Integration of GPS, Accelerometer and Optical Fiber Sensors for Structural Deformation Monitoring

Monitoring the response of structures, especially tall buildings, under severe loading conditions is an important requirement for the validation of their design and construction, as well as being a maintenance concern. Traditionally such response has been measured using accelerometers. However it is impossible to measure the static or quasi-static components of movement with such sensors. An integrated system comprising RTK-GPS, accelerometer, and optical fiber sensors has been proposed for monitoring structural deformation, with the objective being to assess the integrity of structures. The GPS and accelerometer sensors have been installed on a 108m tall steel tower in Tokyo, together with other sensors such as anemometer and strain gauge. In this paper the seismic and wind-induced responses of the tower are analysed using Fast Fourier Transformation (FFT) of the GPS and accelerometer measurements. Then the correlated signals are extracted by a digital filtering technique. The filtered data sets are also converted to displacement (in the case of accelerometer) and acceleration (in the case of GPS) through double integration and double differentiation respectively, for the purpose of direct comparison. The results agree with each other very well, except that the static component is missing from the accelerometer derived results. Meanwhile, extensive indoor experiments have been conducted to test optical fiber Bragg grating (FBG) sensors for the measurement of distributed strain. The FBG sensors have demonstrated excellent performance with respect to sensitivity, linearity, repeatability and dynamic range, characteristics which complement the GPS and accelerometer sensors. The FBG system will be installed along side the GPS and accelerometer sensors when it is ready for field testing. In this paper the feasibility of integrating advanced sensing technologies such as GPS and FBG with traditional accelerometer sensors, for structural deformation monitoring, has been demonstrated.