Dissipative exoskeletons based on self-centering sma braces for seismic retrofit of rc buildings

A great number of buildings in seismic-prone areas were designed without provisions for earthquake resistance. Therefore, they are not expected to possess the necessary properties to withstand earthquake excitations, which cause strong plastic deformations, performance deterioration, and damage. This has stimulated the development of a new generation of seismic codes based not only on stiffness, strength, and ductility requirements but also on structural resilience, which is the ability to rapidly resume the use of structures following an earthquake. In recent years, the resilience of structural retrofit systems for existing buildings has attracted more and more attention. Moreover, a variety of external sub-structure retrofitting methods have been proposed in the literature generally based on non-dissipative steel exoskeletons. This article presents the design and assessment of dissipative exoskeletons based on recentering shape memory alloy (SMA) dampers for the seismic retrofit of RC buildings. Although many studies have been presented in the literature on SMA bracing systems, most of them are devoted to experimental and numerical investigations on small-scale SMA devices or brace components. Only a few studies focus their attention on the application of SMA-brace devices to full-scale RC buildings. This paper focuses on evaluating the effect of using self-centering shape memory alloy dampers for buckling-restrained braces in dissipative exoskeletons applied for the seismic retrofit of a reinforced concrete (RC) school building structure. A design method has been implemented to size the SMA dampers to be placed on selected spans and stories of the exoskeletons. The effectiveness of the design procedure has been demonstrated by nonlinear time-history analyses under different sets of earthquake-strong ground motions.