The Complete Concrete Strength Use Criterion of Biaxially Bent Columns of Frame Structural Systems

The precast flat plate frame structural system of buildings is the most effective and demanded for the construction of residential and civil facilities. It requires improving the methods of calculating its carrying capacity to guarantee the reliability and safety of building operation. The article reflects the actual state of methods for determining the carrying capacity of reinforced concrete columns in a flat plate frame structural system and suggests directions for their improvement. It is demonstrated using finite element modeling of the spatial frame operation that its columns undergo biaxial bending. The problem of defining the calculated ultimate values of fiber concrete strain in the biaxially bent reinforced concrete elements is solved. These are the important values in calculating the carrying capacity of columns. The strength criterion for biaxially bent reinforced concrete columns is proposed, provided the reinforcement operates in the elastic stage. The diagram of the design values of the ultimate fiber strain of concrete in biaxially bent columns is constructed based on the formulated criterion. The diagram allows designing concrete structures with optimal reinforcement. For practical implementation, an approach has been proposed to evaluate the carrying capacity of reinforced concrete columns using the determined strain parameters. The application of the developed method is illustrated by an example.