Softening behaviour of concrete prisms under eccentric compressive forces

Abstract

The behaviour of reinforced concrete elements has been analysed by means of tests on prisms subjected to normal forces with different degrees of eccentricity. The tests were performed in strain-controlled conditions until failure. Along the fibres running parallel to the axis of the specimen, stress–strain curves are seen to be homogeneous before peak load is reached, whereas the deformations measured in the softening branch are more scattered and are found to depend on gauge length due to strain localisation within the compressive zone. This behaviour is also verified for specimens subjected to centred compression and makes it difficult to define the stress–strain plot in the softening branch. By assuming a σ–ε constitutive law based on the deformation measured over a predetermined gauge length in centred compression tests, the results of tests conducted with eccentric loads were compared to those obtained under the commonly accepted assumption of plane section remaining plane and the possibility of stress integration. In this case, all specimens were of the same size and the measurements were performed over the same gauge length. The maximum loads obtained experimentally for each test were seen to be higher than the theoretical loads and to increase in percentage with increasing eccentricity. Since increasing eccentricity corresponds to a decrease in the size of the compression zone, it can be inferred that the scale effect on the compressive strength of concrete is a function of the height of the compression zone.