Civil Engineering Association

Effectiveness of modified pushover analysis procedure for the estimation of seismic demands of buildings subjected to near-fault ground motions having fling step

Near-fault ground motions with long-period
pulses have been identified as being critical in the design of
structures. These motions, which have caused severe dam-
age in recent disastrous earthquakes, are characterized by a
short-duration impulsive motion that transmits large amounts
of energy into the structures at the beginning of the earth-
quake. In nearly all of the past near-fault earthquakes, signif-
icant higher mode contributions have been evident in build-
ing structures near the fault rupture, resulting in the migra-
tion of dynamic demands (i.e. drifts) from the lower to the
upper stories. Due to this, the static nonlinear pushover anal-
ysis (which utilizes a load pattern proportional to the shape
of the fundamental mode of vibration) may not produce ac-
curate results when used in the analysis of structures sub-
jected to near-fault ground motions. The objective of this pa-
per is to improve the accuracy of the pushover method in
these situations by introducing a new load pattern into the
common pushover procedure. Several pushover analyses are
performed for six existing reinforced concrete buildings that
possess a variety of natural periods. Then, a comparison is
made between the pushover analyses’ results (with four new
load patterns) and those of FEMA (Federal Emergency Man-
agement Agency)-356 with reference to nonlinear dynamic
time-history analyses. The comparison shows that, generally,
the proposed pushover method yields better results than all
FEMA-356 pushover analysis procedures for all investigated
response quantities and is a closer match to the nonlinear
time-history responses. In general, the method is able to re-
produce the essential response features providing a reason-
able measure of the likely contribution of higher modes in all
phases of the response