Problems in applying code-specified capacity design procedures to seismic design of tall piers

This paper deals with the analysis of the seismic behaviour of bridges characterized by tall piers, focusing on the effectiveness of current “capacity design” methods. It is shown, in particular, that this design strategy may prove inadequate in bridges whose seismic behaviour is governed by pier dynamics and, specifically, in the case of tall piers. To this end, a typical prestressed concrete segmental bridge was designed according to different criteria; then, a series of nonlinear dynamic time-history analyses was carried out in order to evaluate the influence of the characteristics of the excitation (i.e., duration and shape) on the seismic response. Finally, the overall capacity of the structure and the position of the dissipation zones, as forced in the capacity design, were verified, in order to validate indirectly the entire bridge design strategy that is currently adopted in seismic codes.