The seismic performance of reinforced concrete (RC)
buildings with setback irregularities under sequential mainshock-aftershock
sequences is a critical case but often overlooked in conventional design
practices. This study presents a comprehensive analysis of the nonlinear
seismic response of a G+8 RC building with setback irregularities subjected to
earthquake sequences. Three models were developed: the first model is a regular
RC frame, the second model has vertical irregularity (setback irregularity) where
the floor area reduces by nearly 26% from the 7th to 9th story, and the third
model has vertical irregularity between the 4th and 9th storey.
The hybrid nonlinear modelling is employed by incorporating
plastic hinges for beams and fibre hinges for columns, with hysteretic energy
dissipation defined for concrete and steel fibres. The models are analysed by
considering three different ground motions (low, medium, and higher
intensities) resulting from major earthquakes: Chamoli (1999), Valparaíso
(1985), and Coalinga (1983), incorporating both mainshocks and their
aftershocks. The nonlinear time history analyses are performed using the latest
ETABS software v22.3.0 to capture the dynamic response under these complex
ground motion accelerations.
The results reveal that the setback irregular buildings
exhibited higher vulnerability, marked by increased storey displacements,
amplified inter-storey drifts, and a critical demand-to-capacity (D/C) ratio,
with the third model showing the most severe response. Notably, the third model
experiences a peak lateral displacement of nearly 275mm and a maximum
inter-storey drift ratio of 0.018613, exceeding safety thresholds under several
loading conditions, whereas the first model recorded the lowest displacement of
about 41 mm and the minimum inter-storey drift of 0.002430, thereby
demonstrating the highest efficiency among all models. The formation of plastic
hinges signifies a substantial risk of failure/collapse.
The findings underscore the critical need to incorporate the
effects of setback irregularities, nonlinear behaviour, and main shock and
aftershocks sequences in seismic design protocols, to ensure reliable
performance and predictions to enhance structural resilience against
catastrophic events. In view of practical application, such considerations can
guide safer design and performance-based evaluation of RC buildings.
Author(s) Details
Tulsi Meena
Maulana Azad National Institute of Technology, Bhopal, India.
M.S. Hora
Maulana Azad National Institute of Technology, Bhopal, India.
Please see the book here :- https://doi.org/10.9734/bpi/erpra/v10/6153
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