Monotonic Behavior of High-Strength Steel Unstiffened Extended End-Plate Moment Connections

The paper presents experimental investigations on the monotonic inelastic behavior of unstiffened extended end-plate moment connections fabricated from high-strength steel. Three tests were conducted on connections using conventional (grade Q355) steel beams and high-strength (grade Q690) steel columns and end plates. The effect of end plate and column flange thickness was examined, thus resulting in failure modes being either end-plate fracture or bolt rupture. Experimental results are provided in detail, including observations of the two failure modes, moment-drift and moment-rotation curves, and main mechanical indices to characterize inelastic response. The initial rotational stiffness, yield and ultimate moment resistances, and ultimate plastic rotation of these connections, combined with existing experimental results on high-strength (grades Q460, Q690 and Q960) steel end-plate connections, are evaluated and compared with those predicted by Eurocode 3 Part 1-8. The results indicate that the code overestimates the initial stiffness of connections with hand-tightened bolts but underestimates those with preloaded bolts, predicts well the yield resistance, and is acceptable on connection rotation requirements. A more accurate, but simple criterion on connection rotation is proposed.