CONCLUSIONSTo improve the properties of magnesite patching powders, it is advisable to treat with from 1.5 to 3.5% of mineral oils, because the oil-treated powders have a number of advantages in comparison with dry powders of the same grain-size composition: enhanced compactibility, improving the quality of the patching layer; reduced dust content, improving the working conditions during loading, transport, ~ and furnace patching; absence of caking during storage; the sinterability is no worse than that of ordinary patching powders, because the combustion of the oil is complete,

The calculation of thin-walled rods is extremely relevant problem of structural mechanics and not only from the scientific standpoint, but also due to the widespread use of so-called lightweight thin-walled steel structures for construction engineering sector. Regardless of a sufficiently large number of studies connected with the statics of thin-walled rods, the dynamics of such systems have not been thoroughly studied yet. Based on one of the forward-looking theories of calculation i.e. the semi-shear theory by Slicker, the paper provides a technique for solving the dynamics problems of thin-walled rods. The stiffness and mass matrices of the finite element system are obtained for linear approximation of the form functions, and the natural vibration frequencies of the rods are calculated. The obtained solution is accomplished by the extrapolation method of estimating the accuracy of numerical methods for solving mathematical problems.

For elastic frames authors offer a method of solving the tasks of optimal control of the stress state, when the boundary loads are the controlling parameters. In difference from other papers it is offered to use deformation energy as a merit functional. This functional estimates the deviation between two functions: optimal function and given function. Examples of the solution are given.

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