A NEW EXPLANATION FOR SIZE EFFECTS ON THE FLEXURAL STRENGTH OF CONCRETE

The size dependence of the flexural strength of concrete beams is disc ussed. It is shown that existing approaches fail to predict the streng th of real-sized structures. The scaling of the modulus of rupture sig ma(u) can be consistently modelled by means of a multifractal scaling law the influence of microstructural disorder being predominant for th e shallowest beams. At larger scales, homogenisation comes into play, leading to the definition of an asymptotic constant strength f(t). Thi s transition occurs more rapidly in the case of high-strength concrete , where a mol-e brittle behaviour is observed, accompanied by the rapi d vanishing of size effects. Validation of the law is pursued by means of best-fitting of relevant experimental data, which allows for deter mination of the asymptotic value of sigma(u), valid for real-sized mem bers.