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To investigate the behavior of moment connections under the column removal scenario simulating the progressive collapse, two tubular column-to-H beam connections with the outer-diaphragm in a beam-to-column assembly, including a beam-to-column connection with two half-span beams, were statically tested, followed by finite element analysis. The results indicate that the failures occur at the sections connecting the outer-diaphragm and the beams with the beam chord rotation greater than 0. 08 rad. For specimen CO-W with the welded web, fracture initiates at the bottom flange and extends to the top flange, while for specimen CO-WB with the bolted web the fracture is restrained in bottom flange followed by the bolts bearing. At beginning, the beam-to-column assemblies resist the upper load through the flexural mechanism, and the dominant force transfer mechanism is shifted to the catenary mechanism with the increasing deformation. Remarkable axial force in beams is observed in specimen CO-WB even after the fracture of the bottom flange, resulting in the higher bearing capacity provided by the catenary mechanism in the later stage, exhibiting a better strength redundancy than the specimen with the welded web. [ABSTRACT FROM AUTHOR]