Accounting for steel relaxation in prestressed concrete by finite element packages

The stresses and strains in a prestressed concrete structure are subject to changes over a long period of time, during which creep and shrinkage of concrete and relaxation of the steel prestressing tendons develop gradually. If these time-dependent deformations are not considered properly during design with suitable measures taken during construction, cracking or other problems may occur afterwards. Although some commercial finite element packages can model creep and shrinkage of concrete, seldom can they model steel relaxation accurately. This paper presents a practical method to model steel relaxation in commercially available packages that are mostly competent at modelling complicated geometry. The accuracy and reliability of the methods are examined by comparing the results with available solutions. Good agreement with numerical solutions obtained from the same assumptions is observed. Reasonable agreement with available experimental results is observed and possible reasons leading to the discrepancies observed are discussed.