Diagnosis of instant and long-term damages in cable-stayed bridges based on the variation of cable forces

This study aims to develop effective methods for the damage diagnosis of cable-stayed bridges based on the variation of cable forces. The air temperature is firstly adopted to eliminate the environmental temperature effects from the cable force variation. The instant damage scenario caused by earthquake is investigated using a methodology recently proposed by the authors. The other two damage scenarios regarding the unequal settlement and the asphalt pavement overlay are also considered. For these two types of long-term damages, a new approach by taking the moving average is established to remove the daily variations. A transfer coefficient is subsequently obtained to take out the long-term temperature effect from the averaged variation history of cable force. According to the data collected from Ai-Lan Bridge, the thresholds for diagnosing the long-term damages are determined. The FE models for Chi-Lu Bridge and Ai-Lan Bridge are then constructed to simulate various damage scenarios and assess the diagnosis methodology. It is demonstrated that mild seismic damages can be effectively detected. The identification of an unequal settlement reaching 9 mm or more is also found to be feasible. Moreover, the asphalt pavement overlay with a thickness of 3.2 cm can be distinctly detected.