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- Dimensionamento de Contraventamentos Metálicos para Reforço sísmico de estruturas de Betão ArmadoPublication . Sousa, Romain; Miguel Castro, JoséA entrada em vigor da nova regulamentação europeia para o dimensionamento sísmico fará com que um grande número de estruturas de betão armado existentes não apresente resistência sísmica adequada, conduzindo por isso à necessidade do seu reforço. Nesse sentido, apesar do contraventamento de estruturas de betão armado com elementos metálicos surgir como uma boa solução de reforço, o seu uso é limitado devido à falta de regulamentação aplicável neste domínio. O principal objectivo deste trabalho consiste no desenvolvimento de um método de dimensionamento simples e expedito que possa promover o reforço de estruturas porticadas betão armado com contraventamentos metálicos. Nos últimos anos, a comunidade científica tem demonstrado que o dimensionamento sísmico com base em deslocamentos é mais adequado e rigoroso que os métodos tradicionais baseados em forças. Com vista à obtenção de parâmetros fundamentais para a aplicação deste novo método, foram realizadas análises não lineares estáticas e dinâmicas em estruturas porticadas de betão armado reforçadas com contraventamentos metálicos concêntricos. Os resultados fornecidos pelas análises permitiram determinar uma variedade parâmetros tais como o perfil de deslocamentos laterais, o deslocamento de cedência, o deslocamento alvo, entre outros. Com base nos resultados obtidos propõe-se um método de dimensionamento baseado em deslocamentos que permite, de uma forma simples e expedita, dimensionar o sistema de reforço de modo a que a estrutura híbrida apresente um comportamento sísmico adequado.
- 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.
- Comportamento Sísmico de um Pavilhão Pré-Fabricado de Betão ArmadoPublication . Batalha, Nádia; Rodrigues, Hugo; Varum, Humberto; A. L. Fernandes, Paulo; Sousa, RomainOs pavilhões pré-fabricados de betão armado são muito comuns no parque industrial em Portugal, tendo mostrado um desempenho por vezes deficiente em sismos recentes tanto ao nível dos elementos estruturais como não-estruturais. Torna-se importante a sua caraterização a fim de conhecer melhor o seu comportamento sísmico. Os pavilhões industriais de um piso, com uma estrutura porticada de vigas e pilares, com ligação encastrada na base e rotulada no topo, sobre a qual vigas de secção variável são posteriormente apoiadas é a solução mais recorrente em Portugal. Nesse sentido, este trabalho aborda o comportamento sísmico de um pórtico de um edifício industrial-tipo existente, com estrutura em betão pré‐fabricado. Essa caracterização é feita através de análises estáticas não lineares (pushover) e análises dinâmicas. Os resultados obtidos são apresentados e discutidos.
- 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.
- Modelling strain penetration effects in RC walls with smooth steel barsPublication . Caruso, Claudia; Bento, Rita; Sousa, Romain; Correia, António A.Reinforced-concrete (RC) dual wall–frame structures comprise an important proportion of the building stock in some European cities. However, many were constructed without seismic provisions and it is therefore important to assess their ability to withstand seismic events and to define strategies to reduce their potential vulnerability. This work focuses on the numerical simulation of the seismic behaviour of RC walls making use of fibre-based non-linear beam elements. Even though it is common to assume perfect bond between reinforcing bars and concrete, the relative bond–slip deformations between the two materials can contribute up to 40% of the total lateral deformation of columns when ribbed rebars are used and up to 90% in the case of smooth rebars. The aim of this paper is to provide a contribution towards understanding the importance of these effects in old RC walls and to provide indications regarding the use of a simplified bond–slip model.
- 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.
- Seismic precast. Seismic performance assessment of existing precast industrial buildingsPublication . Furtado, André; Arêde, António; Rodrigues, Fernanda; Rodrigues, Hugo; Vitorino, Hugo; Varum, Humberto; Ostetto, Liana; Batalha, Nádia; Fernandes, Paulo; Sousa, Romain; Silva, VítorPast seismic events exposed important fragilities in precast reinforced concrete buildings and highlight the need to undertake measures to mitigate future losses.The study presented identify potential structural and nonstructural fragilities of the Portuguese building stock and provide guidance to reduce the associated direct and indirect socio-economic impact
- Seismic design of RC frames retrofitted with concentric steel bracesPublication . Sousa, Romain; Castro, J. MiguelThe implementation in Europe of a new seismic design code (Eurocode 8) will impose strict performance requirements to building structures. This will result in a significant number of existing reinforced concrete structures showing inadequate seismic resistance and hence requiring intervention. One of the available retrofitting techniques consists of inserting steel braces in the original RC structure. In spite of the advantages of using this retrofitting approach, the adoption of this technique is still limited due to the lack of seismic design rules. The interaction between the steel braces and the RC members turns the design in an intricate task. The main goal of the research presented in this paper was to develop a simple yet reliable design procedure that can promote the retrofitting of reinforced concrete frames with steel braces. The proposed method is based on displacements and accounts for the interaction of the steel elements on the deformation capacity of the RC members. To this end, nonlinear static and time-history analysis of reinforced concrete structures strengthened with concentric steel braces have been performed with the objective of deriving a number of key parameters (displacement profiles, yield drifts and target displacements) which are essential for the application of the new design procedure. The paper closes with an application of the proposed method to a RC structure with inadequate seismic resistance. The performance assessment of the retrofitted structure, carried out with nonlinear static analysis, confirms the validity of the design procedure and demonstrates the merits of adopting displacement-based seismic design approaches.
