Experimental Study of Combined Size and Strain Rate Effects on the Fracture of Reinforced Concrete

This paper presents very recent results of an experimental program aimed at disclosing size and strain rate effects on the fracture behavior of reinforced concrete beams. Thirty-six reinforced beams made from two microconcretes with different Hillerborg’s characteristic length [one is $66\mathrm{mm}$ (material A), the other is $105\mathrm{mm}$ (material B)], of three sizes (75, 150, and $300\mathrm{mm}$ in depth), were tested under four strain rates ( $1.05\times {10}^{-5}$ , $1.25\times {10}^{-3}$ , $1.25\times {10}^{-2}$ , and $3.75\times {10}^{-2}{\mathrm{s}}^{-1}$ ). The results show that the peak loads increase with an increase in the strain rate; the rate dependence of the peak load is stronger for larger specimens than for smaller ones. Moreover, size effect is only shown under the nominal strain rate $1.05\times {10}^{-5}{\mathrm{s}}^{-1}$ ; under the higher strain rates, it is inconspicuous. These results seem to reveal an apparent physical inconsistency, since there is no obvious reason that the size effect disappears when the strain rate increases. The explanation to this is sought numerically using an explicit cohesive model.