Field-Measured Natural Frequencies of Delaware Memorial Bridge
The Delaware Memorial Bridge is a major suspension bridge that is critical to the tristate region of northern Delaware, southern New Jersey, and southeastern Pennsylvania. The Delaware Memorial Bridge consists of two nearly identical suspension bridges (hence, the nickname Twin Spans) that cross the Delaware River from southern New Jersey to northern Delaware. Field ambient vibration measurements of Structures 1 and 2 of the Delaware Memorial Bridge were conducted in June 2001 and September 2003. These measurements were used to derive the natural frequencies and modes of vibration for these structures. These field-measured frequencies and modes were then compared with each other and with computer-generated natural frequencies and modes of vibration derived for Structure 2 of the Delaware Memorial Bridge in 1997. Specifically, the 2001 seismometer-generated results for Structure 1 were compared with the 2003 accelerometer-generated results for Structure 1; the 2003 field-measured results for Structure 2 were compared with the 2003 field-measured results for Structure 1; and the 2003 field-measured results for Structure 2 were compared with the 1997 computer-generated results for Structure 2. Overall, these three types of comparisons indicated relatively good correlation for transverse motion but only fair correlation for longitudinal and vertical motion.
Ambient Vibration Studies of Golden Gate Bridge: I. Suspended Structure
Extensive experimental investigations were conducted on the Golden Gate Bridge in San Francisco, California, to determine, using ambient vibration data, parameters of major interest in both wind and earthquake problems, such as effective damping, the three‐dimensional mode shapes, and the associated frequencies of the bridge vibration. The paper deals with the tests that involved the simultaneous measurement of vertical, lateral, and longitudinal vibration of the suspended structure; a subsequent paper addresses the measurement of the tower vibration. Measurements were made at selected points on different cross sections of the stiffening structure: 12 were on the main span and 6 on the side span. 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 vertical, torsional, lateral, and longitudinal vibrational modes. In all, 91 modal frequencies and modal displacement shapes of the suspe...
Correlation of Predicted and Observed Suspension Bridge Behavior
Validity of model tests concerning behavior of suspension bridge in wind depends on possible scale effect, and difference between natural wind and wind used in model tests; test data are presented to demonstrate that turbulent or dynamic effects dominate wind action on bridges; behavior of Tacoma Narrows Bridge and Golden Gate Bridge provides good correlation with predictions from model tests and analysis.