Numerical simulation of galvanized rebars pullout

The usage of rebars in construction is the most common method for reinforcing plain concrete and thus bridging the tensile stresses along the concrete crack surfaces. Usually design codes for modelling the bond behaviour of rebars and concrete suggest a local bond stress – slip relationship that comprises distinct reinforcement mechanisms, such as adhesion, friction and mechanical anchorage. In this work, numerical simulations of pullout tests were performed using the finite element method framework. The interaction between rebar and concrete was modelled using cohesive elements. Distinct local bond laws were used and compared with ones proposed by the Model Code 2010. Finally an attempt was made to model the geometry of the rebar ribs in conjunction with a material damaged plasticity model for concrete

Pullout behaviour of hooked-end steel fibres in self-compacting concrete

Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/18002/2004

Analytical model for bond-slip of hooked-end steel fibres

In this work an analytical model for obtaining the local bond stress-slip relationship of hooked-end steel fibres is presented. The mathematical representation of the pullout problem is described and the numerical algorithm of the model is detailed. Furthermore, the performance of the developed model is assessed using results obtained in fibre pullout experimental tests

An integrated approach for modelling the tensile behaviour of steel fibre reinforced self-compacting concrete

The present work resumes the experimental and numerical research carried out for the development of a numerical tool able of simulating the tensile behaviour of steel fibre reinforced self-compacting concrete (SFRSCC). SFRSCC is assumed as a two phase material, where the nonlinear material behaviour of SCC matrix is modelled by a 3D smeared crack model, and steel fibres are assumed as embedded short cables distributed within the SCC matrix according to a Monte Carlo method. The internal forces in the steel fibres are obtained from the stress - slip laws derived from the executed fibre pullout tests. The performance of this numerical strategy was appraised by simulating the tensile tests carried out. The numerical simulations showed a good agreement with the experimental results.The first author acknowledges the support provided by the grant SFRH/BD/18002/2004. The study reported in this paper forms a part of the research program PONTALUMIS, Project no. 3456, QREN. The authors also acknowledge the support of Civitest Company on the production of the SFRSCC specimens

Bond-slip mechanisms of hooked-end steel fibers in self-compacting concrete

The experimental results of hooked-end steel fibers pullout tests on a self-compacting concrete medium are presented and discussed in this work. The influence of fiber embedment length on the fiber pullout behavior is studied. The role of the end hook of the fiber on the overall pullout behavior is also investigated by carrying out tests with fibers without its end hook, in order to separate the contribution of the frictional bond component from those derived from the mechanisms provided by the end hook of the fiber. Finally, the experimental bond-slip relationships are modeled by an analytical model

Modelação analítica da influência da idade de betão auto-compactável reforçado com fibras de aço no seu comportamento à compressão

Neste artigo são apresentados os resultados de ensaios à compressão uniaxial em provetes de betão auto-compactável reforçado com fibras de aço, BACRFA. A influência da idade nas propriedades mecânicas do BACRFA é aferida. Adicionalmente, propõem-se relações tensão-extensão para modelar o comportamento à compressão do BACRFA, e recomendam-se expressões analíticas para determinar as principais propriedades mecânicas deste compósito.O estudo reportado neste artigo é parte integrante do programa de investigação: “Prefabricated sandwich steel fibre reinforced panels” cofinanciados pela FEDER e MCT, e promovido pela ADI. Este projecto envolve as empresas PREGAIA e CIVITEST, e a Universidade do Minho. Os autores agradecem os materiais gentilmente cedidos pela Bekaert (fibras), SECIL (cimento), Degussa (superplastificante) e Comital (filler calcário). O primeiro autor deseja, igualmente, agradecer à FCT pela bolsa concedida, SFRH/BD/18002/2004

Influência da geometria e propriedades mecânicas de fibras de aço no desempenho ao arrancamento

A eficiência de uma fibra como meio de transferência de tensões é frequentemente determinada por intermédio de ensaios de arrancamento, sendo o deslizamento da fibra monitorizado em função da força de arrancamento aplicada na fibra. Nas últimas três décadas, vários fabricantes introduziram no mercado fibras com geometria melhorada, reivindicando melhores desempenhos comparativamente com as fibras lisas. Hoje em dia as fibras adicionadas a uma matriz cimentícia possuem, em geral, uma ancoragem mecânica. Recorrentemente, as fibras são produzidas por deformação mecânica das suas extremidades em forma de ganchos, cones, remos, etc. Não obstante, devido a diferentes materiais e processos de fabrico, as propriedades mecânicas das fibras como, a resistência à tracção, a eficiência da ancoragem mecânica diferem entre os vários fabricantes, mesmo considerando o mesmo tipo de fibra. Estas diferenças têm influência no comportamento ao arrancamento de uma fibra e, consequentemente, no comportamento mecânico de um material compósito reforçado com fibras. No presente trabalho é realizada uma análise comparativa de três tipos de fibras de aço com ancoragens em forma de gancho produzidas por três fabricantes distintos. A influência da variação das dimensões da geometria das fibras e das propriedades mecânicas destas no comportamento ao arrancamento foi avaliada. Ensaios à tracção e de arrancamento com fibras dos distintos fabricantes são apresentados, sendo analisados os resultados obtidos

Compression behaviour of steel fibre reinforced self-compacting concrete : age influence and modeling

Technical report 06-DEC/E-0

Numerical simulation of three-point bending tests : two distinct approaches

In this work are presented and discussed the numerical simulations carried out for indirect tensile tests of steel fibre reinforced self-compacting concrete specimens. The post-cracking behaviour was modelled with two distinct approaches. Within the scope of the first one, the s-w relationships were obtained by an inverse analysis procedure up to distinct ultimate crack widths. The other approach consisted on modelling the behaviour of the composite based upon the micro-mechanical behaviour of the fibres. For this purpose the composite was modelled as two-phase material under the FEM basis, with an unreinforced concrete matrix phase (paste + aggregates) and a fibre phase. The fibre phase comprises information about fibre density and orientation depending on where and how the material is applied