Scale Bridging Uncertainty Modeling and Computational Simulation of Fiber Reinforced Concrete

M.Sc. Stefanie Roskosch



Reinforced concrete structures like bridges exhibit damage even before they reach the aimed service life. The durability of those structures is controlled by closely interacting transport and degradation processes. To ensure a longer service life, durability oriented models are necessary. These models require input data and constitutive equations, which due to measuring accuracy, can only be quantified up to a certain degree of precision. Therefore, environmental conditions and human imprecision have to be connected with uncertainties.

Fiber reinforced concrete is a composite of Portland cement, aggregate, and steel fibers. If plain concrete is exposed to bending, the concrete immediately breaks, because unreinforced concrete is brittle with a low tensile strength and strain capacity. Fibers are generally utilized in concrete to minimize the crack size. However, the magnitude of the influence of fibers in the composite depends on the orientation of the fibers. A direct quantification of the scatter of the fiber orientation is practically unfeasible at the structure scale, which leads to additional uncertainty.




Figure 1: Numerical analyses of a notched FRC beam assuming three different fibre distribution density functions (red ellipsoids) and the scatter of experimental results [RILEM Technical Committees. RILEM TC 162-TDF: Test and design methods for steel fibre reinforced concrete uniaxial tension test for steel fibre reinforced concrete. Materials and Structures, 34, 2001, pp. 3-6.]




Figure 2: Simulation based reduction of uncertainties of FRC: a) Two stages of the computational simulation of the casting process of FRC [Gudzulic, V.: Computational modelling of fiber flow during casting of fresh concrete. Master thesis RuhrUniversityBochum, 2017], b) Illustration of the spatial distribution of the fibre orientation tensor as ellipsoids and histograms at two selected locations from multiple realizations.


In the current research cohesive interface crack models with discrete embedded truss elements are used to simulate reinforced, prestressed reinforced and fiber reinforced concrete structures and its’ durability. It is analyzed how uncertainties at the material scale like fiber distribution and crack roughness in combination with human imprecisions like the reinforcement position affect the structural reliability.



Figure 3: Prestressed reinforced concrete beam as a sample model to analyze uncertainties. Top: Geometries and material parameters of the sample model. Bottom: Analyzing crack roughness and 1D moisture transport after applying prestress within the truss element and displacement at the top of beam.




Contact


M.Sc. Stefanie Roskosch
stefanie.roskosch@rub.de
+49 234 / 32-27792

↑