Bond Characteristics of ASTM A1035 Steel Reinforcing Bars

The results of a coordinated research program on the bond characteristics of the high-strength steel reinforcing bars that conform to ASTM A1035 are presented. Concrete with nominal strengths of 5000 and 8000 psi (35 and 55 MPa) were used. Sixtynine large-scale beam-splice specimens were tested. Maximum bar stresses are compared with predictions obtained using the bond equations in the ACI 318-05 code provisions and those proposed by ACI Committee 408. Maximum stress levels of 120, 110, and 96 ksi (830, 760, and 660 MPa) were developed in No. 5, No. 8, and No. 11 (No. 16, No. 25, and No. 36) bars, respectively, not confined by transverse reinforcement. Providing confinement for No. 8 and No. 11 (No. 25 and No. 36) spliced bars using transverse reinforcement allowed stresses of up to 150 ksi (1035 MPa) to be developed. The ACI Committee 408 equation provides a reasonable estimate of the strength for both unconfined and confined splices using a strength reduction factor (f-factor) of 0.82 and design parameters (cover, spacing, and concrete strengths) comparable to those used in this test program. The design equations in ACI 318 are less conservative, with a large percentage of the developed/calculated strength ratios below 1.0, and should not be used for development and splice design with high-strength reinforcing steel in their present form.