Development of a Quasi-Static Bidirectional Loading Protocol for the Seismic Evaluation of Hybrid RC-SCC Beam-Column Joints

Reinforced concrete (RC) structures are prone to damage during seismic events, especially in the presence of vertical irregularities such as open-ground storey. In such cases, provision of steel-concrete composite (SCC) columns resulting in hybrid RC-SCC buildings with RC beams and SCC columns significantly improves the lateral strength of the structure and reduces the scope for damage. The seismic performance assessment and design of beam-column joints in multi-storey structures has been conventionally performed on 2D frames under unidirectional loading. However, past earthquakes have demonstrated that the analysis of beam-column joints under unidirectional loading is not representative of the bidirectional shear demand experienced by the beam-column joints due to the multi-directional nature of the earthquake. Therefore, in this study, an evidence-based quasi-static bidirectional loading protocol has been developed for the seismic evaluation of hybrid RC-SCC beam-column joints. To achieve this objective, a 3-storey hybrid RC-SCC building was modelled on OpenSees software and subjected to bidirectional non-linear response history analyses (NRHA) accounting for the variability of ground motion (GM) records and angle of seismic incidence (ASI). Further, the inter-storey drift ratio (IDR) response history data of beam-column joints was idealised in the form of elliptical loops. Ultimately, based on the statistical analysis of the characteristics of the elliptical loops, two variants of a bidirectional loading protocol have been proposed corresponding to the variability of GM records and ASI. Between the two variants, the loading protocol accounting for the variability of GM records is preferred as it is not only conservative but also representative of a wider range of GM records expected at the site. It is expected that the testing of hybrid RC-SCC beam-column joints under this quasi-static bidirectional loading protocol will provide new insights into their qualitative and quantitative response.