An innovative approach to achieve re-centering and ductility of cement mortar beams through randomly distributed pseudo-elastic shape memory alloy fibers

Abstract

Fibers can play a major role in post cracking behavior of concrete members, because of their ability to bridge cracks and distribute the stress across the crack. Addition of steel fibers in mortar and concrete can improve toughness of the structural member and impart significant energy dissipation through slow pull out. However, steel fibers undergo plastic deformation at low strain levels, and cannot regain their shape upon unloading. This is a major disadvantage in strong cyclic loading conditions, such as those caused by earthquakes, where self-centering ability of the fibers is a desired characteristic in addition to ductility of the reinforced cement concrete. Fibers made from an alternative material such as shape memory alloy (SMA) could offer a scope for re-centering, thus improving performance especially after a severe loading has occurred. In this study, the load-deformation characteristics of SMA fiber reinforced cement mortar beams under cyclic loading conditions were investigated to assess the re-centering performance. This study involved experiments on prismatic members, and related analysis for the assessment and prediction of re-centering. The performances of NiTi fiber reinforced mortars are compared with mortars with same volume fraction of steel fibers. Since re-entrant corners and beam columns joints are prone to failure during a strong ground motion, a study was conducted to determine the behavior of these reinforced with NiTi fiber. Comparison is made with the results of steel fiber reinforced cases. NiTi fibers showed significantly improved re-centering and energy dissipation characteristics compared to the steel fibers.

Energy-dissipating and self-repairing SMA-ECC composite material system

“…SMAs, such as Nickel-Titanium alloys [14,15] or Copper-Alluminium-Manganese alloys [16][17][18][19], feature shape memory effect and superelasticity. SMAs have been studied as partial replacement of steel rebars [20][21][22][23][24][25][26][27][28][29], the confinement for column [30][31][32][33][34][35][36][37], fibers [38][39][40][41][42], and external devices and dampers [43][44][45][46][47][48][49][50][51] for concrete structures. These studies showed that with particular prestrain, SMA can improve energy dissipation capacity of RC members while reducing residual crack width and deformation.…”

Crack-closing of cement mortar beams using NiTi cold-drawn SMA short fibers

“…To overcome these problems, concrete or cement composites with shape memory alloys (SMAs) are proposed and considered as smart composites that can generate recovery stress of SMAs due to the shape memory effect (SME) to provide pre-stress or crack-curing capacity in cement composites. This has been investigated by many studies (Czaderski et al 2014, Choi et al 2014a, Shajil et al 2012.…”