Abstract:
Masonry infill wall in frame structures have long been known to affect strength,
stiffness and post peak behavior of the infilled framed structures. The interaction
between the wall and the frame under lateral load dramatically changes the overall
characteristics of the composite structure. In seismic areas, ignoring the composite
action of infill panel and frame is not always on the safe side. So, response to seismic
loads creates a major source of hazard during seismic events.
The present study consists of two parts. At first, lateral load – displacement curve for
column and masonry wall is obtained using non-linear FE analysis from which lateral
stiffness of column and infills has been found. Secondly, this stiffness which is
equivalent to the stiffness of a nonlinear spring is then used in a multi-degree of
freedom (MDOF) spring-mass-dashpot system. The MDOF system is modeled in
MATLAB where dynamic equilibrium equations have been solved by state-space
method. Detailed parametric study with different PGA values, earthquake frequency
and varying number of stories has been performed to obtain a guideline of collapse of
different types of buildings under seismic loading.
After performing nonlinear dynamic analysis, behavior of these structures is
compared. It is evident that natural frequency is completely different from codeprovision
of natural frequency due to the presence of infill. Soft-storey frame
collapses earlier than bare and infilled frame for all seismic excitations. As, number of
storey increases, soft storey collapse initiates earlier than buildings with smaller
number of stories.
