Numerical modeling of the tension stiffening in reinforced concrete members via discontinuum models

[prova tipográfica]This study presents a numerical investigation on the fracture mechanism of tension stiffening phenomenon in reinforced concrete members. A novel approach using the discrete element method (DEM) is proposed, where three-dimensional randomly generated distinct polyhedral blocks are used, representing concrete and one-dimensional truss elements are utilized, representing steel reinforcements. Thus, an explicit representation of reinforced concrete members is achieved, and the mechanical behavior of the system is solved by integrating the equations of motion for each block using the central difference algorithm. The inter-block interactions are taken into consideration at each contact point with springs and cohesive frictional elements. Once the applied modeling strategy is validated, based on previously published experimental findings, a sensitivity analysis is performed for bond stiffness, cohesion strength, and the number of truss elements. Hence, valuable inferences are made regarding discontinuum analysis of reinforced concrete members, including concrete-steel interaction and their macro behavior. The results demonstrate that the proposed phenomenological modeling strategy successfully captures the concrete-steel interaction and provides an accurate estimation of the macro behavior

FERTILISATION STRATEGIES ACROSS EUROPE: CURRENT SITUATION, POTENTIAL AND LIMITS FOR A HARMONISED APPROACH

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Damage evolution in different types of concrete by means of splitting tests

A new splitting test has been used for evaluating damage in different types of concrete. The set up was developed at the Stevin Laboratory of Delft University of Technology and comprises a completely new loading device in which a perfectly horizontal splitting load can be applied to concrete specimens. In addition to classical mechanical measurements, a high resolution optical microscope has been adopted for crack detection at the surface of the thin specimens. Microscale information was obtained on the topological characteristics of the damage patterns. Fractal dimensions were computed. In total, three cement paste mixtures, four mortars and four different types of concrete will be discussed in this paper. The concretes contained either river gravel with different maximum aggregate size (2 and 16 mm), phosphorous-slag aggregates or Lytag lightweight aggregates. To obtain a better understanding of the failure mechanisms at the interface between matrix and composite, tests were performed where a single (cylindrical) aggregate was embedded in a matrix of cement paste or mortar. It will be shown that the concrete mixture with phosphorous-slag aggregates yields the highest peak load and the most brittle post-peak behavior whereas the concrete with large river gravel aggregates shows the most ductile load-displacement response. Furthermore the interfacial strength is affected substantially by the density of the aggregates. This provides a different failure mechanism for the lightweight concrete as indicated by the microscopic observations. The fractal analysis of the different damage patterns confirmed different behaviors, strictly related to peculiar microscopic mechanisms.Stevin LaboratoryCivil Engineering and Geoscience