where r , m are empirical constants ( r n d / m < 1 ). The deterministic formula (5) is recovered as the limit case for m → → ∞ ∞ . (Fig. 2d) shows a comparison of the last formula with the test results for many different concretes, plotted as dimensionless strength σ σ N / f t ′ versus dimensionless structure size D / D 0 .