Filtering Low-Cost GNSS Measurements to Determine Structural Behaviors: The Case of Davutpaşa Pedestrian Bridge

This study investigates the dynamic responses of the Davutpaşa Pedestrian Bridge to pedestrian loads using low-cost and high-cost Global Navigation Satellite Systems (GNSS) along with accelerometers. Traditionally, expensive dual-frequency GNSS receivers were employed for structural monitoring, but recent advancements in low-cost GNSS technology have provided a cost-effective alternative. The study employs signal filtering techniques and Fast Fourier Transform (FFT) to analyse datasets in time and frequency domains. Specifically, the Yule-Walker Design of Infinite Impulse Response (IIR) Band-pass Filter is applied to GNSS measurements to reveal natural frequencies obscured by noise. The accuracy was assessed by comparing frequency values obtained through full-scale monitoring with those from a Finite Element (FE) model. After filtering analysis, it has been determined that the natural frequencies obtained from geodetic GNSS agree with accelerometer frequencies with a maximum difference of 0.12 Hz (3%). In low-cost GNSS receivers, for the A10 antenna, a maximum difference of 0.09 Hz (3%), and for the UBX antenna, a maximum difference of 0.10 Hz (3%) has been obtained, showing compatibility with the accelerometer. As a result, it has been found that with appropriate filtering techniques and selecting sampling intervals suitable for structural dynamics, even rigid structures like pedestrian bridges can have their natural frequencies determined using geodetic equipment.