Application Study of Shape Memory Alloy Deployment in the Rehabilitation of Heritage Masonry Buildings

Abstract

It is beyond doubt that the dynamically modifying loading framework due to climate change and the difficulty in predicting natural hazards, such as earthquakes, reiterates the need for pursuing high-performance materials and enhanced structural systems that can address the vulnerability threat posed by ill-designed, abandoned, and damaged existing structures. In the case of heritage buildings, particularly those mostly consisting of unreinforced masonry, additional requirements such as reversibility, ease of inspection, less maintenance, and construction versatility increase the level of complexity toward adopting appropriate restoration strategies and identifying the most suitable retrofit scheme. Within this framework, the present work investigated the application of shape memory alloys (SMAs) in restoration, exploiting materials' ability to recover their initial geometry due to their shape memory or superelastic effect. For this study, nickel–titanium (Ni–Ti) and copper–aluminum–manganese (Cu–Al–Mn) retrofit schemes were applied to a characteristic architectural heritage building in Thessaloniki, Greece. Through numerical investigation and response spectrum analysis, the enhanced masonry seismic capacity was evaluated. Linear analysis showed primarily that retrofit-SMA options resulted in a maximum displacement reduction. Moreover, nonlinear pushover analysis showed a slight increase in capacity, with the Ni–Ti and Cu–Al–Mn restoration application competing with traditional steel, while dynamic time-history analysis revealed reduced residual displacements with the Ni–Ti scheme compared to steel. With respect to the effective deployment of these advanced materials for historical buildings’ preservation, the study produced results that can be valuable for practicing engineers in this special architectural and structural design field while constituting a basis for future more sophisticated examination and experimental validation. Shape memory alloys (SMAs) are unique materials that can remember their original shape and return to it after being stressed. Results produced by this study highlight the potential of the Ni–Ti scheme in significantly reducing residual displacement after seismic activity, providing the ability for the building to recenter itself after an earthquake. This smart metallic material can be utilized for the effective protection of old historical buildings against seismic excitation, rendering their retrofitting more sustainable and improving overall performance as the yielding of steel as an energy dissipation mechanism is substituted with the yielding-like, recentering behavior of SMAs. As the concept of residual structural deformation still plays an important role in current codification in the evaluation of damage in seismic design and assessment approach, this work can inform researchers and field engineers engaging with heritage masonry buildings’ retrofit about the potential of this advanced material aiming at introducing a recentering approach, mitigating damage and preserving building heritage.