An arbitrary section can only be checked for strength according to the formulas given in the strength of materials manual. However, when you have to consider the elastoplastic stage of work, check for the web buckling, check for the out-of-plane buckling, or to make some other checks according to design codes, it appears that all the codes are oriented only toward certain types of cross-sections. Engineers usually use the following approach – the strength is checked for a real cross-section and all the other checks are carried out for a "similar" section, the geometrical properties of which are selected according to the consideration of equivalence.

The equivalence is understood as the proximity of the cross-sectional geometrical properties (an area, moments of inertia, moments of resistance, etc.). Sometimes in the process of reduction some additional considerations are used which can help to specify the very concept of equivalence. For example, only the equality of the moments of inertia has to be achieved, if it is only the buckling that has to be checked.

The Sezam program is intended for finding such a section (in this version only a hollow section, a channel, a Tee section, or an I-beam), which approximates an arbitrary section set by the user according to its geometrical properties the best. An initial section can be set:

- as a file created by the Section Builder program;
- as a file created by the Consul program;
- as a file created by the Tonus program;
- by the set of geometrical properties;
- as a compound section from the set of prototypes given in the program (e.g. two channels, two I-beams, etc.).

At any method of a section setting only geometrical properties are used for the calculation in the program. The following properties are approximated for a section:

- area (A);
- principal moments of inertia (I
_{u}, I_{v}); - resisting moments (W
_{u+}, W_{u-}, W_{v+}, W_{v-}).

Apart from the parameters mentioned above, it is necessary to set weight coefficients for each of the properties (all the weights are equal to 1 by default).

The task is to select geometrical dimensions of a hollow section, a channel, a Tee section, or an I-beam at which the functional is minimized.

\[ \begin{array}{l} k_{1} \left( {1-\frac{A}{A^{0}}} \right)^{2}+k_{2} \left( {1-\frac{I_{u} }{I_{u}^{0} }} \right)^{2}+k_{3} \left( {1-\frac{I_{v} }{I_{v}^{0} }} \right)^{2}+k_{4} \left( {1-\frac{W_{u+} }{W_{u+}^{0} }} \right)^{2}+k_{5} \left( {1-\frac{W_{u-} }{W_{u-}^{0} }} \right)^{2}+ \\ +k_{6} \left( {1-\frac{W_{v+} }{W_{v+}^{0} }} \right)^{2}+k_{7} \left( {1-\frac{W_{v-} }{W_{v-}^{0} }} \right)^{2}\quad , \\ \end{array} \]

where A^{0}, I_{u}^{0}, I_{v}^{0},
W^{0}_{u+}, W^{0}_{u-}, W^{0}_{v+},
W^{0}_{v-} are respective geometrical properties of the
equivalent section (a hollow section, a channel, a Tee section, or an
I-beam).

Coefficients k_{i}
(i=1…7) indicate the importance
assigned to each geometrical property; in particular, by setting one of
the coefficients equal to zero it is possible to reject the approximation
of a corresponding geometrical property.