Mário Pimentel

The Effect of Fibre Orientation on the Uniaxial Tensile Response of UHPFRC: Experimental Evaluation and Analytical Modelling

The tensile strength of Ultra-High Performance Fibre-Reinforced cementitious Composites (UHPFRC) depends primarily on the properties of the matrix and fibre’s length and geometry, but can also vary significantly according to the fibre orientation. In this study an experimental campaign is developed involving 22 uniaxial tensile tests on UHPFRC specimens with varying fibre content (1.5% and 3% in volume) and fibre orientation profiles (well oriented, randomly oriented and poorly oriented). The different fibre orientation profiles were obtained using a magnetic setup for orienting the fibres along a pre-defined direction during casting. The fibre orientation profiles were quantitatively analysed using image analysis algorithms, allowing the determination of fibre orientation angle distributions and other scalar fibre orientation indicators.

Modelling and Experimental Characterization of the Tensile Response of Ultra-High Performance Fibre-Reinforced Cementitious Composites

In this research, an experimental programme is developed to investigate the influence of fibre orientation on the tensile behaviour of UHPFRC from micro-mechanics to composite level. The micro-mechanical aspects of fibre reinforcement are analysed by performing single fibre pull-out test on the short fibres embedded in an ultra-high performance cementitious matrix. The influence of fibre embedded length (\( l_{f} /2 \) and \( l_{f} /4 \), l f being the fibre length) and fibre orientation (0°, 30° and 60°) on the pull-out behaviour are appraised. At the composite level, uniaxial tensile tests (UTT) on UHPFRC specimens with varying fibre contents (1.5%, 2.3% and 3.0% volume fractions) and fibre orientation profiles (parallel to the loading direction, randomly oriented and perpendicular to the loading direction) are performed. The different fibre orientation profiles were obtained using a magnetic setup for orienting the fibres along a pre-defined direction during casting. An image analysis technique is employed to determine the fibre orientation angle distributions and other scalar fibre orientation indicators. The results of this experimental programme clearly evidence the effect of fibre orientation not only on the tensile strength, but also on the development of the hardening branch that is typical of this type of cementitious composites.

Determination of the Tensile Response of UHPFRC Layers Using a Non-Destructive Method for Assessing the Fiber Content and Orientation

A procedure is developed for estimating the representative tensile response of existing thin Ultra-High Performance Fiber-Reinforced cement Composite (UHPFRC) layers. The procedure relies on non-destructive (NDT) measurements and on a previous tensile characterization campaign of the composite material, thereby avoiding the extraction of samples from the real structure. Two reliable indicators of the fiber content and fiber orientation within the UHPFRC layer are derived from the NDT measurements along two orthogonal directions. It is shown that these two indicators can be directly correlated to the parameters of a mechanical model providing the tensile response of the composite. The procedure is applied for the prediction of the peak stress of 36 Double-Edge Wedge Split tests and of the structural behavior of slab strips strengthened with a UHPFRC layer.

Avaliação analítica, numérica e experimental de uma viga-parede indiretamente apoiada

O presente trabalho tem por objetivo apresentar os resultados obtidos de uma viga-parede indiretamente apoiada, atraves da avaliacao analitica, numerica e experimental. Trata-se de um caso de dimensionamento complexo, uma vez que tal elemento nao respeita a hipotese de manutencao das secoes planas e deformacoes lineares ao longo da secao. Para o dimensionamento desses elementos deve-se recorrer a metodos que levem em conta essa particularidade, sendo que Metodo das Bielas em parceria com o Metodo dos Elementos Finitos tem se constituido em ferramentas excepcionais para tal atividade. Os resultados apresentados no presente trabalho comprovam a potencialidade dos metodos supracitados na avaliacao de regioes sujeitas a descontinuidades (“Regioes D”), possibilitando racionalidade e seguranca no dimensionamento de estruturas especiais em concreto estrutural.