This　paper　aimed　to　propose　an　analytical　framework　for　assessing　the　postearthquake　traffic　flow　capacity　of　girder　bridges　based　on　the　loss　model　of　vertical　load-carrying　capacity.　For　this　purpose,　a　loss　model　of　the　vertical　load-carrying　capacity　of　a　reinforced　concrete　(RC)　column　associated　with　the　residual　drift　ratio　and　the　damage　level　(i.e.,　the　modified　Park-Ang　index)　was　developed　to　determine　the　postearthquake　vertical　load-carrying　capacity　accurately　and　quantitatively.　Subsequently,　the　probability　seismic　demand　analysis　(PSDA)　was　performed　to　obtain　the　probability　distribution　functions　(PDFs)　of　engineering　demand　parameters　(EDPs)　(i.e.,　the　residual　drift　and　the　damage　indicator)　and　the　PDF　of　postearthquake　vertical　load-carrying　capacity　was　determined　based　on　the　developed　loss　model.　Furthermore,　the　reliability　analysis　was　utilized　to　calculate　the　postearthquake　reliability　index　of　a　bridge　by　adjusting　the　mean　values　of　the　live　load　(which　reflects　the　traffic　flow　capacity),　and　the　postearthquake　traffic　flow　capacity　could　then　be　quantitatively　determined　based　on　the　live　load　ratio　at　a　target　reliability　index.　Finally,　the　proposed　framework　was　implemented　on　a　single-column　bridge　to　demonstrate　its　efficiency.　Compared　to　traditional　qualitative　and　subjective　postearthquake　functionality　assessment　of　the　damaged　bridge,　the　proposed　analytical　approach　offered　a　mathematical　model　for　the　decision-making　process.　　©　2023　American　Society　of　Civil　Engineers.