Full Scale Experiments of a Composite Steel Moment Resisting Frame: Behavioral Insights and Implications on Seismic Design

This paper discusses the cyclic performance of a heavily instrumented 2-bay full-scale composite-steel moment resisting frame (CMRF) sub-system from the onset of structural damage up until incipient collapse. The CMRF featured stiffened end plate bolted connections and was subjected to a series of lateral load histories that mimicked the asymmetric hysteretic response (i.e., ratcheting) of structures prior to structural collapse. It is shown that the primary deteriorating mechanism of the CMRF sub-system was local buckling near the steel beam ends followed by crack initiation and propagation due to ultra- low cycle fatigue. While two of the four steel beams attained nearly zero flexural strength at a lateral drift demand of about 15% rad, the reserved capacity of the CMRF was at least 30% of its peak story shear resistance due to the slab restraint and framing action. Both mechanisms, which are not captured in traditional beam-to-column subassemblies with idealized boundary conditions, caused straightening of local buckles within the dissipative zones of the steel beams. The experimental data is considered unique for ongoing efforts on the further development of the new seismic design provisions of Eurocode 8 Part 1-2.