Failure Surface for Concrete under Multiaxial Load—a Unified Approach

A new unified five-parameter failure surface has been proposed for use with normal strength (NC), high strength (HSC), and steel fiber-reinforced (SFRC) concrete under biaxial, triaxial, or axisymmetric loads. The study covers concrete with strengths ranging from 20to130MPa. The failure surface developed for plain concrete has been modified to account for the presence of steel fibers. The proposed failure surface was verified against experimental data of unconfined NC, HSC, and SFRC under multiaxial loads, as well as concrete confined by steel tubes. To facilitate the implementation of the failure surface into a finite-element package, a closed-form solution for predicting the state of stress in concrete has been developed. This failure criterion was successfully incorporated into constitutive models for plain concrete and SFRC. Experiments of plain concrete cubes and SFRC plates under multiaxial loads, as well as SFRC beams under two-point load, were modeled to illustrate the application of the failure surface to a wide range of concrete under varying load conditions. Good agreement between analytical and experimental results is observed.