Effectiveness of High-Strength Hoops in High-Strength Flexural Members

This paper evaluates cyclic behavior of reinforced concrete (RC) flexural members using high-strength steel and concrete materials. The specified yield strength (f(y)) of high-strength longitudinal and transverse reinforcement used in this study is 100 and 115 ksi (690 and 785 MPa), respectively. A total of 10 specimens were tested under displacement reversals. The primary test parameters were the ratio between transverse reinforcement spacing and longitudinal bar diameter (s/d(b) ratio), hoop configuration, and specimen-normalized shear demands. Test results showed that all specimens achieved flexural capacity before failure initiated by buckling of longitudinal reinforcement. Among the three hoop configurations investigated in this study, specimens with welded one-piece close hoops exhibited the largest deformation capacity with all other conditions being equal to each other. A usable shear strength between 54 and 120 ksi (375 and 827 MPa) was observed in the specimens using high-strength transverse reinforcement. A maximum s/d(b) of 6 appears to be acceptable for the high-strength longitudinal reinforcement in specimens with shear demand of 3.5 root f(c)' (psi) (0.29 root f(c)' [MPa]) or less. Those specimens exhibited a minimum drift capacity of 4.8%. For specimens with shear demand of approximately 5.5 root f(c)' (psi) (0.46 root f(c)' [MPa]), a minimum deformation capacity of 3.5% drift can be achieved by limiting the s/d(b) to less than 5.