Contemporary analysis and numerical simulation of revisited long-term creep tests on reinforced concrete beams from the Sixties

The stresses and deformations in concrete change over time as a result of the creep- and shrinkage deformations of concrete. Different material models are available in literature in order to predict this time-dependent behaviour. These material models mostly have been calibrated on large datasets of creep specimens. In order to verify the accuracy of the contemporary material models with respect to the prediction of the creep behaviour of reinforced concrete beams, a cross-sectional calculation tool which employs the age-adjusted effective modulus has been developed and used to analyse an original set of 4 year-long creep data on reinforced beams from the 1960's. Six commonly used material models for the prediction of creep and shrinkage are considered in the current investigation: CEB-FIP Model Code 1990–1999, fib Model Code 2010, the model of EN1992-1-1, model B3, the Gardner Lockmann 2000 model, and ACI 209. The data on reinforced beams relates to an experimental investigation in collaboration with six major research institutes in Belgium. From 1967 until 1972 thirty-two reinforced beams with different reinforcement ratios were subjected, up until 4.5 years, to different stress levels in a four point bending configuration with a span of 2.8 m. In this paper a comparison between the measurements and the calculated deflections and strains is reported. Further, the deflections were also predicted using the contemporary creep models in combination with the nonlinear creep correction factor provided in EN1992-1-1, since the maximum concrete stresses in the beams were outside the service stress range of each of the models. Correcting for the nonlinearity of the creep coefficient significantly improves the calculated deflections. The most accurate predictions of the deflections at early age were obtained by the model of fib Model Code 2010. The Gardner Lockmann 2000 model exhibits the highest accuracy with respect to deflections at the end of loading and with respect to the creep rate.

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