Bond behavior of iron-based shape memory alloy reinforcing bars embedded in concrete
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ORIGINAL ARTICLE
Bond behavior of iron-based shape memory alloy reinforcing bars embedded in concrete Ghassan Fawaz . Juan Murcia-Delso
Received: 4 November 2019 / Accepted: 12 August 2020 RILEM 2020
Abstract Iron-based shape memory alloys (FeSMA) have shown a strong potential for strengthening applications in concrete structures. This paper presents an experimental study on the bond strength and bondslip behavior of ribbed Fe-SMA bars embedded in concrete. A total of nineteen pullout tests were conducted to study the bond behavior of 16-mm FeSMA bars embedded in concrete specimens with different levels of passive confinement. Prior to specimen fabrication, the bars were pre-strained (at 4% or 8%) and then activated by resistive heating after concrete casting. The experimental study considered different activation temperatures (160 C, 300 C, and no activation) to evaluate their effects on bond performance. Five specimens with conventional steel bars were also tested to establish a direct comparison with conventional reinforcement. Unconfined pullout specimens failed by splitting of concrete in most of the cases, while confined specimens presented pullout failures and higher bond strengths. In general, the FeSMA bars presented similar bond performance as conventional steel bars. However, the bond strength of unconfined specimens was reduced with the activation
G. Fawaz J. Murcia-Delso (&) Department of Civil, Architectural, and Environmental Engineering, The University of Texas at Austin, Austin, TX 78712, USA e-mail: [email protected] G. Fawaz e-mail: [email protected]
temperature. For confined specimens, the activation temperature had a minor effect on the bond strength. Local bond stress-slip relations derived from tests have also been compared with two analytical bondslip laws available in the literature. Finally, the transfer length of Fe-SMA bars in prestressing applications has been estimated based on the experimental data and a simple analytical model of the bond stress distribution along the embedment length of a bar. Keywords Iron-based shape memory alloys (FeSMA) Reinforcing bar Bond strength Bond-slip behavior Activation temperature Transfer length
1 Introduction Shape memory alloys (SMAs) provide new opportunities for design, repair and strengthening of civil structures owing to their ability to recover strains upon heating, i.e. shape memory effect, and, in some cases, superelastic behavior. A significant number of research studies (e.g. [1–6]) have been conducted in the last two decades on the use of nickel–titanium (Ni– Ti) alloys in civil structures. However, the high production costs of Ni–Ti SMAs limit their potential to be used in the construction industry [7]. More recently, iron-based SMAs (Fe-SMAs) have been explored as a less expensive alternative to Ni–Ti alloys
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in structural applications [8]. In general, Fe-SMAs do not present superelastic properties at ambient temperatures, but they exhibit lower acti
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