Since high strength concrete is sensitive to defects and crack propagation, the measured compressive strength seems to be affected by such characteristics of testing machine as platen size, geometry of bearing block and stiffness that have been latent in conventional concrete. The paper deals with experiments and finite element analyses which were carried out to clear the effects of pinned and fixed behabiour of spherical bearing block on the measured strength, the distribution of stress and the failure mode of specimens. The results show that tilting of spherical bearing block under load produces increasingly erroneous results for higher strength concrete. It is recommended that spherical bearing block should be effectively locked during loading high strength concrete by being lublicated with a petroleum-type mobile oil.
