Experimental and finite element analysis of the long-term behaviour of GFRP-concrete hybrid beams fabricated using adhesive bonding

This paper presents experimental and numerical investigations about the short- and long-term behaviour of a hybrid beam consisting of a GFRP pultruded profile bonded by an epoxy adhesive joint to a reinforced concrete slab. The experimental program included flexural creep tests on GFRP I-profiles and on hybrid beams subjected to constant loads. The deflections and the longitudinal strains were measured in natural environmental conditions and recorded for time durations up to 3500 h. Also, three-dimensional models, based on the incremental form of the linear viscoelastic theory, were proposed to study the evolution of strains and stresses over time for the structures. The results of the sustained-load test show that creep deflections on the order of 27-37% of the initial static deflections were observed for the hybrid beams after about 5 months of loading. It is also found that, for the hybrid beam, the rapid degradation of bond strength, resulted from the combined effect of environmental conditions and applied loading, leads to debonding and subsequently a brutal failure. Furthermore, the finite-element analysis is found to be able to simulate the long-term behaviour of the hybrid beam and help understand the complex changes in the stress state that occur over time.