Calibration of GPS for dynamic displacement measurement of long span cable-supported bridges in vertical direction

Global Positioning System (GPS) is an emerging tool for measuring and monitoring both static and dynamic displacement responses of long span cable-supported bridges under gust winds. Since vertical vibration of a long span cable-supported bridge is more significant than its lateral vibration, this paper focuses on the assessment of dynamic displacement measurement accuracy of GPS in vertical direction. In the first phase of work, the accuracy of GPS in measuring vertical sinusoidal displacement motions is examined by using a motion simulation table. The comparison of the table motion recorded by the GPS with the original motion generated by the table shows that the GPS can measure accurately sinusoidal dynamic displacements within certain frequency and amplitude ranges. In the second phase of work, the capability of the GPS in tracking the measured wind-induced bridge deck motion of Tsing Ma Bridge during Typhoon Victor is examined. To reduce multi-path effects on GPS measurements, an adaptive filter based on the recursive least-squares (RLS) algorithm is used to enhance the measurement accuracy of GPS. The comparative results demonstrate that the GPS can trace wind-induced dynamic response of long span cable-supported bridges satisfactorily.