Modeling Time-Dependent Deformations: Application for Reinforced Concrete Beams with Recycled Concrete Aggregates

This paper describes the development and validation of a time-dependent fiber-based (that is, layered) numerical model for the service-load deflection analysis of reinforced concrete structures. Specifically, the model is applied to analyze the effect of recycled concrete aggregates (RCA) on the deflections of beams. Previous research has shown that increased deflections (rather than reduced strength) may be a greater limitation for the use of RCA to replace natural coarse aggregates (for example, gravel and crushed limestone) for increased sustainability. Analysis and design tools are needed to quantify this increase in deflections so that limits on the use of recycled aggregates can be established. To aid in quantifying these increased deflections, a new time-dependent concrete fiber including creep and shrinkage strains was developed in the open-source structural analysis program, OpenSees (Open System for Earthquake Engineering Simulation). This paper describes the validation of the model, including recent data from service-load tests of slender cracked and uncracked RCA concrete beams. The model was able to predict the time-dependent deflections of reinforced concrete structural members under various load scenarios; however, the initial (instantaneous) deflections were generally underestimated because of underestimations in the extent of cracking. The model was also able to predict the total strains and increased neutral axis depth over time as a result of creep and shrinkage strains, except for the tension strains that were underestimated because of the inability of the model to accurately predict the amount of cracking. It was found that the shrinkage strains had a large effect on the time-dependent deflections of the beam test specimens, which was not a finding available from the experimental measurements. While the paper focuses on RCA concrete applications, the numerical model is a general-purpose tool that can be used to analyze the time-dependent axial-flexural deformations of conventional reinforced concrete structures as well.