The effect of the reduction of concrete material strength and the deformations and stress level due to the non-uniform temperature distribution within a structural element such as a storage tank has a coupled negative effect on the post-tensioned concrete design. Heated strands embedded in a heated concrete element will elongate, hence reducing the post-tensioning force. This reduction will reduce the confinement of concrete, which added to the temperature gradient derived tension results in a greater level of damage and cracking. This study sets up a strongly non-linear model that attempts to account for all these effects. The results show that cracking localization grows surrounding the tendon duct, producing a sharp decrease in the post-tensioning force and a significant reduction of global stiffness.

The effect of high temperature in concrete has been addressed in a variety of ranges and applications.Concrete shows a significant reduction in its strength, both compressive and tensile, as well as in its stiffness due to a decrease of the modulus of elasticity. Besides, fracture energy drops also with temperature increase, diminishing the ductility of the structural element.

The structural element considered is a post-tensioned concrete cylindrical storage tank. The design of these tanks for energy storage systems, impose temperature levels on the inner side of the shaft much higher than those measured at the outer face of the concrete wall. A material model combining macro-cracking, continuous displacement fields, damage and plasticity has been used to characterize concrete. The main model parameters are considered as temperature dependent. Elastic-plastic models and a fictitious no-tension steel strand host are used.

The results attempt to show that the consideration of temperature dependent fracture parameters is essential to evaluate properly the stress level of the section, the post-tensioning force and the measurable strains. The convenience of post-tensioning vertically the structure is also shown for certain ranges of pressure that may be associated to a temperature gradient.
 

Access to the document: Third International Conference on Mechanical Models in Structural Engineering

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