Seismic response analysis of slender bridge piers

Many bridges are built on tall and slender piers, whose seismic response may be strongly influenced by second-order effects and higher modes contributions related to the distributed pier mass. In bridge design practice, the second-order effects are often taken into account by introducing amplification factors based on an oversimplified SDOF description of the pier behavior. In this paper, the influence of both axial load and higher-order modes on the dynamic behavior and seismic response of slender bridge piers is investigated by an analytical formulation and a continuous model that overcome some limitations of the models employed in previous studies. A dimensional analysis of the eigenvalue problem is carried out to make explicit the characteristic parameters governing the system dynamic behavior, and a parametric study is performed to study their influence on the modal properties. Further, a solving method is proposed for the seismic analysis and applied to a realistic bridge. The accuracy of the proposed model and of the kinematic assumptions, leading to a linear problem, is finally tested by comparison with the results obtained by a large displacement formulation. The case study results put in evidence some aspects characteristic of the dynamic behavior of slender piers that require further investigation. The proposed analytical formulation may be efficiently used to perform extensive parametric studies for different pier and seismic input properties.