Summary
The paper briefly discusses the time-dependent effects of thermal stressing of prestressed concrete beams with reference to long sustained temperature crossfalls. Certain principles and assumptions are presented and an iterative numerical method is introduced to allow for creep in the calculation of the variation with time of stresses, strains and displacements. The results of tests on heated simply supported and continuous prestressed beams are compared with the predictions of the theory. The measure of agreement shows that the method can indicate the magnitude of the severe time-dependent effects with reasonable accuracy. Finally, it is demonstrated in general terms that under a prolonged temperature crossfall, a prestressed concrete beam will, in general, reach a stable stress distribution. This distribution can be calculated without reference to the elastic modulus and coefficient of expansion of the concrete. The limiting stresses thus calculated have been verified in various examples by the iterative analysis described earlier. These steady-state stresses are useful in that they form a limit to the range of possible stresses, and they can be calculated directly without iteration.
