| dc.description.abstract | The earthquake resistant design of structures requires that structures should sustain, safely,
any ground motions of an intensity that might occur during their construction or in their
normal use. However ground motions are unique in the effects they have on structural
responses. The most accurate analysis procedure for structures subjected to strong ground
motions is the time-history analysis. This analysis involves the integration of the equations
of motion of a multi-degree-of-freedom system, MDOF, in the time domain using a
stepwise solution in order to represent the actual response of a structure. This method is
time-consuming though for application in all practical purposes. The necessity for faster
methods that would ensure a reliable structural assessment or design of structures subjected
to seismic loading led to the pushover analysis.
Pushover analysis is based on the assumption that structures oscillate predominantly in the
first mode or in the lower modes of vibration during a seismic event. This leads to a
reduction of the multi-degree-of-freedom, MDOF system, to an equivalent single-degreeof-
freedom, ESDOF system, with properties predicted by a nonlinear static analysis of the
MDOF system. The ESDOF system is then subsequently subjected to a nonlinear timehistory
analysis or to a response spectrum analysis with constant-ductility spectra, or
damped spectra. The seismic demands calculated for the ESDOF system are transformed
through modal relationships to the seismic demands of the MDOF system.
In this study the applicability of the pushover method as an alternative mean to general
design and assessment is examined. Initially a series of SDOF systems is subjected to two
different pushover methods and to nonlinear-time-history analyses. The results from this
study show that pushover analysis is not able to capture the seismic demands imposed by
far-field or near-fault ground motions, especially for short-period systems for which it can
lead to significant errors in the estimation of the seismic demands. In the case of near-fault
ground motions the results suggest that pushover analysis may underestimate the
displacement demands for systems with periods lower than half the dominant pulse period
of the ground motion and overestimate them for systems with periods equal or higher than
half the dominant pulse period of the ground motion. Subsequently a two-degree-offreedom,
2-DOF, is studied in the same manner with specific intention to assess the
accuracy of the different load patterns proposed in the literature. For this system pushover
analysis performed similarly as in the SDOF study. Finally the method is applied on a
four-storey reinforced concrete frame structure. For this study pushover analysis was not
effective in capturing the seismic demands imposed by both a far-field and a near-fault
ground motion. Overall pushover analysis can be unconservative in estimating seismic
demands of structures and it may lead to unsafe design. | en |
