INFLUENCE OF ACCIDENTAL ECCENTRICITY ON INELASTIC SEISMIC TORSIONAL EFFECTS IN BUILDINGS

This paper aims, firstly to define, evaluate and compare a number of alternative interpretations of the application of code accidental torsional provisions. The extent to which the distribution of element design strength is affected by each approach adopted for the accidental component of the design eccentricity specified by seismic codes is examined, Secondly, the effectiveness of the protection given to the flexible-edge element in torsionally responding structures by a number of major code static torsional provisions is quantified and compared. Finally, a proposal is made with regard to a relevant interpretation of codified accidental eccentricity provisions, by which a minimum value is specified for laterally responding systems, with the remainder (if any) of the accidental eccentricity being incorporated into the allowance made in design for dynamic inelastic torsional effects. Evaluation of the results from inelastic dynamic analyses based on this proposal lead to the conclusion that all codes satisfactorily control the ductility demand for the flexible-edge element in torsionally unbalanced structures, and that the element deformation demand has a consistent relationship with variations of lateral period and static eccentricity, for all the codes considered. For the stiff-edge element in torsionally unbalanced systems, the previously noted deficiencies of codes which permit large reductions of design strength for this side of the structure have been confirmed by the presentation of some key results.