SIZE EFFECT LAW FOR NOMINAL STRENGTH OF STIRRUP-CONFINED CIRCULAR CONCRETE COLUMNS UNDER AXIAL COMPRESSION

The failure modes and mechanisms of reinforced concrete (RC) members are far different from those of the concrete material. It is therefore debatable to use the size effect theory and formula based on the concrete material to describe the size effect of RC members. Moreover, the size effect formula of the concrete material is difficult to describe the influence of other important structural parameters on the size effect of RC structural members. Taking circular concrete columns confined by stirrups for the research objects, combined with the physical test and numerical results, the main parameter of stirrup ratio that affects the size effect of nominal compressive strength was revealed. Furthermore, combined with the influence mechanism of the confining effect on the axial compressive strength of RC columns and based on the basic theory of the Size Effect Law (SEL) proposed by Bažant, a semi-theoretical and semi-empirical formula for the size effect of the uniaxial compressive strength of stirrup-confined RC columns was established. The experimental and numerical results in the present study as well as other experimental data verify the accuracy and rationality of thesemi-theoretical and semiempirical formula of the size effect on the RC member level.