Crack-based analysis of concrete with brittle reinforcement

Brittle reinforcement (such as fibre-reinforced plastic) is being developed as an alternative to traditional steel reinforcement. The lack of ductility in a brittle-reinforced beam means that there is very little potential for stress redistribution, and the lower-bound theorem of plasticity (which allows many of the assumptions made in steel-reinforced concrete analysis) cannot be applied. Analysis of brittle-reinforced concrete must be based on a detailed examination of compatibility requirements within a beam, of which the cracks form an important part. A crack-based model is developed in this article, based on compatibility requirements where reinforcement crosses a crack, and compatibility in the compression-zone concrete. The analysis incorporates dowel-rupture of the reinforcement, and the reduced strength of a corner of a stirrup. It highlights the need for further research into flexure-shear of the compression zone, dowel-splitting, and local failure of the concrete. The crack-based model is used to illustrate the importance of compatibility in both the flexural and shear analysis of brittle reinforced concrete. In particular, the current proposals for shear design (which assume pseudo-plastic reinforcement) are examined, and contrasted with compatibility requirements within the beam.