ResumoThis paper does a review of the recent achievements on the knowledge of UHPFRC properties and in the development of design procedures. UHPFRC is defined as a new material, with unique properties (high ductility, low permeability, very high strength capacity in compression, higher toughness) in comparison to conventional concrete. It is important to know both material and mechanical properties to fully take advantage of its outstanding properties for structural applications. However, since this is a new material, the current design codes are not well suited and should be reviewed before being applied to UHPFRC. In the first part, the following material properties are addressed: hydration process; permeability; fibers role; mix design; fiber-matrix bond properties workability; mixing procedure; and curing. In the second part, the mechanical properties of the material are discussed, together with some design recommendations. The aspects herein examined are: size effect; compressive and flexural strength; tensile stress-strain relation; shear and punching shear capacity; creep and shrinkage; fracture energy; steel bars anchorage and adherence. Besides, the tensile mechanical characterization is described using inverse analysis based on bending tests data. In the last part, material behavior at high temperature is discussed, including physical-chemical transformations of the concrete, spalling effect, and transient creep. In the latter case, a new Load Induced Thermal Strain (LITS) semi-empirical model is described and compared with UHPC experimental results.Keywords: Ultra-High Performance Fiber Reinforced Concrete (UHPFRC), material properties, design procedures, mechanical behavior, high temperature.Este artigo faz uma análise dos recentes avanços nas pesquisas das propriedades do CUADRF e dos seus procedimentos normativos. O CUA-DRF pode ser definido como um novo material, com propriedades muito superiores (grande ductilidade, baixíssima permeabilidade, altíssima capacidade resistente à compressão e elevada tenacidade) às do concreto convencional. O conhecimento das propriedades mecânicas e do material do CUADRF é importante para que todo o seu potencial seja plenamente utilizado. Entretanto, como este é um novo material, as recomendações normativas atuais não são plenamente válidas. Na primeira parte, as seguintes propriedades do material são descritas: processo de hidratação; permeabilidade; efeito dos diferentes tipos de fibras; definição do traço; aderência entre as fibras e o concreto; trabalhabilidade; procedimentos de mistura; e cura. Na segunda parte, as propriedades mecânicas e algumas recomendações normativas são discutidas. Neste caso são examinados o efeito escala, a resistência à compressão e à flexão, a relação tensão-deformação à tração, a força de cisalhamento e de punção, a fluência e a retração, a energia de fratura, a ancoragem e aderência das barras de aço. Além disso, são descritos alguns métodos de análise inversa para a caracterização do material à tração por meio de ensaios ...
The effect of fibre reinforcement on Load Induced Thermal Strains (LITS) has not yet been significantly investigated up to now. Creep is becoming a key research topic only in the last few years. A semi-empirical model able to take into account both the thermo-mechanical damage associated to coarse aggregates and the thermo-chemical damage induced in the matrix and calibrated on the basis of the main results on plain concrete available in the scientific literature is presented. Some tests in uniaxial compression on Fibre Reinforced Concrete (FRC) cylinders characterized by a long age – 11-years-old – have been investigated and compared with the model to highlight fibre effects, if any. The uniaxial compressive strength at 28 days of the SFRC was 75 MPa; the specimens after 11 years showed a compressive strength exceeding 110 MPa. A strong increase of SLS residual strength was observed in post-cracking tension due to the long aging, while ULS residual strengths weakly increased. The cylindrical specimens were exposed to a maximum temperature of 200°C and 400°C and loaded with two load thresholds corresponding to 20% and 40% of the compressive strength detected at 28 days of aging, that means about 12.5% and 25% of the 11-years-old specimens. Two paths were investigated: pre-heated specimens up to 200°C or 400°C, then loaded with a compression stress equal to 0.2fc,28 and 0.4fc,28; and pre-loaded specimens up to 0.2fc,28 and 0.4fc,28 and then heated up to 200°C or 400°C. The duration of each test did not exceed 12 hours. Two main fibre effects were observed: a significant reduction of irreversible strains when the specimens were loaded and then heated and cooled and a different evolution in LITS passing from 200°C to 400°C, characterized by a significant reduction of the expected deformation.
