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Abstract(s)
A presente tese descreve um estudo experimental que teve por objetivo avaliar a ductilidade à
flexão e o comportamento plástico de vigas de betão de agregados leves de argila expandida.
Com este propósito, um conjunto de vigas simplesmente apoiadas foram produzidas e testadas
até à rotura, com duas cargas concentradas simétricas aplicadas aproximadamente a terços de
vão. A zona central, entre as cargas aplicadas, foi submetida à flexão pura. As principais
variáveis estudadas foram a resistência à compressão do betão e a taxa de armadura longitudinal
de tração. Neste sentido, as vigas combinaram diferentes taxas de armadura longitudinal de
tração entre 0,13% a 2,69% com diferentes misturas de betão de agregados leves (BAL) com
resistências à compressão entre 22 e 60 MPa e massa volúmica seca entre 1651 e 1953 kg/m3.
A produção do BAL e a betonagem das vigas foram suportadas por um programa experimental.
Esse programa mostrou que é possível produzir em estaleiro de forma satisfatória BAL com alta
resistência, sem segregação, mesmo para aplicações estruturais em vigas de betão armado. Além
disso, foram obtidas algumas correlações específicas entre a resistência à compressão, a razão
água cimento e a massa volúmica seca. A variabilidade da resistência à compressão foi também
discutida para diferentes processos de amostragem e controle de produção em estaleiro.
A ductilidade à flexão foi avaliada através de índices de ductilidade e os resultados mostraram
que o parâmetro mais influente sobre a ductilidade é a taxa de armadura longitudinal de tração.
Os resultados mostraram também que a ductilidade aumenta ligeiramente com o incremento da
resistência à compressão do betão.
A capacidade de rotação plástica das vigas testadas foi caracterizada por um parâmetro
designado de Parâmetro de Tendência Plástica (PTP). Os resultados obtidos através deste
parâmetro confirmaram a tendência verificada através dos índices de ductilidade.
Adicionalmente foi proposto um intervalo adequado para a taxa de armadura longitudinal de
tração de modo a garantir a ductilidade e capacidade de rotação plástica.
Os resultados deste estudo foram comparados com os requisitos de alguns documentos
normativos. A partir desta análise, verificou-se que, comparativamente com os códigos europeus,
os requisitos do ACI oferecem mais garantias tanto no que respeita à ductilidade como à
capacidade de rotação plástica.
This thesis describes an experimental study that aimed to evaluate the flexural ductility and the plastic behaviour of expanded clay lightweight-aggregate concrete beams. For this propose, a set of simply supported beams were produced and tested until failure, with two symmetrical concentrated loads applied at approximately one third of the span. The central zone, between the applied loads, was subjected to pure flexure. The main variables studied were the concrete compressive strength and the longitudinal tensile reinforcement ratio. In this sense, beams have combined different longitudinal tensile reinforcement ratios of 0,13% to 2,69% with different lightweight-aggregate concrete (LWAC) mixtures of compressive strengths between 22 and 60 MPa and dry densities between 1651 and 1953 kg/m3 . The production of the LWAC and the concreting of the beams were supported by an experimental program. Such research program showed that it is possible to satisfactorily produce LWAC with high strength in construction site without segregation, even for structural applications in reinforced concrete beams. Additionally, some specific correlations were obtained between the compressive strength, the water to cement ratio and the dry density. Variability of compressive strength was also discussed for different sampling process and production control on site. The flexural ductility was studied by defining ductility indexes and the results have shown that the parameter with higher influence on ductility is the longitudinal tensile reinforcement ratio. The results also shown that the flexural ductility slightly increases as the concrete compressive strength increases. The plastic rotation capacity of the tested beams was characterized by a parameter called Plastic Trend Parameter (PTP). The results obtained from this parameter confirmed those obtained from the ductility indexes. Additionally an appropriate range for the longitudinal tensile reinforcement ratio to ensure ductility and plastic rotation capacity was proposed. The results of this study were also compared with the requirements from some codes of practice. From this analysis, it was shown that ACI Code requirements give more guaranties as far as ductility and plastic rotation capacity are concerned, when compared with European codes.
This thesis describes an experimental study that aimed to evaluate the flexural ductility and the plastic behaviour of expanded clay lightweight-aggregate concrete beams. For this propose, a set of simply supported beams were produced and tested until failure, with two symmetrical concentrated loads applied at approximately one third of the span. The central zone, between the applied loads, was subjected to pure flexure. The main variables studied were the concrete compressive strength and the longitudinal tensile reinforcement ratio. In this sense, beams have combined different longitudinal tensile reinforcement ratios of 0,13% to 2,69% with different lightweight-aggregate concrete (LWAC) mixtures of compressive strengths between 22 and 60 MPa and dry densities between 1651 and 1953 kg/m3 . The production of the LWAC and the concreting of the beams were supported by an experimental program. Such research program showed that it is possible to satisfactorily produce LWAC with high strength in construction site without segregation, even for structural applications in reinforced concrete beams. Additionally, some specific correlations were obtained between the compressive strength, the water to cement ratio and the dry density. Variability of compressive strength was also discussed for different sampling process and production control on site. The flexural ductility was studied by defining ductility indexes and the results have shown that the parameter with higher influence on ductility is the longitudinal tensile reinforcement ratio. The results also shown that the flexural ductility slightly increases as the concrete compressive strength increases. The plastic rotation capacity of the tested beams was characterized by a parameter called Plastic Trend Parameter (PTP). The results obtained from this parameter confirmed those obtained from the ductility indexes. Additionally an appropriate range for the longitudinal tensile reinforcement ratio to ensure ductility and plastic rotation capacity was proposed. The results of this study were also compared with the requirements from some codes of practice. From this analysis, it was shown that ACI Code requirements give more guaranties as far as ductility and plastic rotation capacity are concerned, when compared with European codes.
Description
Keywords
Vigas de betão - Ductilidade Vigas de betão - Rotação plástica Betão armado Betão de agregados leves Códigos estruturais - Estudo comparativo