ABSTRACT
This chapter describes the mechanical model, experimental determination of the parameters, mathematical expression, and other formulation of the unified strength theory (UST). Strength theory deals with the strength of material under the complex stress state. In 1991, ninety years after the establishment of the Mohr-Coulomb failure criterion, a new unified strength theory appeared. The solo-shear strength theory is the lower bound, and no admissible limit surface may exceed that of the solo-shear strength theory (Mohr–Coulomb strength theory) from below. The twin-shear strength theory is the upper bound, and no admissible limit surface may exceed that of the twin-shear strength theory from above. The UST encompasses many well established criteria as its special cases or linear approximations. The UST is convenient for application to analytic solution of plasticity and engineering problems. Several unified solutions for plastic behavior of structures were introduced by using the UST.
