpenSees, a modern and comprehensive finite element software that has recently been extended with reliability and response sensitivity analysis capabilities. These new implementations enable reliability-based design optimization for comprehensive real-world structures that exhibit nonlinear behaviour. This thesis considers the problem of minimizing the initial cost plus the expected cost of failure subject to reliability and structural constraints. This involves reliability terms in both objective and constraint functions. In the two implemented approaches, the reliability analysis and the optimization evaluation are decoupled, although they are not bi-level approaches, thus allowing flexibility in the choice of the optimization algorithm and the reliability method. Both solution approaches employ the same reformulation of the optimization problem into a deterministic optimization problem. The decoupled sequential approach using the method of outer approximation (DSA-MOOA) applies a semi-infinite optimization algorithm to solve this deterministic optimization problem. An important feature of the DSA-MOOA approach is that a convergence proof exists in the first-order approximation. The simplified decoupled sequential approach (DSA-S) utilizes an inequality constrained optimization algorithm to solve the deterministic optimization problem. The DSA-S approach is demonstrated to result in a consistent design, which lacks the convergence proof but requires less computational time than the DSA-MOOA approach. The gradients of the finite element response with respect to model parameters are needed in reliability-based design optimization. These gradients are obtained using the direct differentiation method, which entails the derivation and implementation of analytical derivatives of the finite element response. The potential negative effect of response gradient discontinuities due to sudden yielding events is stressed in the thesis. The problem is remedied through the use of the smooth material model and a section discretization scheme. Object-oriented programming is utilized when extending optimization and sensitivity capabilities to OpenSees. The superior extensibility and maintainability features of this approach are emphasized. A numerical example involving a nonlinear finite element analysis of a three-bay, sixstorey building is presented in the thesis to demonstrate new implementations in OpenSees. Three cases are studied: a linear pushover analysis using elasticBeam elements, a nonlinear pushover analysis using beamWithHinges elements, and a nonlinear pushover analysis using dispBeamColumn elements with fibre sections. This thesis also touches on practical experiences by comparing two implemented approaches, two gradient computation methods, and linear and nonlinear analyses. The experience of speeding up the convergence procedure by removing inactive constraints and scaling the involved functions is also discussed.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

碩士
國立暨南國際大學
地震與防災工程研究所
95
In this thesis, a brick wall in a reinforced concrete (RC) frame is modeled as an equivalent diagonal bracing. The equivalent diagonal bracing model of the brick wall is incorporated into the finite element (FE) model of the RC frame to conduct lateral push-over analysis of the RC framed brick wall by using OpenSees software. First, the material properties and failure modes of brick walls are summarized from the literature. The in-plain lateral force-deformation behavior of brick walls can be derived from these factors. Then, the lateral force-deformation behavior is simulated by an equivalent diagonal bracing. Finally, the equivalent diagonal bracing combined with the RC frame is implemented in OpenSees to execute push-over analysis of the framed brick wall system. The analytical results reveal that the analytical lateral strength is generally very close to experimental data. The analytical stiffness in the ascending branch, however, is higher than the experimental results because the FE model of RC frame overestimates stiffness in the ascending branch. It is concluded that the equivalent diagonal bracing FE model presented in this thesis provides reasonably accurate analytical outcome for RC framed brick walls.

碩士
國立暨南國際大學
土木工程學系
93
ABSTRACT The objective of the study is to investigate the software framework of OpenSees and to improve performance of the finite element (FE) procedure by parametric studies on example problems. First of all, the configuration of OpenSees software framework is introduced and its practical implementation is studied by incorporating three new classes into OpenSees. The source code compiling and building procedure is investigated. Second, convergence of FE analysis of complex RC structures usually can not be easily achieved because of the nonlinear behavior of structures as well as material. So effect of the analytical parameters is studied. The analytical parameters: convergence criteria, types of the Newton-Raphson solution algorithm, the displacement increment, number of fibers in the section, and number of sections of an element are examined; optimum parameter setting is sought. Finally, the effects of the material modules Steel01 and Steel02 are also studied. The analytical results using the two material modules are compared with tests to see which is better.

