Effects of Cyclic Temperature on the Time-Dependent Behavior of Posttensioned Concrete Bridges

Typically, measurement and analysis of concrete time-dependent behaviors such as creep and shrinkage are performed under the assumption of constant temperature conditions. However, many structures in the field are subject to variable seasonal and daily temperatures. This paper explores how changes in temperature affect the time-dependent behavior of concrete structures, with a particular focus on posttensioned concrete bridges. Temperature-dependent creep, shrinkage, aging, and relaxation models were incorporated into structural finite-element analyses examining a posttensioned concrete beam under variable thermal loading. The impacts of uniform temperature changes on the time-dependent deflections, strains, and stresses were accounted for using an Arrhenius-adjusted age based on the structure temperature. However, nonuniform temperature changes, such as thermal gradients through the depth of the cross-section, caused time-dependent behavior that could not be accounted for using the Arrhenius-adjusted age based on the average structure temperature. Time-dependent vertical deflections and especially longitudinal stresses throughout the structure were altered by the repeated application of thermal gradients. The different creep and shrinkage strain rates through the depth of the section, driven by the temperature and stress differences from the applied thermal gradients, induced residual stresses. The presence of these residual stresses implies that time-dependent stress changes from a creep and shrinkage analysis at a constant temperature cannot be linearly superimposed with the stresses caused by thermal gradients computed using an independent elastic analysis.