A Study on EN 1998-1:2003 Equivalent Static Torsional Provision for Vertically Regular Multi-Story RC Buildings
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Date
2020-06
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Addis Ababa University
Abstract
Asymmetric building structures exist in modern construction to satisfy functional and
architectural requirements. This asymmetry is the main reason for the failure of
reinforced concrete buildings unless it is designed to accommodate the response of
structures when subjected to different loadings.
In this paper one form of plan irregularity i.e. torsional irregularity condition is studied
under the equivalent static torsional provision of EN 1998-1:2003. Three-story
torsionally flexible reinforced concrete buildings subjected to seismic action are studied
using both response spectrum and equivalent static method of analysis. Both methods are
used through the analytical study of 30 random samples and analyses of 2 test models
using ETABS. The response spectrum method of analysis is used as a reference method.
Therefore the response of the structures computed using the equivalent static method
shall be equal to or greater than the response computed using the response spectrum
method. However, the result shows, the equivalent static method underestimates the
response of structures when torsional irregularity exists. This means the response of the
fundamental mode only becomes inadequate because higher modes turn into significant.
In such situations, a modifying factor that magnifies the response of an equivalent static
analysis method shall be used. Hence the application of the torsional provision shall be
limited to torsionally regular buildings or the modification of the analysis method shall
be used while the irregularity occurs.
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Keywords
Analytical study, Torsionally flexible, Torsionally regular, Response spectrum analysis, Equivalent static analysis