Axial compressive behaviour of hybrid FRP confined concrete

Abstract

Fibre Reinforced Polymers (FRP) composites can be effectively used as passive confinement system of concrete columns. Regarding to this option, however, two main drawbacks can be pointed out: (i) in several cases the ultimate lateral strain in the confinement is significantly lower than the tensile strain at failure of the composite, and (ii) the conventional composites experience brittle failure, in an explosive manner in the case of confined concrete without warning which, associated with insufficient residual integrity, requires conservative design. In the present work, different combinations of the following dry unidirectional fabric materials were adopted in materialization of confining systems of concrete cylinders under axial loading: high-modulus carbon, standard carbon and E-glass. From the obtained results it is demonstrated that hybridisation can effectively contribute to maximize the lateral strain efficiency of FRP, exploiting the known hybrid effect of this innovative solution. Furthermore, it also is demonstrated that pseudo-ductile responses are obtained with high-modulus carbon/E-glass combination, which contributes to the elimination of the brittle failure of system. An existing analysis-oriented confinement model in the literature for non-hybrid FRP was satisfactorily modified to predict both: (i) dilation behaviour and (ii) compressive stress-strain behaviour of hybrid confined concrete.