Keywords: creep, shrinkage, reinforced concrete, hydro-thermo-mechanical analysis, engineering practice.

This paper presents a model for hydro-thermo-mechanical analysis of civil engineering structures that is applicable for broad engineering practice. The whole solution procedure was implemented in a finite element package ATENA [1] and was used carry out a few creep and shrinkage and moisture and heat transport sample analyses at the end of the paper.

Practical use of this model is imperative, because too advanced and sophisticated creep models are often (due to their complexity) of very low use for practical engineers that have to design not a simple laboratory beam, but a whole building etc. and such a design is not a three years long research project but, has to be completed within a few weeks. Hence, several simplifying assumptions have to be introduced in the proposed analysis. They were carefully chosen so that their use will not unacceptably impair accuracy of the whole analysis.

We use so called staggered solution scheme, i.e. if needed, the thermal analysis of the structure precedes its mechanical analysis. This decoupling is usually acceptable because thermal conditions, i.e. temperature and moisture history of structures are in most cases nearly independent of its mechanical properties, strains, stresses etc. (Obviously, it does not apply the other way around).

The creep and shrinkage mechanical analysis itself is based on the assumption of linear creep applied to nonlinear instant material behaviour. The time dependent structural conditions appear only as an input into a model for prediction of material creep and shrinkage. Several such models are supported, e.g. creep models by Bazant et al. [2,3], models proposed by CEB-FIP, ACI etc. to name a few. Note that structural loading due to thermal expansion plays also sometimes an important role and must be included.

The assumption of linear creep limits using of the proposed model to loading levels up to about 60-70% of their ultimate load. In most practical cases it is sufficient, because the usual serviceability design criteria impose even lower limits on the maximum load level allowed in the structure,

As for the instant constitutive law, it accounts for all cracks, crushes and other nonlinearities in the material. Of course, these cannot be neglected. The fracture-plastic constitutive law for mechanical behaviour is based on fracture mechanics and plasticity. It employs the cohesive crack model due to Hillerborg within the smeared crack model combined with the plasticity model based on Menetrey-Willam surface.

If loading level of the structure remains limited as mentioned above, the hydro-thermo-mechanical analysis procedure yields in most cases good quality results and at the same time we get significant reduction of execution cost both in terms of CPU time and RAM requirements. This make possible to carry out such an analysis in engineering practice.

1

J. Cervenka and L. Jendele, "Atena User's Manual, Part 1-7", Prague: Cervenka Consl., 2000-2006.

2

Z.P. Bazant, "Mathematical Modeling of Creep and Shrinkage of Concrete", New York: John Wiley & Sons,1988.

3

Z.P. Bazant, "Prediction of Concrete Creep Effects Using Age-Adjusted Effective Modulus Method", ACI Journal, 69 (4), 212-217, 1972.

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