Associated people

J. Schröder, D. Brands, M. Pise in cooperation with S. Anders, G. Gebuhr (Bergische Universität Wuppertal)
 

Abstract

Systematic investigations of the deterioration of high- (HPC) and ultra-high-performance concrete (UHPC) subjected to fatigue loading are currently not available. This holds especially true for steel-fiber modified HPC and UHPC. Furthermore, numerical approaches and models are often calibrated using experimental data from literature, which does not allow a comprehensive calibration due to lacking coordination between experiments and numerical models. Therefore, this project aims at testing, describing and modeling the ongoing deterioration of steel-fiber modified HPC and UHPC subjected to fatigue loading, using multiscale approaches and phase-field theory. Here, two common concrete mixtures are applied: (i) HPC with a strength category C50/60 and (ii) UHPC with a compressive strength of about 150 MPa. The HPC will be modified using hooked-end steel-fibers with contents ranging from 23 kg/m² to 115 kg/m³, whereas the UHPC will contain short, straight high-strength fibers with contents ranging from 57 kg/m³ to 115 kg/m³.The fiber performance in the concrete matrix will be investigated in pull-out tests on single fibers. Additionally, static and cyclic 3-point-bending tests as well as cyclic uniaxial compression tests will be performed comparing fiber-free and fiber modified mixtures of the mentioned concretes each considering different load-levels. From these tests, damage indicators such as development of strain, stiffness or dissipated energy will be calculated and used to describe damage evolution using a strain-based formulation. Furthermore, a comprehensive energy function controlling the material degradation for a macroscopic model will be developed and implemented.Numerical simulations based on multiscale approaches are used for modelling and prediction of the macroscopic material behavior. On the mesoscale an ellipsoidal unitcell, serving as a representative volume element consisting of concrete matrix with a single embedded fiber, will be constructed and calibrated. In order to reduce complexity of the macroscopic simulations, an effective material model including an orientation distribution function for the fibers is constructed. The damage localization and crack propagation are modelled using the Phase-field Theory.An Experimental-Virtual-Lab approach, which is represented by the planned working program will be evaluated and optimized finishing the first funding period. Based on this approach a procedure evaluating fatigue performance of general (U)HPC mixtures will be developed, combining only a couple of experiments together with numerical techniques

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