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Considering the interaction between concrete shrinkage and concrete creep and between the relaxation of prestressing steel and concrete creep in the prestressed concrete member, a refined method for estimating the time-dependent prestress losses is developed. Using the integral mean value theorem, the integrations regarding the coupling terms in the derived equation are transformed into a one-step calculation. Through step-by-step numerical analysis, the median coefficients and their simplified expressions as a function of loaded age and age of observation are established based on the models in fib MC 2010 and AASHTO-LRFD 2014. A case study of the time-dependent prestress losses in a simply supported girder with a T-shaped cross-section is conducted. The effectiveness of the proposed method is verified by performing a comparison with the numerical results obtained by the step-by-step method which is regarded as a relatively exact solution and compared with the results obtained by the methods recommended in EN 1992-1-1:2004 and AASHTO-LRFD 2014. It is demonstrated that the proposed method achieves good accuracy compared to the results of the step-by-step numerical method.
Yang et al. (Thu,) studied this question.