Size effect tests of torsional failure of plain and reinforced concrete beams

The current design code formulae for the torsional failure of plain or longitudinally reinforced beams exhibit no size effect, i.e. the failure of geometrically similar beams of different sizes is supposed to occur at the same nominal stress. Experiments on reduced-scale beams were carried out, and the results confirm that there is a significant size effect, such that the nominal stress at failure decreases as the beam size increases. This is found for both plain and longitudinally reinforced beams. The results are consistent with the recently proposed Bažant's size-effect law. However, the scatter of the results and the scope, and range limitations prevent it from being concluded that the applicability of this law is proven.