Bond-slip models for super ductile TMT bars with normal strength concrete exposed to elevated temperatures

Abstract

This paper presents the outcomes of an experimental study carried out to investigate the residual bond behavior of normal strength concrete with super ductile thermo-mechanically treated (SD TMT) reinforcing steel bars exposed to elevated temperatures. SD TMT bars category is relatively new compared to conventional reinforcing steel due to special chemical and post-rolling treatment making the rebars more ductile and suitable for earthquake-prone areas. SD TMT provides better bonding characteristics with concrete due to distinctive and unique rib patterns, greater rib height, closer rib spacing, and steep rib face angle. For this objective, cylindrical pullout specimens were prepared as per RILEM specifications with normal strength concrete and SD TMT bars of sizes (8 mmØ, 10 mmØ, 12 mmØ, 16 mmØ and 20 mmØ) and embedment lengths of 5 times rebar diameter. The specimens were exposed to elevated temperatures (200 °C, 400 °C, 500 °C, 600 °C, 700 °C & 800 °C) and then cooled down to ambient conditions. The specimens were tested in a displacement controlled UTM in pullout mode to failure. The slip of the rebar, at the loaded as well as the unloaded end, was recorded through a set of linear variable displacement transducers (LVDT) arrangement. The study presents unique bond-slip response curves depicting the overall behavior of the bond mechanism. A detailed account of the test results, analysis, discussion, and comparisons with information previously available from literature is presented. The results showed better bond behavior of SD TMT bars with concrete after exposure to elevated temperatures. Based on test results, a correlation is proposed for the bond-slip model as well as bond-temperature interaction and resulting degradation. The findings of this study have direct implications on procedures used for predicting the post heated behavior of structural elements.