Prestress Losses Due to the Effect of Shrinkage and Creep on Nontensioned Steel
Paul W. Abeles and Richard Kung
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beams (supports): compression;high temperature: humidity:research;strains: stresses.
Comparative tests on four types of beams, (three beams of each tvpe) all h avinq the same initial prestressing force (being cast in the same prestressing bed), were carried out by the authors at the University Southampton, 1970-71. All four types were of about the same ultimate resistance, but had different amounts of nontensioned steel in the ratios 1 : 2.68 : 4.0 : 5.22. Intensified and accelerated curing of the I2 beams was carried out during 86 days, at an average temperature of 38 C (100 F) and a humidity of 32 percent. Different kinds of strain measurements were made and showed very good agreement with the formulas suggested by CEB-FIP, according to which shrinkage and creep values can be calculated for varying conditions. The effective prestress with maximum amount of nontensioned steel was only 60 percent of that with minimum amount of nontensioned steel. Based on the good agreement between measurements and CEB-FIP formulas, the losses were evaluated for humidities between 50 percent and 100 percent for the four types of beams of different percentages of nontensioned steel which indicates that the prestressing losses at infinity increase substantially with reduced humidity and enlarged percentage of nontensioned reinforcement.