Browsing by Author "Barros, Rui"
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- Análise paramétrica da rigidez de impacto em colisões entre sistemas estruturais com 1GDL com comportamento não-linearPublication . Folhento, Pedro Leonel Pamplona; Barros, Rui; Braz-César, ManuelA ocorrência de impactos estruturais entre edifícios durante sismos de grande intensidade é muito comum em cidades, onde a construção de edifícios é realizada deixando espaço insuficiente entre as estruturas devido aos custos elevados dos terrenos de construção. Estas colisões são uma problemática relevante, que possui importância na investigação dos seus efeitos e consequências no comportamento dinâmico das estruturas e mitigação dos mesmos. Este estudo paramétrico considera a variação da rigidez de impacto, um parâmetro relevante nos elementos de simulação de contactos, para uma gama de valores adequados ao estudo de impactos entre edifícios. Os edifícios serão modelados como modelos de um grau de liberdade admitindo comportamento linear elástico e não-linear inelástico, através do uso de um modelo histerético. A escolha de um valor adequado para a rigidez de impacto é importante, tendo uma maior influência nas acelerações e forças de impacto e menor influência nas forças laterais.
- Analysis of the dynamic behavior of a radar towerPublication . Barros, Rui; Guimarães, Hugo; Braz-César, ManuelThe present work addresses the study of the dynamic behavior of a metallic steel tower 45 meters high, supporting a radar antenna. Some methodologies are followed for the characterization of the major external excitation on the radar tower, namely the environmental actions due to wind and the seismic action as well. A complementary study associated with the dynamic effects due to the antenna rotation is also emphasized, since it is related with crucial malfunctioning of the mounted equipment. Finally it is proposed a solution for the control of vibrations, through the design and installation of tuned liquid dampers at the instrumental platform near the top of the radar tower; a few advantages associated with such improved implementation are discussed.
- Analysis of the dynamic behavior of a radar towerPublication . Barros, Rui; Guimarães, Hugo; Braz-César, ManuelThe present work addresses the study of the dynamic behavior of a metallic steel tower 45 m high, supporting a radar antenna. Some methodologies are followed for the characterization of the major external excitation on the radar tower, namely the environmental actions due to wind and the seismic action as well. A complementary study associated with the dynamic effects due to the antenna rotation is also emphasized, since it is related with crucial malfunctioning of the mounted equipment. Finally, it is proposed a solution for the control of vibrations, through the design and installation of tuned liquid dampers at the instrumental platform near the top of the radar tower; a few advantages associated with such improved implementation are discussed.
- ANFIS optimized semi-active fuzzy logic controller for magnetorheological dampersPublication . Braz-César, Manuel; Barros, RuiIn this paper, we report on the development of a neuro-fuzzy controller for magnetorheological dampers using an Adaptive Neuro-Fuzzy Inference System or ANFIS. Fuzzy logic based controllers are capable to deal with non-linear or uncertain systems, which make them particularly well suited for civil engineering applications. The main objective is to develop a semi-active control system with a MR damper to reduce the response of a three degrees-of-freedom (DOFs) building structure. The control system is designed using ANFIS to optimize the fuzzy inference rule of a simple fuzzy logic controller. The results show that the proposed semi-active neuro-fuzzy based controller is effective in reducing the response of structural system.
- Assessment of long term use and aging in the electomagnetic and mechanical characteristics of a magneto-rheological fluid sponge damperPublication . Braz-César, Manuel; Barros, RuiThis paper aims to evaluate the long term use and aging effects on the electromagnetic and mechanical characteristics of a magneto-rheological (MR) fluid sponge damper. The device was used in several experimental research projects for ten years followed by four years of inactivity. It was used back in the last year during an experimental campaign to evaluate its effectiveness after these years of heavy use and inactivity. Thus, the dynamic behaviour of a MR fluid sponge damper at several mechanic and magnetic excitations is studied. Finally, the possible causes of the variation in the electromagnetic and mechanical responses of the MR damper with respect to the initial specifications are discussed.
