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.　©　2020　American　Society　of　Civil　Engineers.