Effect of core compaction on deformation capacity of FRP-jacketed concrete columns

Well-established confinement models can adequately estimate the axial strain capacity of FRP-strengthened columns with low-to-moderate confinement, but there is a tendency for overestimation of the effect of FRP-induced confinement on deformation capacity in the range of high confining pressures. Results are particularly evident in the case of existing columns comprising low-strength concrete. For high ratios of lateral pressure over concrete uniaxial strength, concrete compaction due to collapse of the porous structure of the matrix leads to pulverization and volume reduction of the encased core. This, in turn, reduces the Poisson-like lateral dilation phenomena of concrete which engage the FRP jackets thereby reducing their effectiveness as confining devices. This phenomenon is modeled using principles of concrete plasticity and is integrated in established confinement models. Calculated values of deformation capacity using this approach are compared with reported experimental results from 496 specimens tested under compression, of which 169 were reinforced concrete columns, demonstrating significantly improved correlation and dependability of the analytical estimates.