To　solve　the　durability　problem　of　expansion　joints　and　bearings,　integral　abutment　bridges　(IABs)　have　become　increasingly　popular.　Soil　Structure　Interaction　(SSI)　is　a　fundamental　aspect　for　reaching　a　thorough　understanding　of　this　type　of　structure　not　only　for　newly　built　bridges　but　also　in　the　retrofitting　of　existing　ones.　Under　imposed　actions,　e.g.,　horizontal　expansion　and　contraction　induced　by　thermal　variation　and　time-dependent　effects　(creep　and　shrinkage),　the　connection　between　a　super-　and　substructure　responding　as　a　frame　structure　makes　IABs　different　from　other　conventional　bridges　that　introduce　forces　due　to　SSI.　Therefore,　the　overall　horizontal　stiffness　is　mainly　due　to　i)　the　piles＇　stiffness,　which　is　usually　flexible　enough　to　allow　for　the　deformation　of　the　superstructure　and　strong　enough　to　carry　out　the　vertical　loads,　and　ii)　the　type　of　soil　behind　the　bridge　abutment,　which　has　a　different　stiffness　depending　on　its　compaction　and　composition.　Several　approaches　have　been　proposed　in　the　literature　to　consider　these　types　of　interaction.　In　this　paper,　the　accuracy　of　different　formulations　commonly　used　in　IABs＇　design　and　based　on　p-y　curves　was　evaluated.　Formulations　for　piles　and　abutments　were　first　introduced.　Then,　a　fully　integral　abutment　bridge　built　in　China　was　considered　as　a　case　study.　A　finite　element　model　of　the　bridge　using　SAP2000　software　was　implemented,　and　the　influence　of　different　methods　and　formulations　was　investigated.　Finally,　the　obtained　results　for　different　types　of　soil　and　approaches　were　compared　and　discussed.