How Different Seismic Codes Define Torsionally Unbalanced Structure?

Marzie Shahini, S. Rasoul Mirghaderi, Ali Keyhani

Research output: Contribution to conferenceUnpublished paper

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Intensive research in restricting inelastic damage in torsionally unbalanced
building has been done. But it is not clear what can be defined as a torsionally
irregular building? In this study, the torsional irregularities criteria as suggested
by 54 countries seismic codes are compared with each other.
Generally, seismic codes consider either in plan eccentricity or/and story
drift for assessing torsionally irregularity. But seismic codes differ from each
other in two aspects: 1) Definition of the above parameters (i.e. plan eccentricity
and story drift) 2) The numerical limits of the above parameters where a building
can be considered torsionally balanced system.
In order to compare various code provisions, we classified one 8 stories
either as regular or irregular according to different codes. The results were in
contradiction to each other, i.e. while the building was regular according to some
codes, it was irregular due to others.
These contradictory results are mainly due to non uniform definition for
an unbalanced system. The complexity involved in determining parameters such
as location of center of rigidity can be another reason for contradiction results.
Hence, it seems that more research is needed to reach generally accepted criteria
for defining a torsionally unbalanced system.
Original languageEnglish
Publication statusPublished - 2010
Event9th US National and 10th Canadian Conference on Earthquake Engineering -
Duration: 11 May 2010 → …


Conference9th US National and 10th Canadian Conference on Earthquake Engineering
Period11/05/10 → …


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