Investigating the effect of extremely low cyclic fatigue in steel moment frames with reduced beam section connections

Studies on damaged connections in recent earthquakes have shown that damage to some of the structures cannot be justified by the use of common failure mechanisms. This is due to the extremely low cyclic fatigue created by the critical cycle on the connections, which leads to a failure in the examined connections. In recent years, a lot of research efforts have been made to create a method for predicting a failure due to extremely low cycle fatigue to interpret the failure mechanism in steel materials and structural components. It can be said that the failure is due to the extremely low cycle fatigue state governing the steel structures in severe earthquakes. On the other hand, after the Northridge earthquake, the use of moment connection with reduced beam section, which showed good ductility in laboratory studies, expanded rapidly. But studies on this kind of connection have focused on capacity, and the extremely low cycle fatigue and failure mechanisms in this type of connection have not been considered. The present study focuses on the effect of extremely low cyclic fatigue on damaged connections with reduced beam section beams in moment steel frames. In this regard, the effects of extremely low cyclic fatigue were studied in a 6-story steel moment frame complex with reduced beam sections. Comparison of the indices of start cracking by extremely low cycle fatigue in different floor showed that this index is far from the beginning of the failure. In other words, the connections with reduced beam sections in this structure will not damage by extremely low cycle fatigue.