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：Bolted joint loosening is one of the important modes of bolted joint failure. In the project, the bolted joints are often subjected to alternating lateral dynamic loads, and the bolts tend to loosening very easily as the bolt axis is perpendicular to the direction of the pretension forces. The reductions of the preload will change the inherent mechanical properties of the bolted joints and even cause the failure of entire structure. In order to study the critical loosening load of the bolted joint under the lateral load, the mechanical model of the bolted joint is established, and the forces of thread are analyzed. A new computing method of the bolted critical loosening load with flexible thread is derived. A set of experimental device for lateral vibration is designed and assembled, which is used to test the mechanical behavior of bolted joint under lateral vibration. The presented calculation method of bolted critical loosening load is verified by comparing the theoretical calculation and experimental results. The distribution law of thread stress under lateral load is given based on the new theoretical calculation method, and the stress distribution characteristics of rigid thread model and flexible thread model are compared. The results show that the thread stress given by flexible thread model can reflect the overall variation of thread stress.

The dynamic bending rigidity of aluminium cable steel reinforced (ACSR) is a key parameter for analyzing the breeze vibration, galloping and de-icing vibration response of overhead transmission lines. In this paper, the calculation formula of the dynamic bending rigidity under axial force is derived based on the theory of Bernoulli-Euler beam. The dynamic response of one typical ACSR with different spans and different axial forces are studied by white-noise excitation and hammer excitation. The variation rules of dynamic bending rigidity of ACSR are presented. The comparison between the experimental results of the static and dynamic bending rigidity shows that the dynamic bending rigidity of the ACSR is much larger than the static bending rigidity.