Ambient Vibration Studies of Golden Gate Bridge

Dynamic characteristics such as natural frequencies, mode shapes, and damping ratios of the Golden Gate Bridge tower were determined using ambient vibration data. The ambient vibration tests involved the simultaneous measurement of longitudinal and lateral vibrations of the main tower (San Francisco side). Measurements were made at different elevations of the tower and on the pier, at a total of 10 stations. Good modal identification was achieved by special deployment and orientation of the motion-sensing accelerometers and by summing and subtracting records to identify and enhance definition of longitudinal, torsional, and lateral vibration modes of the tower. A total of 46 modal frequencies and modal displacement shapes of the tower were identified: 20 longitudinal, 15 torsional, and 11 lateral, all in the frequency range of 0.0–5.0 Hz. Finally, comparison with previously computed two- and three-dimensional mode shapes and frequencies shows good agreement with the experimental results, thus confirming both the accuracy of the experimental determination and the reliability of the methods of computation.