Accelerometer and displacement transducer are two common sensors used for structural displacement measurement. Due to their incapability of measuring static deflection of a structure, Global Positioning System (GPS) is developed as a novel sensor for measuring and monitoring both static and dynamic displacement responses of large civil engineering structures under gust winds. However, the accuracy of dynamic displacement measurement with GPS at the sub-centimeter to millimeter level depends on many factors such as required data update rate, satellite coverage, atmospheric effect, multi-path effect, and GPS data processing methods. Therefore, this paper focuses on the assessment of dynamic displacement measurement accuracy of GPS in two orthogonal directions. A 2-D motion simulation table is first developed as a test bed simulating various types of two perpendicular translational motions of tall buildings. The 2-D motion simulation table was then used to assess the performance of GPS through a series of field measurements in an open area. A band-pass filtering scheme is finally designed and applied to the table motion data recorded by the GPS. The comparison of the table motion recorded by the GPS with the original motion generated by the table shows that the GPS can measure sinusoidal or circular dynamic displacements accurately within certain amplitude and frequency ranges. The comparative results also demonstrate that the GPS can trace wind-induced dynamic responses of tall buildings satisfactorily.
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.