Os incêndios em edifícios representam um fenómeno que pode ter consequências devastadoras quando não controlado, não só em termos de perdas de vidas humanas, como em termos económicos. No passado, a ocorrência de incêndios de grandes dimensões mostrou os efeitos do fogo descontrolado nos edifícios, assim como a ineficiência dos meios de segurança ativa ao fogo. Nas últimas duas décadas, estas questões motivaram o estudo e compreensão da ação dos incêndios nas estruturas dos edifícios. Neste trabalho estuda-se a modelação da ação do fogo em estruturas metálicas e mistas, com o objetivo de contribuir para a sua melhor caracterização. A presente tese foca-se na validação e compreensão da implementação de análises termo-mecânicas a estruturas mistas no software de elementos finitos OpenSees (Open System for Earthquake Engineering Simulation), contribuindo assim para futuros estudos, não só de análises de estruturas mistas sujeitas a incêndio, mas também de análises de estruturas mistas sujeitas a eventos consecutivos, como sismo seguido de incêndio. Neste trabalho é feita uma breve descrição do fenómeno fogo, assim como dos processos inerentes à dinâmica de um incêndio que constituem uma fonte de incerteza para a modelação de cenários de incêndio num edifício. Posto isto, são abordados alguns modelos de incêndios presentes nos Eurocódigos, assim como o recente modelo de fogos móveis(“Travelling fires”). São realizados exemplos de aplicação no software e dois casos de estudo. O primeiro consiste na modelação de dois ensaios ao fogo realizados na Alemanha em 1986 em estruturas metálicas à escala 1/4. O segundo consiste na modelação de um ensaio ao fogo a uma viga de betão armado simplesmente apoiada, realizado no Instituto Superior Técnico em 2010. Os modelos numéricos desenvolvidos no OpenSees contabilizam as não linearidades físicas e geométricas, com elementos finitos de plasticidade distribuída e com uma formulação baseada em deslocamentos. Os resultados numéricos são então comparados com os experimentais, de modo a validar as análises termo-mecânicas no OpenSees.

碩士
國立暨南國際大學
土木工程學系
96
Corrosion and deterioration of concrete piles are common problems for wharf structures. Wave impacts, cyclic wetting and drying due to tidal action, and high concentration of chlorine ions result in accelerated deterioration of marine concrete piles. Retrofit schemes for corroded marine concrete piles are similar to those for reinforced concrete (RC) columns. Among the popular retrofit methods, FRP jacketing has been attracting intensive interests in research as well as in practical application. Despite the rapid development of research and application of FRP jacketing for RC column retrofit, study on FRP jacketing for marine concrete piles is rare. As the corrosion condition facing marine piles is much different from that for RC columns, the effectiveness of the retrofit technique for corroded marine piles needs to be re-examined. A case of corrosion of prestressed concrete (PC) piles supporting landing stage structures in a harbor of Taiwan was investigated. A series of 7 reduce-scaled PC pile specimens simulating the corroded and the FRP-repaired PC piles were tested to investigate the lateral load-carrying behavior of the PC piles for the landing stage structures. The present thesis presents the analytical study on the experiments. The forced-based finite fiber element (FFE) model that has been built in the OpenSees software framework is employed. Each specimen is modeled by a forced-based FFE, which consists of 8 controlled cross sections. Each of the controlled sections is sub-divided into a number of fibers that represent the stress-strain behavior of the constituent materials, concrete or reinforcing steel, of the cross section. Two models for stirrup-confined concrete and three models for FRP-confined concrete are used and evaluated to model the uniaxial stress-strain behavior of concrete. By using OpenSees cyclic static analyses of the force-based FFE are conducted to analytically simulate the cyclic tests of the pile specimens. The analytical results are compared with the experimental curves to validate the analytical models.

