Experimental Evaluation of Wedge-Type Anchorage Systems for Smooth-Surfaced NiTi SMA Bars

SMA bars, particularly those based on NiTi, exhibit superelastic and self-centering properties, providing damage-resistant, self-centering structural systems. However, their natural smoothness and low machinability pose a significant challenge to adequate mechanical anchorage. This paper experimentally measures the efficiency of two feasible wedge-type anchorage systems, wedge-and-barrel (WB) and spring anchor (SA), which are typically used in post-tensioning systems, and assesses their applicability for anchoring smooth-surfaced NiTi SMA bars. A total of 24 testing configurations were examined in this study. A complete monotonic tensile test regime was performed at steady loads with desired strain levels. The findings validate that both wedge-type anchorage systems were able to effectively anchor the SMA bars, although some performance differences were observed. The WB anchorage system showed increased stress capacity, improved load transfer efficiency, and less scatter across repeated tests, which can be attributed to its greater mechanical confinement and frictional interlock, exhibiting an increase of approximately 27% in stress capacity compared to the SA anchorage system. On the other hand, the SA system exhibited good anchorage performance. It showed a slightly lower stress response and greater variation at higher levels of deformation due to the spring’s compression mechanism. The results demonstrate the feasibility of using wedge-type anchorage systems to anchor SMA rebars for seismic applications and provide guidance for future anchorage design.