Dynamic behaviour of a GFRP-steel hybrid pedestrian bridge in serviceability conditions. Part 1: Experimental study

Glass fibre reinforced polymer (GFRP) composites are being increasingly used in bridge engineering in a wide range of forms, including pultruded thin-walled multicellular deck panels, which allow for the fast installation of lightweight and slender footbridges. The lightness and slenderness of these panels, together with the damping and low elasticity modulus of the pultruded GFRP material, render these bridge decks potentially more susceptible to human-induced vibrations when compared to other equally slender non-composite systems. However, very limited information is available about the serviceability dynamic behaviour of GFRP footbridges, in particular about composite deck-to-girder systems. In this context, this paper presents an experimental study about the static and dynamic responses of the St. Mateus footbridge (recently built in Portugal), representative of a typical GFRP-steel hybrid solution. The investigation included: (i) static load tests, (ii) modal identification tests, and (iii) vibration tests for different dynamic pedestrian load cases. In general, the acceleration-time records obtained attested an adequate structural responses of the footbridge, in terms of both vertical peak and root mean squared (RMS) acceleration values, even for the most severe load cases (deck loaded at 33% and crowded condition). In spite of relatively high acceleration peaks for pedestrians crossing in running mode, results obtained also show that there is low probability of user discomfort. In a companion paper (Part 2), the experimental results presented herein are used to assess the accuracy of conventional numerical models and analytical formulae in predicting the vibration response of the St. Mateus footbridge.