Numerical prediction of the ultimate condition of circular concrete columns confined with a fiber reinforced polymer jacket

Circular concrete columns confined with a fiber reinforced polymer (FRP) jacket fail because of the rupture of the FRP jacket due to hoop tension at an average hoop strain considerably lower than the FRP tensile strain at failure obtained from tensile tests of flat coupons. This well-established phenomenon, referred to as premature rupture, is governed by the interaction between a heterogeneous material (i.e., concrete) and a brittle material (i.e., FRP) and has been difficult to explain. The present study adopts a meso-scale model, the so-called Lattice Discrete Particle Model (LDPM), for the simulation of concrete, in conjunction with the Spectral Stiffness Microplane Model (SSMM) for simulating the fracturing behavior of the FRP jacket. The numerical predictions, experimentally validated, demonstrate clearly that due to the heterogeneity of concrete, the circumferential strain is highly non-uniform around the circumference of the column right from the beginning of the loading process rather than uniform as conventionally assumed or expected. This strain non-uniformity is the main reason for the premature rupture of the FRP jacket. In addition, stress concentrations at the finishing end of the FRP jacket are also shown to have a significant effect on the premature rupture of the FRP jacket.