Evaluation of Energy-Based Modal Pushover Analysis in Reinforced Concrete Frames with Elevation Irregularity

In nonlinear static (pushover) methods of analysis as an alternative to time history
analysis, the capacity curve of the structure is established with respect to the roof displacement.
Disproportionate increases in the roof displacement and even outright reversals of the higher modes can
distort the capacity curve of the equivalent single degree of freedom system in these kinds of method,
including MPA. To overcome this problem, recently, Energy-Based" the Modal Pushover Analysis
(Energy-Based MPA) method has been introduced. In this method, the absorbed energy and/or the external
work in the pushover analysis is considered. Accordingly, the assessment of the Energy-Based MPA
method is important in the seismic analysis of asymmetrical and tall buildings. In this paper, the seismic
demands of concrete structures with irregularity in elevation are determined, using Energy-Based MPA.
For assessment of the presented technique, the results are compared with those from the Non-Linear
Time History Analysis (NL-THA). Seven examples including a 2-D simulation of a 12-story building are
modeled, using the Opensees Code. For each case, dierent types of irregularity, such as mass, geometry
and variations due to the dierence in elevation are considered. Story-drifts and
oor-displacements are
used as the main parameters for assessment of the results. Based on a study of the structural performance
of the models, it has been made clear that dierent types of the above-mentioned irregularity in elevation
do not have any signicant eect on the Energy-Based MPA method. Consequently, this method can be
considered as an accurate alternative technique for NL-THA, to fairly estimate the seismic demands of
structures.