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Accidental eccentricity is automatically included during response-spectrum analysis in ETABS, though equivalent static-load procedures are also available for manual evaluation. Note that floor diaphragms must be rigid, otherwise torsional effects are not substantialDiaphragm assignments, either rigid or semi-rigid, are necessary at each floor level.
Manual implementation
Two basic approaches which enable the manual formulation of accidental eccentricity are described as follows:
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- Fahjan, Y., Tuzun, C., Kubin, J. (2006). An Alternative Procedure for Accidental Eccentricity in Dynamic Modal Analyses of Buildings. First European Conference on Earthquake Engineering and Seismology, 1166.