Engineering Structures 28 (2006) 289–303 www.elsevier.com/locate/engstruct The effect of material and ground motion uncertainty on the seismic vulnerability curves of RC structure Oh-Sung Kwon a,∗ , Amr Elnashai b a University of Illinois, 205 North Mathews, Urbana, IL 61801, United States b Mid-America Earthquake Center, University of Illinois, 205 North Mathews, Urbana, IL 61801, United States Received 23 September 2004; received in revised form 17 June 2005; accepted 12 July 2005 Available online 3 October 2005 Abstract Starting from the premise that vulnerability curves are an indispensable ingredient of earthquake loss assessment, this paper focuses on establishing the relative effect of strong-motion variability and random structural parameters on the ensuing vulnerability curves. Moreover, the effect of the selection of statistical models used to present simulation results is studied. A three story ordinary moment resisting reinforced concrete frame, previously shake-table tested, is used as a basis for the fragility analysis. The analytical environment and the structural model are verified through comparison with shaking-table test results. The selection of ground motion sets, definition of limit states, statistical manipulation of simulation results, and the effect of material variability are investigated. No approximations are used to reduce the sample size or minimize the analytical effort, in order that attention is focused on the parameters under investigation. Notwithstanding the limited scope of the study, the results presented indicate that the effect of randomness in material response parameters is far less significant than the effect of strong-motion characteristics. Therefore, the importance of scrupulous selection and scaling of strong-motion and use of appropriate limit states and statistical models is emphasized. © 2005 Elsevier Ltd. All rights reserved. Keywords: Seismic vulnerability; Ground motion uncertainty; Material uncertainty; Ordinary moment resisting concrete frame 1. Introduction Vulnerability curves relate strong-motion shaking sever- ity to the probability of reaching or exceeding a specified performance limit state. Strong-motion shaking severity may be expressed by an intensity ( I ), peak ground parameters (a , v or d ) or spectral ordinates ( S a , S v or S d ) corresponding to an important structural period. The number of limit states used varies between three and five. In this paper, three limit states considered as the most significant are used; service- ability, damage control and collapse prevention. Vulnerability curves play a critical role in regional seismic risk and loss estimation as they give the probability of attaining a certain damage state when a structure is ∗ Corresponding author. Tel.: +1 217 265 5497; fax: +1 217 333 3821. E-mail addresses: okwon2@uiuc.edu (O.-S. Kwon), aelnash@uiuc.edu (A. Elnashai). 0141-0296/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2005.07.010 subjected to a specified demand. Such loss estimations are essential for the important purposes of disaster planning and formulating risk reduction policies. The driving technical engines of a regional seismic risk and loss estimation system are [12]: • Seismic hazard maps (i.e. peak ground parameters or spectral ordinates). • Vulnerability functions (i.e. relationships of conditional probability of reaching or exceeding a performance limit state given the measure of earthquake shaking). • Inventory data (i.e. numbers, location and characteristics of the exposed system or elements of a system). • Integration and visualization capabilities (i.e. data management framework, integration or seismic risk and graphical projection of the results). The scope of this study is to present vulnerability curves of a reinforced concrete structure subjected to