Stress relaxation due to steam curing

A new equation for isothermal relaxation of stress-relieved steel previously derived, has been modified to study stress losses in prestressed elements due to steam curing of concrete. A calculation method is proposed, which takes into account the effect of loosening during heating and of releasing of the prestressing force. The theory predicts a complete stress stabilization after steam curing up to times depending on temperature and duration of the steam curing. Furthermore, for longer periods the theory predicts an increase of the relaxation values. Tests performed show an excellent agreement between theory and experimental results.