Low cycle fatigue life prediction of four bolt extended unstiffened end plate moment connections

The end plate moment connection (EPMC) has been studied for many years to investigate and understood its behavior under monotonic and cyclic loading. After the 1994 Northridge, California earthquake, additional research on EPMCs was performed as a part of the SAC steel project. Results from this research concluded that the EPMC could be designed to resist large cyclic (seismic) forces and provide a large amount of ductility. While the research on the behavior of EPMC under cyclic loading has been conducted, very little information on the LCF behavior is available. To evaluate the accumulation of LCF damage, the LCF life prediction, three phases of experimental tests were conducted. To investigate critical geometric parameters for 4E EPMCs in the LCF behavior, parametric study was conducted using a validated FEM model. In the first phase of the experimental testing four reduced EPMCs (T-stubs) were tested to investigate the general behavior of the connection. In second phase of the experimental testing, three different levels of constant peak displacement loading were applied to three full scale EPMCs for developing a LCF model in second phase of the experimental test. In the last phase, an accumulated damage model was evaluated using one full scale EPMC test subjected to random loading. In all phases three-dimensional finite element numerical analysis and theoretical analysis were adopted to predict the experimental behavior. The results of the experimental tests were used to develop the LCF model for the 4E EPMC and it closely predicted the observed LCF life of connection. The parametric study identified the end plate thickness, the beam flange thickness, and the bolt pitch distance as the three critical geometry parameters.