Tests to determine the modulus of elasticity for CFRP confined concrete columns in stage above the bearing capacity of unconfined concrete

This study covered investigations into the compressive behaviors of concretes strengthened by CFRP of various qualities. Concrete of three strengths were used - 20, 40 and 60MPa in cubic strength. The confined specimens had the size of diameter: 150, 250, 350mm keeping the shape ratio of height to diameter = 3 unchanged. The wrapping was 3, 5 and 7 layers for small size specimens (150mm x 450mm) and 5 layers for medium size (250mm x 750mm). The results were that no scale effect was observed between two dimension ratios of concrete samples. It was shown that the loading paths in the normalized stress space merge to the single master curve determined by the line of the concrete strength as function of the lateral pressure. From this observation follows, that in the nonlinear region the tangent modulus of the confined concrete E2 and differential Poisson ratio a can be expressed a simple formulae. The non-dimensional parameter is a function of only non-dimensional parameter , where the lateral modulus El = Ej h/R ( - radius of specimen, - thickness of carbon confinement, - modulus of confinement). The confined column breaks when the stress in the composite jacket reaches its critical level.