POST-EARTHQUAKE RESIDUAL DISPLACEMENTS OF BILINEAR OSCILLATORS

Abstract

Structures subjected to large inelastic deformations during violent ground shaking do not always return to their initial ‘at-rest’ position but may have residual displacements. Even if collapse does not occur, large residual displacements may render them unusable or irreparable. In order to investigate the likely magnitude of residual displacement many bilinear single-degree-of-freedom oscillators with specified ductilities of 2·0, 4·0 and 6·0, stiffness ratios ranging from −0·25 to 1·0 and fundamental periods from 0 to 3·0s were subjected to 11 earthquake records from various ground types. It is shown that bilinear oscillators with positive stiffness ratios generally have small residual displacements, while those with negative stiffness ratios tend to undergo little inelastic reversal of deformation and have larger residual displacements. Reasons for this behaviour were able to be explained by means of a ‘hysteresis centre curve’. A design example for structures able to be modelled as single-degree-of-freedom oscillators is provided. © 1997 John Wiley & Sons, Ltd.