Minimum reinforcement for bending: theory, experiments and comparison with recommendations

Abstract

Minimum reinforcement in building codes in usually calculated in agreement with limit state theories (plasticity), whose results are not size dependent. Nevertheless, lightly reinforced beams show size effect: maximum load grows slower than beam depth in proportional beams, reinforcement ratio and steel characteristics remaining constant. Concrete fracture mechanics catches this size effect: this paper presents a new reinforcement ratio formula, based on fracture mechanics, obtained through a model and an experimental program. This expression is also compared with building codes and another authors formulae. This comparison shows the convenience of revising Spanish EH-91 in this subject, because its minimum reinforcement recommendations do not depend on the beam size and seem to be too conservative.