FWF - Mindestbewehrung - Material Law and Model to Estimate Minimum Reinforcement

Massive concrete structures tend to develop cracks over the period of hardening which are caused by stresses. Using existing approaches, the formation of cracks cannot be predicted or controlled satisfactory. Reasons therefore are uncertainties of available material models as well as particular characteristics of massive concrete structures. Furthermore, the influence of concentrated reinforcement positioned near border zones is not taken into account sufficiently by the existing models. Up to now, the material properties of hardening concrete have been described by design models without considering its history of stress. Yet early exposure to loads affects the material very negatively, in particular its tensile strength. To predict the force, time and location at which cracks appear by using the existing material model delivers unreliable results. Therefore, the model will be expanded by the influence of stress-dependent aging under consideration of viscoelasticity. Limitation of crack-width is realised by reinforcing the concrete. Today's design approach bases on investigations on hardened concrete. The expanded material model which is to be developed will comprise an improved bond model and a new calculation approach for young concrete. The new developed material and bond model will be incorporated in a FE-model. Special characteristics of massive concrete structures are going to be considered; stress and crack formation will be predicted. The model will be validated by on site measurements. Parameter studies and model calculations will build the basis for developing the required design model of massive concrete structures.