Abstract:The concept and rationality of using plastic complementary energy(PCE) as the criterion of structures¢ stability are illustrated. Based on the concept of constraint-equilibrium in non-equilibrium thermodynamics,deformation reinforcement theory,which analyzes the mechanical behaviors of unstable structure with unbalanced forces exceeding the yield surface,is presented. Compared with the results obtained by ABAQUS,TFINE and theory respectively,the stabilities of cylinder rock specimens and homogeneous slope are analyzed. The influence of mesh sizes of the dam-heel in FEM on PCE is studied based on Drucker-Prager yield criteria. By adopting the load with the same magnitude but in opposite direction with unbalanced forces,the bearing capacities of rectangular column and strip foundation before and after reinforcement are analyzed and compared with the theoretical solution. The results show that PCE is the scalar norm of plastic strain from the perspectives of integral degree,as well as the distance away from safety. Hence PCE could be a reasonable evaluation criterion of structure. Furthermore,the reinforcement calculation and analysis based on unbalanced forces clearly present the area and size of reinforcement under a certain safety degree. This type of reinforcement is very efficient and could provide guidance for practical engineering.