Ultra-high performance fiber-reinforced concrete (UHPFRC) is usually applied for thin-walled and lean constructions because of its excellent mechanical properties. However, these lightweight constructions such as bridge girders, masts, towers, and railway tracks, for example, are susceptible to oscillations due to cyclic loading. A model describing the fatigue behavior of UHPFRC is required. Therefore, the material behavior of all mixture components and the composite itself, each subjected to cyclic tensile loading, is studied experimentally and numerically on the mesoscale at iBMB, Division of Concrete Construction and Institute of Structural Analysis both at TU Braunschweig. In this paper, first findings concerning bond processes of single and multiple micro steel fibers embedded in ultra-high performance concrete as well as a new geometrically and physically nonlinear bond model are presented.
K E Y W O R D Sbond stress-slip behavior, damage processes, micro steel fiber, nonlinear bond model, ultra-high performance concrete
Accurate prognoses of the durability of concrete structures require a detailed description of the continuously running aging processes and a consideration of the complete load history. Therefore, in the framework of continuous porous media mechanics a model is developed, which allows a detailed analysis of the most important aging processes of concrete as well as a flexible coupling of different processes. An overview of the prediction model and the balance equations is given. The material dependent model equations, the consequences of coupling different processes and the solution scheme are discussed. In two case studies the aging of concrete due to hydration and chloride penetration are presented, which illustrate the capabilities and the characteristics of the developed model.
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