Concrete utilized in engineering structures is usually subject to the action of multi-axial stress. The strength theory of concrete is significant to structure design and saving of construction material. Experimental results have revealed that lightweight aggregate (LWA) concrete represents platform flow plasticity under high compressive stress. The ultimate strength surface of LWA concrete under multi-axial stress intersects with the hydrostatic stress axis at two different points, which is completely different from that of the normal concrete as the ultimate strength surface is open-ended. So the strength criterion aimed at normal concrete cannot fit LWA concrete. In this paper, a fourparameter multi-axial strength criterion for LWA concrete is presented. The strength envelope of the proposed model in the deviatoric plane adopted elliptic curve similar to that of Willam-Warnke model, and the tensile and compressive meridians are represented by quadratic functions with four parameters. Two methods can be used for the determination of the four parameters and their merits and drawbacks are compared by the analysis of experimental data.


Concrete utilized in engineering structures is usually subject to the action of multi-axial stress (Yu, 2002). A lot of research works have been done to the study of strength theory of concrete and many strength criteria that conform to these characteristics have been proposed. Most of them can be divided into three categories (Fan and Wang, 2002). The first category is basically empirical, such as the five-parameter model built by Willam- Warnke; the second is physical, for example the Mohr-Coulomb model; and the third is phenomenological as the model of Ottosen's criterion. The tensile and compressive meridians both employ parabolic forms. It has been observed that the five-parameter model of Willam- Warnke agrees closely with the experimental results in the lower stress state.

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