Purpose. The purpose is to study free vibrations of thin-walled bar with combined bisymmetrical section allowing for the effects of shear strains. Methods. We used the main hypothesis of V.Z. Vlasov concerning thin-walled bars. Solving motion equations analytically, we used the method of initial parameters and the known methods for differential equations solution. In the natural experiment we applied Autodesk Inventor system. In the course of the natural experiment on shaker, we used the method of smooth change in the frequency of sinusoidal vibrations. Results. We provide the analytical solutions of the shapes and the natural frequencies of thin-walled bar with combined bisymmetrical section allowing for shears caused by bends and constrained torsion. We compared the results of the calculations conducted in CAE system and the results of the full-scale experiment to determine the frequencies of vibrations of box beam. Conclusions. The results showed that the analytical calculations are in good compliance with the results of numerical and physical experiments and can be used for dynamic calculations of thin-walled structural elements, in particular, for the prevention of the destruction of structures in the event of resonance phenomena.

The paper presents the development of approaches to the crack detection in metal rod structures based on the analysis of the lowest eigen-frequency modes. Full-scale experiments and numerical calculations are carried out, and the obtained results are compared. A vibration analyzer is used for full-scale experiments, and numerical calculations are performed by using Autodesk Inventor. With regard to the internal friction, the antinodes of various vibration forms were identified using a specially developed program. The model includes sensors for the the field experiment as masses affecting the frequency-response characteristics. The dependences are obtained for eigen-frequencies in the presence of cracks and for the crack locations. The polynomial dependences of the crack location on the lowest eigen-frequency modes of the rod can be used to analyze the crack position of in cantilever beams.

Improvement of dowel joints in order to increase their load-carrying capacity and reliability at the present time remains actual one. A special place among them is occupied by connections with the use of dowel plates. In order to increase the bearing capacity of metal nailed plates developed in NGASU (Sibstrin) with the use of reinforced dowel it is suggested to strengthen the nailed plates in metal plates by means of tight installation on the last metal stamped gear washers. In order to determine the strength and deformability of the developed connections they were prepared and tested under the action of short-term loads along and across the fibers. On the basis of the received data the analysis of short-term bearing capacity and deformability of the offered joints has been carried out. The method of calculation of such connections on limiting states of the first group is offered. The interaction of the limiting load-carrying capacities obtained on the basis of the proposed method with the results of short load action tests of the compounds under consideration was performed.

ДВУХЭТАПНЫЙ ПРОЦЕСС ОПТИМИЗАЦИИ УПРУГИХ СТЕРЖНЕВЫХ СИСТЕМ ПРИ ИМПУЛЬСОМ НАГРУЖЕНИИ И ВАРЬИРОВАНИИ ПАРАМЕТРОВ СЕЧЕНИЙ ЭЛЕМЕНТОВ И ДОПОЛНИТЕЛЬНЫХ УЗЛОВЫХ МАССАннотация. Рассмотрена задача оптимизации упругих стержневых систем при им пульсном нагружении в случае, когда вектор варьируемых параметров состоит из двух групп: группы геометрических параметров сечений элементов и группы дополнительных узловых масс. Для увеличения скорости сходимости предложен двухэтапный итерацион ный процесс оптимизации, где на каждой итерации решались две самостоятельные задачи оптимизации с различными целевыми функциями.В качестве примера реализации предложенного двухэтапного процесса рассмотрена за дача оптимизации пятиэтажной двухпролетной стальной рамы при действии кратковремен ной импульсной и статической нагрузок. Результаты решения поставленной задачи свиде тельствуют об эффективности использования предложенного двухэтапного процесса опти мизации, а также дополнительных узловых масс в качестве варьируемых параметров.