INTERRELATIONSHIPS BETWEEN REINFORCING-BAR PHYSICAL-PROPERTIES AND SEISMIC DEMANDS

A theoretical study was performed on the interrelationships between re inforcing-bar physical properties and seismic demands for Grade 60 ste el in beams of reinforced concrete rigid frames subjected to a limitin g lateral drift of 2 percent. The study indicates that the generally a ccepted requirement of a minimum tensile/yield ratio of 1.25 for reinf orcing steel in seismic design is both prudent and probably satisfacto ry. However considering high steel strains exhibited in the calculatio ns particularly for beams having a small ratio of length to depth, the study strongly suggests that it would be prudent for seismic-resistan t reinforced concrete structures, to either specify A706 steel or to s pecify A615 steel to have at least a 10 percent minimum elongation in 8 inches (203 mm). For reinforcing in very squatty beams (with close t o the minimum length-to-depth ratio permitted by ACI 318-95) the calcu lations indicate that the stress-strain curve for the reinforcing stee l should not exhibit too low a tangent modulus of elasticity at onset of strain hardening (possibly causing ductility capacity to be exceede d) or too high a tangent modulus (possibly causing tensile strength ca pacity to be exceeded).