Methodology of Long-Term Real-Time Condition Assessment for Existing Cable-Stayed Bridges

Difficulty in measuring the total stress of bridge girders in service (due to dead, live, and environmental loads) raises a significant problem in assessing existing cable-stayed bridges without a complete monitoring record from construction to service. To address this problem, this paper develops a practical monitoring methodology that needs to focus only on the variation of the bridge condition during the service period. In the proposed methodology, the variation of the bridge condition is considered with respect to two sub-conditions: the long-term load condition and the service live load condition. Using the varying cable forces as a reflection of the long-term load condition, the effect of time-dependent loads can be entirely traced back from the present to the bridge's completion. The service live load condition is real-time monitored using strain sensors distributed across different cross-sections. Specific bridge design codes are used to set up the assessment criterion by specifying the stress threshold envelopes for checking each sub-condition of the bridge. By using a three-dimensional solid finite element model in the study of service live load condition, it becomes feasible to arrange measurement stations at the exactly same positions as those on the real structure. A case study is conducted through which the advantages of the proposed methodology are demonstrated.