The role of seismic input on the performance of bridge piers on cylindrical caisson foundations

In this paper, the influence of high-intensity ground motion properties on the performance of bridge piers founded on cylindrical caissons is investigated. The role of the frequency content and of the significant duration of seismic input is assessed to this purpose through a parametric study in which finite element coupled dynamic analyses are carried out in the time domain and in three-dimensional conditions. Real seismic records, of different frequency contents and significant durations, are scaled to similar values of the Arias intensity and are applied at the bedrock depth in terms of horizontal acceleration time histories. Mechanical soil behaviour is described by an elasto-plastic constitutive model with isotropic hardening. Coupled dynamic analyses are performed in terms of effective stresses assuming undrained conditions. Performance of the soil-caisson-pier system is evaluated through the maximum and permanent values of the horizontal displacements of the deck. The studied caisson foundations are characterized by different slenderness ratios but by the same value of the static safety factor against bearing capacity, in order to evaluate the seismic performance of systems given the same initial conditions. The effects of caisson construction stages are also simulated in the analyses.