Effect of Length on Compressive Strain Softening of Concrete

The concept of localization during the postpeak of compressive strain softening is presented. To explore localization in compression, a feedback-control method using a linear combination of displacement and force that partially subtracts the elastic response of the specimen to give a stable feedback signal is used. Results are presented from two test series (45 and 90 MPa) that use this method to test cylinders with length-to-diameter ratios ranging from 2.0 to 5.5 It is shown that compression failure is in fact a localized phenomenon. The compressive fracture energy is divided into energy dissipated in the prepeak and the postpeak portions of the stress-deformation response. It is found that the amount of energy required to propagate the compression failure during postpeak is independent of length for this range of specimens. The compressive fracture energies are compared for the normal and high-strength concretes.