The paper summarises the results of dynamic analyses of some single-stem and double-stem bridge piers responding to a range of earthquake ground motions, including both natural and synthetic earthquake records. The influence of foundation flexibility was modelled by an 'extended leg' analogy and by a more refined approach in which the soil is replaced by an equivalent spring system. A bilinear moment-curvature loop was assumed to model the plastic hinge behaviour. The curvature ductility factor demand of bridge piers with different foundation flexibilities was determined and compared with the rigid foundation case.