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Resistance surface concept for concrete fracture

Resistance surface concept is presented in the paper, which brings a new perspective into the part of fracture mechanics of quasi-brittle materials. This concept is based on equivalent elastic crack models and resistance curves (R-curves) with the extension to the three-dimensional space. Third dimension is constraint parameter T-stress or dimensionless biaxiality factor B evaluated at the elastic equivalent crack tip. It results from experimental and numerical studies, that R-curves of specimens with various testing configurations possibly are subsets of a R-surface. In the paper four typical testing configurations with different constraint conditions are studied: three point bending of notched beam, double edge notched cube under eccentric compression, double edge notched cube under uniaxial tension and single edge notched cube under compact tension.