Dynamic assessment of an FRP pedestrian bridge using FEM and operational modal analysis

Fibre-reinforced polymer (FRP) pedestrian bridges offer high durability due to their corrosion resistance, but limited design confidence restricts wider adoption. While their low weight provides advantages over traditional bridges, it also increases susceptibility to wind- and footfall-induced vibrations. This paper presents a dynamic assessment of a curved FRP modular pedestrian bridge designed by Network Rail using finite element modelling (FEM), accelerometer- and fibre-optic-based modal identification, and vibration serviceability verification under human excitation. FEM predictions incorporating explicit modelling of connection stiffness showed an average error of approximately 14 % compared with operational modal analysis, whereas neglecting connectivity increased errors up to 33 %. This demonstrates the critical role of realistic connection modelling in accurately predicting the dynamic behaviour of modular FRP bridges. Modal identification using accelerometer data showed good agreement for the first mode, with an 8 % difference, while strain-based fibre-optic measurements captured the second and third modes with an average agreement of 15 %. A methodology for decoupling vibrational modes in curved bridge geometries in the two principal horizontal directions was achieved by cross-correlating power spectral densities of rotated acceleration components. Damping ratios obtained from accelerometer data were mode- and direction-dependent ranging from 0.28 % to 1.72 %. The findings support improved dynamic modelling and serviceability assessment of curved, modular FRP pedestrian bridges.