This paper compares the results between a non-linear three-dimensional numerical analysis of pile caps with two piles and the experimental study conducted by Delalibera. It is verified the load-carrying capacity, the crack pattern distribution, the principal stress in concrete and steel, the deflection and the fracture of the pile cap. The numerical analysis is executed with the finite-element software ATENA 3D, considering a perfect bond between concrete and steel. The numerical and experimental results are presented and have demonstrated a good approximation, reasserting the results of the experimental model and corroborating the theory.Keywords: pile caps, finite elements, reinforced concrete, foundation.Neste artigo é realizado um estudo comparativo entre o comportamento experimental de blocos de concreto armado apoiados sobre duas estacas, a partir de modelo experimental de Delalibera, e o obtido a partir de análise numérica tridimensional não-linear. A comprovação de resultados é feita observando-se a força última, o panorama de fissuração, o fluxo de tensões atuantes no concreto e no aço, as deformações e o padrão de ruína. A simulação numérica do comportamento estrutural do bloco de concreto armado é realizada com o emprego do programa computacional de elementos finitos ATENA 3D, considerando a aderência perfeita entre as barras de aço da armadura e o concreto. Os resultados numéricos e experimentais são apresentados e quando comparados apresentam uma boa aproximação, comprovando os fundamentos teóricos e os resultados experimentais.Palavras-chave: blocos sobre estacas, elementos finitos, concreto armado, fundacões. Campinas, almeida@fec.unicamp.br, Campus Zeferino Vaz -Av. Albert Einstein, 951 -Campinas-SP -Brasil Received: 21 Nov 2011 • Accepted: 27 Feb 2012 • Available Online: 02 Apr 2012 Abstract Resumo Three-dimensional analysis of two-pile caps
This paper carries out a design analysis of reinforced concrete beams with steel fibers following the fib Model Code 2010 (MC 2010) procedures. The values obtained from the design calculations are compared with the experimental results of reinforced concrete beams with 20kg/m3 and 60 kg/m3 of steel fibers submitted to four-point bending tests. In the first part, the procedures for the classification and characterization of the material are explained. The experimental results of three-point bending tests performed on notched steel fiber reinforced concrete (FRC) beams following EN 14651 procedures are described. Moreover, the characterization of the FRC beams according to MC 2010, are carried out. In the second part, the flexural design of reinforced concrete beams with steel fibers, according to MC 2010, is carried out. A sectional analysis is performed in order to obtain the moment-curvature and the force-vertical displacement curves. The theoretical values are compared with the experimental results. Besides, a linear statistic analysis by means of the Rule of Mixture is carried out in order to analyze the variation of the flexural capacity of the reinforced beams with different amounts of steel fibers. The results demonstrated that the design rules described in the MC 2010 are on the safe side. The flexural resistance of concretes with different amounts of fiber incorporation can be determined by the Rule of Mixture, which has shown a high correlation factor (R2) with the experimental values.
The paper discusses the effect of aging on steel fibre reinforced concrete (SFRC) after 10 years. The aim is to observe the change in mechanical properties, especially of the residual post-cracking tensile strength, due to long-term aging. For this purpose, a comparison between the results of four-point bending tests (4PB) at the age of 1 year and 10 years was carried out and it indicates that aging affects the serviceability post-cracking residual strength, increasing fibre interfacial bond strength. Material classification is performed according to fib Model Code 2010 for 1-year old and 10-year old specimens. The objective is to estimate possible changes in the material class through the years. Three-and four-point bending test results on 10-year old specimens are described, together with a comparison between those tests. Both tests showed very similar results; slightly higher values were obtained with the three-point bending (3PB) test. The tensile constitutive law is obtained according to fib Model Code 2010 and is compared with results of direct tensile tests on cylindrical specimens and Double Edge Wedge Splitting tests on prismatic specimens. A plane section (PS) approach adopting the tensile constitutive law is applied to predict the bending behaviour in terms of nominal stress against crack mouth opening displacement and it is compared with the bending test results.
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