Flexural creep response of pultruded GFRP deck panels: Proposal for obtaining full-section viscoelastic moduli and creep coefficients

Glass fiber reinforced polymer (GFRP) pultruded flexural members are generally analyzed for serviceability limit states using shear-deformable beam theories, considering their short-term full-section moduli. However, regarding long-term design, for which the effect of viscoelasticity must be taken into account, the time-dependency of those full-section properties were not yet properly defined, namely for multicellular panels used in bridge decks. To address this issue, this paper describes an experimental study about the flexural creep response of full-scale multicellular GFRP pultruded deck panels subjected to uniformly distributed loads for about 5 months under normal laboratory environmental conditions. The creep behaviour of the panels was first successfully modelled using Findley's power law, confirming the ability of this empirical approach to simulate the viscoelastic response of multicellular deck panels. Next, an experimental methodology involving the measurement of creep deflections in panels with different spans and applying the Timoshenko beam theory in the time domain was proposed in order to characterize simultaneously the full-section flexural and shear moduli over time. The results obtained, including design formulae for the time-dependent creep coefficients for shear and bending, indicate that the creepocity due to shear is much higher, with reductions after 50-years in the effective flexural and shear stiffness of 22% and 43%, respectively. Finally, a comparison is made between these creep coefficients and those suggested in the most relevant design guidelines.