Plasticity models for the biaxial behaviour of concrete at elevated temperatures, Part I: Failure criterion

The mechanical response of concrete at elevated temperatures under a generalized state of stress is extremely nonlinear, with both the plastic behaviour and mechanical properties highly temperature dependent. In this and a companion article the plastic response is modelled as possible. Initially, a general analytical form of the failure surface is developed from the available biaxial test data. The envelope is written in terms of stress invariants as a function of temperature, and shows good agreement with experiment. For a given temperature, the loading surface is found by scaling the failure envelope using a hardening parameter. The model is used in the sequel to develop incremental elastic-plastic relationships, and to study deformations in a range of biaxial tests