Drainage methods for liquefaction remediation have been in use since the 1970's and have traditionally included stone columns, gravel drains, and more recently prefabricated vertical drains. The traditional drainage techniques such as stone columns and gravel drains rely upon a combination of drainage and densification to mitigate liquefaction and thus, the improvement observed as a result of these techniques cannot be ascribed solely to drainage. Therefore, uncertainty exists as to the effectiveness of pure drainage, and there is some hesitancy among engineers to use newer drainage methods such as prefabricated vertical drains, which rely primarily on drainage rather than the combination of drainage and densification. Additionally, the design methods for prefabricated vertical drains are based on the design methods developed for stone columns and gravel drains even though the primary mechanisms for remediation are not the same. The objectives of this research are to use physical and numerical models to assess the effectiveness of drainage as a liquefaction remediation technique and to identify the controlling behavioral mechanisms that most influence the performance of sites treated with prefabricated vertical drains. In the first part of this research, a suite of three large-scale dynamic centrifuge tests of untreated and drain-treated sloping soil profiles was performed. Acceleration, pore pressure, and deformation data was used to evaluate the effectiveness of drainage in reducing liquefaction-induced lateral deformations. The results showed that the drains reduced the generated peak excess pore pressures and expedited the dissipated of pore water pressures both during and after shaking. The influence of the drains on the excess pore pressure response was found to be sensitive to the characteristics of the input motion. The drainage resulted in a 30 to 60% reduction in the horizontal deformations and a 20 to 60% reduction in the vertical settlements. In the second part of this research, the data and insights gained from the centrifuge tests was used to develop numerical models that can be used to investigate the factors that most influence the performance of untreated and drain-treated lateral spread sites. Finite element modeling was performed using the OpenSees platform. Three types of numerical models were developed - 2D infinite slope unit cell models of the area of influence around a single drain, 3D infinite slope unit cell models of the area of influence around a single drain, and a full 2D plane strain model of the centrifuge tests that included both the untreated and drain-treated slopes as well as the centrifuge container. There was a fairly good match between the experimental and simulated excess pore pressures. The unit cell models predicted larger horizontal deformations than were observed in the centrifuge tests because of the infinite slope geometry. Issues were identified with the constitutive model used to represent the liquefiable sand. These issues included a coefficient of volumetric compressibility that was too low and a sensitivity to low level accelerations when the stress path is near the failure surface. In the final part of this research, the simulated and experimental data was used to examine the relationship between the generated excess pore water pressures and the resulting horizontal deformations. It was found that the deformations are directly influenced by both the excess pore pressures and the intensity of shaking. There is an excess pore pressure threshold above which deformations begin to become significant. The horizontal deformations correlate well to the integral of the average excess pore pressure ratio-time history above this threshold. They also correlate well to the Arias intensity and cumulative absolute velocity intensity measures.
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In recent years, the designers of girder bridges in seismic areas have frequently opted for a continuous structural scheme, in which the abutments are called to carry large seismic forces engaging the dynamic response of the soil-abutment system. It follows that the abutment response assumes a central role in evaluating the seismic performance of a bridge as an effect of its strong interaction with both the soil and the superstructure. This consideration introduces the cardinal question pursued in the present research: how and to what extent can the dynamic response of the abutments alter the global behaviour of a bridge and vice versa? To this end, this study proposes a method of analysis based on two complementary macro-elements, which simulate the salient aspects of the dynamic soil-abutment-superstructure interaction in the structural and geotechnical analyses of the bridge, preserving a manageable computational demand of the numerical soil-structure models. The two models consist of a macro-element of the soil-abutment system, developed as a useful tool for the structural analysis, and a macro-element of the superstructure to be included in the local model of the abutment instead. The internal responses of the macro-elements define a link between the dynamic response of the soil-abutment system and the global response of the superstructure, representing a step forward to a semi-direct approach for the study of the dynamic soil-structure interaction. The macro-elements were coded in the open-source finite element analysis framework OpenSees and validated against the results obtained with advanced nonlinear dynamic analyses of fully coupled soil-structure interaction models implemented in OpenSees.

The full-scale base-isolated structure studied in this dissertation is the only base-isolated building in South Island of New Zealand. It sustained hundreds of earthquake ground motions from September 2010 and well into 2012. Several large earthquake responses were recorded in December 2011 by NEES@UCLA and by GeoNet recording station nearby Christchurch Women's Hospital. The primary focus of this dissertation is to advance the state-of-the art of the methods to evaluate performance of seismic-isolated structures and the effects of soil-structure interaction by developing new data processing methodologies to overcome current limitations and by implementing advanced numerical modeling in OpenSees for direct analysis of soil-structure interaction.

