Size effect of concrete under uniaxial and flexural compression

Abstract

This paper presents an analytical and a numerical approach to evaluate the size (slenderness) effect on the post-peak behavior of concrete in compression. The analytical approach takes into account the specimen height in the calculation of the ductility of plain concrete under uniaxial compression and the uniform moment zone length in the calculation of the ductility of reinforced concrete beams. The uniaxial compressive response of concrete is considered using a strain localization-based approach that accounts for the size-dependent stress-strain response. The type of modeling used in this work is conceptually similar to the one considered previously for localization of deformations under tensile loading. The compressive response of concrete is modelled by dividing the response into bulk and damaged sections. These different responses are used in the formulation of a simple approach for predicting the size-dependent moment-strain response of reinforced beams under pure bending. The decrease in post-peak ductility of longer reinforced concrete beams is captured by accounting for the effects of damage localization in the compression zone of the beam. A numerical modeling using the computer program DIANA was carried out to evaluate the size dependence for concrete in compression. The non-linear hardening model of Thorenfeldt and the non-linear softening model of Hordijk had been used together with smeared crack models. In addition, recent experimental results of beams with different sizes have been found to correlate reasonably well with the ones predicted by both the analytical approach and the numerical modelling.