The calculation of optimal parameters of flat-oval pipes is given by an approximate method, the correctness of which is confirmed by testing using standardized profiles. A new layout of gratings made of flat-oval shaped pipes is presented, developed for truss systems based on steel rod structures of coatings with replacement of bar-shaped bent elements with tubular ones. The caseless junctions of belts and lattices with direct joining of rod elements to each other without alignment are developed, as well as with structural eccentricities limited to 0.25 of the height of the waist elements, which allows not to take them into account in calculations and provides an increase in the degree of unification of the nodes of the upper and lower belts of carrier’s constructions. The prospects of using a new technical solution in light metal structures of buildings and structures are shown. The area of its rational application is outlined, where by means of variant design of typical, known and new solutions, a quantitative estimate of the reduction in the consumption of structural material is given. The whole diagram of changes in the design parameters of flat-oval pipes is shown in the transformation of their cross-sections from vertical configurations to horizontal ones, including the transition through the outline of a circular shape.

A new technical solution for re-profiling round tubes into flat-oval ones with a ratio of 1 / 3,064 is presented, which increases their bending strength. The calculation of the optimal parameters of thin-walled sections of the flat-oval shape is given by an approximate method, the correctness of which is confirmed by testing from the standard profiles used. This calculation is repeated with respect to thin-walled sections of the oval shape. The whole diagram of changes in the design parameters of flat-oval and oval pipes is presented in the transformation of their cross-sections from vertical configurations to horizontal ones, including the transition through the outline of a circular shape. The comparative analysis of optimized cross sections of flat oval, oval and round tubes is carried out taking into account the elastic and elastic-plastic deformations of the structural material, where the length of the midline of the thin-walled section is taken as the dividing line between these deformations. The choice is substantiated in favour of flat-oval profile pipes due to their simpler shape including faces of constant curvature (flat and semi-circular), relatively low cost, lower height, greater compactness, higher resistance moment.