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Open AccessArticle

Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys

1
Institute of Structural Engineering, Department of Civil Engineering and Natural Hazards, University of Natural Resources and Life Science (BOKU), Vienna 1190, Austria
2
IPEK—Institute of Product Engineering at Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
3
Department of Structural Engineering, Ghent University, 9052 Ghent, Belgium
*
Author to whom correspondence should be addressed.
Materials 2019, 12(3), 345; https://doi.org/10.3390/ma12030345
Received: 30 November 2018 / Revised: 16 January 2019 / Accepted: 18 January 2019 / Published: 22 January 2019
(This article belongs to the Special Issue Shape Memory Alloys (SMAs) for Engineering Applications)
Iron based shape memory alloys (Fe-SMA) have recently been used as active flexural strengthening material for reinforced concrete (RC) beams. Fe-SMAs are characterized by a shape memory effect (SME) which allows the recovery of previously induced plastic deformations through heating. If these deformations are restrained a recovery stress is generated by the SME. This recovery stress can be used to prestress a SMA applied as a strengthening material. This paper investigates the performance and the load deformation behavior of RC beams strengthened with mechanical end anchored unbonded Fe-SMA strips activated by sequentially infrared heating. The performance of a single loop loaded and a double loop loaded SMA strengthened RC beam are compared to an un-strengthened beam and a reference beam strengthened with commercially available structural steel. In these tests the SMA strengthened beam had the highest cracking load and the highest ultimate load. It is shown that the serviceability behavior of a concrete beam can be improved by a second thermal activation. The sequential heating procedure causes different temperature and stress states during activation along the SMA strip that have not been researched previously. The possible effect of this different temperature and stress states on metal lattice phase transformation is modeled and discussed. Moreover the role of the martensitic transformation during the cooling process on leveling the inhomogeneity of phase state in the overheated section is pointed out. View Full-Text
Keywords: iron-based shape memory alloys; strengthening RC beams; sequential activation; infrared heating iron-based shape memory alloys; strengthening RC beams; sequential activation; infrared heating
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MDPI and ACS Style

Strieder, E.; Aigner, C.; Petautschnig, G.; Horn, S.; Marcon, M.; Schwenn, M.; Zeman, O.; Castillo, P.; Wan-Wendner, R.; Bergmeister, K. Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys. Materials 2019, 12, 345.

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