Hybrid simulations were conducted to evaluate the system-level seismic response of a 4-story steel moment frame building and its gravity framing system through various levels of ground motion shaking. The experimental substructure examined in detail corresponds to a half-scale 1½-bay by 1½-story subassembly of the steel gravity frame. Unlike typical beam-to-column connection tests, the subassembly, which represented typical gravity framing steel construction, captured the redistribution of force demands in beams, columns, panel zones, and the composite floor slab while exhibiting inelastic behavior. Horizontal as well as varying vertical forces were applied on the test specimen to mimic realistic boundary and loading conditions. This paper focuses on the experimental response of the gravity framing system and its contribution to the lateral resistance of a steel frame building. In particular, the lateral resistance and failure mechanisms of the test frame are described and compared to numerical simulations based on state-of-the-art modeling approaches. The data generated from these experiments provides valuable insight on gravity frame behavior towards improvement and verification of frame models at the system level.