Influence of bolt arrangement and stiffening on the seismic performance of extended thin end-plate connections

Steel structures are typically recognized for their high ductility and strength under seismic loads. However, following the Northridge earthquake, several instances of brittle failure were reported in welded connections. As a solution, extended endplate connections have been proposed. This study experimentally investigates the behavior of four-bolted extended end-plate connections under cyclic loading, focusing on bolt configurations and the presence of the stiffener. Twelve specimens were designed, consisting of six stiffened and six unstiffened extended end-plate connections (SEECs and UEECs). Key parameters such as the bolt distance from the beam's flange (pf) and gage distance (g), were varied to examine their influence on the moment capacity. In addition, the experimental results were compared with the theoretical equations from existing literature. When the test results were evaluated, the maximum and plastic moment capacities increased with the decrease of pf value and g value. The effects on pf and g were more pronounced in SEECs. The stiffener increased the moment capacity but decreased the rotational capacity. AISC predicts the moment capacity of the SEECs more accurately than that of UEECs, conversely, Eurocode 3 predicts the moment capacity of the UEECs more accurately than that of SEECs. Moreover, the prediction of moment capacity proposed by Özkiliç (2023a, 2023b) gave more accurate estimates than other models. This prediction is better as pf and g values decrease.