The paper attacks the problem of steel redundant structures reliability. In calculations the probabilistic method of limit equilibrium is applied. All possible mechanisms of structural failure are considered. The influence of each section on the work of the frame as a whole is taken into account. Stochastic strength and load characteristics are used in the calculations. The proposed method of calculation allows to obtain structures with a given reliability. The calculation provides an opportunity to take into account the existing reserves of frames. The numerical example uses the logic of probabilistic transformations. The graphs of specific contributions of individual sections and the most probable mechanisms of destruction are presented. The probabilistic method takes into account the correlation between the individual mechanisms of destruction. The developed method determines the limiting moments, but it is allowed to take into account the action of the longitudinal force. In this example, the task was to align the impact of the frame sections without reducing the specified reliability, but it is possible to obtain a design with the same specific contributions, which is most economically justified. Specific contributions are increased or decreased as necessary to obtain a design with equal probability of failure. In the design, the influence of destruction individual mechanisms is used, because the cross sections of the beam span or floor column do not change from the design conditions. The method provides an opportunity to obtain more optimal designs and the use of modern software systems for static calculation. Recommendations for the design of these structures have been developed. It is proposed to use the reliability coefficient of redundant steel structures.