Measured dynamic properties of web-core sandwich panel FRP composite footbridges and their relation to pedestrian comfort analysis

Abstract

This paper reports experimental data for the dynamic properties (i.e. first fundamental flexural frequency, damping ratio, comfort class) of ten web-core sandwich panel FRP composite footbridges in Belgium, which contributes to the assessment of relevant input parameters for design and assessment of this promising bridge type, quickly gaining popularity in recent years. The data is gathered based on smartphone accelerometers, enabling easy, quick, affordable, and abundant measurements, while at the same time yielding reliable experimental values. Given the relatively short spans, the heel and excitation test methods are used, rather than the ambient vibration method. The tests indicate damping ratios of one to three percent, which are strongly dependent on the number of people on the bridge during the measurement. Additionally, comfort analysis tests with up to 58 people (0.5 P/m²) were conducted on five out of the ten bridges. The results indicate that the current design guidelines for pedestrian comfort analysis are overconservative and do not reflect the effect of pedestrian-induced damping, which is especially apparent for this bridge type given its very low modal mass and relatively low damping ratio.

Modal Parameter Identification and Comfort Assessment of GFRP Lightweight Footbridges in Relation to Human–Structure Interaction

“…Before processing the vibration data, a bandpass filter with low and high cut-off frequencies of, respectively, 0.5 Hz below and 0.5 Hz above the estimated first natural flexural frequency directly obtained from the iDynamics application is applied in the postprocessing tab of the iDynamics application. This operation will remove second-order effects and outliers from the raw vibration data, resulting in data that are more suitable for the further determination of the first natural flexural frequency and the structural damping ratio [51,68]. After applying the filter to the raw vibration data, for every heel test, the processed z-vibration data are split into four individual vibrations (e.g., the second vibration in Figure 4 runs from 8 s to 14 s).…”

“…This paper presents the implementation, execution and results of different vibration tests performed on four GFRP and four steel simply supported footbridges in the Flanders region of Belgium [67] during two measuring campaigns. The type and implementation of the vibration tests and the analysis of the vibration data are identical to those in [68]. As human-structure interaction is expected to occur in all lightweight footbridges, the dynamic behaviour of GFRP footbridges is compared with that of steel footbridges [69,70].…”

“…This paper will contribute to the understanding of human-induced vibrations and damping and further expand the knowledge related to human-structure interaction for lightweight GFRP and steel footbridges. The novelty of this paper in comparison with [68] lies in the reciprocal comparison of steel and GFRP footbridges and a new approach to better estimate the evolution of the structural damping value with increasing pedestrian density. Furthermore, a more accurate calculation based on experimentally obtained values of the structural damping at different pedestrian densities is implemented in the analytical calculation of the vertical accelerations in the design of lightweight footbridges.…”

Vibration-based monitoring of an FRP footbridge with embedded fiber-Bragg gratings: Influence of temperature vs. damage

“…The working principle of VBM is based on the relation between the stiffness, mass and energy dissipation of a structure and its dynamic behaviour, which is entirely determined by the modal characteristics: natural frequencies, damping ratios and mode shapes [11,12,13]. VBM is already used for monitoring concrete [14,15], steel [16,17] and composite bridges [18,19,20].…”

“…Operational damage induced by e.g., fatigue, impact loading or overloading, results in non-visible deterioration of the internal matrix of the FRP that can lead to delamination, matrix cracks or internal adhesive joints failure. VBM is a promising alternative for the time consuming and costly Non Destructive Testing methods currently available [49] and has been used for monitoring several FRP structures [20,50,51].…”