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A preliminary
prediction of seismic damage-based degradation in RC structures |
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Vinay K. Gupta 1 *,
Søren R. K. Nielsen 2,
Poul H. Kirkegaard 2 |
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1Department
of Civil Engineering, Indian Institute of Technology, Kanpur 208016, India |
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Keywords |
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reinforced concrete structures; Clough-Johnston
oscillator; stiffness degradation; strength degradation; damage index;
effects of aftershocks |
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Abstract |
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Estimation of structural damage from a known increase in
the fundamental period of a structure after an earthquake or prediction of
degradation of stiffness and strength for a known damage requires reliable
correlations between these response functionals. This study proposes a
modified Clough-Johnston single-degree-of-freedom oscillator to establish
these correlations in the case of a simple elasto-plastic oscillator. It is
assumed that the proposed oscillator closely models the response of a given
multi-degree-of-freedom system in its fundamental mode throughout the
duration of the excitation. The proposed model considers the yield
displacement level and ductility supply ratio-related parameter as two input
parameters which must be estimated over a narrow range of ductility supply
ratio from a frequency degradation curve. This curve is to be identified from
a set of recorded excitation and response time-histories. Useful correlations
of strength and stiffness degradation with damage have been obtained wherein
a simple damage index based on maximum and yield displacements and ductility
supply ratio has been considered. As an application, the proposed model has
been used to demonstrate that ignoring the effects of aftershocks in the case
of impulsive ground motions may lead to unsafe designs. |