Seismic Evaluation of Cumulative Low-Cycle Fatigue in Steel Moment Frame Connections

After Northridge earthquake, many researches were introduced low cycle fatigue as one of the reasons of failure of connections under cyclic earthquake loads.The most of the studies of low cycle fatigue in flexural steel frame structures, has been experimentally and analyticaly done in local scale. Therefore, the evaluation of all critical points of structure and the effect of seismic parameters in global scale is necessary. In the present study modelling and dynamical analisys of an flexural steel frame and also the effect of low cycle fatigue under various earthquakes in the mentioned frame connections has been investigated. The amount of damage or decrease in fatigue life has been properly coordinated with response of various earthquakes. On the other hand, the result shows that the increase of the first acceleration of earthquake leads to increase of damage due to fatigue in connections. Also, as time of earthquake decreases down to 68 percent, the fatigue damage in connection has been decreases about 17 percent.