Elasto-plastic multi-fixed smeared crack model for concrete

Relatório 04-DEC/E-0

Modelação de vigas reforçadas com laminados de CFRP inseridos no betão de recobrimento

São descritas as principais características do modelo numérico desenvolvido, que no âmbito do presente trabalho é aplicado na análise de estruturas de betão reforçadas com laminados de CFRP inseridos no betão de recobrimento. O desempenho do modelo é avaliado por intermédio da simulação do comportamento registado em ensaios experimentais

Crack constitutive model to simulate the behavior of fiber reinforced concrete structures failing in punching

For some structural applications, mainly with redundant supports, adding fibers to concrete can be an economic strategy, especially when shear brittle failure mode has a high risk of occurrence. In the present work, a crack constitutive model is proposed to simulate localized failure modes due to punching. The performance of the developed constitutive model was appraised by simulating the behavior observed in punching tests with lightweight panel prototypes of steel fiber reinforced self-compacting concrete (SFRSCC). The values of the parameters required by fracture mode I of the SFRSCC were obtained by inverse analysis.Fundação para a Ciência e a Tecnologia (FCT) - projecto POCTI/ECM/57518/2004 “FICOFIRE - High performance fiber reinforced concrete of enhanced fire resistance”, bolsa de doutoramento SFRH/BD/23326/2005

Implementação da técnica do arc-length e métodos relacionados no programa de elementos finitos FEMIX

Relatório 06-DEC/E-2

Software no ensino e no projecto de estruturas

No presente trabalho descrevem-se os aspectos essenciais do software desenvolvido para a análise linear e não linear de estruturas, baseado nas técnicas do MEF e concebido de forma a ser simples e eficiente a implementação de novos tipos de elementos finitos e de novos modelos constitutivos. A estrutura da informação que serve de base a uma análise linear ou não linear é descrita neste artigo, bem como as características de algumas técnicas computacionais. No final são apresentados alguns exemplos ilustrativos das ferramentas desenvolvidas

Multi-fixed smeared 3d crack model to simulate the behavior of fiber reinforced concrete structures

When a concrete structure is subjected to a multi-stress state, different crack modes can be developed. To simulate with enough accuracy these fracture modes, a three dimensional model must be used. In the present work, a multi fixed smeared 3D crack model is proposed to predict the normal and shear failure modes of concrete structures. Softening stress strain diagrams are proposed to model, after crack initiation, the normal and shear components. The performance of the developed model was appraised by simulating the behavior observed in punching tests with lightweight panels of steel fiber reinforced self compacting concrete (SFRSCC).Fundação para a Ciência e a Tecnologia (FCT) - bolsa de doutoramento SFRH/BD/23326/2005, PABERPRO : Conception and implementation of production system of lightweight steel fibre reinforced self-compacting concrete panels” Program POCI 2010 – IDEIA, nº 13-05-04-FDR-00007, contrato ADI/2007/V4.1/0049

Numerical simulation of the nonlinear behavior of RC beams strengthened with NSM CFRP strips

This paper describes some experimental tests carried out in the context of the evaluation of the bond behavior associated with NSM CFRP reinforcement. These results were used in the numerical simulation of the material nonlinear behavior of RC beams strengthened with NSM strips. For this purpose, an elasto-plastic multi-fixed smeared crack model was developed and implemented in the FEMIX computer code. The obtained numerical results are compared with those recorded in the experimental tests

Bond behavior of near-surface mounted CFRP laminate strips under monotonic and cyclic loading

Near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminate strips are used to increase the load-carrying capacity of concrete structures by inserting them into slits made in the concrete cover of the elements to be strengthened and gluing them to the concrete with an epoxy adhesive. In several cases the NSM technique has substantial advantages when compared with externally bonded laminates. In order to assess the bond behavior between the CFRP and concrete under monotonic and cyclic loading, an experimental program, based on a series of pullout bending tests, was carried out. The influence of the bond length and loading history on the bond behavior was investigated. In this work the details of the tests are described, and the obtained results are discussed. Using the experimental data and an analytical-numerical strategy, a local bond stress-slip relationship was determined. A finite element analysis was performed to evaluate the influence of the adhesive on the global response observed in the pullout bending tests.The first author wishes to acknowledge the grant SFRH/BD/3259/2000 provided by FCT (Portuguese Foundation for Science and Technology) and FSE (European Social Fund). The tests were performed at the Structural Technology Laboratory of the Technical University of Catalonia, Spain, with the help of Miguel Angel Martín and Ernesto Diaz. The authors wish to acknowledge the support provided by S&P and Bettor MBT who supplied the material used in the study

Near surface mounted CFRP strips for the flexural strengthening of RC columns: experimental and numerical research

In the present work, a strengthening technique based on near surface mounted (NSM) carbon fibre laminate strips bonded into slits opened on the concrete cover is used to improve the flexural capacity of columns subjected to bending and compression. This technique avoids the occurrence of the peeling phenomenon, is able to mobilize the full strengthening capacity of the strips, and provides higher protection against fire and vandalism acts. The present paper describes the adopted strengthening technique and reports the experimental characterization of the materials involved in the strengthening process. The results obtained in two series of reinforced concrete columns, subjected to axial compression and lateral cyclic loading, show that a significant increase on the load carrying capacity can be achieved by using the NSM technique. Cyclic material constitutive laws were implemented in a finite element program and the tests with reinforced concrete columns strengthened with the NSM technique were numerically simulated under cyclic loading. These numerical simulations reproduce the experimental load-displacement diagrams satisfactorily.The study reported in this paper is included in the research program "CUTINSHEAR-Performance assessment of an innovative Structural FRP strengthening technique using an integrated system based oil optical fiber sensors" Supported by FCT, POCTI/ECM/59033/2004. The second author acknowledges the support provided by the grant in the ambit of this research project

Stress-crack opening relationship of enhanced performance concrete

Force-deflection responses obtained from three-point bending tests with notched beams of enhanced performance concrete were used to determine, by means of an inverse analysis, the stress at crack initiation, the shape of the stress-crack opening relationship and the fracture energy of this material. This inverse analysis was performed with non-linear finite element software where crack opening and crack propagation were simulated by discrete crack models using interface finite elements. The influence of both the concrete age and the percentage of binder replaced by fly-ash on the fracture parameters was analysed. In the present work, the numerical strategy is described, and the obtained results are presented and analysed.ADI - PABERFIA