High-rate (20 Hz) single-frequency GPS/GALILEO variometric approach for real-time structural health monitoring and rapid risk assessment

Real-time monitoring and the rapid risk assessment of the engineering structures after a natural event is crucial to prevent further disasters. Global Navigation Satellite System (GNSS) relative positioning and Precise Point Positioning (PPP) have been widely used in determining the seismic waveform and structural displacement. On the other hand, variometric approach (VA) is a future-promising method in capturing the real-time dynamic motions. VA technique has been broadly used in real-time co-seismic displacement retrieval so far. However, the usability of the high-rate single-frequency (SF) variometric approach in real-time structural health monitoring has not been investigated in the literature, yet. This paper examines the ability of the SF-VA based on 20 Hz GPS-only and GPS/GALILEO observations to capture high-frequency dynamic displacement and time difference displacement. The dynamic harmonic motions with various frequency and amplitude values were created using a single-axis shake table. In addition to that 1995 Kobe earthquake's ground motion was also tested on the shake table to evaluate the performance of SF-VA for GNSS seismology applications. Displacement time and frequency series of SF-VA were compared with a series of Linear Variable Differential Transformer (LVDT) sensor installed to the shake-table. The comparisons show that SF-VA can effectively capture the harmonic motions’ vibrational frequencies and displacement amplitudes. The observed amplitudes of the displacement of harmonic movements are slightly different from the LVDT values at the order of millimeters. Thus, it is found that the SF-VA approach is a powerful and reliable tool in real-time structural health monitoring and rapid risk assessment.