Fatigue experimental study on the joint plate under out-of-plane vibration in steel tubular transmission towers

Vortex-induced vibration (VIV) of steel tubular members in transmission towers under light wind conditions leads to long-term out-of-plane vibration of the joint plates at the ends of the members, which in turn causes fatigue cracking. Given the current inability to fully elucidate the mechanism of VIV, this study focuses on investigating the fatigue performance of such joints to guide fatigue design and ensure the structural safety. In this study, a series of fatigue tests are conducted to explore the influence of two methods—raising the ring plate height and increasing the joint plate thickness—on the fatigue performance of the joints. The analysis includes aspects such as fatigue failure modes, stiffness degradation, crack propagation, life prediction, and changes in dynamic properties. The results indicate that both methods contribute to improving the fatigue life in the two stages of the fatigue failure process to varying degrees. Furthermore, the S-N curve established based on average hot spot stress can effectively predict the fatigue life in the first failure stage. The study also finds a near-linear relationship between crack propagation on the joint plate and stiffness degradation, with the slope depending on the initial stiffness of the joint. Measurements of dynamic properties throughout various stages of fatigue damage indicated a substantial decrease in both the damping ratio and natural frequency of the system as the joint plate incurred fatigue damage.