Tie　bars　on　through　tied　arch　bridges　are　often　in　poor　condition　and　may　serve　as　an　external　cause　of　a　tie-bar　failure　accident;　nevertheless,　bridge　structural　robustness　contributes　greatly　in　resisting　progressive　collapse,　and　poor　robustness　tends　to　be　the　essential　internal　cause　of　possible　accident.　To　study　the　dynamic　effect　of　tie-bar　failure　of　a　through　tied　arch　bridge　and　to　reveal　the　mechanism　of　how　structural　robustness　reduces　dynamic　effects,　a　finite-element　model　of　a　typical　rigid-frame　through　tied　arch　bridge　is　developed　based　on　the　most　adverse　tie-bar　breaking　time,　a　transient-unloading　method　with　equivalent　load　is　adopted　to　analyze　the　dynamic　response　of　tie-bar　failure,　and　the　results　under　different　working　conditions　are　compared.　Furthermore,　parameter　analysis　of　the　arch-to-pier　stiffness　ratio　is　conducted　for　the　dynamic-amplification　effect.　The　results　indicate　that　both　the　pier　and　the　arch　rib　have　significant　dynamic-amplification　effects　with　respect　to　tie-bar　breakage,　and　the　remaining　tie　bars　are　the　most　vulnerable　elements　of　the　bridge;　thus,　they　should　be　considered　the　most　important　elements　when　conducting　tie-bar　failure　analysis;　the　most　adverse　breaking　time　adopted　in　cable　breakage　analysis　can　be　taken　as　0.01　T;　a　greater　arch-to-pier　stiffness　ratio　is　beneficial　to　reduce　the　dynamic　response　brought　on　by　tie-bar　breakage;　therefore,　a　rigid-frame　through　tied　arch　bridge　should　be　designed　with　a　large　pier　thrust　stiffness,　while　a　simply　supported　tied　arch　bridge　should　not　be　used　in　future　through　arch　bridges,　and　existing　ones　should　be　retrofitted　as　soon　as　possible.　(c)　2020　American　Society　of　Civil　Engineers.