- Brain emotional learning based control of a sdof structural system with a MR damperPublication . Braz-César, Manuel; Gonçalves, José; Coelho, João Paulo; Barros, RuiThis paper describes the application of a Brain Emotional Learning (BEL) controller to improve the response of a SDOF structural system under an earthquake excitation using a magnetorheological (MR) damper. The main goal is to study the performance of a BEL based semi-active control system to generate the control signal for a MR damper. The proposed approach consists of a two controllers: a primary controller based on a BEL algorithm that determines the desired damping force from the system response and a secondary controller that modifies the input current to the MR damper to generate a reference damping force. A parametric model of the damper is used to predict the damping force based on the piston motion and also the current input. A Simulink model of the structural system is developed to analyze the effectiveness of the semi-active controller. Finally, the numerical results are presented and discussed.
- Colisões estruturais induzidas por sismos entre estruturas de edifícios adjacentes com alturas diferentesPublication . Folhento, Pedro Leonel Pamplona; Barros, Rui; Braz-César, ManuelA quantidade substancial de energia libertada através de sismos é em parte absorvida pelos edifícios afetados pelas consequentes vibrações. Esta energia de entrada nas estruturas tende a ser dissipada através do amortecimento e deformação inelástica estrutural. Os eventos sísmicos promovem colisões estruturais entre edifícios adjacentes insuficientemente separados, conduzindo a trocas de energia inesperadas entre as estruturas, podendo reduzir ou amplificar as respetivas respostas dinâmicas. Este estudo considera diferentes configurações de dois edifícios com comportamento elástico, que poderão ter alturas iguais ou desiguais, e sujeitos a diferentes sinais sísmicos. Os impactos consideram-se entre pisos e objetiva-se investigar a influência destes no comportamento dinâmico e no equilíbrio energético dos sistemas considerados, simulados com modelos simplificados. Verificou-se que edifícios adjacentes com alturas diferentes sujeitos a impactos induzidos por sismos tendem a ter respostas dinâmicas mais gravosas e a provocar mais trocas de energia.
- Comparison of cyclic response of reinforced concrete infilled frames with experimental resultsPublication . Braz-César, Manuel; Oliveira, Daniel V.; Barros, RuiThis paper intends to estimate the numerical cyclic response of RC frames with and without masonry infill through a simplified nonlinear analysis using a commercial FEM package. The numerical model is based on the experiments carried out in the National Laboratory of Civil Engineering (LNEC) and the numerical and experimental results are compared to assess the accuracy of the simplified analysis based on the inelastic hinge method either for the bare frame and the infill frame.
- Control action of a tuned mass damper in mitigating earthquake-induced structural pounding between building floorsPublication . Folhento, Pedro Leonel Pamplona; Barros, Rui; Braz-César, ManuelPassive control devices are widely used in the reduction of lateral vibrations of building structures. The control of these lateral vibrations is vital in preventing collisions between adjacent building structures during a seismic event. These collisions modify the dynamic behavior of the intervenient structures and cause substantial local damage. In this way, the implementation of a Tuned Mass Damper (TMD) can be a solution in mitigating the earthquake-induced building pounding. However, there are concerns regarding the effectiveness and practical applicability of solutions for this purpose. In fact, non-linear inelastic behavior of building structures, expected during earthquakes, is one of these concerns that should be considered in the assessment of the TMD effectiveness. Hence, this study addresses the investigation of the control action effectiveness of a TMD in reducing the lateral displacements of one of two building structures modelled with elastic and inelastic behavior that are prone to earthquake-induced structural pounding. Results show that TMD is effective in reducing displacements, pounding forces, and number of impacts, under elastic building behavior. However, when inelastic behavior is considered the TMD becomes less effective. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
- Cyclic experimental response of reinforced concrete frames: validation methodologyPublication . Braz-César, Manuel; Oliveira, Daniel V.; Barros, RuiThis article validates numerically the experimental behavior of a reinforced concrete frame subject to cyclical loads, resorting to a commercial program using finite element analysis. The experimental results were obtained in the National Laboratory of Civil Engineering (LNEC). In the numerical simulation several constitutive models were used, with different degrees of complexity, based on the concept of local plastification in critical zones (plastic hinges) of the elements that constitute the frame as well as on fiber models.