Cyclic stress-strain behavior of reinforcing steel including effect of buckling

It is expected that during strong earthquakes, longitudinal reinforcing steel in reinforced concrete structural elements may undergo large tension and compression strain reversals. Because of insufficient tie spacing, this repeated loading into the inelastic range may lead to buckling of steel reinforcing bars. Even though this problem has been studied by several researchers, most of these studies have been based on monotonic behavior. In this research, steel coupons were machined from steel reinforcing bars conforming to most of the ASTM A 706 specifications. These specimens were tested under axial-strain-controlled monotonic and reversed cyclic axial loading. The tests were performed until the specimens failed, in all cases under compressive loading. To study the effects of the ratio of spacing of lateral supports (S-h) to bar diameter (D) on reinforcement stability, tests were performed for S-h/D ratios of 2.5, 4, 6, and 8. Based on observed buckling behavior in reinforcing bars under cyclic (reversed) loading, a procedure is proposed for predicting onset of buckling. The use of this procedure, along with an analytical model proposed in I:he Literature for the cyclic behavior of reinforcing steel, gave results that were in good agreement with experimental results obtained in this study.