Interrelationships between Reinforcing-Bar Physical Properties and Seismic Demands

Abstract

A theoretical study was performed on the interrelationships between reinforcing-bar physical properties and seismic demands for Grade 60 steel in beams of reinforced concrete rigid frames subjected to a limiting lateral drift of 2%. The study indicates that the generally accepted requirement of a minimum tensile/yield ratio of 1.25 for reinforcing steel in seismic design is both prudent and probably satisfactory. However, considering high steel strains exhibited in the calculations, particularly for beams having a small ratio of length to depth, the study strongly suggests that it would be prudent, for seismic-resistant reinforced concrete structures, to either specify A706 steel or to specify A615 steel to have at least a 10% minimum elongation in 8 in (203 mm). For reinforcing in very squatty beams (with close to the minimum length-to-depth ratio permitted by ACI 318-95), the calculations indicate that the stress-strain curve for the reinforcing steel should not exhibit too low a tangent modulus of elasticity at onset of strain hardening (possibly causing ductility capacity to be exceeded) or too high a tangent modulus (possibly causing tensile strength capacity to be exceeded).