Past　earthquakes　have　repeatedly　demonstrated　that　skewed　bridges　are　more　vulnerable　to　earthquake-induced　failure　than　straight　bridges　because　of　their　complex,　irregular　geometries　and　unique　load-transfer　mechanisms.　This　study　focused　on　analyzing　the　seismic　performances　of　prestressed　concrete　box-girder　highway　bridges　with　seat-type　abutments　under　bidirectional　near-fault　ground　motions,　especially　with　respect　to　abutment　skew　angle,　gap　size　at　the　expansion　joint　between　the　superstructure　and　the　abutment　in　the　longitudinal　direction,　and　initial　gap　size　between　the　the　superstructure　and　abutment　shear　keys　in　the　transverse　direction.　Three　dimensional　models　of　single-and　two-span　bridges　with　seat-type　abutments　were　developed　considering　nonlinear　characteristics　of　skew-angled　abutments,　bridge　key　components,　abutment-soil　interaction,　soil-pile　interaction,　and　the　pounding　effect　between　the　superstructure　and　the　abutments.　Nonlinear　time-history　analyses　were　performed　for　various　skewed　highway　bridge　models　using　seven　sets　of　near-fault　ground　motions　with　two　horizontal　components.　Results　showed　that　the　skew　angle　and　gap　size　in　longitudinal　and　transversal　directions　have　significant　impact　on　the　seismic　behavior　of　skewed　highway　bridges.　The　deck　displacement　in　the　longitudinal　direction　and　rotation　response　will　increase　with　the　increase　of　the　skew　angle,　but　the　transverse　displacement　response　exhibits　a　more　severe　response　after　the　skew　angle　reaches　30　degrees.　The　longitudinal　deck　displacement　and　rotation　of　skewed　bridges　increase　with　decreasing　gap　size　at　the　expansion　joint　in　a　longitudinal　direction.　Furthermore,　the　behavior　of　shear　keys　may　have　an　important　effect　on　the　overall　seismic　response　of　skewed　highway　bridges,　especially　the　probability　of　collapse　due　to　excessive　deck　rotation.　(C)　2017　American　Society　of　Civil　Engineers.