Experimental study of immediate and time-dependent deflections of GFRP reinforced concrete beams

Due to the mechanical properties of fibre reinforced polymer (FRP) bars, deflections often drive the design of FRP reinforced concrete (RC) flexural members. This has led to an increasing number of studies focused on the analysis of short-term deflections of FRP RC beams. However, investigations and experimental data focused on long-term deflections are scarce. The time-dependent deflection in RC beams is a function of member geometry, material properties and loading characteristics. Maximum service loads, as well as repeated loading, affect the deflections under sustained loads. This paper presents the results and discussion of an experimental programme concerning eight glass FRP RC beams tested at service load, and subsequently subjected to sustained loading for 250 days. Two reinforcement ratios and two levels of sustained load were considered. The experimental results revealed an effect of the loading–unloading processes and the reinforcement ratio on short and time-dependent deflections. No significant influence of the sustained load level was observed. Moreover, the theoretical predictions obtained with different models have been compared with the experimental results. The modified time-dependent factor presented in ACI 440.1R-06, together with the modified Bischoff’s equation to compute the immediate deflections due to sustained load, give the best agreement with experimental deflections.