The influence of the beam-column connection on the global results of multi-storey reinforced concrete structures

Abstract The effect of the semi-rigid connection between beams and columns on the global behavior of reinforced concrete (RC) structures was investigated. The relative rotations in the nodes of the spatial frames were determined using the analytical approach proposed by Alva and El Debs. The rotational restraint factor ( α r) was defined and applied in each node of the spatial frames. RC spatial frames with total heights of 21, 42, and 63 m were considered. It was found that the semi-rigid connection increases the lateral displacements, the 2nd order effects, and the γ z values. The lower the stiffness of the nodes, the lower the influence of α r on the global results. The total fixed beam-column connections can lead to an unrealistic behavior of the spatial frame and thus to global results

Evaluation of Ultra-High-Performance Concrete Columns at High Temperatures after 180 Days of Curing

Ultra-high-performance concrete (UHPC) is a material that has high compactness, low porosity, and high mechanical strength, with especially high tensile strength. Due to these characteristics, the behavior of the material when exposed to high temperatures is debatable. The high amount of fibers in the mixture, which makes UHPC present a high tensile strength, is seen as one of the arguments for the good performance of the material when exposed to high temperatures. The objective of this study was to evaluate the behaviors of ultra-high-performance concrete columns with hybrid steel and polypropylene fibers and no loose reinforcements when subjected to elevated temperatures after 180 days of curing. The exposure of concrete with a low age, less than 90 days, to high temperatures results in greater damage to the concrete due to spalling, and because of this, this study sought to evaluate the UHPC with a higher age. Two columns were manufactured with a cross-section of 250 mm × 250 mm and a height of 2800 mm. A heating regime followed the heating curve of standard ISO 834-1. The physical characteristics of the samples were evaluated during and after exposure to high temperatures with measurements of the decreases in the cross-section and surface aspect. Effects on the compressive strength, modulus of elasticity, and apparent density were evaluated with cylindrical test bodies of 100 mm in diameter and 200 mm in height. These samples were cured for 180 days, subjected to the same heating regime, and evaluated after cooling. The results showed an increase in the compressive strength with an increasing temperature up to a factor of 30% at a temperature of 400 °C. The modulus of elasticity and apparent density decreased gradually as the temperature increased, with maximum decreases of 29% and 6%, respectively. Throughout heating, audible cracks were heard from the columns because of spalling. The spalling frequency peaked at an oven temperature of 600 °C, and testing was suspended at 78 min after the complete rupture of a column section. On average, 46.5% of the column cross-sections suffered from spalling

Avaliação da resistência residual de lajes alveolares em concreto armado em uma edificação industrial após incêndio

O concreto, durante exposição a elevadas temperaturas, caracteriza-se pela baixa difusividade térmica e incombustibilidade,resultando em desempenho satisfatório frente ao fogo. Todavia, constatam-se transformaçõesquímicas e físicas em seus componentes. A estabilidade do composto relaciona-se com a microestrutura,portanto consegue-se verificar a degradação do material através de técnicas avançadas de análise microestrutural.Neste contexto, o uso de ensaios no material, como a difratometria e fluorescência de raios X, mostraseatraente. Neste artigo, é descrita a inspeção de laje alveolar pré-fabricada de uma edificação industrial, aqual sofreu exposição às altas temperaturas provindas de um incêndio no subsolo da edificação. Avaliou-se oelemento estrutural através de ensaios de caracterização química, em diferentes espessuras da laje de concreto,estimando a temperatura alcançada em cada camada e, consequentemente, a perda de resistência do elementoestrutural. A partir dos resultados, constatou-se a temperatura de, aproximadamente, 700 ºC na superfícieda laje e menos de 100 ºC nas camadas mais profundas. Estimou-se a redução na resistência à compressãodo concreto na ordem de 25 % na camada de 20 mm e redução praticamente desprezável na região dosfios protendidos, atestando a segurança estrutural da estrutura após o sinistro