APPROXIMATE SEISMIC ANALYSIS OF INELASTIC ASYMMETRIC STRUCTURES

This paper examines the approximate method of the single element model for analysing inelastic asymmetric structures. It simplifies the analysis by treating only a single resisting element having dynamic as well as yielding properties equivalent to the original structure with many resisting elements. The range of validity of the single element model for earthquake response calculations is defined in the paper. The study considers inelastic asymmetric one-storey structural models whose properties are varied to simulate a wide range of typical structural buildings. These properties include lateral period, torsional-to-lateral frequencies ratio, magnitude of structural eccentricity, number of resisting elements in the original structure, and yield strength of the structural model. The prime concern of the paper is to assess the accuracy of the displacement ductility demand estimated using the approximate method. For long period structures the single element model generally gives conservative estimates of displacement ductility demand. For such a range a better estimate using a modified single element model is proposed in which the single element is located at the plastic centre of strength instead of the centre of stiffness. The accuracy of the approximate method is found to considerably improve as the number of resisting elements in the original structure increases. For highly inelastic stiff structures, no approximate method can reasonably estimate their ductility demand values.