Post-peak behavior of concrete specimens undergoing deformation localization in uniaxial compression

It is generally recognized that the failure of concrete in compression is characterized by the localization of deformations in the so-called localized fracture zone. Experimental investigations have shown that this zone is not constant, but gradually extends during the softening process to reach its final length at the complete failure. This paper presents a mechanism of the deformation localization by Mode I crack propagation on a considering the growth of the localized fracture zone. With the proposed mechanism, stress-strain relations for different locations in the localized fracture zone are extracted from the total stress-displacement curves derived from tests of specimens with low boundary restraint and with different sizes and L/D-ratios. Good agreement between calculated and experimental total stress-strain curves implies that the proposed mechanism of the localization of deformations is realistic. The stress-strain curve of the of the localized fracture zone developed at the peak stress is then considered as a material model for unconfined concrete in the modeling of the confinement in reinforced concrete columns with transverse reinforcement.