ABSTRACT: 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. KEY WORDS: Rocking; Seismic performance; Soil structure interaction; Port structures. 1 INTRODUCTION In this paper the transversal stability of a R.C. precast caisson structures for a pier container terminal is assessed under seismic excitation. The main aspect investigated is the rocking stability of the selected caisson, characterized by a shallow foundation, and the possible overturning during earthquakes. Concrete caissons are cellular gravity structures built in a construction plant, towed to the site taking advantage of their buoyancy capacity and then sunk to the seabed. While sinking, the caisson is balanced by pumping or sucking water. Once the target position is achieved, the cells are filled up with ballast to stabilize the caisson as needed. During the construction phase, the scaffolding system consists of traditional formworks for the base slab and sliding formworks for the vertical walls. In the transportation phase the caisson leaves the construction plant towed by a tugboat. A typical caisson arrangement is shown in Figure 1. The caisson has vertical and horizontal cross sections according to Figure 2. Conservatively, the beneficial stability effect due to the connection of one caisson alignment to the adjacent ones through the deck is not considered. The permanent loads considered, in addition to the self-weight of the R.C. caisson and the weight of the filling material, are constituted by the deck structure (prestressed precast beams plus R.C. slab) and the finishing, while for live loads a portion of the load due to containers is considered (participation coefficient  2 = 0.8). The paper considers solely along the quay excitation, therefore rocking movements around y axis (Figure 2). 19,91 19,91 19,91 19,91 19,91 14,00 Selected Caisson Figure 1. Typical pier arrangement and selected caisson. +0.0 -21.1 A A B B AA BB y x y x Figure 2. Cross sections of the selected caisson. Seismic performance of partially submerged R.C. caissons used in port structures Andrea Belleri 1 and Paolo Riva 1 1 Department of Engineering, University of Bergamo, Viale Marconi 5, 24044 Dalmine, Italy email: andrea.belleri@unibg.it, paolo.riva@unibg.it Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014 Porto, Portugal, 30 June - 2 July 2014 A. Cunha, E. Caetano, P. Ribeiro, G. Müller (eds.) ISSN: 2311-9020; ISBN: 978-972-752-165-4 485