This dissertation presents a novel method for recovering force-displacement relations within the isolators of building structures with unknown nonlinearities from sparse seismic-response measurements of floor accelerations. The method requires only direct matrix calculations (factorizations and multiplications); no iterative trial-and-error methods are required. The method requires a mass matrix, or at least an estimate of the floor masses. A stiffness matrix may be used, but is not necessary. Essentially, the method operates on a matrix of incomplete measurements of floor accelerations. In the special case of complete floor measurements of systems with linear dynamics, real modes, and equal floor masses, the principal components of this matrix are the modal responses. In the more general case of partial measurements and nonlinear dynamics, the method extracts a number of linearly-dependent components from Hankel matrices of measured horizontal response accelerations, assembles these components row-wise and extracts principal components from the singular value decomposition of this large matrix of linearly-dependent components. These principal components are then interpolated between floors in a way that minimizes the curvature energy of the interpolation. This interpolation step can make use of a reduced-order stiffness matrix, a backward difference matrix or a central difference matrix. The measured and interpolated floor acceleration components at all floors are then assembled and multiplied by a mass matrix. The recovered in-service force-displacement relations are then incorporated into the OpenSees soil structure interaction model.

Numerical simulations of soil-structure interaction involving non-uniform soil behavior are conducted following the development of the complete soil-structure interaction model of Christchurch Women's Hospital in OpenSees. In these 2D OpenSees models, the superstructure is modeled as two-dimensional frames in short span and long span respectively. The lead rubber bearings are modeled as elastomeric bearing (Bouc Wen) elements. The soil underlying the concrete raft foundation is modeled with linear elastic plane strain quadrilateral element. The non-uniformity of the soil profile is incorporated by extraction and interpolation of shear wave velocity profile from the Canterbury Geotechnical Database. The validity of the complete two-dimensional soil-structure interaction OpenSees model for the hospital is checked by comparing the results of peak floor responses and force-displacement relations within the isolation system achieved from OpenSees simulations to the recorded measurements. General explanations and implications, supported by displacement drifts, floor acceleration and displacement responses, force-displacement relations are described to address the effects of soil-structure interaction.

Dissertation

A ocorrência, cada vez mais frequente, de eventos extremos em estruturas, com consequências por vezes devastadoras, tem alertado a comunidade cientí-fica para a importância da robustez estrutural, isto é, a capacidade das estruturas de resistirem a danos severos sem colapsar. Apesar da sua importância, a questão da robustez estrutural é ainda abordada de forma supérflua pela maioria da re-gulamentação existente, que considera a verificação da segurança de uma estru-tura como uma verificação da segurança individual dos seus elementos estrutu-rais constituintes, desprezando o comportamento global do sistema estrutural e a contribuição de elementos não-estruturais, como as paredes de alvenaria. A ex-periência tem demonstrado, no entanto, que as paredes de alvenaria de preen-chimento dos pórticos têm uma influência determinante no comportamento dos mesmos, quer quando sujeitos a acções laterais horizontais, quer após a rotura local de um ou mais pilares, na sequência de eventos extremos. Face ao exposto, pretende-se com esta dissertação apresentar, discutir e va-lidar a aplicação de macro-modelos numéricos desenvolvidos para a simulação dos efeitos das paredes de alvenaria em pórticos sujeitos a acções horizontais, no contexto de estruturas porticadas de betão armado. Para o efeito desenvolveram-se, usando o software OpenSees, diversos mo-delos numéricos de elementos finitos com base em formulações propostas na li-teratura para solicitações horizontais, e os resultados obtidos foram comparados com os resultados experimentais do projecto Robust Brick [1]. A comparação estabelecida permitiu concluir que existem formulações pro-postas na literatura para simular o efeito das paredes no comportamento de pór-ticos de betão armado sujeitos a acções verticais, em particular na rigidez, resis-tência e desenvolvimento do mecanismo de colapso dos mesmos.

Trabalho de investigação desenvolvido na Universidade de Tecnologia e Economia de Budapeste
Tese de mestrado. Mestrado Integrado em Engenharia Civil - Especialização em Estruturas. Faculdade de Engenharia. Universidade do Porto. 2012

Trabalho de investigação desenvolvido na Universidade de Tecnologia e Economia de Budapeste
Tese de mestrado. Mestrado Integrado em Engenharia Civil - Especialização em Estruturas. Faculdade de Engenharia. Universidade do Porto. 2012