using the method of complete stress-strain curves [6] under the supervision of I. M. Bezgodov proved that the descending arm exists only for the concrete with prismatic strength of 40-45 MPa. For the concretes of higher grades, it does not exist. However, under the European norms, according to the results obtained when testing 1/2 ration cylinders the complete curve diagrams are described for the cylinders with a strength of up to 80 MPa. It should be noted that the Russian regulatory document SP 52-101-2003 designates the ultimate strain of concrete to equal 200*10-5 rel. u. European norms state an ultimate strain, both for the peak load and on the descending arm depending on concrete grade, and it turns out that the ultimate stress-strain performance for concrete of 20 and 100 MPa strength differs by 50%. Studies conducted in paper [6] also indicate that the ultimate stress-strain performance differs depending on the concrete grade; this fact must be taken into account when calculating the stress-strain state of building structures.