Aggregate size effects and general static loading response on mechanical behavior of passively confined concrete

There exist limited studies on the size effects on mechanical behavior of confined concrete subjected to general three dimensional (3D) loading conditions. In this study, a novel general 3D loading test system is applied to create passive confinement. Concrete cube specimens were tested to examine the size effects on the material stress-strain behavior. Based on the conceptual design of the confining system, models are proposed for the confining pressure and confining rigidity for 3D passive confinement. Using test data and for non-uniform confined concrete, increasing stress and lateral strain with increases in axial strain can be established. The size effect on 3D stress-strain relationship is scrutinized and compared to stress-strain relationship benchmarks available. It is observed that the compressive stress and strain are related to the confining rigidity and size. The size shows a significant effect on the transition stress. A new model is proposed to illustrate the transition stress based on the conceptual design of confining plates. Furthermore, a new stress-strain model for confined concrete is also proposed based on test results.