Prestress losses and camber growth in wing-shaped structural members

摘要

Prestressed concrete wing-shaped members are frequently used in the construction of long-span roofs in precast concrete buildings. Roofs spanning more than 30 m (100 ft) are built by assembling a number of these thin-walled members. To optimize their design and take advantage of their potential load-carrying capacity, the transfer of large forces from the pretensioned strands to the concrete is critical. Information on the evolution of these forces and of the ensuing deformations is necessary, not only in the long run, but also immediately after concrete casting and during the first few weeks. The Department of Civil and Environmental Engineering of the University of Perugia in Italy and a major prefabrication firm of central Italy have completed an experimental program on pretensioned wing-shaped members to investigate the evolution of prestressing stresses and of camber during the different stages of concrete hardening. The result allowed the careful evaluation of the pre-stress losses that occur in the first three weeks during concrete placement and curing to emphasize the influence of the temperature history on the development of prestress losses and to calibrate suitable parameters for the prediction of camber growth. Numerical comparisons based on Eurocode 2 are also performed to check the reliability of the numerical procedure adopted by the authors and to ascertain whether using self-consolidating concrete (as in the manufacture of the specimens tested in this project) makes any sizeable difference with respect to the predictions based on Eurocode 2, which refers to ordinary concrete.