Civil and Environmental Engineering Department
No Thumbnail Available
Date
2017-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Nonductile reinforced concrete frames with masonry infill walls are a popular form of
construction in seismic regions worldwide. The typical multi-story construction in Ethiopia
comprises reinforced concrete (RC) frames with HCB masonry infills. Unreinforced
masonry infill wall panels may not contribute towards resisting gravity loads, but contribute
significantly, in terms of enhanced stiffness and strength under earthquake (or wind) induced
lateral loading. However, in practice, the infill stiffness is commonly ignored in frame
analysis, resulting in an under-estimation of stiffness and natural frequency. Also, the
infill has energy dissipation characteristics that contribute to improved seismic resistance. It
is instructive to study the implications of the common practice of ignoring the infill stiffness
with regard to performance under seismic loading. This research quantifies the effect of
the presence and configuration of masonry infill walls on seismic collapse risk. Seismic
analysis of such buildings indicates that the fully-infilled frame has the lowest collapse risk
and the bare frame is found to be the most vulnerable to earthquake-induced collapse.
A typical existing office building located in severe seismic zones of Ethiopia (as per
ESEN1998) is identified. The office medium rise building is analyzed for earthquake force
by considering three type of structural system. i.e. Bare Frame system ,partially-infilled and
fully- Infilled Frame system. Effectiveness of masonry wall has been studied with the help of
five different models. Infills were modeled using the equivalent strut approach. Nonlinear
static analyses for lateral loads were performed by using standard package ETABS,2015
software. The comparison of these models for different earthquake response parameters like
base shear vs roof displacement, Story displacement, Story shear, member forces and seismic
performance assessment are carried out. It is observed that the seismic demand in the bare
frame is significantly large when infill stiffness is not considered, with larger displacements.
This effect, however, is not found to be significant in the infilled frame systems.The results
are described in detail in this paper.
Key words: Bare frame; Infilled frame; Equivalent Diagonal strut; infill; plastic Hinge
Description
Keywords
Bare frame; Infilled frame; Equivalent Diagonal strut; infill; plastic Hinge