Earthquake-induced　debris　flow　landslides　pose　a　serious　threat　to　bridge　structures.　However,　current　research　on　the　dynamic　response　and　damage　mechanisms　of　bridges　due　to　debris　flow　landslides　is　still　insufficient;　the　fragility　analysis　of　bridges　under　the　combined　effects　of　earthquakes　and　related　geological　hazards　needs　further　improvement.　In　this　paper,　a　bridge　dynamic　response　simulation　method　is　proposed　for　the　coupled　effects　of　transverse　earthquakes　and　debris　flow　landslides.　The　method　first　establishes　an　integrated　model　of　the　mountain　and　bridge　piers,　using　the　discrete　element　method　to　calculate　the　dynamic　impact　of　the　landslide　on　the　piers.　Subsequently,　a　nonlinear　dynamic　model　of　the　bridge　is　established　using　the　finite　element　method.　By　inputting　the　time　histories　of　transverse　seismic　motion　and　landslide　impact,　the　coupled　effects　of　transverse　earthquakes　and　landslides　are　analyzed.　The　paper　analyzes　the　influence　of　sliding　distance,　landslide　length,　and　slope　gradient　on　the　dynamic　response　and　fragility　of　bridges　through　case　studies.　Research　reveals　that　the　shear　capacity　of　the　pier　under　the　coupled　effects　of　earthquakes　and　landslides　should　be　considered.　The　combined　effects　also　increase　the　displacement　response　of　the　piers,　with　the　maximum　pier　top　drift　ratio　of　the　case　bridge　increasing　by　334　%　at　a　35°　slope　compared　to　the　earthquake-only　condition.　Under　the　coupled　effects　of　earthquakes　and　landslides,　the　piers　will　experience　significant　residual　deformation　in　the　direction　of　the　landslide.　Increases　in　sliding　distance,　landslide　length,　and　slope　gradient　all　increase　the　fragility　of　bridges　under　various　damage　states,　with　the　complete　damage　probability　of　the　case　bridge　rising　from　5　%　under　earthquake-only　conditions　to　47　%　at　a　35°　slope.　The　slope　gradient　has　the　greatest　sensitivity　to　the　fragility　of　bridges,　followed　by　the　sliding　distance,　and　finally　the　landslide　length.　©　2024　Elsevier　Ltd