Deviations from the Principle of Superposition and their Consequences on Structural Behavior


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Title: Deviations from the Principle of Superposition and their Consequences on Structural Behavior

Author(s): S. Staquet and B. Espion

Publication: Special Publication

Volume: 227


Appears on pages(s): 67-84

Keywords: bridge; composite beam; creep properties; creep recovery; early age; heat curing; prestress loss; prestressing; shrinkage

Date: 3/1/2005

This research focuses on deviations from the linear viscoelastic behavior of concrete occuring at high stress levels (from 0.5 f’c to 0.7 f’c), at early age loading (1 to 2 days) and in case of unloading implying strain reversal. A large series of creep tests was performed on high strength concrete specimens undergoing creep under constant stress, followed by a period of recording of the creep recovery after complete unloading. Some specimens were heat cured before loading. Some nonlinear effects at very early age have been observed. After unloading, experimental data show that the creep recovery deviates strongly from the numerical predictions obtained by the application of the principle of superposition but seems to conform rather well to the recovery model proposed by Yue and Taerwe3. This model was then applied, through a step-by-step approach, for the time-dependent structural analysis of a precast composite prestressed bridge deck with 26 m span. The application of the recovery model yielded computed strains which are in good agreement with in situ measured strains, and in better agreement than the strains computed by the application of the principle of superposition. This enhanced approach was then used to optimize the phases of construction of this kind of structure. Thanks to this research, the age at transfer of prestress could be significantly reduced.