Conventional piled foundation designs tend to be overly conservative since the beneficial role of the raft is often neglected by assuming the piles to be the only part of the structure interacting with the soil. The contribution of the raft to the global response of the foundation is particularly important in the case of "large"piled rafts, where the pile length is comparable to the raft width. This configuration, although not theoretically optimal, is common for existing foundations of bridges and high-rise buildings. Although the beneficial effect of raft-pile-soil interaction on both bearing capacity and stiffness is generally acknowledged, simple and reliable approaches recognized by design codes are not yet available. Aiming at providing simple tools for designing large piled rafts under static and dynamic/cyclic loads, in this paper a numerical study is presented, with preliminary finite element analyses performed to examine the mechanical behaviour of a "large"piled raft under vertical centred loads and positioned on a dry sand layer. This paper presents the findings of this study, comparing the performance of the piled raft to the corresponding pile group and unpiled raft, and highlights the importance of considering the presence of rafts in the design of piled foundations.

The current effort towards the progressive switch from carbon-based to renewable energy production is leading to a relevant spreading of both on- and off-shore wind turbine towers. Regarding reinforced concrete shallow foundations of onshore wind turbine steel towers, possible reductions of reinforcement may increase their sustainability, speed of erection, and competitiveness. The article presents the results of an experimental program carried out at Politecnico di Milano concerning both cyclic and monotonic loading, simulating extreme wind conditions on 1:15 scaled models of wind turbine steel towers connected by stud bolt adapters to reinforced concrete shallow foundations embedded in a sandy soil. Three couples of foundation specimens were tested with different reinforcement layouts: (a) similar to current praxis, (b) without shear reinforcement, and (c) without shear reinforcement and with 50% of ordinary steel rebars replaced by steel fibers. Additional vertical loads were added to the small-scale models in order to ensure similarity in terms of stresses. The test results allowed to (i) characterize the mechanical behavior of the foundation element considering soil-structure interaction under both service and ultimate load conditions, (ii) assess the foundation failure mode, (iii) highlight the role of each typology of reinforcing bars forming the cage, and (iv) provide hints for the optimization of these latter.