Original Article Journal of Intelligent Material Systems and Structures 2019, Vol. 30(18-19) 2670–2687 Ó The Author(s) 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1045389X19873408 journals.sagepub.com/home/jim Seismic fragility analyses of steel building frames installed with superelastic shape memory alloy dampers: Comparison with yielding dampers Sourav Gur, Yazhou Xie and Reginald DesRoches Abstract Smart materials such as shape memory alloys have unique material properties that can potentially mitigate earthquake hazards on the built environment. Implementation of shape memory alloy-based devices on building structures should incorporate two key factors: (1) distinct mechanical features of the devices and (2) inherent large uncertainty stemming from material properties, building geometry, and ground motions. This study conducts seismic fragility analyses of steel building frames installed with superelastic shape memory alloy dampers, which enable both factors to be appropriately considered. First, a thermomechanical constitutive model is utilized to capture all essential characteristics of the shape memory alloy damper. Next, a probabilistic seismic analysis framework is developed to obtain the seismic demands of three critical engineering demand parameters (i.e. peak interstory drift ratio, residual drift ratio, and top floor accelera- tion) of the building when subjected to modeling uncertainty and a large set of realistic groundmotion inputs. Nonlinear time history responses and the associated short-time Fourier transform demonstrate the superior control efficiency of the shape memory alloy damper in limiting the building’s residual drift and top floor acceleration. Furthermore, seismic fragilities of the buildings when installed with shape memory alloy dampers are compared with those when equipped with yielding dampers. The study indicates that under different levels of ground motions and various ranges of modeling uncertainty in structural parameters, shape memory alloy damper consistently outperforms the yielding damper in reducing the seismic fragility of the building at both component and system levels. Keywords seismic fragility, steel building frame, yielding damper, shape memory alloy damper, modeling uncertainty 1. Introduction Vibration control of civil structures using various types of passive dampers has achieved significant attention from the research community (DenHartog, 1934; Soong and Dargush, 1997). However, exhaustive previ- ous studies have shown that most of these dampers bear inherent limitations. For instance, mass dampers are used to suppress the externally induced vibration of flexible structures, whereas they require the structures to have large spaces to house their huge masses. Linear mass dampers can be smaller in size when they are con- nected to the structure with nonlinear energy sinks (Inaudi and Kelly, 1995; Ru¨dinger, 2006). Yet, non- linear mass dampers might not be effective under cer- tain excitation frequencies, which restricts their wide range of applications. To be specific, the yielding of the nonlinear energy sinks may cause de-tuning of the sys- tem dynamics, resulting in a damper control efficiency that is frequency sensitive. For instance, studies have shown that nonlinear mass dampers perform poorer than conventional mass dampers when the natural fre- quency of the structure is within the range of 0.85–1.15 times of the dominant frequency of the ground excita- tion (Jaiswal et al., 2008). Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA Corresponding author: Yazhou Xie, Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005, USA. Email: yxie@rice.edu