Effect of Floor Diaphragm Flexibility in Tall Rectangular Reinforced Concrete Buildings
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Date
2019-10
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Addis Ababa University
Abstract
Under seismic loading, floor and roof systems in reinforced concrete (RC) buildings act
as diaphragms to transfer lateral earthquake loads to the vertical lateral load resisting
system (VLLR). In most cases, horizontal diaphragms are typically assumed to be rigid,
thus neglecting the effect of their in-plane movement relative to the VLLR system.
Though number of studies have been conducted on the effect of diaphragm flexibility,
some types of buildings are not addressed. For this reason, many researches have to be
conducted to address different types of reinforced concrete buildings. These types of
buildings depend on their aspect ratio, height, shape, shear wall arrangement and so on.
In this study, the effect of floor diaphragm flexibility in tall rectangular reinforced concrete
buildings of story G+15, G+25 and G+35 with aspect ratio of 1:3 and 1:4 were studied and
comparative study of their dynamic response during seismic loading were discussed.
ETABS
®
(2017 v 17.0.1) software was used for the modeling and analysis.
All buildings were designed according to ES-EN 1992-1-1:2015 and ES-EN 1998-1:2015
and modeled with rigid floor assumptions and flexible floor diaphragm. Modal response
spectrum analysis was used to check the buildings response in terms of story shear force,
modal periods, story drift and columns shear force.
It is concluded from the study that, buildings with aspect ratio 1:4 has larger story drift,
fundamental period and column shear force received by the columns when modeled with
flexible floor diaphragm than rigid floor diaphragm assumption. The effect of diaphragm
flexibility is larger on G+15 story than the G+25 and G+35 story building, but most of all,
lateral load received by the columns which are found at the middle of the buildings when
modeled with flexible diaphragm shows large increase and these increase may cause clear
variation of design output between rigid and flexible diaphragm.
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Keywords
Diaphragm flexibility, Tall building, Aspect ratio, Earthquake response