Abstract
In the ductility design of a bridge pile-foundation, it is required that the pile foundation be designed for the lateral force and bending moment corresponding to the flexural strength of a column. It is required in such design that the flexural strength of the pile foundation thus designed should be larger than the flexural strength of the column so that the plastic deformation of the pile foundation be minimized. However, since the plastic deformation of the pile foundation is unavoidable when it is subjected to strong ground shaking, it is important to evaluate how larger flexural strength should be provided in the pile foundation. This paper presents a series of nonlinear dynamic response analysis of two bridge-column-pile foundation systems to clarify the relation between the plastic deformation of the pile foundation and the modified yield strength ratio which is defined as a ratio of yield strength of the foundation to that of the column.