Title: Bond Characteristics of High-Strength Steel Reinforcement

Author(s): Sami Rizkalla, Raafat El-Hacha, and Hossam Elagroudy

Publication: Structural Journal

Volume: 103

Issue: 6

Appears on pages(s): 771-782

Keywords: bond; confinement; flexure; splice; strength; steel

DOI: 10.14359/18227

Date: 11/1/2006

Abstract:
This paper summarizes an investigation undertaken to study the bond characteristics of high-strength steel reinforcement bars commercially known as microcomposite, multistructural, formable steel (MMFX). The objective of the investigation is to examine the applicability of the ACI 318-02 equation and a current proposed equation by Zuo and Darwin on bond behavior of steel reinforcement to the concrete member. The experimental program included two phases. The first phase of the experimental program consisted of testing four beam-end specimens reinforced with MMFX steel bars, whereas the second phase included testing eight beam-splice specimens reinforced with MMFX steel bars. The selected four factors considered in this study were bar size, level of confinement, bonded length, and bar cast position. The bond behavior of the MMFX steel bars was found to be similar to that of conventional Grade 420 MPa (60 ksi) steel up to the proportional limit of 550 MPa (80 ksi). The bond strength of the MMFX significantly changes as the tensile stresses developed in the bar exceed the proportional limit. The test results indicated that both the ACI 318-02 equation and the current proposed equation by Zuo and Darwin on bond are adequate and resulted in conservative prediction at low stress levels up to 550 MPa (80 ksi). At high stress levels, however, the prediction using both equations is unconservative due to the nonlinear behavior of the MMFX stress-strain relationship. Based on the limited number of specimens considered in this study, modification to both the ACI 318-02 equation and the Zuo and Darwin equation is proposed to predict the bond forces beyond the proportional limit for MMFX steel bars.