The variation characteristics of axial force of bolts under alternating temperature

• A bolt axial force test under alternating temperature considering the influence of multiple parameters was conducted. • The mechanism of axial force variation of bolts under alternating temperature was proposed. • The finite element model of bolt axial force under alternating temperature based on the indirect coupling method was established. • The calculation model and evaluation method of the axial force of bolts under alternating temperature were proposed. This paper focus on the variation characteristics of axial force of bolts under alternating temperature. The temperature distribution characteristics of various regions in China were considered, and a typical alternating temperature load (0∼25 °C) was selected. Eight sets of bolt connections were designed with different bolt strength grades, specifications and initial torques, and the experimental study on the variation characteristics of bolt axial force under alternating temperature was conducted. From the perspective of the difference in linear expansion coefficients between bolts and connecting plates, the variation mechanism of bolt axial force under alternating temperature is Proposed. Finally, a corresponding calculation model for the variation of bolt axial force and its evaluation method for axial force relaxation are constructed, and the degree of attenuation of axial force of transmission tower bolts under alternating temperature during their service life is evaluated. The results show that the effect of alternating temperature causes the axial force of the connecting bolts to change interactively, and the axial force of the bolts exhibits a continuous attenuation characteristic as the alternating cycle increases. The greater the initial torques of the bolt and the larger the bolt size, the greater the impact of the alternating temperature on the bolt axial force. Under alternating temperatures, the axial force of transmission tower bolts can decay by up to 3.46 % within the first month and 4.58 % after three months. The greater the alternating temperature difference, the more significant the drop in axial force. The attenuation of bolt axial force under alternating temperature is significantly greater than that under constant temperature. The research results can provide some reference for the operations and maintenance of transmission towers.