Feasibility of iron-based shape memory alloy strips for prestressed strengthening of concrete structures

Abstract Near-surface mounted reinforcement (NSMR) is a strengthening method for concrete structures, such as buildings or bridges. NSMR involves strips or bars that are glued into grooves in the cover of the concrete. In this paper, a feasibility study is presented that uses iron-based shape memory alloy (Fe-SMA) strips instead of fiber-reinforced polymer (FRP) strips for NSMR. SMAs can more easily be prestressed than FRP. Because prestressing of SMAs does not require any mechanical jacks and anchor heads, the additional openings on the concrete surface beside the grooves that are needed to clamp the NSMR are significantly smaller. The recovery stresses (i.e., the prestresses) were investigated in a tensile testing machine combined with a climate chamber. The temperature of the strips was increased up to 160 °C to provoke the phase transformation in the SMA. The bond behavior of the Fe-SMA strips glued into a groove with cement-based mortar was studied in lap-shear experiments using a 3D image-correlation measurement system. The result was compared with the bond behavior of CFRP strips glued with epoxy. Finally, two concrete bars with lengths of 70 cm were each reinforced with an Fe-SMA strip. After the concrete was cured, the Fe-SMA strips were activated (i.e., prestressed) by resistive heating, and the prestressing effect on the concrete bar was measured on the concrete surface using a mechanical strain gauge. The study demonstrated the general feasibility of Fe-SMA strips in prestressed NSMR. The recovery stresses were in the range of 250–300 MPa. A sufficient bond behavior was observed. Concrete bars could be successfully prestressed with a centrally embedded Fe-SMA strip.

[1]  C. Leinenbach,et al.  Stress recovery behaviour of an Fe–Mn–Si–Cr–Ni–VC shape memory alloy used for prestressing , 2013 .

[2]  Emidio Nigro,et al.  Bond Efficiency of EBR and NSM FRP Systems for Strengthening Concrete Members , 2011 .

[3]  Glauco Feltrin,et al.  Phase transformation behavior under uniaxial deformation of an Fe-Mn-Si-Cr-Ni-VC shape memory alloy , 2013 .

[4]  M. Branco,et al.  Effect of load cycling on the phase transformations in Ni–Ti wires for civil engineering applications , 2012 .

[5]  Raafat El-Hacha,et al.  Flexural Strengthening of Reinforced Concrete Beams Using Prestressed, Near-Surface-Mounted CFRP Bars , 2011 .

[6]  Dongkeun Lee,et al.  Bond of NSM systems in concrete strengthening - Examining design issues of strength, groove detailing and bond-dependent coefficient , 2013 .

[7]  Christoph Czaderski,et al.  Applications of shape memory alloys in civil engineering structures—Overview, limits and new ideas , 2005 .

[8]  Hendrik Kramer,et al.  Thermo‐Mechanical Properties of an Fe–Mn–Si–Cr–Ni–VC Shape Memory Alloy with Low Transformation Temperature , 2012 .

[9]  Takehiko Kikuchi,et al.  Remarkable improvement of shape memory effect in Fe-Mn-Si based shape memory alloys by producing NbC precipitates , 2001 .

[10]  H. Kubo,et al.  Ferrous (Fe-based) shape memory alloys (SMAs): properties, processing and applications , 2011 .

[11]  X. Balandraud,et al.  Recovery stresses in SMA wires for civil engineering applications: experimental analysis and thermomechanical modelling , 2011 .

[12]  Antoni Cladera,et al.  Iron-based shape memory alloys for civil engineering structures: An overview , 2014 .

[13]  Christoph Czaderski,et al.  RC beam with variable stiffness and strength , 2006 .

[14]  Andrea Bergamini,et al.  A Novel Fe‐Mn‐Si Shape Memory Alloy With Improved Shape Recovery Properties by VC Precipitation , 2009 .

[15]  Wanquan Sun.  Seismic response control of high arch dams including contraction joint using nonlinear super-elastic SMA damper , 2011 .

[16]  L. Lorenzis,et al.  Near-surface mounted FRP reinforcement: An emerging technique for strengthening structures , 2007 .

[17]  J. Shaw,et al.  Shape Memory Alloys , 2010 .

[18]  K. Borchert,et al.  Bond behaviour of NSM FRP strips in service , 2008 .

[19]  Andrea Bergamini,et al.  Feasibility of concrete prestressed by shape memory alloy short fibers , 2005 .

[20]  Deric J. Oehlers,et al.  Bond Strength of Near-Surface Mounted FRP Strip-to-Concrete Joints , 2007 .

[21]  A. Sato,et al.  Shape memory effect in γ⇄ϵ transformation in Fe-30Mn-1Si alloy single crystals , 1982 .

[22]  J. Barros,et al.  Bond Between Near-Surface Mounted Carbon-Fiber-Reinforced Polymer Laminate Strips and Concrete , 2004 .

[23]  Shoichi Matsuda,et al.  Effects of Alloying Additions on Fe-Mn-Si Shape Memory Alloys , 1990 .

[24]  M. Shahria Alam,et al.  Seismic performance of concrete columns reinforced with hybrid shape memory alloy (SMA) and fiber reinforced polymer (FRP) bars , 2012 .