A comparison of seismic low cycle fatigue and extremely low cycle fatigue on steel moment frames with reduced beam section connection (RBS)

Damage to the connections of buildings with steel moment frames during past earthquakes indicates that the damage to some buildings cannot be justified by the mechanisms of common failure. This is due to the effects of low cycle fatigue (LCF) and extremely low cycle fatigue (ELCF) on the moment frame connections. On the other hand, studies on moment connections have mostly focused on the permitted connection capacity, and the issue of fatigue (LCF and ELCF) has not been considered in these types of connections. The present study focused on the effects of LCF and ELCF on a prequalified reduced beam section connection (RBS) in the steel moment frames of a 6-floor commercial complex and compared these two effects. The results showed that although the RBS connections of the studied structure were not damaged by LCF and ELCF, low cycle fatigue was effective when the behavior of the structure's material was linear. The extremely low cycle fatigue index was significant when the connection's material stresses, caused by an earthquake, exceeded the yield stress. In addition, the comparison of the damage ratios induced in the LCF method and the failure indices in the ELCF method on different floors indicated that the ratios of these two indices were consistent across all the floors.