Shape Memory NiTi-Nb Alloys for Seismic-Resilient Beam-Column Connections in Steel Moment Frames

Yunfeng Zhang1, Reginald DesRoches2, Canxing Qiu3
1 Department of Civil Engineering, Tongji University, Shanghai 200092, China
2 School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
3 Department of Civil Engineering, Tongji University, Shanghai 200092, China
Published: 2026-05-18 · JAMS Vol. 1, No. 1 (2026)

Abstract

Conventional steel beam-column connections in moment-resisting frames suffer permanent deformation after major earthquakes, often requiring costly replacement. This paper presents a novel self-centering connection using superelastic NiTi-Nb shape memory alloy (SMA) bolts that can recover up to 6% strain upon unloading. Quasi-static cyclic tests on full-scale W24×68 beam-to-W14×176 column connections demonstrate near-zero residual drift (< 0.15% at 4% peak story drift) and stable energy dissipation over 30 fully-reversed cycles. Computational modeling using calibrated SMA constitutive laws is validated against experimental results, enabling parametric studies for codifiable design recommendations.

Keywords: shape memory alloys, seismic resilience, self-centering connections, beam-column joints, superelastic NiTi-Nb

1. Introduction

The 1994 Northridge and 1995 Kobe earthquakes revealed the vulnerability of welded steel moment frame connections, leading to brittle fractures at beam-column interfaces. While post-Northridge connection details (RBS, BFP) improved ductility, these connections still accumulate significant residual drift after design-level earthquakes, resulting in buildings that must be demolished despite being "life-safe." Self-centering structural systems using shape memory alloys (SMAs) offer a paradigm shift from damage-tolerance to damage-free performance.

2. Experimental Program

NiTi-Nb SMA bolts (M24 × 200 mm) were machined from hot-extruded rods and solution-treated at 850°C for 30 min. The bolts exhibit an austenite finish temperature Af = -15°C (superelastic at room temperature), a transformation stress of 450 MPa, and a recoverable strain of 6.2%. Full-scale T-stub connections using eight SMA bolts per flange were tested under SAC loading protocol to ±4% story drift.

00.61.31.92.50.020.351% drift0.050.822% drift0.081.453% drift0.152.14% driftSMA connectionConventional
Figure 1. Moment-rotation hysteresis: SMA-bolted connection (flag-shaped) vs. conventional high-strength bolt connection (fat hysteresis with residual drift)

3. Results

The SMA-bolted connection exhibits flag-shaped hysteresis with residual rotation below 0.15% at 4% peak drift, compared to 2.1% residual for the conventional high-strength bolt benchmark. The equivalent viscous damping ratio is 12.8% at 4% drift. No bolt fracture or SMA functional degradation was observed after 30 cycles, and post-test tensile testing confirmed full recovery of superelastic properties. The moment capacity reached 1.05Mp of the beam, with yielding confined to a replaceable energy-dissipating fuse plate.

4. Conclusions

NiTi-Nb SMA-bolted beam-column connections achieve near-zero residual drift while providing adequate energy dissipation through flag-shaped hysteretic behavior. The technology enables "earthquake-proof" steel moment frames that can return to service immediately after major seismic events without structural repair, fundamentally changing the economics of seismic resilience for critical infrastructure.

References

  1. DesRoches, R.; McCormick, J.; Delemont, M. Cyclic Properties of Superelastic Shape Memory Alloy Wires and Bars. J. Struct. Eng. 2004, 130, 38-46.
  2. Ocel, J. M.; DesRoches, R.; Leon, R. T.; Hess, W. G.; Krumme, R.; Hayes, J. R.; Sweeney, S. Steel Beam-Column Connections Using Shape Memory Alloys. J. Struct. Eng. 2004, 130, 732-740.
  3. Wang, B.; Zhu, S. Superelastic SMA U-Shaped Dampers with Self-Centering Function. Smart Mater. Struct. 2018, 27, 055003.
  4. Fang, C.; Wang, W.; He, C.; Chen, Y. Self-Centering Behaviour of Steel and Steel-Concrete Composite Connections Equipped with NiTi SMA Bolts. Eng. Struct. 2017, 150, 390-408.

This article is published under the Creative Commons Attribution 4.0 International License (CC BY 4.0).