Compared　with　those　of　other　bridge　types,　the　structural　system　of　through　tied-arch　bridges　is　particularly　susceptible　to　failure　owing　to　the　deterioration　and　fracturing　of　tie-bars　as　well　as　a　lack　of　structural　robustness,　which　are　the　main　internal　and　external　causes　of　progressive　collapse　accidents,　respectively.　In　particular,　low　structural　robustness　strongly　influences　the　severity　of　accidents　induced　by　tie-bar　breakage.　To　objectively　reflect　the　possible　failure　mode　induced　by　tie-bar　failure　and　to　provide　improved　structural　robustness　in　through　tied-arch　bridges,　within　which　the　suspended　deck　system　is　relatively　independent,　a　robustness　assessment　framework　considering　tie-bar　failure　is　proposed　in　this　study,　by　considering　the　design　and　maintenance　essentials.　First,　the　main　analysis　parameters　for　the　extreme-event　limit　state　considering　tie-bar　failure　are　put　forward,　including　the　critical　tie-bar　failure　rate,　partial　factor　for　load　effects,　transverse　reduction　factor　of　multilane　loading,　dynamic　magnification　factor　of　material　strength,　and　reduction　factors　of　residual　strength.　Second,　the　quantitative　assessment　index　of　structural　robustness　I-T,I-rob　is　proposed　based　on　the　safety　redundancy　of　the　remaining　structural　members,　and　robustness　assessment　rules　are　put　forward　in　accordance　with　the　different　calculation　results　of　I-T,I-rob　and　horizontal　displacement.　A　typical　rigid-framed　through　tied-arch　bridges　is　assessed　using　the　proposed　framework.　The　assessment　results　reveal　that　multiple　fortifications　against　extreme　events　of　tie-bar　failure　can　be　established　by　designing　the　tie-bars　and　the　piers　with　sufficient　safety　features　to　form　the　first　and　final　line　of　defense　against　the　tie-bar　breakage　effect.　Moreover,　proper　maintenance　should　be　conducted　to　guarantee　the　structural　robustness　of　bridges　in　use.　The　methodology　is　well　suited　for　the　design　of　new　through　tied-arch　bridges　and　to　access　the　robustness　of　existing　bridges　to　ensure　the　safety　of　transportation　services.