Feasibility of self-pre-stressing concrete members using shape memory alloys

Abstract

Shape memory alloys are a class of smart materials that recover apparent plastic deformation (∼6%–8% strain) after heating, thus “remembering” the original shape. This shape memory effect can be exploited for self-post-tensioning applications, and NiTi-based shape memory alloys are promising as shape memory effect is possible at elevated temperatures amenable to practical application compared to conventional NiTi. This study investigates the feasibility of self-post-tensioned concrete elements by activating the shape memory effect of NiTiNb, a class of wide-hysteresis shape memory alloys, using the heat of hydration of grout. First, the microstructure characterization of the NiTiNb wide-hysteresis shape memory alloys is discussed. Then, the tensile stress-induced martensitic transformations in NiTiNb shape memory alloy tendons are studied. Next, the temperature increase due to the heat of hydration of four commercially available grouts is investigated. Pull-out tests are also conducted to investigate the bond between the grout and shape memory alloy bar. Results show that the increase in temperature due to hydration heat can provide significant strain recovery during a free recovery experiment, while the same temperature increase only partially activates the shape memory alloys during a constrained recovery.

Thermomechanical and electrical response of a superelastic NiTi shape memory alloy cable

“…However, the cable exhibited a high positive forward transformation slope over the transformation range. The low forward transformation stress and high transformation slope indicate a non-uniform transformation initiation for the various strands and wires across the cross-section of the cable (Ozbulut et al, 2015b). This might be attributed to the fact that multilayered strand configuration requires the length of wires at the outer layer strands to be longer compared to the wires in the inner core strands which leads to a nonuniform strain distribution at the individual wires of the cable (Reedlunn et al, 2013a(Reedlunn et al, , 2013b.…”

“…The experimental results indicated that the 7 × 7 cable configuration has a tensile response similar to the single wire, while the 1 × 27 configuration has lower transformation stress levels. Ozbulut et al (2015b) characterized a large-diameter SMA cable with an outer diameter of 8 mm. The cable had a 7 × 7 configuration and composed of individual wires with a diameter of 0.885 mm.…”

Experimental study of new axial recentering dampers equipped with shape memory alloy plates

“…These properties correspond to phase transformation from martensite to austenite and vice versa. There are several studies regarding SMA dampers and their performance in the frame structures 17,19–31 …”

Behavior of mortar beams with randomly distributed superelastic shape memory alloy fibers

“…Over the past decade, the performance and behavior of SMAs in concrete structures have been explored by a number of researchers (Alam et al, 2009; Billah and Alam, 2012; Ozbulut et al, 2015; Shin and Andrawes, 2011; Shrestha et al, 2015; Wierschem and Andrawes, 2010). Within the fiber-reinforced concrete community, several studies have investigated the effect of SMA fibers in cementitious composites.…”