The reduction phenomena of compressive strength with the size for the concrete is an important topic. However, in the present, appropriate analytical or experimental techniques of understanding this condition have still not been found. The research described herein were conducted to find out the size effect on the compressive strength of concrete members in two fields (i.e. axial compression and flexural compression).
In the first field, the fracture mechanics type size effect on the compressive strength of cylindrical concrete specimens was studied, with the diameter and the height/diameter ratio of cylinder considered as the main parameters. For this purpose, theoretical and statistical analyses were conducted. The test results from literatures were curve fitted using Least Square Method(LSM) to obtain the new parameters for Modified Size Effect Law(MSEL). The proposed equation shows good agreement with the existing test results for concrete cylinders.
In the second field, the size effect of a flexural compression member was investigated by experiments. For this purpose, a series of C-shaped specimens subjected to axial compressive load and bending moment was tested.
Size effect was apparent, i.e., the flexural compressive strength at failure decreases as the specimen size increases. New parameter values of MSEL are suggested which well predicts the reduction phenomena of the strength. The MSEL curve graphed with new parameters is compared with uniaxial compressive strength of concrete cylinder test results. And the results show a much stronger size effect in C-shaped member compared to the cylinder members.
Length and thickness effect of a flexural compression member was also investigated by experiments. Effect of specimen length and thickness were apparent. New parameter values of MSEL are suggested which well predicts the reduction phenomena of the strength. More general parameter values of MSEL are also suggested using the existing data. For C-shaped specimens with a length-to-depth ratios greater than 3.0, length effect of flexural compressive strengths is not apparent.
