Hyperbolic Functions for Prestress Loss and Camber

Prestress loss and camber of prestressed concrete beams were found to grow with time at a decreasing rate provided no dead or live load was applied to relieve the beam from the eccentric prestressing force. Nineteen full-size bridge beams made of normal weight and lightweight concrete were studied. Simple hyperbolic functions to predict the time-dependent prestress loss and camber were developed. Predicted results by this method and the rate of creep method were compared with measured values. Comparisons between predicted and measured results of tests reported by others were also made. It was found that: (1) the prestress loss and camber of the bridge beams, stored in the open air in Houston, Texas, attained their ultimate values within 100 days to 150 days after prestressing, and ; (2) predicted values by both methods were in close overall agreement with measured values.