Size effect in normal and high-strength concrete cylinders subjected to static and dynamic axial compressive loads

Concrete structures have traditionally been-designed on the basis of strength criteria. This implies that geometrically similar structures of different sizes should fail at the same nominal stress. However, this is not quite true in many cases because of the Size Effect, which may be understood as the dependence of the concrete structure on its characteristic dimension. The Size Effect in normal strength concrete (NSC) is a phenomenon explained by a combination of plasticity and fracture mechanics, and it is related to the energy balance during the damage/fracture process which causes a change in the mode of failure of the concrete member with the increase in its size, thus causing a reduction in its strength. In this study, the Size Effect phenomenon was investigated under compressive static and impact loads for both normal and high-strength concrete cylinders. This study was conducted by performing 127 compressive static and impact tests on both normal and high strength concrete and 192 numerical simulations. The tests provided data whose analysis produced evidence on the effect of loading rate and material strength on the Size Effect for structural concrete in compression Parallel pre- and post-test computational simulations were used to perform 'numerical tests' of the same specimens, and to explore the role of the time dimension on the physical phenomena that contribute to the Size Effect. Comparisons between test and numerical data assisted and guided the investigators in identifying the governing parameters that define the physical phenomena. In addition, the precision test data assisted in validating the computational tools used for the study. Two material models were developed to simulate the dynamic Size Effect that was proved to exist in this study. The study also proved the existence of Size Effect in parameters other than strength such as the modulus of elasticity and the strain at maximum stress. This necessitated modifying the existing Size Effect which was mainly confined to the strength parameter only. Use of high-speed photography enabled the detection of several modes of failure experienced by concrete cylinders subjected to axial impact. (Abstract shortened by UMI.)...