Investigation of dynamic properties of a long-span cable-stayed bridge during typhoon events based on structural health monitoring

Three typhoons approached the southeast coast of China during August 2012. The structural health monitoring (SHM) system recorded in-situ environmental factors (including wind speed and temperature) and structural responses (including displacements and acceleration) during the whole period. Based on the recorded SHM data, the variation features of the environmental factors and structural responses are investigated respectively. Furthermore, modal parameters including natural frequencies and damping ratios of SCB are identified and tracked during this period; such that, the relationship between modal parameters and environmental factors is studied. Results show that the variation of acceleration amplitude of the deck is mainly caused by the high-frequency excitations between 1.0 and 7.0 Hz which may correspond to the traffic and high-frequency wind loads. The low-frequency wind load, smaller than 1.0 Hz, is the major factor that controls the variation of dynamic displacements of the deck. In addition, a clear relationship between damping ratios and wind speed can be observed for the first three vertical modes, based on which, the aerodynamic damping can be subtracted. Conclusions can provide references for serviceability and safety assessment of similar long-span bridges.