FALL 2013
Nonlinear
Seismic Response
of RC Structures with Soft Stories
by
Md. Sharif Hossain & Jesmin Akter
This thesis work presents a study the nonlinear seismic behavior on RC ‘soft
stories’ buildings in presence of masonry infill. Lateral stiffness of infill
walls is calculated using the ‘Equivalent Diagonal Strut’ model. Four RC
buildings of different heights (3-, 6-, 12- and 24- storied) are analyzed and
designed for vertical loads only, using both the USD and WSD methods. The
nonlinear dynamic analyses of the structure are performed for
Moment-curvature relationships are of the column and beam sections are derived
numerically. They show that without seismic detailing the column section fail
quite rapidly after the spalling of concrete covers. Ductility improves
significantly after detailing and the ultimate curvature depends on the amount
of detailing.
The floor deflections and the column moment are
obtained numerically by for the El Centro ground motion using nonlinear dynamic
analysis (using ETABS 13) with no infill and partial infill (no infill at 1st
floor) as well as full infills. The moment-time relationship for columns
and displacement-time relation and floors (for 3- and 6-storied buildings) show
that the structures survive for full infill, but not for no infill and partial
infill even with major detailing and even after over-designing column sections
by WSD.