- Problematiche di Modellazione nella Valutazione Sismica delle Strutture EsistentiPublication . Sousa, Romain; Bianchi, F.; Nascimbene, Roberto; Pinho, RuiProblemi di modellazione per l’analisi sismica delle strutture esistenti Molti edifici in c.a. del patrimonio edilizio esistente sono stati progettati per i soli carichi verticali, presentando un’inadeguata resistenza ai carichi laterali e scarsi dettagli costruttivi. Inoltre, il concetto di regolarità in pianta e in elevazione, tipico di una buona progettazione sismica, spesso è stato trascurato. Per valutare il comportamento sismico di tali edifici, alcune recenti normative in materia sismica - quali l’EC8 e le NTC08 - hanno introdotto diverse prescrizioni sulle tipologie di analisi, le distribuzioni di carico, l’eccentricità accidentale, ecc., lasciando, però, ai progettisti piena autonomia a proposito delle strategie di modellazione (es. impalcati, tamponamenti verticali, tipologia di elementi finiti, masse, ecc.). L’obiettivo del presente lavoro è quello di stimare, tramite l’esecuzione di analisi non-lineari (statiche e dinamiche) per un edificio reale, l’influenza di tali strategie nella valutazione sismica delle strutture, al fine di fornire indicazioni sull’importanza di ogni scelta progettuale.
- Development and Verification of Innovative Modelling Approaches for the Analysis of Framed Structures Subjected to Earthquake ActionPublication . Sousa, RomainThe last decades have witnessed significant progresses in the development of improved numerical models for structural analysis, as proven by hundreds of dissertations, theses, reports and journal papers dedicated to advanced constitutive models of materials and algorithms to model sectional, element and structural response. Nevertheless, the seismic behaviour of structures involves a number of nonlinear material and geometrical phenomena that, ultimately, are impossible to capture exhaustively in a single model. Furthermore, past studies showed that the most correct modelling options from the scientific viewpoint are sometimes challenged by experimental evidence. This thesis intends to contribute to the ongoing effort of progressively bridging the existing gap between solid theoretical principles adopted in nonlinear modelling and experimental results from shake table or other experimental techniques. Such goal is firstly pursued through the application of a sensitivity analysis to the simulation of the dynamic behaviour of three distinct structures with distributed plasticity beam-column fibre-based elements based on Euler-Bernoulli beam theory. The latter were tested in international blind prediction challenges wherein the author and/or supervisors participated with encouraging results. The goodness-of-fit for each approach is assessed through comparisons between numerical and experimental results in terms of lateral displacements as well as accelerations (when available), following two post-processing strategies: a more conventional one based on the error associated to the peak values measured during each record, and another using the frequency content characteristics of the entire response history. Sensitivity parameters included equivalent viscous damping, element discretization scheme, strain penetration effects, material constitutive models, numerical integration algorithms and analysis time-step size. The conclusions, which are interpreted in the light of state-of-the-practice recommendations and established theoretical frameworks, address fundamental modelling decisions for engineers and researchers. The referred sensitivity analysis identified the simulation of strain penetration effects as particularly relevant. They can significantly impact the seismic response of structures, contributing up to 40% of the overall lateral deformation of RC framed structures. Within this context, the last chapters of the thesis present a novel bond-slip model for RC structures that simulates the member-end deformations associated with strain penetration effects. The model, which in its final form is implemented as a zero-length element, was developed so that it is compatible with any general fibre-based frame analysis software. In a nutshell, the element response is determined from cross-sectional fibre integration, where at each rebar the anchorage mechanism is explicitly modelled through a series of virtual integration points distributed along the anchorage length. The analysis is carried out by an algorithm that enforces both equilibrium and compatibility at every integration point, making use of a state-of-the-art bond stress-slip cyclic constitutive relation applicable to a wide variety of anchorage conditions. Therefore, features such as the expected failure mode (pullout or splitting), or parameters such as the concrete strength, embedment length, cyclic degradation, amplitude of steel strains, rebar type (plain or ribbed), transverse pressure, level of confinement and bond conditions can be explicitly modelled. The element was implemented in a structural analysis software and its performance was assessed against several experimental tests, showing an encouraging accuracy while retaining appreciable computational efficiency.