AbstractThis research explores the cyclic behavior and strength of the composite concrete‐filled steel deck diaphragm system through experimental pushout and cantilever diaphragm tests. This work is part of the Steel Diaphragm Innovation Initiative (SDII), a multi‐institutional project that is investigating the behavior of composite steel deck diaphragms in steel buildings structures in high seismic zones. Sixteen unique pushout tests were conducted at Northeastern University as part of SDII. These specimens had variations in the orientation of the steel deck, concrete density, effective slab width, shear stud position and grouping. Additionally, seven of these tests were cyclic. Eight cantilever diaphragm tests were conducted at Virginia Tech as part of SDII. The parameters included deck height, slab thickness, concrete density, layout of shear studs, and reinforcement. These experimental tests provide valuable knowledge that aids in the characterization of the behavior and strength prediction of this structural system.