AbstractFor through tied-arch bridges, the corrosion and degradation of the cable’s load-bearing capacity are the main external causes of cable breakage and subsequent structural failure; nevertheless, the progressive collapse after cable breakage is primarily attributed to the weak structural robustness, which makes a huge potential risk of bridge operation and maintenance (O&M). Whereas, as the basis of O&M, current condition evaluation method has not yet taken into consideration the influence of different consequences of cable breakage, resulting in unscientific conclusions for O&M decisions frequently. In this study, a robustness-based condition evaluation framework for the overall structure of the through tied-arch bridge is presented, consisting of three stages: (1) structural robustness assessment associated with tie-bar and suspender failure respectively; (2) classification of evaluation process by the results of robustness assessment, within which the overall structure is either evaluated using the code method or evaluated directly as unqualified (Condition I and II), or the structural member weightings are adjusted according to the robustness weightings (Condition III); and (3) condition evaluation of entire bridge. The evaluation processes of three conditions are further presented in accordance with the tied-arch structure and suspended deck system. To establish the robustness weightings in Condition III, the safety redundancy indexes of through tied-arch structures as well as the suspended deck system are calculated separately, combined with robustness assessment result. Applying the proposed framework to evaluating the condition of a through tied-arch bridge with different structures, the analysis and comparison indicates that, due to the robustness of the through tied-arch structure and suspended deck system, the variation in the potential risk of accidents induced by cable failure is shown intuitively through the evaluation results, which better meets the needs of guiding bridge O&M decisions consequently.

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