Creep response of GFRP–concrete hybrid structures: Application to a footbridge prototype

Glass fibre reinforced polymer (GFRP) pultruded profiles have been increasingly used in civil engineering structural applications in the past few decades owing to their high strength, low weight and corrosion resistance. Nevertheless, the low material moduli, which makes design most often governed by deformability and instability phenomena, the brittle failure mechanisms and the high initial costs, have been delaying their widespread use. Hybrid GFRP–concrete structural solutions have been proposed to overcome the aforementioned limitations, namely the low material moduli. Furthermore, GFRP material creep models suggest that such hybrid structures may reduce the creep deformations when compared to full GFRP structures. In this context, this paper presents experimental and analytical investigations about the creep behaviour of a hybrid GFRP–concrete footbridge comprising two I-shaped GFRP pultruded profiles and a thin deck made of steel fibre reinforced self-compacting concrete (SFRSCC). The experiments comprised flexural creep tests on a 6.0 m long footbridge prototype subjected to a uniformly distributed load for up to 2642 h, during which deflections and axial deformations were monitored. In order to assess the influence of loading and environmental conditions on the creep behaviour of the structural system, the prototype was tested for three different combinations of load levels and seasons. Experimental results showed that (i) GFRP–concrete hybrid structures lead to a considerable decrease of the creep deformations of GFRP structures and that (ii) environmental conditions significantly influence the viscoelastic response of these hybrid structures. The models proposed, based on the creep response of the constituent materials, were able to predict the observed structural response for the different load levels and environmental conditions with very good accuracy. Therefore, they are proposed to predict the long-term response of GFRP–concrete structures instead of empirical models based on short-term experimental data.