Abstract：When bolted connections are required in the structures with large spans or heavy loads, the ultra-large capacity end-plate connection with 12 bolts or 16 bolts arranged in the tension region should be applied if the ordinary end-plate connection or the large capacity end-plate connection cannot satisfy the capacity requirement. In order to study the behavior of ultra-large capacity end-plate connections, four full-scale specimens were tested under the monotonic loads. Based on the tests, the moment-rotation curves for all specimens were obtained, and the moment resistance, the rotational stiffness and the distribution of the tensile strain increment of bolt in the tension region were analyzed with different bolt diameters, different end-plate thickness and different layout of bolts. According to the results, the ultra-large capacity end-plate connections in the tests may fail in the mode that the bolts fail after the yielding of end plate, and the thickness of end plate may obviously affect the resistance of connections. Significant non-uniform distribution of the tensile strain increments in bolts was observed. Since they contribute little to the moment resistance of connections, it is recommended that the bolts at the corners should be removed or should be considered as shear resistant ones. In the design of this connection, the resistance of the panel zone still can be calculated according to the current code, and it is recommended that the equivalent number of the bolts in tension should be 7.
