Modal identification and damping performance of a full‐scale GFRP‐SFRSCC hybrid footbridge

Abstract

Slender footbridges are prone to excessive vibrations due to pedestrian effects, and comfort criteria often govern their design. In this sense, composite materials that combine high damping capacity with relatively high stiffness and low mass can provide functional benefits. This paper presents a study of the dynamic behaviour of an 11 m long hybrid footbridge made of two I-shaped pultruded glass fibre reinforced polymer (GFRP) main girders and a thin steel fibre reinforced self-compacting concrete (SFRSCC) deck, in operation since 2015. The main goals were (i) to improve the knowledge of the dynamic properties of composite footbridges and (ii) to assess the benefits of using a structure made of pultruded GFRP instead of a conventional material (steel), namely, considering its greater ability to dissipate energy. The resonant frequencies, damping ratios, and mode shapes of the footbridge were identified based on experimental testing. A finite element (FE) model of the footbridge was developed and calibrated with test data and used to simulate the effects of pedestrian loads. Simulations of the same type were conducted on an equivalent structural system made of steel profiles. The simulation results of the two short-span footbridges with similar natural frequencies enhance the impact of high-order harmonics of the pedestrian load in the dynamic response. It is also shown that polymer-based components can contribute to limiting vibrations in footbridges or even act as self-dampers.