PROPOSED MODIFICATION TO THE ACI 318-02 CODE EQUATIONON BOND STRENGTH FOR MMFX STEEL

摘要

This paper summarizes an investigation undertaken to study the bond characteristics ofMicro-composite Multi-structural Formable reinforcing steel rebars, commercially known as MMFX, withconcrete. The objective of the investigation is to examine the applicability of the current equation of theACI 318-02 Code on bond to predict the bond capacity of the MMFX steel rebars. The experimentalprogram consisted of testing eight beam-splice specimens reinforced with MMFX steel rebars. The bondbehaviour of the MMFX steel rebars was found to be similar to that of conventional Grade 420 MPa (60ksi) steel up to the proportional limit of 550 MPa (80 ksi). The bond strength of the MMFX significantlychanges as the tensile stresses developed in the rebar exceed the proportional limit. Therefore, testresults indicated that the current ACI 318-02 Code equation on bond is adequate and resulted inconservative prediction at low stress levels. However, at high stress levels, the prediction isunconservative due to the nonlinear behaviour of MMFX stress-strain curve. This paper proposes amodification to the ACI 318-02 Code equation, using same format, to predict the bond forces beyond theproportional limit for MMFX steel rebars.