Creep behavior of pultruded GFRP elements – Part 1: Literature review and experimental study

This paper first presents a state-of-the-art review about the viscoelastic time-dependent – creep behavior of fibre reinforced polymer (FRP) materials in general, and pultruded glass fibre reinforced polymers (GFRPs) in particular, at different element scales. The literature review aims at pointing out the present gaps regarding the understanding of this phenomenon and guiding the future developments lines for the application of pultruded GFRP in civil infrastructure, including bridges and buildings. The paper then presents results of experimental investigations carried out on pultruded GFRP material made of polyester and E-glass fibres at two different scales: (i) laminate and (ii) full-scale profile. The test programme included (i) flexural creep tests on 8 mm thick small-scale specimens with a span of 160 mm, subjected to sustained loads corresponding to stress levels ranging from 20% to 80% of their ultimate stress; and (ii) a flexural creep test on an I-profile (150 × 75 × 8 mm) with a span of 1800 mm, subjected to a constant load of 1/3 of its ultimate load. The deflections and axial strains over time, measured in laboratory environmental conditions, were recorded for time durations up to 1600 h. The results obtained confirm an important effect of the creep phenomenon on pultruded GFRP profiles, with small-scale specimens having failed for load levels as low as 50% of the ultimate stress; in addition, the creepocity measured on both types of elements was quite significant after the first hours, even for an average load level of 30%. Subsequently, the experimental results were used for material characterisation by means of empirical and phenomenological formulations (Part 2).