Formulation of Mathematical Model for Stress-Strain Relationship of Normal and High Strength Concrete Under Compression

The research includes a new model proposed for the stress-strain relationship of unconfined concrete in compression valid for normal and high strength concrete. A wide range of experimental data with varied lab circumstances has been used for fitting and other data for verifying the model. It is noted that the current model has a good agreement with the experimental data for both its ascending and descending branches in normal and high strength concrete depending on the mean of average values of experimental to calculated stresses, coefficient of variation, and difference ratio. Where values of the average experimental to calculated stresses ranged from 0.723 to 1.354 for 38 samples with a mean of 0.994, while the coefficient of variation values ranged from 16.099 to 48.562 with a mean of 27.704 % for these specimens. Also, difference ratio values ranged from 0.86 % to 31.804 % with a mean of 9.009 % for these specimens. The model gives the best results in comparison with other models.