Seismic performance of partially submerged R.C. caissons used in port structures

In this paper the transversal stability under seismic excitation of a possible structural solution for a pier container terminal is investigated. The considered solution adopts R.C. caisson structures resting on shallow foundations as vertical elements for the pier. The main aspect investigated is the caissons attitude to overturn due to excessive rocking at the base during earthquakes being the structure characterized by a shallow foundation. Being the caissons partially submerged bodies, the hydrodynamic effects associated to seismic excitation are included. The structure is verified by means of nonlinear time history analyses considering a set of spectrum compatible earthquake records. In the finite element model the caisson is schematized with mono-dimensional beam type elements. Soil-structure interaction is accounted for by placing compression-only axial springs with stiffness compatible to gravel soils. Both linear- elastic and elasto-plastic springs are considered. The resulting non-linear dynamic behaviour is characterized by limited uplift of the foundation relative to the soil, this uplift is responsible of the non-linearity, mainly geometric, related to soil-structure interaction. The analyses showed limited displacements of the caisson top, with higher values in the case of elasto-plastic soil with low elastic stiffness.