In this article on increasing the efficiency of steel combined structures, the tasks of rational design, regulation and control of structural parameters of elements, the use of steels with increased mechanical properties are considered. It is shown that for a six-span stiffening girder of a combined truss with elastic supports, which operates under a distributed load, the moment is 72 times smaller than the moment of a single-span beam. It is suggested to use high-strength steel for truss braces. Rationality criteria are proposed. On the basis of rationality criteria, new steel combined trusses were developed and their models were designed for stress tests. The results of experimental studies of models of combined trusses are presented. The results of experimental studies conducted on models of steel combined trusses qualitatively and quantitatively confirmed the theoretical results obtained on the basis of the proposed theory.

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