Modification of Park-Ang Damage Index to Accommodate Effect of Aftershocks on RC Structures

Document Type : Research Article


1 International Institute of Earthquake Engineering and Seismology (IIEES)

2 University of Kurdistan


Seismic design codes do not consider the effects of aftershocks on structures.
Moreover, most damage estimation methods disregard the effects of consecutive
earthquakes. Recent earthquakes have demonstrated that the aftershocks can cause
major damage to mainshock-damaged structures. After a strong seismic event, it
should be determined if a mainshock-damaged building is safe for reoccupation in
the event of aftershocks. This study examined the effects of both the main shock and
aftershocks on the damage index of reinforced concrete (RC) structures. Records
from 19 mainshocks that occurred in the Japan seismic region with moment
magnitudes of greater than 4 were examined. More than 100 acceleration time
series from these events (mainshock + aftershock events) were applied to evaluate
the damage index. Seismic damage analysis was performed on a series of RC
columns and RC frames. The natural period of these structures varied from 0.1 to 2.5
s. The damage index introduced by Park and Ang was employed to estimate the
structural damage. Acceleration time series were applied to the structures in two
steps. First, only mainshocks were applied to the structures and the damage index
was obtained. Next, both the mainshock and aftershocks were applied to the
structures and structures damaged by a mainshock were analyzed under periodic
aftershock events. The results showed that the increase in structural period and the
PGA of the aftershocks amplified the damage index under the effects of the
aftershocks. A modification to Park-Ang damage index is proposed using a dimensionless
term to accommodate the effect of aftershocks.


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