FALL 2013


Nonlinear Seismic Response of RC Structures with Soft Stories


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 El Centro earthquake ground motion, incorporating provisions for major and moderate seismic detailing.

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.