Refined calculation of time-dependent prestress losses in prestressed concrete girders

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.