Browsing by Author "Barros, Joaquim"
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- An efficient confinement strategy with CFRP sheets to increase the energy absorption capacity of RC concrete columnsPublication . Barros, Joaquim; Ferreira, DéboraThe present work evidences the performances of distinct partial and full confinement CFRP systems, in terms of increasing the load carrying capacity and energy absorption capacity of reinforced concrete column elements. The influence of the strip’s width, the number of CFRP layers per strip and the stiffness of the CFRP sheet for these properties, is assessed. The experimental program is described and the main results are presented and analyzed
- Análise experimental de pilares de betão armado reforçados com laminados de carbono sob acções cíclicasPublication . Barros, Joaquim; Cruz, Sena; Ferreira, Débora; Lourenço, Paulo B.Neste trabalho apresentam-se e analisam-se os resultados obtidos numa campanha de ensaios experimentais em pilares de betão armado reforçados com o sistema de reforço referido e submetidos a acções cíclicas, dando-se especial relevo aos parâmetros que permitem avaliar a capacidade dissipativa de energia dos elementos ensaiados. Ensaios preliminares de arranque com o sistema de reforço proposto foram efectuados, sendo os resultados obtidos analisados.
- Aplicação de laminados de fibras de carbono no reforço de pilares de betão armadoPublication . Ferreira, Débora; Barros, Joaquim; Lourenço, Paulo B.Um número elevado de edifícios de betão armado construídos até ao início da década de 80 foram projectados sem atender ao efeito das acções horizontais. Por este motivo, a ocorrência de acções sísmicas poderá introduzir nessas estruturas danos de intensidade elevada. Os pilares são os elementos que merecem especial atenção, dado que o seu colapso conduz, geralmente, à rotura global da estrutura. Com o objectivo de desenvolver técnicas que permitam reforçar pilares, de maneira mais eficaz e mais económica que as técnicas convencionais, foi efectuado um conjunto de ensaios cíclicos envolvendo a aplicação de laminados de fibras de carbono no reforço à flexão dos referidos elementos estruturais. O reforço é constituído por laminados de fibras de carbono com 9.5×1.5 mm2 de secção transversal embutidos no betão de recobrimento recorrendo à utilização de ligantes epóxidos. Foram reforçados e ensaiados elementos de pilar intactos e elementos de pilar pré-danificados. Os resultados dos ensaios são apresentados e discutidos no presente trabalho
- Assessing the effectiveness of embedding CFRP laminates in the near surface for structural strengtheningPublication . Ferreira, Débora; Barros, Joaquim; Fortes, Adriano S.; Dias, SalvadorThe Near Surface Mounted (NSM) technique is a recent strengthening strategy, using Fiber Reinforced Polymer (CFRP) systems, that is being developed to increase the bending and the shear resistance of structural elements. To assess the effectiveness of the NSM technique, an experimental program is carried out involving reinforced concrete (RC) columns, RC beams and masonry panels. In columns failing in bending the present work shows that CFRP failure strain can be attained using the NSM technique. In this study, beams of distinct steel reinforcement ratio failing in bending are strengthened with CFRP laminate strips in order to double their load carrying capacity. This goal was attained and maximum strain levels of about 90% of the CFRP failure strain were recorded. The effectiveness of externally bonded reinforcing (EBR) and NMS techniques are compared by carrying out three-point-bending tests with masonry panels failing in bending. The NMS technique has provided a higher increase of the load carrying capacity, deflection at panel failure and more homogeneous behavior during panel deformability. Performance of both EBR and NMS techniques are also compared for strengthening RC beams failing in shear. NMS is shown to be much more effective, not only in terms of the increase of the load carrying capacity and deformability at beam failure, but also with respect to the time consuming nature of the corresponding strengthening procedures.
- Assessing the efficiency of CFRP discrete confinement systems for concrete cylindersPublication . Barros, Joaquim; Ferreira, DéboraConcrete columns requiring strengthening intervention always contain a certain percentage of steel hoops. Applying strips of wet lay-up carbon fiber reinforced polymer (CFRP) sheets in-between the existent steel hoops might, therefore, be an appropriate confinement technique with both technical and economic advantages, when full wrapping of a concrete column is taken as a basis of comparison. To assess the effectiveness of this discrete confinement strategy, circular cross section concrete elements confined by distinct arrangements of strips of CFRP sheet are submitted to a direct compression load up to the failure point. The influence of the width of the strip, distance between strips, number of CFRP layers per strip, CFRP stiffness and concrete strength class on the increase of the load carrying capacity and ductility of concrete columns, is evaluated. An analytical model is developed to predict the compressive stress-strain relationship of concrete columns confined by discrete and continuous CFRP arrangements. The main results of the experimental program are presented and analyzed and used to assess the model performance
- CFRP - Confined reinforced concrete elements subjected to cyclic compressive loadingPublication . Ferreira, Débora; Barros, Joaquim; Varma, RajendraThe effectiveness of discrete and continuous CFRP wrapping arrangements for reinforced concrete (RC) short column subjected to monotonic and cyclic compressive loading is assessed in this work. The experimental program is composed of four series of RC columns with discrete wrapping arrangements and one series of full wrapped RC columns. Each series is composed of a monotonic and a cyclic test. Strain gauges were installed along the height of each column to measure the strain field in the CFRP during the test. The variation of the stiffness of the unloading and reloading branches of each loading cycle was determined. A constitutive model to simulate FRP-confined RC concrete elements subjected to cyclic compressive loading was developed and implemented into a computer program based on the finite element method. This model was appraised with the data obtained from the carried out experimental program.
- CFRP-Based confinement strategies for RC columns-experimental and analytical researchPublication . Ferreira, Débora; Barros, JoaquimThe present work aims to compare the confinement effectiveness of full and partial wrapping of concrete elements under compression loads. The main results of the experimental program are presented and analysed. The Lam and Teng analytical model was applied to predict the compression stress-strain behaviour of concrete column elements partially confined by strips of CFRP lay-up sheets. The model performance is assessed using the experimental results.
- Comportamento de pilares de betão armado reforçados com laminados de fibras de carbonoPublication . Barros, Joaquim; Ferreira, Débora; Lourenço, Paulo B.Os resultados obtidos em ensaios cíclicos com elementos de pilar de betão armado pré- e pós-reforçados com laminados de fibras de carbono são apresentados e analisados no presente trabalho. Verificou-se que, desde que as operações de reforço sejam devidamente efectuadas e a qualidade dos materiais aplicados seja assegurada, os laminados permitem aumentar significativamente a capacidade de carga de pilares de betão armado danificados.
- Confinamento de pilares de betão armado reforçados total e parcialmente com mantas de CFRP submetidos a carregamentos cíclicos de compressãoPublication . Ferreira, Débora; Barros, JoaquimNo sentido de contribuir para o aumento do conhecimento no âmbito do confinamento com sistemas de CFRP de elementos de pilar submetidos a carregamentos cíclicos de compressão, foi efectuado um programa experimental, cujos resultados são apresentados e analisados no presente trabalho.
- Confinamento de provetes cilíndricos de betão com mantas de CFRP- cintagem parcial e totalPublication . Ferreira, Débora; Barros, JoaquimProvetes cilíndricos de betão de 150 mm de diâmetro e 300 mm de altura foram cintados com faixas de manta de fibras de carbono com o objectivo de avaliar a influência da largura e número de faixas, e do número de camadas no aumento da resistência e da ductilidade do betão. Alguns dos resultados obtidos são apresentados e comentados.
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