Effect of non-uniform straining in concrete compressive strength tests

If a concrete specimen is tested to failure in compression and the machine allows the longitudinal strain in the specimen to be non-uniform over the cross-section of the specimen at its maximum load, then that load is lower than it would be if the strains were uniform. The results of an experimental study on the magnitude of the effect of non-uniform straining on apparent concrete strength are presented, showing how it varies for low, medium, and high strength concrete. Simple theoretical modeling is shown to reproduce the measured results well. Suggestions are also included for the application of the information presented.