Engineering Structures 30 (2008) 675–682 www.elsevier.com/locate/engstruct Inﬂuence of passive supplemental damping systems on structural and nonstructural seismic fragilities of a steel building Assawin Wanitkorkul, Andr´ e Filiatrault ∗ Department of Civil, Structural, and Environmental Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA Received 23 March 2006; received in revised form 16 May 2007; accepted 23 May 2007 Available online 27 June 2007 Abstract This paper presents the results of a numerical study on the inﬂuence of structural passive supplemental damping systems on structural and nonstructural seismic fragilities of a steel framed building. Hysteretic and viscous bracing systems were used to retroﬁt a four-storey steel framed building containing generic rigidly anchored and vibration isolated secondary nonstructural components located at various ﬂoor levels in the building. The Incremental Dynamic Analysis (IDA) procedure was utilized with an ensemble of 44 scaled historical ground motions to construct structural and nonstructural fragility curves for various performance objectives. The results obtained indicate that both supplemental damping systems improved the seismic behaviour of the original building by increasing the median values of the structural fragility curves and reducing the probabilities of exceedence at the Design Basis Earthquake (DBE) and Maximum Credible Earthquake (MCE) levels. The nonstructural components mounted on vibration isolation systems exhibited reduced seismic fragilities compared to that of rigidly anchored nonstructural components. Retroﬁtting the building with viscous dampers reduced the seismic fragility of nonstructural components mounted to the roof of the building. Retroﬁtting the building with hysteretic dampers, on the other hand, was detrimental to the seismic fragility of acceleration sensitive rigidly anchored nonstructural components at the roof level. c  2007 Elsevier Ltd. All rights reserved. Keywords: Seismic fragility; Nonstructural components; Dampers; Retroﬁt; Steel structure 1. Introduction Achieving a given target seismic performance objective requires the harmonization of the performance levels between structural and nonstructural components and systems. Even if the structural system of a building maintains an immediate occupancy performance level during a seismic event, failure of nonstructural components inside the building can lower the performance level of the entire building system. Further to crippling building operation, failure of nonstructural components can become safety hazards for occupants evacuating the building or rescue workers entering the building. In this study, structural passive supplemental hysteretic and viscous damping systems are considered for retroﬁtting a four-storey steel framed building containing generic rigidly anchored and vibration isolated secondary nonstructural ∗ Corresponding author. Tel.: +1 716 645 2114x2434; fax: +1 716 645 3733. E-mail address: af36@buffalo.edu (A. Filiatrault). components installed in various locations in the building. Nonlinear Incremental Dynamic Analyses (IDA) with an ensemble of 44 scaled historical ground motions were used to construct fragility curves for the structural system and nonstructural components based on various performance objectives in order to compare the inﬂuence of each passive supplemental damping system. The case study illustrates also how structural and nonstructural fragility data can be generated and used to support the decision process for the performance- based seismic design or retroﬁt of a building. 2. Building structure and modeling A four-storey steel framed building model assumed to be part of an existing critical facility located in Southern California was selected for the case study. The building was assumed to have been constructed in the early 1970s and was designed according to the 1970 edition of the Uniform Building Code [1] with an importance factor of 1.5. The rectangular and symmetrical building is composed of four 0141-0296/$ - see front matter c  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2007.05.013