Mohssen Izadinia a,⁎, Mohammad Ali Rahgozar b, Omid Mohammadrezaei a
a Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
b Department of Civil Engineering, Faculty of Engineering, University of Isfahan, Isfahan, Iran
a r t i c l e i n f o a b s t r a c t
Article history:
Received 26 August 2011
Accepted 23 July 2012
Available online 30 August 2012
Keywords:
Response modification factor
Conventional pushover analysis
Adaptive pushover analysis
Steel moment-resisting frames
The earthquake loads imposed to the structures are generally much more than what they are designed for.
This reduction of design loads by seismic codes is through the application of response modification factor
(R-factor). During moderate to severe earthquakes, structures usually behave inelastically, and therefore inelastic
analysis is required for design. Inelastic dynamic analysis is time consuming and interpretation of its
results demands high level of expertise. Pushover analysis, recently commonly used, is however, a simple
way of estimating inelastic response of structures. Despite its capabilities, conventional pushover analysis
(CPA) does not account for higher mode effects and member stiffness changes. Adaptive pushover analysis
(APA) method however, overcomes these drawbacks. This research deals with derivation and comparison
of some seismic demand parameters such as ductility based reduction factor, Rμ, overstrength factor, Ω,
and in particular, response modification factor, R, from capacity curves obtained from different methods of
APA and CPA. Three steel moment-resisting frames of 3, 9 and 20 stories adopted from SAC steel project
are analyzed. In pushover analyses for each frame, eight different constant as well as adaptive lateral load
patterns are used. Among the main conclusions drawn is that the maximum relative difference for response
modification factors was about 16% obtained by the methods of conventional and adaptive pushover
analyses.

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