engleski

Fracture of concrete at high loading rates

In the paper the results of numerical failure analysis of plain concrete beam loaded by impact three-point bending load are presented and discussed. The theoretical framework used in the numerical analysis is continuum mechanics, irreversible thermodynamics and finite element method. As a strain measure Green-Lagrange stain tensor is used. The constitutive law is based on the rate sensitive microplane model together with the co-rotational stress tensor. To assure objectivity of the analysis with respect to the size of the finite elements, crack band method is used. The contactimpact analysis is based on the mechanical interaction between two bodies – concrete beam (master) and dropping hammer (slave) falling at the mid span of the beam. The contact constrains are satisfied by Lagrange multiplier method, which is adapted for the explicit time integration scheme. The numerical results are evaluated, discussed and compared with test results known from the literature. It is shown that the beam resistance and failure mode depend on the loading rate. For lower loading rates beam fails in bending (mode-I fracture). However, with increase of loading rate there is a transition of the failure mechanism from bending to shear. The results are in good agreement with theoretical and experimental results known from the literature.

fracture of concrete; high loading rates; microplane model

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