Assessment of the structural condition of a cable-stayed footbridge based on dynamic tests



This paper presents an investigation on the structural condition of a cable-stayed footbridge based on data collected in two dynamic tests, performed at different times. The natural frequencies and mode shapes were obtained by applying output only modal identification methods. At least four experimental mode shapes of the footbridge and stay cables were identified in Operational Modal Analysis. A 3D finite element model of the footbridge was calibrated by adjusting its dynamic properties to the experimentally identified in the first test. The procedure showed, besides an approximation of the dynamic behavior, an approximation of its static behavior, which was confronted to the structural design. The analysis found a discrepancy between the required reinforcement based on the updated model stresses and the existing steel reinforcement. The second test, performed one year later, provided different natural frequency values to those found in the first test and the spectrum presented inconsistency in one of its peaks. It was concluded that the structure presents conditioning problems, thus warning to future structural problems.