Nonlinear fracture mechanics investigation on the ductility of reinforced concrete beams

Investigação sobre a ductilidade de vigas de concreto armado com base na mecânica da fratura não-linear

Investigação sobre a ductilidade de vigas de concreto armado com base na mecânica da fratura não-linear

Nonlinear fracture mechanics investigation on the ductility of reinforced concrete beams

A. Carpinteri^I; M. Corrado^II

^IPolitecnico di Torino, Department of Structural Engineering and Geotechnics, [e-mail], Corso Duca degli Abruzzi 24, 10129, Torino, Italy, [e-mail]

^IIPolitecnico di Torino, Department of Structural Engineering and Geotechnics, [e-mail], Corso Duca degli Abruzzi 24, 10129, Torino, Italy, [e-mail]

RESUMO

Neste artigo, um algoritmo numérico baseado no método dos elementos finitos é proposto para a predição da resposta mecânica de vigas de concreto armado carregadas em flexão. A principal novodade de tal abordagem é a introdução do modelo de superposição de fissuras, baseado em conceitos de mecânica da fratura não linear, para descrver o esmagamento do concreto. De acordo com esse modelo, o dano em compressão do concreto é representado por meio de uma interpenetração fictícia. Quanto maior a interpenetração, menores são as forças transferidas através da zona danificada. O conhecido Modelo de fissura coesiva em tração e uma relação tensão versus abertura da fissura elasto-perfeitamente plástica descrevendo o comportamento da armadura de aço são também integrados no algoritmo numérico.

A aplicação do Modelo de Fissura Coesiva superposta para a avaliação da armadura mínima necessária para prevenir propagação ins- tável de fissura por tração e para a avaliação da capacidade rotacional de rótulas plásticas, permite prever efeito escala evidenciado por vários programas experimentais disponíveis na literatura. De acordo com os resultados númericos obtidos, novos fórmulas e diagramas para projeto são propostos para aprimoramento de normas atuais que usualmente desprezam efeito escala.

Palavras-chave: Mecânica da Fratura Não Linear, Concreto armado, capacidade rotacional, efeito escala, prescrições de normas.

ABSTRACT

In the present paper, a numerical algorithm based on the finite element method is proposed for the prediction of the mechanical response of reinforced concrete (RC) beams under bending loading. The main novelty of such an approach is the introduction of the Overlapping Crack Model, based on nonlinear fracture mechanics concepts, to describe concrete crushing. According to this model, the concrete dam- age in compression is represented by means of a fictitious interpenetration. The larger is the interpenetration, the lower are the transferred forces across the damaged zone. The well-known Cohesive Crack Model in tension and an elastic-perfectly plastic stress versus crack opening displacement relationship describing the steel reinforcement behavior are also integrated into the numerical algorithm.

The application of the proposed Cohesive-Overlapping Crack Model to the assessment of the minimum reinforcement amount neces- sary to prevent unstable tensile crack propagation and to the evaluation of the rotational capacity of plastic hinges, permits to predict the size-scale effects evidenced by several experimental programs available in the literature. According to the obtained numerical results, new practical design formulae and diagrams are proposed for the improvement of the current code provisions which usually disregard the size effects.

Keywords: Nonlinear Fracture Mechanics, Reinforced concrete, Minimum reinforcement, Rotational capacity, Size effects, Codes provisions.

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Received: 17 Mar 2010

Accepted: 05 Apr 2010

Available Online: 30 Jun 2010

Publication Dates

• Publication in this collection
  18 Sept 2014
• Date of issue
  June 2010

History

• Received
  17 Mar 2010
• Accepted
  05 Apr 2010