The dynamic characteristics of the Kao-Ping-Hsi cable-stayed bridge, located inbetween Kaohsiung and Pingtung county, Taiwan, is monitored under daily trafficflow for assessing its health conditions. The bridge is an asymmetric single towercable-stayed bridge with the main span of 330 m, and side span 180 m. The height ofthe inverse Y-shaped pylon is 183.5 m, measured from the foundation to the top ofpylon. Experimental data were measured from servo-velocity sensors, with sixchannels, were placed at various locations on the bridge. Data sampling rate was 100Hz, and system-identification techniques, such as the random decrement (RD)technique and Ibrahim time-domain (ITD) method, were adopted for data reduction.The vibrational modes of the bridge were identified for their natural frequencies anddamping ratios under different traffic loading conditions. The loading conditions areclassified by the root-mean-square (RMS) deck velocities. The magnitude of thetorsion mode of the Kao-Ping-Hsi cable-stayed bridge is found to be one order-ofmagnitudeless than that of the transverse mode, and two orders-of-magnitude lessthan that of the vertical modes. Conventionally, through monitoring the naturalfrequencies, vibrations induced by traffic flow can be used to reliably monitor thehealth of the bridge. However, we found that the damping ratios may serve as a moresensitive indicator to describe the condition of the bridge, due to its high sensitivity tothe RMS velocities. It is expected that damping ratio may be more sensitive to localchange in material properties or component connectivities. Therefore, use of both ofthe natural frequencies and damping ratios may provide a more accurate description ofthe health of cable-stayed bridges.
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