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Abstract
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This paper presents a numerical investigation on seismic performance of reinforced concrete (RC) cantilever
columns under unidirectional and bidirectional excitations. The influence of cross-sectional geometry and
multiple excitations have been examined in this study. An advanced nonlinear finite element model is employed
to model different failure modes of RC columns under seismic excitation. The model simulates degradation of
materials under cyclic loading, including inelastic buckling and low-cycle fatigue degradation of longitudinal
reinforcement. A series of monotonic pushover and incremental dynamic analyses (IDA) are conducted on hypothetical rectangular and circular columns. Proposing a unique algorithm, an existing inclusive damage index is
implemented to quantify the different sources of damage including flexural, shear and reinforcement slippage
damage under bidirectional excitation. Ground motion records are carefully selected using conditional mean
spectrum (CMS) to generate as-recorded real mainshock and aftershock (MSAS) sequences. Results show that
multiple bidirectional excitations significantly increase the damage that accumulates in RC columns. Moreover,
inelastic buckling and low-cycle fatigue degradation of longitudinal bars have an evident contribution to the
failure of RC columns. It is also found that the rectangular column is more prone to collapse under bidirectional
loading in comparison to circular section. The analyses results show that the impact of bidirectional excitation on
the seismic performance of the studied cantilever columns is considerable. This implies that seismic performance
assessment of RC structures using unidirectional excitation can be biased.
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