Discussion on the initial fracture toughness K_(IC)~(ini) in the double-K criterion;

Introduced double-K fracture criterion used in concrete and considered softeni.

Focusing on the Two Parameter Fracture Method and the double-Kcriterion, the following work is carried on in this paper.

Aiming at the problem of dynamical strength failure of single layer latticed shells under strong dynamical load such as seismic,based on the dissipated energy mechanism of single layer latticed shells,a double-control criterion of dynamical strength failure was constructed by linear combination of maximum displacement and plastic accumulative dissipated energy.

the plastic volumetric-strain increment and the equivalent plastic strain increment under yield condition,the double shearing yield criterion is strictly deduced on the basis of plastic flow rule drawn from plastic flow rule of Drucker postulation.