Centrifuge testing of a bridge pier on a rocking isolated foundation supported on unconnected piles

A preceding experimental study carried out at the University of Dundee, as well as independent experimental and numerical research results, have shown the improved seismic performance of rocking shallow foundations in comparison to conventional, conservatively designed foundations, for bridges. By properly reducing the size of the footing, rocking behaviour due to seismic loading can occur about the footing base. It has been shown that rocking foundations can reduce seismic ductility demand on bridge columns and improve bridge performance so much so as to enable them to safely resist very strong seismic motions which lead to collapse of alternative conventional systems. Yet, key concern is the potential for significant settlement accumulation, especially in relatively poor soil conditions. Therefore, current research objectives focus on exploring possible innovative foundation systems that will optimise the seismic performance of rocking foundations. To this end, a series of dynamic centrifuge tests on 1:50 scaled bridge piers on sand were performed. This paper presents results for only one of the investigated alternatives: the rocking foundation is supported by a 4x4 group of unconnected reinforced concrete (RC) piles. Comparative evaluation of the performance of this hybrid foundation system indicates significant reduction of settlements, yet at the cost of increased deck drift. It is shown that particular care must be taken in designing such foundation syste