The article describes a diagrammatic method for evaluating the effectiveness of strengthening structures under load. As an indicator of efficiency, a parameter is introduced that is set as the level of reinforcement loading of concrete by the beginning of the reinforced structure’s concrete destruction. The nonlinear deformation diagrams show the sequence of development and redistribution of stresses in the sections of the conditional inflexible concrete element, amplified without removing the load. The results of the practical calculation of the gain under load for some variations of the strength and the deformative characteristics of concrete are given. The data obtained indicate the possibility of applying the proposed methodology to the evaluation of the strengthening structures effectiveness without removing the load.