A review of scientific research on survivability and protection of buildings from progressive collapse showed that despite the researchers’ increasing interest in the problem, many tasks in this area are waiting to be solved. The subject of the study in this work was the study of the parameters of the capacity curves of cross-sections of reinforced concrete elements of constructive systems of building frames under their static-dynamic loading conditions. This paper presents a methodology for determining the parameters of "load-deflection" curves and the deformation criterion for accidental limit state of a reinforced concrete element of statically indeterminate frame-rod constructive systems under an accidental action caused by removing one of the load-bearing elements from the constructive system. Two stages of loading such systems are considered: static loading to a specified design level and additional dynamic loading caused by a sudden structural rearrangement of the constructive system from the mentioned action. At the first stage of loading, the relative parametric load of cracking in an arbitrary cross-section of the reinforced concrete element of the constructive system and the sequence of formation of plastic hinges in this element is determined using an extraordinary version of the mixed method of structural mechanics of rod systems. At the second stage, the limit value of the relative parametric load is determined on an energy basis without using the structural dynamics apparatus. An algorithm for calculating parameters of the capacity curve of cross-sections of reinforced concrete elements of constructive systems under the considered actions and calculation results of the "relative parametric load-deflection" curve for the most stressed cross-section of the reinforced concrete frame when a middle column is removed from it are presented. The calculated values of the deforming cross-section parameters are compared with experimental data. It is shown that the use of parametric load in the proposed calculated dependencies for analyzing the sequence of formation of plastic hinges in the constructive system is in satisfactory agreement with the test results of such constructive systems under the considered loading regimes.