Bond Characteristics of ASTM A1035 Steel Reinforcing Bars

Abstract

This paper presents results from a study of the bond characteristics of high-strength steel reinforcing bars that conform to ASTM A1035. In the study, a total of 69 large-scale beam-splice specimens were independently tested at 3 universities. Concrete with nominal strengths of 5000 and 8000 psi (35 and 55 MPa) were used. Maximum bar stresses were 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. The failure of beams with spliced bars not confined by transverse reinforcement was sudden and produced explosive spalling of the concrete cover over the entire splice length. 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 design equations in ACI 318 showed a large percentage of the developed/calculated strength ratios below 1.0, indicating they should not be used in their present form for development and splice design with high-strength reinforcing steel The ACI Committee 408 equation is more conservative and provides a reasonable estimate of the strength for both unconfined and confined splices using a strength reduction factor of 0.82 and design parameters (cover, spacing, and concrete strengths) similar to those used in this study.