Large-scale experimental tests, detailed finite element studies, strut-and-tie studies, and hand approaches are conducted on a number of steel beam-column moment frame sub-assemblies with a composite deck slab subjected to large inelastic displacements. The four experimentally tested frame sub-assemblies were designed to have (i) full isolation of the slab from the column, (ii) a shear key within the column web but slab isolated from the outside faces of the column flanges, (iii) a modified shear key within the column web with confinement plates and slab isolated from the outside faces of the column flanges, and (iv) a full depth confined slab around the columns. The finite element and strut-and-tie numerical models were used to describe the experimental tests conducted here, as well as those by others. This information was used in the development of simple methods useful for design.

It was found that slab damage resulting from compression of the slab against the flanges could be avoided by fully isolating the column from the slab with appropriate material, and the design strength was that of the bare frame, although ductility was enhanced. By using a confined full depth slab, the strength increased by almost 50%, and the stiffness by 87% without significant strength loss. The specimens with isolation on the outside of the column flanges, and provision of shear key rebars, had enhanced the strength. However, for the configurations tested degradation of strength to that of the bare steel frame level occurred at large displacements.

The monotonic finite element study matched the envelope of the lateral force-displacement curve with deviation less than 9%. The strut-and-tie model, using simple approaches to capture all relevant mechanism described above captured the key aspects of the cyclic behaviour with deviation less than 7% on peak strength.

Finally, design methods considering all key modes of failure were provided. These are suitable for engineering use, and design examples were provided. The work conducted allows engineers to choose a slab configuration and design appropriately. The modes of slab failure and strength loss were identified. These include crushing, shear fracture at the column tips, longitudinal shear failure, slicing of concrete slab between column flange tips due to unanchored reinforcing bars, shear stud deformation, and yielding of longitudinal or transverse reinforcing steel.