Experimental and FE Investigation of Steel-Concrete Composite Reduced Web Section (RWS) Connections Subjected to Cyclic Loading

Based on the observations from previous earthquakes, brittle failure poses a significant threat to the integrity of steel-concrete composite moment-resisting frames (MRFs). Hence, there has been successful research in developing fuse strategies that cluster deformation demand away from the column face well within the beam. However, this approach involves the extensive intervention of the column and provision of stocky supplemental plates on flanges and the web, making retrofitting of structures complex, particularly if they were not designed with full consideration of capacity design principles. An alternative approach is to use reduced web section (RWS) connections. These rely on perforations made on the beam’s web rather than flange trimming or the use of supplemental plates to increase moment capacity at the column’s face. In particular, it is easier to cut through webs than remove floors to intervene on beam flanges.
Limited attention has been paid to the response of RWS connections with composite slabs subjected to cyclic loads. The presence of composite action over the protected zone has raised concerns about jeopardising the concept of a strong column-weak beam and, thereby, causing an asymmetric yield moment mechanism. The former can lead to weak column (story mechanism) and large panel zone yielding, while the latter can induce excessive strain demands on the beam’s bottom flange. The response mechanism of RWS connections, acting as two partial beams above and below the opening (top and bottom Tee-sections), induces four plastic hinges around the web opening (Vierendeel mechanism). This mechanism can overcome the aforementioned concerns.
The results of experimental and numerical investigations in this research, along with the compiled and extrapolated findings from the literature, were used to assess the cyclic response of RWS connections. This thesis advocates the application of RWS connections in both new seismic-resistant structures and the retrofitting of non-seismically designed structures. The research findings demonstrate the effectiveness of the capacity design concept in achieving the expected ductile response of RWS connections with overlaid slabs. The inelastic demands and slab cracking were alleviated by eliminating composite interaction over the protected zone without compromising the beam’s stability. The test results suggest that RWS connections could be a viable seismic fuse solution for existing and new structures. The experimental and numerical findings established the ability of steel-concrete composite RWS connections to meet the response requirements set by ANSI/AISC 358-16, ANSI/AISC 341-16 and Eurocode 8. These include achieving an inter-storey drift larger than 4% with strength degradation of less than 20% of the beam’s plastic moment capacity and cap shear transfer to non-ductile components of the connections. This was attributed to a highly ductile Vierendeel mechanism that led to an increase in the deformability and ductility of the reduced sections as well as the connections. The analysis of the collected RWS database supports the findings of both experimental and numerical investigations in this research, in which the current design approaches of RWS connections for seismic purposes overlooked the significant effect of a capacity design to ensure a stable yield mechanism is governed.