A Study on EN 1998-1:2003 Equivalent Static Torsional Provision for Vertically Regular Multi-Story RC Buildings

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Addis Ababa University


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.



Analytical study, Torsionally flexible, Torsionally regular, Response spectrum analysis, Equivalent static analysis