Numerical Simulation of Aged Reinforced Concrete Column Nonlinear Creep Due to High Sustained Load

A numerical simulation method for predicting reinforced concrete (RC) column creep under high axial sustained stresses exceeding 75% of concrete short-time strength f'(c) with loading ages greater than 200 days is explored. The objective is to investigate a comprehensive approach to predicting reinforced columns' long-term nonlinear behavior. Nonlinear creep of RC columns is modeled based on combining a theoretical framework for the time-dependent uniaxial behavior of plain concrete under high axial sustained loads and an age-adjusted effective modulus method for calculating linear creep of reinforced concrete columns. The mechanism of the theoretical framework is improved by extending the prediction of linear concrete creep estimated by the GL2000 model to that of nonlinear concrete creep. The measured experimental results of concentrically loaded column tests are compared with the predictions from the numerical simulation method. For the RC columns loaded to 76% of their short-time strength calculated by the ACI equations without considering any strength reduction factor, the difference between the measured and predicted creeps at the end of sustained loading was less than 6%. However, for the RC columns loaded with 98% of column shoer-time strength, the predicted creep was 26% and 18% greater than the measured creep at the end of sustained loading. The research is concluded that the reason caused the predicted creep is greater than the measured creep because transverse reinforcement can restrain concrete creep under higher sustained stresses, especially in the early stage of sustained loading.