The Complementary Characteristics of GPS and Accelerometer in Monitoring Structural Deformation

Traditionally structural response due to severe conditions has been measured using accelerometers. However it is a relative acceleration measurement. The displacement from acceleration measurement cannot be obtained directly by simply applying the laws of motion through double integration. GPS-RTK offers direct displacement measurements for dynamic monitoring, but it has its own limitations. The measurement accuracy can be affected by multipath and depends strongly on the satellite geometry. In this paper a new technique will be described that uses the correlation signals directly detected from GPS-RTK and accelerometer to transform one form of measurement to another. The methodology consists of Fast Fourier Transform (FFT), a filtering technique, and velocity linear trend estimation from both GPS and accelerometer measurements. Two types of datasets are tested, acquired by a combined GPS-RTK and accelerometer system deployed on a 108m steel tower. One dataset was collected from 19:00 to 21:00 Japan Standard Time (JST) during Typhoon No.21 on 1 October 2002. Another was collected from 18:00 to 19:00 JST when an earthquake occurred on 26 May 2003. The lab-based threshold setting for accelerometer suggested by earlier research has been avoided. The false and missing measurements from GPS can be recovered by acceleration transform. The weakness of lacking static and quasi-static components for the acceleration-derived results is also resolved by adding the GPS displacement linear trend. Because of redundancy within the integrated GPS-RTK and accelerometer system has shown robust quality assurance in monitoring structural deformation in full scale.