Piled raft foundation is a geotechnical composite construction consisting of three elements: piles, raft and soil. In piled raft foundation, the superstructure load is shared between the piles and the raft. The analysis of piled raft foundations has improved over the last few decades to account for the combined contribution of raft and piles to provide a more efficient system. In this study, the contribution of cushion between the pile head and the raft on bearing behavior of the piled raft foundation in case of pile tip on hard strata has been conducted. The full interaction between the components of piled raft foundation was accounted by a three-dimensional finite-element method. Abay river bridge has been taken as case study. The raft, pile and soil have been discretized as eight-noded brick elements the raft and piles were modelled with a linear elastic constitutive model whereas, the soil continuum was modelled with Mohr coulomb constitutive model. The foundation settlements and bearing behavior between raft and pile have been investigated to identify the contribution of unconnected piles and cushion to the total capacity of piled raft foundations. In this thesis both connected and unconnected piled raft foundation subjected to comprehensive distributed load has been analyzed using ABAQUS version 6.13 commercial software. The results of the analyses show that the unconnected piled raft vertical settlement is increase due to the negative skin friction b/n the pile and the cushion. The contribution of the interaction b/n the cushion-soil and raft-soil with and without interaction effect is investigated. Hence in case ofunconnected piled raft foundation, the interaction of cushion-soil is significant than without interaction as compared to connected piled raft. A parametric study has been conducted to show the effect of weak layer located under hard stratum below pile tips both on connected and unconnected piled raft behavior. Based on the results, it can be concluded that the effect of this weak layer is negligible for relative stiffness between the weak and hard strata. The stiffness ratio is greater than 0.5 for connected piled raft and 0.3 for un connected piled raft. In addition; the piled raft behavior is not affected if the weak layer is located below 10m for connected piled raft and below 8m for non-connected piled raft. Key words: unconnected piled raft, connected piled raft, cushion, settlement, stiffness ratio