Modelling the time-dependent behaviour of concrete

In many concrete structures such as prestressed pressure vessels or secondary safety containments concrete is subjected to thermal and hygral gradients in external loads. A model is developed to describe materials behaviour under this complex time-dependent state of stress. By means of this model the influence of (a) temperature gradients caused by heat of hydration or external heating, of (b) variation of moisture content, and of (c) further development of degree of hydratation under load on material properties is taken into consideration. It is shown that crack formation in the tensile zone severely influences time-dependent deformation. Crack formation can be expressed as strain softening. The model is first checked and verified by comparison with experimental findings obtained by means of test series on plain concrete. Then the materials model-law is used within a comprehensive computer program. With this program it is possible to calculate the time-dependent stress-strain relation of advanced concrete structures. Examples will be described in detail. Theoretical predictions will be compared with measurements on real structures. (orig.)