The paper considers the results of research on the use of various types of approximations of concrete deformation diagrams on the example of calculating a large-span reinforced concrete truss with a length of 18 m. calculations were performed taking into account the physical nonlinearity of concrete and reinforcement. The following concrete deformation diagrams were used : bilinear, trilinear , and curved with a descending branch. The result of the calculation was the forces in the truss rods, the displacement and the width of the crack opening. Conclusions were made about the influence of the choice of the concrete deformation diagram on the calculation results.

Keywords: concrete, deformation diagram, approximation, physical nonlinearity, stress-strain state, longitudinal force, bending moment, displacement, crack resistance , truss